Research ArticleSynthesis of Poly(lacticacid)-block-poly(NN-dimethylaminoethyl methacrylate)Copolymers with Controllable Block Structures via ReversibleAddition Fragmentation Polymerization from AminolyzedPoly(lactic acid)
Wenwen Yu1 Lijing Zhu2 Jiangao Shi 1 and Cunting Zhao3
1East China Sea Fisheries Research Institute Chinese Academy of Fishery Sciences Shanghai 200090 China2Ningbo Institute of Materials Technology amp Engineering Chinese Academy of Sciences Ningbo 315201 China3Zhejiang New Wood Material Technology Co Ltd Ningbo 315300 China
Correspondence should be addressed to Jiangao Shi jiangaoshi666163com
Received 22 December 2017 Revised 21 March 2018 Accepted 28 March 2018 Published 9 May 2018
Academic Editor Atsushi Sudo
Copyright copy 2018 Wenwen Yu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Poly(lactic acid)-block-poly(NN-dimethylaminoethyl methacrylate) (PLA-PDMAEMA) copolymers were synthesized fromaminolyzed PLA via reversible addition fragmentation (RAFT) polymerization PLA undergoes aminolytic degradation withethylenediamine (EDA) The kinetics of the aminolysis reaction of PLA at different temperatures and EDA concentrations wasinvestigated in detail The molar masses of products rapidly decreased in the initial stage at low aminolytic degree Meanwhilereactive ndashNH2 and ndashOH groups were introduced to the end of shorter PLA chains and used as sites to further immobilize theRAFT agent PLA-PDMAEMA block copolymers were synthesized A pseudo-first-order reaction kinetics was observed for theRAFT polymerization of PDMAEMA at a low conversion By controlling the aminolysis reaction of PLA and RAFT polymerizationdegree of DMAEMA the length distributions of the PLA and PDMAEMA blocks can be controlled This method can be extendedto more systems to obtain block copolymers with controllable block structure
1 Introduction
Poly(lactic acid) (PLA) is classified as an eco-friendly polyes-ter not only because of its biodegradable but also its renewableresources (sugar beet corn starch among others) [1] It hasbeen widely utilized in biomedical fields as drug deliverycarriers scaffolds for tissue regeneration matrices for pro-longed drug delivery systems and degradable surgical suturesdue to its good biocompatibility and excellent processability[2 3] However the serious challenge is associated withhydrophobic nature of PLA As an example in drug deliveryhydrophobic drug-loaded carriers may limit drug solubilityin the blood stream resulting in decreased in vivo drugefficiency [4] In addition the proteins and cells of the bloodand tissue may be adsorbed and deposited on hydrophobiccarriers via hydrophobic interaction causing fatal injury to
patients [5] Therefore PLA often requires modification toimprove hydrophilicity before practical use as a drug carrier[6ndash8]
In recent years PLA-based amphiphilic block copolymersare the most attractive nanocarriers (eg nanoparticlesmicelles and polymersomes) for drugs [9ndash13] In the drug-loaded carriers the hydrophobic PLA chains provide aloading space for hydrophobic drugs and the hydrophilicpolymer chains constitute a stable interface between thehydrophobic carriers and the aqueous medium [14 15]The carrier structure and functionality can be effectivelycontrolled by the selection of polymer composition archi-tecture molecular weight and monomer chemistry [16ndash20] In general hydrophilic blocks include poly(meth)acryl-ates poly(ethylene glycol) (PEG) polypeptides polysac-charides and polyurethanes PLA-b-PEG copolymers are
HindawiInternational Journal of Polymer ScienceVolume 2018 Article ID 7361659 9 pageshttpsdoiorg10115520187361659
2 International Journal of Polymer Science
the most popular and often synthesized by ring open-ing polymerization (ROP) of lactide [21ndash23] The lack offunctional groups in the resulting PEG-PLA block co-polymers that can be used for further bioconjugationshould be overcome PLA-poly(meth)acrylates block co-polymers such as PLA-poly(hydroxyethyl methacrylate)(PLA-PHEMA) [17 24] PLA-poly(NN-dimethylaminoethylmethacrylate) (PLA-PDMAEMA) [11 25] and PLA-poly(N-isopropylacrylamide) (PLA-PNIPAM) [19] are usuallysynthesized via ROP of lactide followed by atom transferradical polymerization (ATRP) or reversible addition frag-mentation chain transfer (RAFT) polymerization of variousmonomers
The end-of-life scenario of poly(L-lactide) products isthe degradation which is often induced by oxidation [26]irradiation [27 28] biological activity (ie enzymes [29] andmicroorganism [30ndash32]) thermal energy [33 34] aqueoussolutions and so on In numerous cases a variety of chemicalphysical and biological processes are always coexistent andaffect each other Aminolysis is a chemical degradationprocess that was developed to modify polyester surfacesAminolysis between the bulk polyester material and aminesolution is considered as nucleophilic substitution conferringthe polyester surface with amino (ndashNH2) and hydroxyl(ndashOH) groups [35 36] The ndashNH2 density and kinetics ofaminolysis occurring on bulk surfaces have been studiedFurthermore the ndashNH2 groups on the surface can be usedas sites to further immobilize bioactive molecules (such aspeptides proteins and polysaccharides) on the aminolyzedPLA membrane surfaces to create highly bioactive materials[37 38] However less attention has been focused on the basicknowledge on the aminolysis reaction of PLA in terms ofreaction kinetics and the detailed structures of the aminolyticPLA chains
In the present work in contrast to the known procedurefor preparation of PLA-based block copolymers combiningROP of lactide and controllable radical polymerizationwe synthesized PLA-PDMAEMA block copolymers via theaminolysis reaction of PLA chains and RAFT polymerizationof DMAEMA for the first time The synthesis strategyconsisted of a three-step procedure (a) controlled aminolysisreaction of PLA initiated by ethylenediamine (EDA) (b)conversion of the functional end-groups with RAFT agentand (c) RAFT polymerization of DMAEMA The aminolysisreaction of PLA was first investigated systematically Thereaction kinetics and chemical structures of the aminolyticPLA were analyzed as functions of temperature reactiontime and diamine concentration The molar masses ofthe copolymers were calculated via theoretical deductionand determined by gel permeation chromatography Thenchemical structures of the resultant PLA-PDMAEMA blockcopolymers and kinetic behaviors of the polymerizationwere characterized in detail The results in this study pro-vide valuable guidance for further synthesis of other PLA-poly(meth)acrylates block copolymers which opens a newpath to reuse PLA residues and reduce the consumption oflactide
2 Experimental Section
21 Materials and Reagents PLA (2002D) was suppliedby Natural Works Ethylenediamine (EDA) 46-dimethyl-2-pyridinamine (DMAP 98) and NN1015840-dicyclohexyl car-bodiimide (DCC 99) were purchased from Aladdin andused without further purification 2-(Dimethylamino) ethylmethacrylate (DMAEMA) was bought from Aladdin andpassed through a column filled with basic alumina toremove the polymerization inhibitors Azobisisobutyronitrile(AIBN) was supplied by Shanghai Chemical Reagent Com-pany and recrystallized twice with ethanol RAFT agent of4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoicacid (CDP) was synthesized according to the reported pro-cedure in the literature [39] All other reagents such as14-dioxane NN1015840-dimethylformamide (DMF) and tetrahy-drofuran (THF) ethanol were brought from SinopharmChemical Reagent Co Ltd China and used directly
22 Aminolysis of PLA We followed the methods of Zhu etal (2015) to synthesize PLA-based block copolymers via theaminolysis reaction of PLA chains and RAFT polymerizationof DMAEMA [40] In a typical aminolysis reaction of PLAwith EDA PLA (5 g) was dissolved in 14-dioxane (45 g)under stirring for 12 h EDA at various concentrations (105 and 01mmolg) was dropped into the above PLAsolution under stirring Immediately the aminolysis of PLAwas carried out at a given temperature (18 30 and 40∘C)After reaction for predetermined time the polymer solutionwas precipitated in excessive water The raw product wasseparated through filtration and thoroughly washed withwater The solid final product was obtained by freeze-dryingfor 24 h and named as PLA-EDA The yield of the degradedPLAs after reprecipitation is 82sim85
23 Synthesis of Macromolecular Chain Transfer Agent (PLA-CDP) In brief the obtained PLA-EDA (5 g) was dissolvedin THF (50mL) under stirring at 25∘C for 1 h Then DCC(105 g 5mmol) DMAP (06 g 5mmol) and CDP (10 g25mmol) were serially added to themixture Amide reactionand esterification between the ndashNH2ndashOH groups of PLA-EDA and the ndashCOOH groups of CDP occurred After 24 hthe mixture was precipitated and thoroughly washed inexcessive ethanol for at least three times The solid productof macromolecular chain transfer agent (PLA-CDP) wasrecovered through filtration and dried in vacuum oven at40∘C
24 Synthesis of PLA-PDMAEMA Block Copolymers PLA-based block copolymers were synthesized via RAFT poly-merization PLA-CDP and AIBN were used as macromolec-ular chain transfer agent and initiator respectively As anexample the synthesis procedures of PLA-PDMAEMA blockcopolymers via RAFT polymerization were briefly shownbelow PLA-CDP (2 g) was dissolved in DMF (20mL) understirring at 20∘C After 1 h DMAEMA (5 g 32mmol) andAIBN (5mg 003mmol) were added and degassed withN2 for an additional 15 h at 20∘C Then the mixture wastransferred to an oil bath at 70∘C under N2 protection
International Journal of Polymer Science 3
CHO C
H
O C
O
O O O
O O O
C
H
O C C
H
O C C OH
H
Poly(lactic acid) (PLA)
CHO C
H
O C CH
O C CH
O C C OH
H
HO C CH
O C CH
O C C OH
H
CHO C
H
O C CH
O CHN C
H
O C CH
O C C OH
H
O O O
C C
H
O
（3（3（3（3
（2EDA （2
（2
（2
（2
（3 （3
（3
（3 （3（3 （3 （3
（3 （3 （3
（3 （3
+（2
+（2
+
minus
minus
P
P
P
nm
O O O O O
（
Figure 1 Aminolysis mechanism of PLA with EDA
and stirring After a predetermined time the reaction wasterminated by quenching in ice water and the polymersolution was precipitated and washed in excessive waterThe solid PLA-PDMAEMA block copolymers were obtainedthrough filtration and freeze dried
25 Characterization 1HNMR spectra were performed witha Bruker Advance III spectrometer at room temperature inCDCl3 or DMSO-d6 with Si(CH3)4 as an internal standardGel permeation chromatography (GPC)was conducted usinga Waters 510 HPLC pump Waters Styragel columns anda Waters 410 differential refractometer (Millipore CorpBedford MA) at 40∘C in THF with a flow rate of 1mLminPMMA was used as a calibration standard The chemicalcompositions of the synthesized block copolymers werecharacterized by Fourier transform infrared spectrometer(FTIR Thermo-Nicolet 6700 US) and X-ray photoelectronspectrometer (XPS Shimadzu Axis UltraDLD Japan) withMg K120572 excitation radiation at a take-off angle of 45∘
3 Results and Discussion
31 Structure and Characterization ofthe Aminolyzed PLA with EDA
311 Chemical Structure Similar to the reaction withpolyethylene terephthalate (PET) [41] amine acts as a nucle-ophile to attack PLA at the electron deficient center ndashC=O Anew active group is introduced to the end units The reaction
of PLA with EDA was studied carefully in this work Theaminolysis mechanism is shown in Figure 1 Figure 2 showsthe structures of raw PLA and PLA-EDA as characterizedby 1H NMR Several signals can be distinguished as followsSignals in the 159sim157 (A) and 519sim514 ppm range (B)belong to the ndashCH3 and ndashCH protons of the PLA main chainunits Compared to raw PLA PLA-EDA exhibits the newpeaks in the 148sim150 (a) and 433sim439 ppm ranges (b)which are attributed to the ndashCH3 and ndashCH protons of thehydroxylated lactyl end units The peaks at 523 and 161 ppm((d) and (c)) are assigned to the ndashCH and ndashCH3 protonsconnecting with EDA groupsThe peaks of the C2H4 protonsfrom residual EDA are presented at 375sim321 ppm range (e)In addition the signals at 525 and 154 ppm ((g) and (f))belong to the ndashCH and ndashCH3 protons of the carboxylatedlactyl end unitsThe 1HNMR results confirmed the proposedaminolysis mechanism illustrated in Figure 1
312 Aminolysis Degree Aminolysis degree (AD ) wasintroduced to evaluate the extent of aminolysis reaction andcalculated from the 1H NMR spectra according to
AD =119878119887119878alltimes 100 (1)
where 119878119887 and 119878all are the integral areas of peak 119887 as shown inFigure 2 and all peaks of the ndashCH protons respectively
The AD of PLA with EDA is dependent on EDA concen-tration reaction time and temperature as shown in Figure 3
4 International Journal of Polymer Science
53 52 51 44 43 17 16 1540 35 30
PLA-EDA
(g)(d)
(g)
(f)
(B) (b)
(b)
(a)
(a)
(f)(c)
(c)
(d)
(A)
(e)
(e)
CDCl3
C C
H
（3 O
O OHPLA CC
H
（3
OHPLA
O
C C
H
（3 O
O NHPLA （2
O C C
H
n
O
8 7 6 5 4(ppm)
3 012
PLA (B)
(B)
(A)(A)（3
＄Ｆ3
Figure 2 1HNMR spectra of raw PLA and PLA-EDA in CDCl3 Aminolysis condition of PLAwith EDA 30∘C 30min [EDA] = 10mmolg
The AD of PLA increases with the prolongation of reactiontime In detail AD is rapidly increased in the initial 10minof aminolysis and slows down from 10 to 60min After60min AD data becomes difficult to obtain because the solidproducts cannot be separated from the precipitation solutionFigure 3(a) shows a faster growth of AD with increasingEDA concentration Furthermore the aminolysis reactionwas also accelerated at higher temperature when the EDAconcentration was 05mmolg (Figure 3(b)) At the EDAconcentration of 10mmolg the AD is as high as 103 afterreacting at 40∘C for 60min
313 Molar Mass Analysis According to the aminolysismechanism of PLA chain scission results in decreasedmolar mass The products were subjected to GPC analysesand the results are shown in Figure 4 The GPC traces(Figure 4(a)) indicated that the molar mass distributionof the measured PLA-EDA remained unimodal suggesting
statistically random scission of the polymer chains Fur-thermore with increasing reaction time the GPC tracesshift toward low molar mass The number average molec-ular weight determined by GPC (119872119899GPC) is exhibited inFigure 4(b) The 119872119899GPC decreased rapidly in the low ADrange and the decline rate slowed down with increasingAD The aminolysis reaction is considered as the reverse ofpolycondensation [42] Lower AD is roughly equivalent tohigher polycondensation extent For the polymer synthesizedvia polycondensation 119872119899GPC increases gradually in theinitial polymerization under high polymerization degree119872119899GPC significantly increases due to a small increase inthe polymerization degree [42] As a result the changingtrend of Mn for the aminolyzed PLA is similar to that ofpolycondensation polymer Moreover similar to the changein polydispersity index (ETH) in polycondensation the ETHof PLA-EDA became narrower with the increase of AD(Figure 4(b)) Lower polycondensation extent indicates less
International Journal of Polymer Science 5
0
2
4
6
8
10A
D (
)
10 20 30 40 50 600Time (min)
05 mmolg10 mmolg
01 mmolg
(a)
0
3
6
9
12
AD
()
10 20 30 40 50 600Time (min)
40∘C30∘C18∘C
(b)
Figure 3 AD as a function of reaction time with different EDA concentrations at 30∘C (a) and different reaction temperatures at an EDAconcentration of 05mmolg
30 35 40 45 50 55 60 6525
20
AD
29
00 3859
ＦＩＡMw
(a)
PDI
0
15
30
45
60
75
2 4 60AD ()
3 4 5 62
2
4
6
13
14
15
16
17
18
19
ETH
times10
3(g
mol
)M
n
Mn０
MnＮＢ
(b)
Figure 4 Evolution of GPC traces (a) and number average molecular weight (119872119899) and molecular weight polydispersity (K = 119872119908119872119899) (b)of the PLA-PEA with aminolysis degree (119860119863)
ETHTheETH decreases with the increasing AD of PLAwith EDAExcept for119872119899GPC the theoretical Mn (119872119899th) of PLA-EDAwas calculated by (2) as shown in Figure 4(b) The 119872119899thvalue is slightly less than the GPC obtained value due tothe different flexibilities of the polymer chains between PLA-EDA and the GPC calibrating standards (PMMA) Howeverthe tendency of119872119899th is in accordance with119872119899GPC
119872119899th =119872119899PLA + AD times119872EDA times119872119899PLA119872PLA1 + AD times119872119899PLA119872PLA
(2)
where 119872119899PLA and 119872PLA are the number average molarmasses of PLA and PLA repeating units respectively119872EDAand AD are the molar mass of EDA and degree of aminolysisrespectively
32 Structure and Characterization of the SynthesizedPLA-Based Block Copolymers
321 Chemical Structure Despite being an eco-friendly bio-plastic with excellent biocompatibility and processability
6 International Journal of Polymer Science
Table 1 Molar weight (Mn) polydispersity (K) of the synthesized PLA-PDMAEMA block copolymers andmass ratio of PDMAEMA blocks(119891PDMAEMA) in the copolymers
Figure 5 Schematic illustration for the preparation of PLA-PDMAEMA block copolymers via RAFT polymerization
PLA is chemically inert without reactive sidechain groupsthereby making its modifications a challenging task [43]After the aminolysis reaction of PLA with EDA the reactivendashNH2 and ndashOH groups can be introduced to the ends of thePLA chains providing opportunity to furthermodify PLA Inthe present work PLA-PDMAEMA block copolymers weresynthesized from PLA segments after aminolysis reaction viaRAFT polymerization Figure 5 shows the fabrication pro-cesses First RAFT agent CDP was immobilized on the reac-tive groups of PLA-EDA via the amide reactionesterificationunder the catalysis ofDCCDMAP inTHFThen the obtainedPLA-CDP was used as the chain transfer agent to regu-late RAFT polymerization of monomers to produce PLA-based block copolymers In the present work a serial ofPLA-PDMAEMA block copolymers were synthesized Themolar weight (Mn) polydispersity (ETH) and mass ratio ofPDMAEMA blocks (119891PDMAEMA) in the copolymers are listedin Table 1
To detect the chemical compositions of the synthesizedPLA-CDP XPS was employed The XPS wide scan andthe elemental mole percentages are shown in Figure 6(a)The peak of S 2p is observed Figure 6(b) shows the 1HNMR spectrum of PLA-CDP The peaks in 425sim413 ppm
range are attributed to the C2H4 protons connected withamide group The peaks of the CH3 protons at (a) and (c)in Figure 2 disappeared These results confirm that PLA-CDP was synthesized successfully It can be used as thechain transfer agent to regulate RAFT polymerization ofDMAEMA
PLA345-PDMAEMA60 block copolymers were character-ized by 1H NMR in CDCl3 and the obtained 1H NMRspectrum is shown in Figure 7(a) The signals in the 519sim514 (A) and 159sim157 ppm range (B) belong to ndashCH andndashCH3 protons of the main chain PLA units The peaks inthe 182 (C) and 091sim106 ppm range (D) are attributed tothe ndashCH2 and ndashCH3 protons of the main chain PDMAEMAunits The signals at 409 (E) and 263 ppm (F) correspondto the ndashCH2 protons connected to the ester and tertiaryamine groups of PDMAEMA respectively The peaks in238sim234 ppm range (G) are attributed to ndashCH3 protonsconnected to the tertiary amine groups In addition FT-IR spectrum of PLA345-PDMAEMA213 block copolymers isshown in Figure 7(b) The peak at around 1758 cmminus1 is thestretching vibration of C=O in ester groups of PLA blocksThe adsorption peaks at about 2823sim2722 and 1730 cmminus1 areascribed to ndashN(CH3)2 and OndashC=O groups of PDMAEMAchains respectively Furthermore the GPC traces of PLA345-PDMAEMA block copolymers with different polymerizationtimes are shown in Figure 7(c) The GPC traces of PLA345-DMAEMA block copolymers exhibit one monomodal distri-butionTheMn of PLA345-PDMAEMA increases from 26300to 58400 gmolwith the increase of polymerization time from1 to 10 h as shown in Table 1 All data indicate that the PLA345-PDMAEMA block copolymers were successfully synthesizedvia RAFT polymerization based on aminolyzed PLA withEDA
322 Kinetic Behavior of the RAFT Polymerization TheRAFT polymerization kinetic behavior of PLA345-PDMAE-MA block copolymers was investigated Conversion andkinetics plots for the RAFT polymerization of the blockcopolymers with increasing polymerization time (1 2 3 4 7and 10 h) are shown in Figure 8 Figure 8(a) further shows thatthe conversion of DMAEMA linearly increases with RAFT
International Journal of Polymer Science 7
Components (mol)C 1s 621O 1s 362S 2p 17
C 1sO 1s
S 2p
164 160168
400 200 0600Binding energy (eV)
(a)
C C
H
O
O NH NHPLA C
O（3
C C SS
S
CN
（3
2（4 12（25
lowast
lowast
6 4 2 08(ppm)
16 151742 4143
(b)
Figure 6 (a) XPS wide scan and elemental mole percentages and (b) 1H NMR spectrum in CDCl3 of PLA345-CDP
＄Ｆ3
8 7 6 5 4(ppm)
3 012
(G) (G)
(G)
(B)
(B)
(C)
(C)
(D)
(D)
(E)
(E)
(A)
(A)
(F)
(F)
O C C
H
nC
C
m
O
O
N
O
（3 （3
（2
(a)
1730
1800 1700
1758minus(（3)2
2000 100030004000
Wavenumbers (＝Ｇminus1)
(b)
(A) (B) (C)
40 44 48 52 5636logMw
(c)
Figure 7 (a) 1HNMR spectrum in CDCl3 and (b) FTIR spectrum of PLA345-PDMAEMA213 block copolymers (c) Evolution of GPC tracesof the synthesized PLA345-PDMAEMA block copolymers with polymerization time of 1 (A) 3 (B) and 10 h (C)
2 4 6 8 100Time (h)
0
20
40
60
Con
vers
ion
()
0
20
40
60
Con
vers
ion
()
1 2 30Time (h)
(a)
0002040608
1 2 30Time (h)
2 4 6 8 100Time (h)
00
02
04
06
08
10
ＦＨ( [M
] 0[
])M
ＦＨ( [M
] 0[
])M
(b)
Figure 8 (a) Conversion and (b) kinetics plots for the RAFT polymerization of PLA-PDMAEMA block copolymers with increasingpolymerization time (1 2 3 4 7 and 10 h)
8 International Journal of Polymer Science
polymerization time in the initial 3 h A pseudo-first-orderkinetics for the RAFT polymerization of PDMAEMA wasdepicted at a low conversion (Figure 8(b)) However the rateof conversion decreases from 3 to 7 h and remains almostunchanged when the polymerization time increases from7 to 10 h These phenomena were mainly attributed to theincreasing viscosity of the reaction solution with the increaseof conversion At higher viscosity the motion of polymerchains becomes more difficult As a result terminationoccurred and the reaction rate decreased
4 Conclusions
PLA undergoes aminolytic degradation with EDA Theaminolysis reaction accelerated at increased EDA concentra-tion and reaction temperature The AD of PLA was rapidlyincreased in the initial stage and then reached a plateauThusthe molar masses of products rapidly decreased in the earlyreaction stage Furthermore ndashNH2 and ndashOH groups wereintroduced to the ends of the produced short PLA chainsThen the RAFT agent was immobilized onto the aminolyzedPLA chains and PLA-PDMAEMA block copolymers weresynthesized via RAFTpolymerization Conversion and kinet-ics plots for the RAFT polymerization of the block copoly-mers with increasing polymerization time were studied Theresults suggested a pseudo-first-order kinetics of the RAFTpolymerization of PDMAEMA at a low conversion Thelength distributions of the PLA and PDMAEMA blocks canbe controlled by controlling the aminolytic reaction andRAFT polymerization degrees in the process
Conflicts of Interest
The authors declare that they have no conflicts of interest
Acknowledgments
The authors are grateful for the financial support of theNational Natural Science Foundation of China (nos 31502213and 51473177) the Central Public-Interest Scientific Institu-tion Basal Research Fund CAFS (no 2018HY-XKQ03-4) andtheOpenFoundation fromFishery Sciences in the First-ClassSubjects of Zhejiang (no 20160014)
References
[1] M Okamoto and B John ldquoSynthetic biopolymer nanocompos-ites for tissue engineering scaffoldsrdquoProgress in Polymer Sciencevol 38 pp 1487ndash1503 2013
[2] N MacKiewicz J Nicolas N Handke et al ldquoPrecise engineer-ing of multifunctional PE gylated polyester nanoparticles forcancer cell targeting and imagingrdquo Chemistry of Materials vol26 no 5 pp 1834ndash1847 2014
[3] I Armentano N Bitinis E Fortunati et al ldquoMultifunctionalnanostructured PLA materials for packaging and tissue engi-neeringrdquo Progress in Polymer Science vol 38 no 10-11 pp 1720ndash1747 2013
[4] S Gupta R Tyagi V S Parmar S K Sharma and R HaagldquoPolyether based amphiphiles for delivery of active compo-nentsrdquoPolymer (UnitedKingdom) vol 53 no 15 pp 3053ndash30782012
[5] P Zhang R Tian R Lv B Na and Q Liu ldquoWater-permeablepolylactide blend membranes for hydrophilicity-based separa-tionrdquo Chemical Engineering Journal vol 269 pp 180ndash185 2015
[6] A J R Lasprilla G A R Martinez B H Lunelli A L Jardiniand R M Filho ldquoPoly-lactic acid synthesis for application inbiomedical devices - A reviewrdquo Biotechnology Advances vol 30no 1 pp 321ndash328 2012
[7] L-J Zhu F Liu X-M Yu A-L Gao and L-X Xue ldquoSurfacezwitterionization of hemocompatible poly(lactic acid) mem-branes for hemodiafiltrationrdquo Journal of Membrane Science vol475 pp 469ndash479 2015
[8] A Khoddami O Avinc and F Ghahremanzadeh ldquoImprove-ment in poly(lactic acid) fabric performance via hydrophiliccoatingrdquo Progress in Organic Coatings vol 72 no 3 pp 299ndash304 2011
[9] J Nicolas S Mura D Brambilla N MacKiewicz and PCouvreur ldquoDesign functionalization strategies and biomedicalapplications of targeted biodegradablebiocompatible polymer-based nanocarriers for drug deliveryrdquoChemical Society Reviewsvol 42 no 3 pp 1147ndash1235 2013
[10] Z Ge and S Liu ldquoFunctional block copolymer assembliesresponsive to tumor and intracellular microenvironments forsite-specific drug delivery and enhanced imaging performancerdquoChemical Society Reviews vol 42 no 17 pp 7289ndash7325 2013
[11] M Spasova L Mespouille O Coulembier et al ldquoAmphiphilicpoly(D- or L-lactide)-b-poly(NN-dimethylamino-2-ethylmethacrylate) block copolymers Controlled synthesis char-acterization and stereocomplex formationrdquo Biomacromole-cules vol 10 no 5 pp 1217ndash1223 2009
[12] K Jelonek S Li X Wu J Kasperczyk and A Marcinkow-ski ldquoSelf-assembled filomicelles prepared from polylactidepoly(ethylene glycol) block copolymers for anticancer drugdeliveryrdquo International Journal of Pharmaceutics vol 485 no1-2 Article ID 14741 pp 357ndash364 2015
[13] H Feng X Lu W Wang N-G Kang and J W MaysldquoBlock copolymers Synthesis self-assembly and applicationsrdquoPolymer vol 9 no 10 article no 494 2017
[14] C Y Zhang Y Q Yang T X Huang et al ldquoSelf-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micellesfor anticancer drug deliveryrdquo Biomaterials vol 33 no 26 pp6273ndash6283 2012
[15] J K Oh ldquoPolylactide (PLA)-based amphiphilic block copoly-mers Synthesis self-assembly and biomedical applicationsrdquoSoft Matter vol 7 no 11 pp 5096ndash5108 2011
[16] L Xiao X Xiong X Sun et al ldquoRole of cellular uptake inthe reversal of multidrug resistance by PEG-b-PLA polymericmicellesrdquo Biomaterials vol 32 no 22 pp 5148ndash5157 2011
[17] V Pertici T Trimaille J Laurin et al ldquoRepair of the injuredspinal cord by implantation of a synthetic degradable blockcopolymer in ratrdquo Biomaterials vol 35 no 24 pp 6248ndash62582014
[18] Z Zhu ldquoEffects of amphiphilic diblock copolymer on drugnanoparticle formation and stabilityrdquo Biomaterials vol 34 no38 pp 10238ndash10248 2013
[19] E Ayano M Karaki T Ishihara H Kanazawa and T OkanoldquoPoly (N-isopropylacrylamide)-PLA and PLA blend nanoparti-cles for temperature-controllable drug release and intracellular
International Journal of Polymer Science 9
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
the most popular and often synthesized by ring open-ing polymerization (ROP) of lactide [21ndash23] The lack offunctional groups in the resulting PEG-PLA block co-polymers that can be used for further bioconjugationshould be overcome PLA-poly(meth)acrylates block co-polymers such as PLA-poly(hydroxyethyl methacrylate)(PLA-PHEMA) [17 24] PLA-poly(NN-dimethylaminoethylmethacrylate) (PLA-PDMAEMA) [11 25] and PLA-poly(N-isopropylacrylamide) (PLA-PNIPAM) [19] are usuallysynthesized via ROP of lactide followed by atom transferradical polymerization (ATRP) or reversible addition frag-mentation chain transfer (RAFT) polymerization of variousmonomers
The end-of-life scenario of poly(L-lactide) products isthe degradation which is often induced by oxidation [26]irradiation [27 28] biological activity (ie enzymes [29] andmicroorganism [30ndash32]) thermal energy [33 34] aqueoussolutions and so on In numerous cases a variety of chemicalphysical and biological processes are always coexistent andaffect each other Aminolysis is a chemical degradationprocess that was developed to modify polyester surfacesAminolysis between the bulk polyester material and aminesolution is considered as nucleophilic substitution conferringthe polyester surface with amino (ndashNH2) and hydroxyl(ndashOH) groups [35 36] The ndashNH2 density and kinetics ofaminolysis occurring on bulk surfaces have been studiedFurthermore the ndashNH2 groups on the surface can be usedas sites to further immobilize bioactive molecules (such aspeptides proteins and polysaccharides) on the aminolyzedPLA membrane surfaces to create highly bioactive materials[37 38] However less attention has been focused on the basicknowledge on the aminolysis reaction of PLA in terms ofreaction kinetics and the detailed structures of the aminolyticPLA chains
In the present work in contrast to the known procedurefor preparation of PLA-based block copolymers combiningROP of lactide and controllable radical polymerizationwe synthesized PLA-PDMAEMA block copolymers via theaminolysis reaction of PLA chains and RAFT polymerizationof DMAEMA for the first time The synthesis strategyconsisted of a three-step procedure (a) controlled aminolysisreaction of PLA initiated by ethylenediamine (EDA) (b)conversion of the functional end-groups with RAFT agentand (c) RAFT polymerization of DMAEMA The aminolysisreaction of PLA was first investigated systematically Thereaction kinetics and chemical structures of the aminolyticPLA were analyzed as functions of temperature reactiontime and diamine concentration The molar masses ofthe copolymers were calculated via theoretical deductionand determined by gel permeation chromatography Thenchemical structures of the resultant PLA-PDMAEMA blockcopolymers and kinetic behaviors of the polymerizationwere characterized in detail The results in this study pro-vide valuable guidance for further synthesis of other PLA-poly(meth)acrylates block copolymers which opens a newpath to reuse PLA residues and reduce the consumption oflactide
2 Experimental Section
21 Materials and Reagents PLA (2002D) was suppliedby Natural Works Ethylenediamine (EDA) 46-dimethyl-2-pyridinamine (DMAP 98) and NN1015840-dicyclohexyl car-bodiimide (DCC 99) were purchased from Aladdin andused without further purification 2-(Dimethylamino) ethylmethacrylate (DMAEMA) was bought from Aladdin andpassed through a column filled with basic alumina toremove the polymerization inhibitors Azobisisobutyronitrile(AIBN) was supplied by Shanghai Chemical Reagent Com-pany and recrystallized twice with ethanol RAFT agent of4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoicacid (CDP) was synthesized according to the reported pro-cedure in the literature [39] All other reagents such as14-dioxane NN1015840-dimethylformamide (DMF) and tetrahy-drofuran (THF) ethanol were brought from SinopharmChemical Reagent Co Ltd China and used directly
22 Aminolysis of PLA We followed the methods of Zhu etal (2015) to synthesize PLA-based block copolymers via theaminolysis reaction of PLA chains and RAFT polymerizationof DMAEMA [40] In a typical aminolysis reaction of PLAwith EDA PLA (5 g) was dissolved in 14-dioxane (45 g)under stirring for 12 h EDA at various concentrations (105 and 01mmolg) was dropped into the above PLAsolution under stirring Immediately the aminolysis of PLAwas carried out at a given temperature (18 30 and 40∘C)After reaction for predetermined time the polymer solutionwas precipitated in excessive water The raw product wasseparated through filtration and thoroughly washed withwater The solid final product was obtained by freeze-dryingfor 24 h and named as PLA-EDA The yield of the degradedPLAs after reprecipitation is 82sim85
23 Synthesis of Macromolecular Chain Transfer Agent (PLA-CDP) In brief the obtained PLA-EDA (5 g) was dissolvedin THF (50mL) under stirring at 25∘C for 1 h Then DCC(105 g 5mmol) DMAP (06 g 5mmol) and CDP (10 g25mmol) were serially added to themixture Amide reactionand esterification between the ndashNH2ndashOH groups of PLA-EDA and the ndashCOOH groups of CDP occurred After 24 hthe mixture was precipitated and thoroughly washed inexcessive ethanol for at least three times The solid productof macromolecular chain transfer agent (PLA-CDP) wasrecovered through filtration and dried in vacuum oven at40∘C
24 Synthesis of PLA-PDMAEMA Block Copolymers PLA-based block copolymers were synthesized via RAFT poly-merization PLA-CDP and AIBN were used as macromolec-ular chain transfer agent and initiator respectively As anexample the synthesis procedures of PLA-PDMAEMA blockcopolymers via RAFT polymerization were briefly shownbelow PLA-CDP (2 g) was dissolved in DMF (20mL) understirring at 20∘C After 1 h DMAEMA (5 g 32mmol) andAIBN (5mg 003mmol) were added and degassed withN2 for an additional 15 h at 20∘C Then the mixture wastransferred to an oil bath at 70∘C under N2 protection
International Journal of Polymer Science 3
CHO C
H
O C
O
O O O
O O O
C
H
O C C
H
O C C OH
H
Poly(lactic acid) (PLA)
CHO C
H
O C CH
O C CH
O C C OH
H
HO C CH
O C CH
O C C OH
H
CHO C
H
O C CH
O CHN C
H
O C CH
O C C OH
H
O O O
C C
H
O
（3（3（3（3
（2EDA （2
（2
（2
（2
（3 （3
（3
（3 （3（3 （3 （3
（3 （3 （3
（3 （3
+（2
+（2
+
minus
minus
P
P
P
nm
O O O O O
（
Figure 1 Aminolysis mechanism of PLA with EDA
and stirring After a predetermined time the reaction wasterminated by quenching in ice water and the polymersolution was precipitated and washed in excessive waterThe solid PLA-PDMAEMA block copolymers were obtainedthrough filtration and freeze dried
25 Characterization 1HNMR spectra were performed witha Bruker Advance III spectrometer at room temperature inCDCl3 or DMSO-d6 with Si(CH3)4 as an internal standardGel permeation chromatography (GPC)was conducted usinga Waters 510 HPLC pump Waters Styragel columns anda Waters 410 differential refractometer (Millipore CorpBedford MA) at 40∘C in THF with a flow rate of 1mLminPMMA was used as a calibration standard The chemicalcompositions of the synthesized block copolymers werecharacterized by Fourier transform infrared spectrometer(FTIR Thermo-Nicolet 6700 US) and X-ray photoelectronspectrometer (XPS Shimadzu Axis UltraDLD Japan) withMg K120572 excitation radiation at a take-off angle of 45∘
3 Results and Discussion
31 Structure and Characterization ofthe Aminolyzed PLA with EDA
311 Chemical Structure Similar to the reaction withpolyethylene terephthalate (PET) [41] amine acts as a nucle-ophile to attack PLA at the electron deficient center ndashC=O Anew active group is introduced to the end units The reaction
of PLA with EDA was studied carefully in this work Theaminolysis mechanism is shown in Figure 1 Figure 2 showsthe structures of raw PLA and PLA-EDA as characterizedby 1H NMR Several signals can be distinguished as followsSignals in the 159sim157 (A) and 519sim514 ppm range (B)belong to the ndashCH3 and ndashCH protons of the PLA main chainunits Compared to raw PLA PLA-EDA exhibits the newpeaks in the 148sim150 (a) and 433sim439 ppm ranges (b)which are attributed to the ndashCH3 and ndashCH protons of thehydroxylated lactyl end units The peaks at 523 and 161 ppm((d) and (c)) are assigned to the ndashCH and ndashCH3 protonsconnecting with EDA groupsThe peaks of the C2H4 protonsfrom residual EDA are presented at 375sim321 ppm range (e)In addition the signals at 525 and 154 ppm ((g) and (f))belong to the ndashCH and ndashCH3 protons of the carboxylatedlactyl end unitsThe 1HNMR results confirmed the proposedaminolysis mechanism illustrated in Figure 1
312 Aminolysis Degree Aminolysis degree (AD ) wasintroduced to evaluate the extent of aminolysis reaction andcalculated from the 1H NMR spectra according to
AD =119878119887119878alltimes 100 (1)
where 119878119887 and 119878all are the integral areas of peak 119887 as shown inFigure 2 and all peaks of the ndashCH protons respectively
The AD of PLA with EDA is dependent on EDA concen-tration reaction time and temperature as shown in Figure 3
4 International Journal of Polymer Science
53 52 51 44 43 17 16 1540 35 30
PLA-EDA
(g)(d)
(g)
(f)
(B) (b)
(b)
(a)
(a)
(f)(c)
(c)
(d)
(A)
(e)
(e)
CDCl3
C C
H
（3 O
O OHPLA CC
H
（3
OHPLA
O
C C
H
（3 O
O NHPLA （2
O C C
H
n
O
8 7 6 5 4(ppm)
3 012
PLA (B)
(B)
(A)(A)（3
＄Ｆ3
Figure 2 1HNMR spectra of raw PLA and PLA-EDA in CDCl3 Aminolysis condition of PLAwith EDA 30∘C 30min [EDA] = 10mmolg
The AD of PLA increases with the prolongation of reactiontime In detail AD is rapidly increased in the initial 10minof aminolysis and slows down from 10 to 60min After60min AD data becomes difficult to obtain because the solidproducts cannot be separated from the precipitation solutionFigure 3(a) shows a faster growth of AD with increasingEDA concentration Furthermore the aminolysis reactionwas also accelerated at higher temperature when the EDAconcentration was 05mmolg (Figure 3(b)) At the EDAconcentration of 10mmolg the AD is as high as 103 afterreacting at 40∘C for 60min
313 Molar Mass Analysis According to the aminolysismechanism of PLA chain scission results in decreasedmolar mass The products were subjected to GPC analysesand the results are shown in Figure 4 The GPC traces(Figure 4(a)) indicated that the molar mass distributionof the measured PLA-EDA remained unimodal suggesting
statistically random scission of the polymer chains Fur-thermore with increasing reaction time the GPC tracesshift toward low molar mass The number average molec-ular weight determined by GPC (119872119899GPC) is exhibited inFigure 4(b) The 119872119899GPC decreased rapidly in the low ADrange and the decline rate slowed down with increasingAD The aminolysis reaction is considered as the reverse ofpolycondensation [42] Lower AD is roughly equivalent tohigher polycondensation extent For the polymer synthesizedvia polycondensation 119872119899GPC increases gradually in theinitial polymerization under high polymerization degree119872119899GPC significantly increases due to a small increase inthe polymerization degree [42] As a result the changingtrend of Mn for the aminolyzed PLA is similar to that ofpolycondensation polymer Moreover similar to the changein polydispersity index (ETH) in polycondensation the ETHof PLA-EDA became narrower with the increase of AD(Figure 4(b)) Lower polycondensation extent indicates less
International Journal of Polymer Science 5
0
2
4
6
8
10A
D (
)
10 20 30 40 50 600Time (min)
05 mmolg10 mmolg
01 mmolg
(a)
0
3
6
9
12
AD
()
10 20 30 40 50 600Time (min)
40∘C30∘C18∘C
(b)
Figure 3 AD as a function of reaction time with different EDA concentrations at 30∘C (a) and different reaction temperatures at an EDAconcentration of 05mmolg
30 35 40 45 50 55 60 6525
20
AD
29
00 3859
ＦＩＡMw
(a)
PDI
0
15
30
45
60
75
2 4 60AD ()
3 4 5 62
2
4
6
13
14
15
16
17
18
19
ETH
times10
3(g
mol
)M
n
Mn０
MnＮＢ
(b)
Figure 4 Evolution of GPC traces (a) and number average molecular weight (119872119899) and molecular weight polydispersity (K = 119872119908119872119899) (b)of the PLA-PEA with aminolysis degree (119860119863)
ETHTheETH decreases with the increasing AD of PLAwith EDAExcept for119872119899GPC the theoretical Mn (119872119899th) of PLA-EDAwas calculated by (2) as shown in Figure 4(b) The 119872119899thvalue is slightly less than the GPC obtained value due tothe different flexibilities of the polymer chains between PLA-EDA and the GPC calibrating standards (PMMA) Howeverthe tendency of119872119899th is in accordance with119872119899GPC
119872119899th =119872119899PLA + AD times119872EDA times119872119899PLA119872PLA1 + AD times119872119899PLA119872PLA
(2)
where 119872119899PLA and 119872PLA are the number average molarmasses of PLA and PLA repeating units respectively119872EDAand AD are the molar mass of EDA and degree of aminolysisrespectively
32 Structure and Characterization of the SynthesizedPLA-Based Block Copolymers
321 Chemical Structure Despite being an eco-friendly bio-plastic with excellent biocompatibility and processability
6 International Journal of Polymer Science
Table 1 Molar weight (Mn) polydispersity (K) of the synthesized PLA-PDMAEMA block copolymers andmass ratio of PDMAEMA blocks(119891PDMAEMA) in the copolymers
Figure 5 Schematic illustration for the preparation of PLA-PDMAEMA block copolymers via RAFT polymerization
PLA is chemically inert without reactive sidechain groupsthereby making its modifications a challenging task [43]After the aminolysis reaction of PLA with EDA the reactivendashNH2 and ndashOH groups can be introduced to the ends of thePLA chains providing opportunity to furthermodify PLA Inthe present work PLA-PDMAEMA block copolymers weresynthesized from PLA segments after aminolysis reaction viaRAFT polymerization Figure 5 shows the fabrication pro-cesses First RAFT agent CDP was immobilized on the reac-tive groups of PLA-EDA via the amide reactionesterificationunder the catalysis ofDCCDMAP inTHFThen the obtainedPLA-CDP was used as the chain transfer agent to regu-late RAFT polymerization of monomers to produce PLA-based block copolymers In the present work a serial ofPLA-PDMAEMA block copolymers were synthesized Themolar weight (Mn) polydispersity (ETH) and mass ratio ofPDMAEMA blocks (119891PDMAEMA) in the copolymers are listedin Table 1
To detect the chemical compositions of the synthesizedPLA-CDP XPS was employed The XPS wide scan andthe elemental mole percentages are shown in Figure 6(a)The peak of S 2p is observed Figure 6(b) shows the 1HNMR spectrum of PLA-CDP The peaks in 425sim413 ppm
range are attributed to the C2H4 protons connected withamide group The peaks of the CH3 protons at (a) and (c)in Figure 2 disappeared These results confirm that PLA-CDP was synthesized successfully It can be used as thechain transfer agent to regulate RAFT polymerization ofDMAEMA
PLA345-PDMAEMA60 block copolymers were character-ized by 1H NMR in CDCl3 and the obtained 1H NMRspectrum is shown in Figure 7(a) The signals in the 519sim514 (A) and 159sim157 ppm range (B) belong to ndashCH andndashCH3 protons of the main chain PLA units The peaks inthe 182 (C) and 091sim106 ppm range (D) are attributed tothe ndashCH2 and ndashCH3 protons of the main chain PDMAEMAunits The signals at 409 (E) and 263 ppm (F) correspondto the ndashCH2 protons connected to the ester and tertiaryamine groups of PDMAEMA respectively The peaks in238sim234 ppm range (G) are attributed to ndashCH3 protonsconnected to the tertiary amine groups In addition FT-IR spectrum of PLA345-PDMAEMA213 block copolymers isshown in Figure 7(b) The peak at around 1758 cmminus1 is thestretching vibration of C=O in ester groups of PLA blocksThe adsorption peaks at about 2823sim2722 and 1730 cmminus1 areascribed to ndashN(CH3)2 and OndashC=O groups of PDMAEMAchains respectively Furthermore the GPC traces of PLA345-PDMAEMA block copolymers with different polymerizationtimes are shown in Figure 7(c) The GPC traces of PLA345-DMAEMA block copolymers exhibit one monomodal distri-butionTheMn of PLA345-PDMAEMA increases from 26300to 58400 gmolwith the increase of polymerization time from1 to 10 h as shown in Table 1 All data indicate that the PLA345-PDMAEMA block copolymers were successfully synthesizedvia RAFT polymerization based on aminolyzed PLA withEDA
322 Kinetic Behavior of the RAFT Polymerization TheRAFT polymerization kinetic behavior of PLA345-PDMAE-MA block copolymers was investigated Conversion andkinetics plots for the RAFT polymerization of the blockcopolymers with increasing polymerization time (1 2 3 4 7and 10 h) are shown in Figure 8 Figure 8(a) further shows thatthe conversion of DMAEMA linearly increases with RAFT
International Journal of Polymer Science 7
Components (mol)C 1s 621O 1s 362S 2p 17
C 1sO 1s
S 2p
164 160168
400 200 0600Binding energy (eV)
(a)
C C
H
O
O NH NHPLA C
O（3
C C SS
S
CN
（3
2（4 12（25
lowast
lowast
6 4 2 08(ppm)
16 151742 4143
(b)
Figure 6 (a) XPS wide scan and elemental mole percentages and (b) 1H NMR spectrum in CDCl3 of PLA345-CDP
＄Ｆ3
8 7 6 5 4(ppm)
3 012
(G) (G)
(G)
(B)
(B)
(C)
(C)
(D)
(D)
(E)
(E)
(A)
(A)
(F)
(F)
O C C
H
nC
C
m
O
O
N
O
（3 （3
（2
(a)
1730
1800 1700
1758minus(（3)2
2000 100030004000
Wavenumbers (＝Ｇminus1)
(b)
(A) (B) (C)
40 44 48 52 5636logMw
(c)
Figure 7 (a) 1HNMR spectrum in CDCl3 and (b) FTIR spectrum of PLA345-PDMAEMA213 block copolymers (c) Evolution of GPC tracesof the synthesized PLA345-PDMAEMA block copolymers with polymerization time of 1 (A) 3 (B) and 10 h (C)
2 4 6 8 100Time (h)
0
20
40
60
Con
vers
ion
()
0
20
40
60
Con
vers
ion
()
1 2 30Time (h)
(a)
0002040608
1 2 30Time (h)
2 4 6 8 100Time (h)
00
02
04
06
08
10
ＦＨ( [M
] 0[
])M
ＦＨ( [M
] 0[
])M
(b)
Figure 8 (a) Conversion and (b) kinetics plots for the RAFT polymerization of PLA-PDMAEMA block copolymers with increasingpolymerization time (1 2 3 4 7 and 10 h)
8 International Journal of Polymer Science
polymerization time in the initial 3 h A pseudo-first-orderkinetics for the RAFT polymerization of PDMAEMA wasdepicted at a low conversion (Figure 8(b)) However the rateof conversion decreases from 3 to 7 h and remains almostunchanged when the polymerization time increases from7 to 10 h These phenomena were mainly attributed to theincreasing viscosity of the reaction solution with the increaseof conversion At higher viscosity the motion of polymerchains becomes more difficult As a result terminationoccurred and the reaction rate decreased
4 Conclusions
PLA undergoes aminolytic degradation with EDA Theaminolysis reaction accelerated at increased EDA concentra-tion and reaction temperature The AD of PLA was rapidlyincreased in the initial stage and then reached a plateauThusthe molar masses of products rapidly decreased in the earlyreaction stage Furthermore ndashNH2 and ndashOH groups wereintroduced to the ends of the produced short PLA chainsThen the RAFT agent was immobilized onto the aminolyzedPLA chains and PLA-PDMAEMA block copolymers weresynthesized via RAFTpolymerization Conversion and kinet-ics plots for the RAFT polymerization of the block copoly-mers with increasing polymerization time were studied Theresults suggested a pseudo-first-order kinetics of the RAFTpolymerization of PDMAEMA at a low conversion Thelength distributions of the PLA and PDMAEMA blocks canbe controlled by controlling the aminolytic reaction andRAFT polymerization degrees in the process
Conflicts of Interest
The authors declare that they have no conflicts of interest
Acknowledgments
The authors are grateful for the financial support of theNational Natural Science Foundation of China (nos 31502213and 51473177) the Central Public-Interest Scientific Institu-tion Basal Research Fund CAFS (no 2018HY-XKQ03-4) andtheOpenFoundation fromFishery Sciences in the First-ClassSubjects of Zhejiang (no 20160014)
References
[1] M Okamoto and B John ldquoSynthetic biopolymer nanocompos-ites for tissue engineering scaffoldsrdquoProgress in Polymer Sciencevol 38 pp 1487ndash1503 2013
[2] N MacKiewicz J Nicolas N Handke et al ldquoPrecise engineer-ing of multifunctional PE gylated polyester nanoparticles forcancer cell targeting and imagingrdquo Chemistry of Materials vol26 no 5 pp 1834ndash1847 2014
[3] I Armentano N Bitinis E Fortunati et al ldquoMultifunctionalnanostructured PLA materials for packaging and tissue engi-neeringrdquo Progress in Polymer Science vol 38 no 10-11 pp 1720ndash1747 2013
[4] S Gupta R Tyagi V S Parmar S K Sharma and R HaagldquoPolyether based amphiphiles for delivery of active compo-nentsrdquoPolymer (UnitedKingdom) vol 53 no 15 pp 3053ndash30782012
[5] P Zhang R Tian R Lv B Na and Q Liu ldquoWater-permeablepolylactide blend membranes for hydrophilicity-based separa-tionrdquo Chemical Engineering Journal vol 269 pp 180ndash185 2015
[6] A J R Lasprilla G A R Martinez B H Lunelli A L Jardiniand R M Filho ldquoPoly-lactic acid synthesis for application inbiomedical devices - A reviewrdquo Biotechnology Advances vol 30no 1 pp 321ndash328 2012
[7] L-J Zhu F Liu X-M Yu A-L Gao and L-X Xue ldquoSurfacezwitterionization of hemocompatible poly(lactic acid) mem-branes for hemodiafiltrationrdquo Journal of Membrane Science vol475 pp 469ndash479 2015
[8] A Khoddami O Avinc and F Ghahremanzadeh ldquoImprove-ment in poly(lactic acid) fabric performance via hydrophiliccoatingrdquo Progress in Organic Coatings vol 72 no 3 pp 299ndash304 2011
[9] J Nicolas S Mura D Brambilla N MacKiewicz and PCouvreur ldquoDesign functionalization strategies and biomedicalapplications of targeted biodegradablebiocompatible polymer-based nanocarriers for drug deliveryrdquoChemical Society Reviewsvol 42 no 3 pp 1147ndash1235 2013
[10] Z Ge and S Liu ldquoFunctional block copolymer assembliesresponsive to tumor and intracellular microenvironments forsite-specific drug delivery and enhanced imaging performancerdquoChemical Society Reviews vol 42 no 17 pp 7289ndash7325 2013
[11] M Spasova L Mespouille O Coulembier et al ldquoAmphiphilicpoly(D- or L-lactide)-b-poly(NN-dimethylamino-2-ethylmethacrylate) block copolymers Controlled synthesis char-acterization and stereocomplex formationrdquo Biomacromole-cules vol 10 no 5 pp 1217ndash1223 2009
[12] K Jelonek S Li X Wu J Kasperczyk and A Marcinkow-ski ldquoSelf-assembled filomicelles prepared from polylactidepoly(ethylene glycol) block copolymers for anticancer drugdeliveryrdquo International Journal of Pharmaceutics vol 485 no1-2 Article ID 14741 pp 357ndash364 2015
[13] H Feng X Lu W Wang N-G Kang and J W MaysldquoBlock copolymers Synthesis self-assembly and applicationsrdquoPolymer vol 9 no 10 article no 494 2017
[14] C Y Zhang Y Q Yang T X Huang et al ldquoSelf-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micellesfor anticancer drug deliveryrdquo Biomaterials vol 33 no 26 pp6273ndash6283 2012
[15] J K Oh ldquoPolylactide (PLA)-based amphiphilic block copoly-mers Synthesis self-assembly and biomedical applicationsrdquoSoft Matter vol 7 no 11 pp 5096ndash5108 2011
[16] L Xiao X Xiong X Sun et al ldquoRole of cellular uptake inthe reversal of multidrug resistance by PEG-b-PLA polymericmicellesrdquo Biomaterials vol 32 no 22 pp 5148ndash5157 2011
[17] V Pertici T Trimaille J Laurin et al ldquoRepair of the injuredspinal cord by implantation of a synthetic degradable blockcopolymer in ratrdquo Biomaterials vol 35 no 24 pp 6248ndash62582014
[18] Z Zhu ldquoEffects of amphiphilic diblock copolymer on drugnanoparticle formation and stabilityrdquo Biomaterials vol 34 no38 pp 10238ndash10248 2013
[19] E Ayano M Karaki T Ishihara H Kanazawa and T OkanoldquoPoly (N-isopropylacrylamide)-PLA and PLA blend nanoparti-cles for temperature-controllable drug release and intracellular
International Journal of Polymer Science 9
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
and stirring After a predetermined time the reaction wasterminated by quenching in ice water and the polymersolution was precipitated and washed in excessive waterThe solid PLA-PDMAEMA block copolymers were obtainedthrough filtration and freeze dried
25 Characterization 1HNMR spectra were performed witha Bruker Advance III spectrometer at room temperature inCDCl3 or DMSO-d6 with Si(CH3)4 as an internal standardGel permeation chromatography (GPC)was conducted usinga Waters 510 HPLC pump Waters Styragel columns anda Waters 410 differential refractometer (Millipore CorpBedford MA) at 40∘C in THF with a flow rate of 1mLminPMMA was used as a calibration standard The chemicalcompositions of the synthesized block copolymers werecharacterized by Fourier transform infrared spectrometer(FTIR Thermo-Nicolet 6700 US) and X-ray photoelectronspectrometer (XPS Shimadzu Axis UltraDLD Japan) withMg K120572 excitation radiation at a take-off angle of 45∘
3 Results and Discussion
31 Structure and Characterization ofthe Aminolyzed PLA with EDA
311 Chemical Structure Similar to the reaction withpolyethylene terephthalate (PET) [41] amine acts as a nucle-ophile to attack PLA at the electron deficient center ndashC=O Anew active group is introduced to the end units The reaction
of PLA with EDA was studied carefully in this work Theaminolysis mechanism is shown in Figure 1 Figure 2 showsthe structures of raw PLA and PLA-EDA as characterizedby 1H NMR Several signals can be distinguished as followsSignals in the 159sim157 (A) and 519sim514 ppm range (B)belong to the ndashCH3 and ndashCH protons of the PLA main chainunits Compared to raw PLA PLA-EDA exhibits the newpeaks in the 148sim150 (a) and 433sim439 ppm ranges (b)which are attributed to the ndashCH3 and ndashCH protons of thehydroxylated lactyl end units The peaks at 523 and 161 ppm((d) and (c)) are assigned to the ndashCH and ndashCH3 protonsconnecting with EDA groupsThe peaks of the C2H4 protonsfrom residual EDA are presented at 375sim321 ppm range (e)In addition the signals at 525 and 154 ppm ((g) and (f))belong to the ndashCH and ndashCH3 protons of the carboxylatedlactyl end unitsThe 1HNMR results confirmed the proposedaminolysis mechanism illustrated in Figure 1
312 Aminolysis Degree Aminolysis degree (AD ) wasintroduced to evaluate the extent of aminolysis reaction andcalculated from the 1H NMR spectra according to
AD =119878119887119878alltimes 100 (1)
where 119878119887 and 119878all are the integral areas of peak 119887 as shown inFigure 2 and all peaks of the ndashCH protons respectively
The AD of PLA with EDA is dependent on EDA concen-tration reaction time and temperature as shown in Figure 3
4 International Journal of Polymer Science
53 52 51 44 43 17 16 1540 35 30
PLA-EDA
(g)(d)
(g)
(f)
(B) (b)
(b)
(a)
(a)
(f)(c)
(c)
(d)
(A)
(e)
(e)
CDCl3
C C
H
（3 O
O OHPLA CC
H
（3
OHPLA
O
C C
H
（3 O
O NHPLA （2
O C C
H
n
O
8 7 6 5 4(ppm)
3 012
PLA (B)
(B)
(A)(A)（3
＄Ｆ3
Figure 2 1HNMR spectra of raw PLA and PLA-EDA in CDCl3 Aminolysis condition of PLAwith EDA 30∘C 30min [EDA] = 10mmolg
The AD of PLA increases with the prolongation of reactiontime In detail AD is rapidly increased in the initial 10minof aminolysis and slows down from 10 to 60min After60min AD data becomes difficult to obtain because the solidproducts cannot be separated from the precipitation solutionFigure 3(a) shows a faster growth of AD with increasingEDA concentration Furthermore the aminolysis reactionwas also accelerated at higher temperature when the EDAconcentration was 05mmolg (Figure 3(b)) At the EDAconcentration of 10mmolg the AD is as high as 103 afterreacting at 40∘C for 60min
313 Molar Mass Analysis According to the aminolysismechanism of PLA chain scission results in decreasedmolar mass The products were subjected to GPC analysesand the results are shown in Figure 4 The GPC traces(Figure 4(a)) indicated that the molar mass distributionof the measured PLA-EDA remained unimodal suggesting
statistically random scission of the polymer chains Fur-thermore with increasing reaction time the GPC tracesshift toward low molar mass The number average molec-ular weight determined by GPC (119872119899GPC) is exhibited inFigure 4(b) The 119872119899GPC decreased rapidly in the low ADrange and the decline rate slowed down with increasingAD The aminolysis reaction is considered as the reverse ofpolycondensation [42] Lower AD is roughly equivalent tohigher polycondensation extent For the polymer synthesizedvia polycondensation 119872119899GPC increases gradually in theinitial polymerization under high polymerization degree119872119899GPC significantly increases due to a small increase inthe polymerization degree [42] As a result the changingtrend of Mn for the aminolyzed PLA is similar to that ofpolycondensation polymer Moreover similar to the changein polydispersity index (ETH) in polycondensation the ETHof PLA-EDA became narrower with the increase of AD(Figure 4(b)) Lower polycondensation extent indicates less
International Journal of Polymer Science 5
0
2
4
6
8
10A
D (
)
10 20 30 40 50 600Time (min)
05 mmolg10 mmolg
01 mmolg
(a)
0
3
6
9
12
AD
()
10 20 30 40 50 600Time (min)
40∘C30∘C18∘C
(b)
Figure 3 AD as a function of reaction time with different EDA concentrations at 30∘C (a) and different reaction temperatures at an EDAconcentration of 05mmolg
30 35 40 45 50 55 60 6525
20
AD
29
00 3859
ＦＩＡMw
(a)
PDI
0
15
30
45
60
75
2 4 60AD ()
3 4 5 62
2
4
6
13
14
15
16
17
18
19
ETH
times10
3(g
mol
)M
n
Mn０
MnＮＢ
(b)
Figure 4 Evolution of GPC traces (a) and number average molecular weight (119872119899) and molecular weight polydispersity (K = 119872119908119872119899) (b)of the PLA-PEA with aminolysis degree (119860119863)
ETHTheETH decreases with the increasing AD of PLAwith EDAExcept for119872119899GPC the theoretical Mn (119872119899th) of PLA-EDAwas calculated by (2) as shown in Figure 4(b) The 119872119899thvalue is slightly less than the GPC obtained value due tothe different flexibilities of the polymer chains between PLA-EDA and the GPC calibrating standards (PMMA) Howeverthe tendency of119872119899th is in accordance with119872119899GPC
119872119899th =119872119899PLA + AD times119872EDA times119872119899PLA119872PLA1 + AD times119872119899PLA119872PLA
(2)
where 119872119899PLA and 119872PLA are the number average molarmasses of PLA and PLA repeating units respectively119872EDAand AD are the molar mass of EDA and degree of aminolysisrespectively
32 Structure and Characterization of the SynthesizedPLA-Based Block Copolymers
321 Chemical Structure Despite being an eco-friendly bio-plastic with excellent biocompatibility and processability
6 International Journal of Polymer Science
Table 1 Molar weight (Mn) polydispersity (K) of the synthesized PLA-PDMAEMA block copolymers andmass ratio of PDMAEMA blocks(119891PDMAEMA) in the copolymers
Figure 5 Schematic illustration for the preparation of PLA-PDMAEMA block copolymers via RAFT polymerization
PLA is chemically inert without reactive sidechain groupsthereby making its modifications a challenging task [43]After the aminolysis reaction of PLA with EDA the reactivendashNH2 and ndashOH groups can be introduced to the ends of thePLA chains providing opportunity to furthermodify PLA Inthe present work PLA-PDMAEMA block copolymers weresynthesized from PLA segments after aminolysis reaction viaRAFT polymerization Figure 5 shows the fabrication pro-cesses First RAFT agent CDP was immobilized on the reac-tive groups of PLA-EDA via the amide reactionesterificationunder the catalysis ofDCCDMAP inTHFThen the obtainedPLA-CDP was used as the chain transfer agent to regu-late RAFT polymerization of monomers to produce PLA-based block copolymers In the present work a serial ofPLA-PDMAEMA block copolymers were synthesized Themolar weight (Mn) polydispersity (ETH) and mass ratio ofPDMAEMA blocks (119891PDMAEMA) in the copolymers are listedin Table 1
To detect the chemical compositions of the synthesizedPLA-CDP XPS was employed The XPS wide scan andthe elemental mole percentages are shown in Figure 6(a)The peak of S 2p is observed Figure 6(b) shows the 1HNMR spectrum of PLA-CDP The peaks in 425sim413 ppm
range are attributed to the C2H4 protons connected withamide group The peaks of the CH3 protons at (a) and (c)in Figure 2 disappeared These results confirm that PLA-CDP was synthesized successfully It can be used as thechain transfer agent to regulate RAFT polymerization ofDMAEMA
PLA345-PDMAEMA60 block copolymers were character-ized by 1H NMR in CDCl3 and the obtained 1H NMRspectrum is shown in Figure 7(a) The signals in the 519sim514 (A) and 159sim157 ppm range (B) belong to ndashCH andndashCH3 protons of the main chain PLA units The peaks inthe 182 (C) and 091sim106 ppm range (D) are attributed tothe ndashCH2 and ndashCH3 protons of the main chain PDMAEMAunits The signals at 409 (E) and 263 ppm (F) correspondto the ndashCH2 protons connected to the ester and tertiaryamine groups of PDMAEMA respectively The peaks in238sim234 ppm range (G) are attributed to ndashCH3 protonsconnected to the tertiary amine groups In addition FT-IR spectrum of PLA345-PDMAEMA213 block copolymers isshown in Figure 7(b) The peak at around 1758 cmminus1 is thestretching vibration of C=O in ester groups of PLA blocksThe adsorption peaks at about 2823sim2722 and 1730 cmminus1 areascribed to ndashN(CH3)2 and OndashC=O groups of PDMAEMAchains respectively Furthermore the GPC traces of PLA345-PDMAEMA block copolymers with different polymerizationtimes are shown in Figure 7(c) The GPC traces of PLA345-DMAEMA block copolymers exhibit one monomodal distri-butionTheMn of PLA345-PDMAEMA increases from 26300to 58400 gmolwith the increase of polymerization time from1 to 10 h as shown in Table 1 All data indicate that the PLA345-PDMAEMA block copolymers were successfully synthesizedvia RAFT polymerization based on aminolyzed PLA withEDA
322 Kinetic Behavior of the RAFT Polymerization TheRAFT polymerization kinetic behavior of PLA345-PDMAE-MA block copolymers was investigated Conversion andkinetics plots for the RAFT polymerization of the blockcopolymers with increasing polymerization time (1 2 3 4 7and 10 h) are shown in Figure 8 Figure 8(a) further shows thatthe conversion of DMAEMA linearly increases with RAFT
International Journal of Polymer Science 7
Components (mol)C 1s 621O 1s 362S 2p 17
C 1sO 1s
S 2p
164 160168
400 200 0600Binding energy (eV)
(a)
C C
H
O
O NH NHPLA C
O（3
C C SS
S
CN
（3
2（4 12（25
lowast
lowast
6 4 2 08(ppm)
16 151742 4143
(b)
Figure 6 (a) XPS wide scan and elemental mole percentages and (b) 1H NMR spectrum in CDCl3 of PLA345-CDP
＄Ｆ3
8 7 6 5 4(ppm)
3 012
(G) (G)
(G)
(B)
(B)
(C)
(C)
(D)
(D)
(E)
(E)
(A)
(A)
(F)
(F)
O C C
H
nC
C
m
O
O
N
O
（3 （3
（2
(a)
1730
1800 1700
1758minus(（3)2
2000 100030004000
Wavenumbers (＝Ｇminus1)
(b)
(A) (B) (C)
40 44 48 52 5636logMw
(c)
Figure 7 (a) 1HNMR spectrum in CDCl3 and (b) FTIR spectrum of PLA345-PDMAEMA213 block copolymers (c) Evolution of GPC tracesof the synthesized PLA345-PDMAEMA block copolymers with polymerization time of 1 (A) 3 (B) and 10 h (C)
2 4 6 8 100Time (h)
0
20
40
60
Con
vers
ion
()
0
20
40
60
Con
vers
ion
()
1 2 30Time (h)
(a)
0002040608
1 2 30Time (h)
2 4 6 8 100Time (h)
00
02
04
06
08
10
ＦＨ( [M
] 0[
])M
ＦＨ( [M
] 0[
])M
(b)
Figure 8 (a) Conversion and (b) kinetics plots for the RAFT polymerization of PLA-PDMAEMA block copolymers with increasingpolymerization time (1 2 3 4 7 and 10 h)
8 International Journal of Polymer Science
polymerization time in the initial 3 h A pseudo-first-orderkinetics for the RAFT polymerization of PDMAEMA wasdepicted at a low conversion (Figure 8(b)) However the rateof conversion decreases from 3 to 7 h and remains almostunchanged when the polymerization time increases from7 to 10 h These phenomena were mainly attributed to theincreasing viscosity of the reaction solution with the increaseof conversion At higher viscosity the motion of polymerchains becomes more difficult As a result terminationoccurred and the reaction rate decreased
4 Conclusions
PLA undergoes aminolytic degradation with EDA Theaminolysis reaction accelerated at increased EDA concentra-tion and reaction temperature The AD of PLA was rapidlyincreased in the initial stage and then reached a plateauThusthe molar masses of products rapidly decreased in the earlyreaction stage Furthermore ndashNH2 and ndashOH groups wereintroduced to the ends of the produced short PLA chainsThen the RAFT agent was immobilized onto the aminolyzedPLA chains and PLA-PDMAEMA block copolymers weresynthesized via RAFTpolymerization Conversion and kinet-ics plots for the RAFT polymerization of the block copoly-mers with increasing polymerization time were studied Theresults suggested a pseudo-first-order kinetics of the RAFTpolymerization of PDMAEMA at a low conversion Thelength distributions of the PLA and PDMAEMA blocks canbe controlled by controlling the aminolytic reaction andRAFT polymerization degrees in the process
Conflicts of Interest
The authors declare that they have no conflicts of interest
Acknowledgments
The authors are grateful for the financial support of theNational Natural Science Foundation of China (nos 31502213and 51473177) the Central Public-Interest Scientific Institu-tion Basal Research Fund CAFS (no 2018HY-XKQ03-4) andtheOpenFoundation fromFishery Sciences in the First-ClassSubjects of Zhejiang (no 20160014)
References
[1] M Okamoto and B John ldquoSynthetic biopolymer nanocompos-ites for tissue engineering scaffoldsrdquoProgress in Polymer Sciencevol 38 pp 1487ndash1503 2013
[2] N MacKiewicz J Nicolas N Handke et al ldquoPrecise engineer-ing of multifunctional PE gylated polyester nanoparticles forcancer cell targeting and imagingrdquo Chemistry of Materials vol26 no 5 pp 1834ndash1847 2014
[3] I Armentano N Bitinis E Fortunati et al ldquoMultifunctionalnanostructured PLA materials for packaging and tissue engi-neeringrdquo Progress in Polymer Science vol 38 no 10-11 pp 1720ndash1747 2013
[4] S Gupta R Tyagi V S Parmar S K Sharma and R HaagldquoPolyether based amphiphiles for delivery of active compo-nentsrdquoPolymer (UnitedKingdom) vol 53 no 15 pp 3053ndash30782012
[5] P Zhang R Tian R Lv B Na and Q Liu ldquoWater-permeablepolylactide blend membranes for hydrophilicity-based separa-tionrdquo Chemical Engineering Journal vol 269 pp 180ndash185 2015
[6] A J R Lasprilla G A R Martinez B H Lunelli A L Jardiniand R M Filho ldquoPoly-lactic acid synthesis for application inbiomedical devices - A reviewrdquo Biotechnology Advances vol 30no 1 pp 321ndash328 2012
[7] L-J Zhu F Liu X-M Yu A-L Gao and L-X Xue ldquoSurfacezwitterionization of hemocompatible poly(lactic acid) mem-branes for hemodiafiltrationrdquo Journal of Membrane Science vol475 pp 469ndash479 2015
[8] A Khoddami O Avinc and F Ghahremanzadeh ldquoImprove-ment in poly(lactic acid) fabric performance via hydrophiliccoatingrdquo Progress in Organic Coatings vol 72 no 3 pp 299ndash304 2011
[9] J Nicolas S Mura D Brambilla N MacKiewicz and PCouvreur ldquoDesign functionalization strategies and biomedicalapplications of targeted biodegradablebiocompatible polymer-based nanocarriers for drug deliveryrdquoChemical Society Reviewsvol 42 no 3 pp 1147ndash1235 2013
[10] Z Ge and S Liu ldquoFunctional block copolymer assembliesresponsive to tumor and intracellular microenvironments forsite-specific drug delivery and enhanced imaging performancerdquoChemical Society Reviews vol 42 no 17 pp 7289ndash7325 2013
[11] M Spasova L Mespouille O Coulembier et al ldquoAmphiphilicpoly(D- or L-lactide)-b-poly(NN-dimethylamino-2-ethylmethacrylate) block copolymers Controlled synthesis char-acterization and stereocomplex formationrdquo Biomacromole-cules vol 10 no 5 pp 1217ndash1223 2009
[12] K Jelonek S Li X Wu J Kasperczyk and A Marcinkow-ski ldquoSelf-assembled filomicelles prepared from polylactidepoly(ethylene glycol) block copolymers for anticancer drugdeliveryrdquo International Journal of Pharmaceutics vol 485 no1-2 Article ID 14741 pp 357ndash364 2015
[13] H Feng X Lu W Wang N-G Kang and J W MaysldquoBlock copolymers Synthesis self-assembly and applicationsrdquoPolymer vol 9 no 10 article no 494 2017
[14] C Y Zhang Y Q Yang T X Huang et al ldquoSelf-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micellesfor anticancer drug deliveryrdquo Biomaterials vol 33 no 26 pp6273ndash6283 2012
[15] J K Oh ldquoPolylactide (PLA)-based amphiphilic block copoly-mers Synthesis self-assembly and biomedical applicationsrdquoSoft Matter vol 7 no 11 pp 5096ndash5108 2011
[16] L Xiao X Xiong X Sun et al ldquoRole of cellular uptake inthe reversal of multidrug resistance by PEG-b-PLA polymericmicellesrdquo Biomaterials vol 32 no 22 pp 5148ndash5157 2011
[17] V Pertici T Trimaille J Laurin et al ldquoRepair of the injuredspinal cord by implantation of a synthetic degradable blockcopolymer in ratrdquo Biomaterials vol 35 no 24 pp 6248ndash62582014
[18] Z Zhu ldquoEffects of amphiphilic diblock copolymer on drugnanoparticle formation and stabilityrdquo Biomaterials vol 34 no38 pp 10238ndash10248 2013
[19] E Ayano M Karaki T Ishihara H Kanazawa and T OkanoldquoPoly (N-isopropylacrylamide)-PLA and PLA blend nanoparti-cles for temperature-controllable drug release and intracellular
International Journal of Polymer Science 9
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Figure 2 1HNMR spectra of raw PLA and PLA-EDA in CDCl3 Aminolysis condition of PLAwith EDA 30∘C 30min [EDA] = 10mmolg
The AD of PLA increases with the prolongation of reactiontime In detail AD is rapidly increased in the initial 10minof aminolysis and slows down from 10 to 60min After60min AD data becomes difficult to obtain because the solidproducts cannot be separated from the precipitation solutionFigure 3(a) shows a faster growth of AD with increasingEDA concentration Furthermore the aminolysis reactionwas also accelerated at higher temperature when the EDAconcentration was 05mmolg (Figure 3(b)) At the EDAconcentration of 10mmolg the AD is as high as 103 afterreacting at 40∘C for 60min
313 Molar Mass Analysis According to the aminolysismechanism of PLA chain scission results in decreasedmolar mass The products were subjected to GPC analysesand the results are shown in Figure 4 The GPC traces(Figure 4(a)) indicated that the molar mass distributionof the measured PLA-EDA remained unimodal suggesting
statistically random scission of the polymer chains Fur-thermore with increasing reaction time the GPC tracesshift toward low molar mass The number average molec-ular weight determined by GPC (119872119899GPC) is exhibited inFigure 4(b) The 119872119899GPC decreased rapidly in the low ADrange and the decline rate slowed down with increasingAD The aminolysis reaction is considered as the reverse ofpolycondensation [42] Lower AD is roughly equivalent tohigher polycondensation extent For the polymer synthesizedvia polycondensation 119872119899GPC increases gradually in theinitial polymerization under high polymerization degree119872119899GPC significantly increases due to a small increase inthe polymerization degree [42] As a result the changingtrend of Mn for the aminolyzed PLA is similar to that ofpolycondensation polymer Moreover similar to the changein polydispersity index (ETH) in polycondensation the ETHof PLA-EDA became narrower with the increase of AD(Figure 4(b)) Lower polycondensation extent indicates less
International Journal of Polymer Science 5
0
2
4
6
8
10A
D (
)
10 20 30 40 50 600Time (min)
05 mmolg10 mmolg
01 mmolg
(a)
0
3
6
9
12
AD
()
10 20 30 40 50 600Time (min)
40∘C30∘C18∘C
(b)
Figure 3 AD as a function of reaction time with different EDA concentrations at 30∘C (a) and different reaction temperatures at an EDAconcentration of 05mmolg
30 35 40 45 50 55 60 6525
20
AD
29
00 3859
ＦＩＡMw
(a)
PDI
0
15
30
45
60
75
2 4 60AD ()
3 4 5 62
2
4
6
13
14
15
16
17
18
19
ETH
times10
3(g
mol
)M
n
Mn０
MnＮＢ
(b)
Figure 4 Evolution of GPC traces (a) and number average molecular weight (119872119899) and molecular weight polydispersity (K = 119872119908119872119899) (b)of the PLA-PEA with aminolysis degree (119860119863)
ETHTheETH decreases with the increasing AD of PLAwith EDAExcept for119872119899GPC the theoretical Mn (119872119899th) of PLA-EDAwas calculated by (2) as shown in Figure 4(b) The 119872119899thvalue is slightly less than the GPC obtained value due tothe different flexibilities of the polymer chains between PLA-EDA and the GPC calibrating standards (PMMA) Howeverthe tendency of119872119899th is in accordance with119872119899GPC
119872119899th =119872119899PLA + AD times119872EDA times119872119899PLA119872PLA1 + AD times119872119899PLA119872PLA
(2)
where 119872119899PLA and 119872PLA are the number average molarmasses of PLA and PLA repeating units respectively119872EDAand AD are the molar mass of EDA and degree of aminolysisrespectively
32 Structure and Characterization of the SynthesizedPLA-Based Block Copolymers
321 Chemical Structure Despite being an eco-friendly bio-plastic with excellent biocompatibility and processability
6 International Journal of Polymer Science
Table 1 Molar weight (Mn) polydispersity (K) of the synthesized PLA-PDMAEMA block copolymers andmass ratio of PDMAEMA blocks(119891PDMAEMA) in the copolymers
Figure 5 Schematic illustration for the preparation of PLA-PDMAEMA block copolymers via RAFT polymerization
PLA is chemically inert without reactive sidechain groupsthereby making its modifications a challenging task [43]After the aminolysis reaction of PLA with EDA the reactivendashNH2 and ndashOH groups can be introduced to the ends of thePLA chains providing opportunity to furthermodify PLA Inthe present work PLA-PDMAEMA block copolymers weresynthesized from PLA segments after aminolysis reaction viaRAFT polymerization Figure 5 shows the fabrication pro-cesses First RAFT agent CDP was immobilized on the reac-tive groups of PLA-EDA via the amide reactionesterificationunder the catalysis ofDCCDMAP inTHFThen the obtainedPLA-CDP was used as the chain transfer agent to regu-late RAFT polymerization of monomers to produce PLA-based block copolymers In the present work a serial ofPLA-PDMAEMA block copolymers were synthesized Themolar weight (Mn) polydispersity (ETH) and mass ratio ofPDMAEMA blocks (119891PDMAEMA) in the copolymers are listedin Table 1
To detect the chemical compositions of the synthesizedPLA-CDP XPS was employed The XPS wide scan andthe elemental mole percentages are shown in Figure 6(a)The peak of S 2p is observed Figure 6(b) shows the 1HNMR spectrum of PLA-CDP The peaks in 425sim413 ppm
range are attributed to the C2H4 protons connected withamide group The peaks of the CH3 protons at (a) and (c)in Figure 2 disappeared These results confirm that PLA-CDP was synthesized successfully It can be used as thechain transfer agent to regulate RAFT polymerization ofDMAEMA
PLA345-PDMAEMA60 block copolymers were character-ized by 1H NMR in CDCl3 and the obtained 1H NMRspectrum is shown in Figure 7(a) The signals in the 519sim514 (A) and 159sim157 ppm range (B) belong to ndashCH andndashCH3 protons of the main chain PLA units The peaks inthe 182 (C) and 091sim106 ppm range (D) are attributed tothe ndashCH2 and ndashCH3 protons of the main chain PDMAEMAunits The signals at 409 (E) and 263 ppm (F) correspondto the ndashCH2 protons connected to the ester and tertiaryamine groups of PDMAEMA respectively The peaks in238sim234 ppm range (G) are attributed to ndashCH3 protonsconnected to the tertiary amine groups In addition FT-IR spectrum of PLA345-PDMAEMA213 block copolymers isshown in Figure 7(b) The peak at around 1758 cmminus1 is thestretching vibration of C=O in ester groups of PLA blocksThe adsorption peaks at about 2823sim2722 and 1730 cmminus1 areascribed to ndashN(CH3)2 and OndashC=O groups of PDMAEMAchains respectively Furthermore the GPC traces of PLA345-PDMAEMA block copolymers with different polymerizationtimes are shown in Figure 7(c) The GPC traces of PLA345-DMAEMA block copolymers exhibit one monomodal distri-butionTheMn of PLA345-PDMAEMA increases from 26300to 58400 gmolwith the increase of polymerization time from1 to 10 h as shown in Table 1 All data indicate that the PLA345-PDMAEMA block copolymers were successfully synthesizedvia RAFT polymerization based on aminolyzed PLA withEDA
322 Kinetic Behavior of the RAFT Polymerization TheRAFT polymerization kinetic behavior of PLA345-PDMAE-MA block copolymers was investigated Conversion andkinetics plots for the RAFT polymerization of the blockcopolymers with increasing polymerization time (1 2 3 4 7and 10 h) are shown in Figure 8 Figure 8(a) further shows thatthe conversion of DMAEMA linearly increases with RAFT
International Journal of Polymer Science 7
Components (mol)C 1s 621O 1s 362S 2p 17
C 1sO 1s
S 2p
164 160168
400 200 0600Binding energy (eV)
(a)
C C
H
O
O NH NHPLA C
O（3
C C SS
S
CN
（3
2（4 12（25
lowast
lowast
6 4 2 08(ppm)
16 151742 4143
(b)
Figure 6 (a) XPS wide scan and elemental mole percentages and (b) 1H NMR spectrum in CDCl3 of PLA345-CDP
＄Ｆ3
8 7 6 5 4(ppm)
3 012
(G) (G)
(G)
(B)
(B)
(C)
(C)
(D)
(D)
(E)
(E)
(A)
(A)
(F)
(F)
O C C
H
nC
C
m
O
O
N
O
（3 （3
（2
(a)
1730
1800 1700
1758minus(（3)2
2000 100030004000
Wavenumbers (＝Ｇminus1)
(b)
(A) (B) (C)
40 44 48 52 5636logMw
(c)
Figure 7 (a) 1HNMR spectrum in CDCl3 and (b) FTIR spectrum of PLA345-PDMAEMA213 block copolymers (c) Evolution of GPC tracesof the synthesized PLA345-PDMAEMA block copolymers with polymerization time of 1 (A) 3 (B) and 10 h (C)
2 4 6 8 100Time (h)
0
20
40
60
Con
vers
ion
()
0
20
40
60
Con
vers
ion
()
1 2 30Time (h)
(a)
0002040608
1 2 30Time (h)
2 4 6 8 100Time (h)
00
02
04
06
08
10
ＦＨ( [M
] 0[
])M
ＦＨ( [M
] 0[
])M
(b)
Figure 8 (a) Conversion and (b) kinetics plots for the RAFT polymerization of PLA-PDMAEMA block copolymers with increasingpolymerization time (1 2 3 4 7 and 10 h)
8 International Journal of Polymer Science
polymerization time in the initial 3 h A pseudo-first-orderkinetics for the RAFT polymerization of PDMAEMA wasdepicted at a low conversion (Figure 8(b)) However the rateof conversion decreases from 3 to 7 h and remains almostunchanged when the polymerization time increases from7 to 10 h These phenomena were mainly attributed to theincreasing viscosity of the reaction solution with the increaseof conversion At higher viscosity the motion of polymerchains becomes more difficult As a result terminationoccurred and the reaction rate decreased
4 Conclusions
PLA undergoes aminolytic degradation with EDA Theaminolysis reaction accelerated at increased EDA concentra-tion and reaction temperature The AD of PLA was rapidlyincreased in the initial stage and then reached a plateauThusthe molar masses of products rapidly decreased in the earlyreaction stage Furthermore ndashNH2 and ndashOH groups wereintroduced to the ends of the produced short PLA chainsThen the RAFT agent was immobilized onto the aminolyzedPLA chains and PLA-PDMAEMA block copolymers weresynthesized via RAFTpolymerization Conversion and kinet-ics plots for the RAFT polymerization of the block copoly-mers with increasing polymerization time were studied Theresults suggested a pseudo-first-order kinetics of the RAFTpolymerization of PDMAEMA at a low conversion Thelength distributions of the PLA and PDMAEMA blocks canbe controlled by controlling the aminolytic reaction andRAFT polymerization degrees in the process
Conflicts of Interest
The authors declare that they have no conflicts of interest
Acknowledgments
The authors are grateful for the financial support of theNational Natural Science Foundation of China (nos 31502213and 51473177) the Central Public-Interest Scientific Institu-tion Basal Research Fund CAFS (no 2018HY-XKQ03-4) andtheOpenFoundation fromFishery Sciences in the First-ClassSubjects of Zhejiang (no 20160014)
References
[1] M Okamoto and B John ldquoSynthetic biopolymer nanocompos-ites for tissue engineering scaffoldsrdquoProgress in Polymer Sciencevol 38 pp 1487ndash1503 2013
[2] N MacKiewicz J Nicolas N Handke et al ldquoPrecise engineer-ing of multifunctional PE gylated polyester nanoparticles forcancer cell targeting and imagingrdquo Chemistry of Materials vol26 no 5 pp 1834ndash1847 2014
[3] I Armentano N Bitinis E Fortunati et al ldquoMultifunctionalnanostructured PLA materials for packaging and tissue engi-neeringrdquo Progress in Polymer Science vol 38 no 10-11 pp 1720ndash1747 2013
[4] S Gupta R Tyagi V S Parmar S K Sharma and R HaagldquoPolyether based amphiphiles for delivery of active compo-nentsrdquoPolymer (UnitedKingdom) vol 53 no 15 pp 3053ndash30782012
[5] P Zhang R Tian R Lv B Na and Q Liu ldquoWater-permeablepolylactide blend membranes for hydrophilicity-based separa-tionrdquo Chemical Engineering Journal vol 269 pp 180ndash185 2015
[6] A J R Lasprilla G A R Martinez B H Lunelli A L Jardiniand R M Filho ldquoPoly-lactic acid synthesis for application inbiomedical devices - A reviewrdquo Biotechnology Advances vol 30no 1 pp 321ndash328 2012
[7] L-J Zhu F Liu X-M Yu A-L Gao and L-X Xue ldquoSurfacezwitterionization of hemocompatible poly(lactic acid) mem-branes for hemodiafiltrationrdquo Journal of Membrane Science vol475 pp 469ndash479 2015
[8] A Khoddami O Avinc and F Ghahremanzadeh ldquoImprove-ment in poly(lactic acid) fabric performance via hydrophiliccoatingrdquo Progress in Organic Coatings vol 72 no 3 pp 299ndash304 2011
[9] J Nicolas S Mura D Brambilla N MacKiewicz and PCouvreur ldquoDesign functionalization strategies and biomedicalapplications of targeted biodegradablebiocompatible polymer-based nanocarriers for drug deliveryrdquoChemical Society Reviewsvol 42 no 3 pp 1147ndash1235 2013
[10] Z Ge and S Liu ldquoFunctional block copolymer assembliesresponsive to tumor and intracellular microenvironments forsite-specific drug delivery and enhanced imaging performancerdquoChemical Society Reviews vol 42 no 17 pp 7289ndash7325 2013
[11] M Spasova L Mespouille O Coulembier et al ldquoAmphiphilicpoly(D- or L-lactide)-b-poly(NN-dimethylamino-2-ethylmethacrylate) block copolymers Controlled synthesis char-acterization and stereocomplex formationrdquo Biomacromole-cules vol 10 no 5 pp 1217ndash1223 2009
[12] K Jelonek S Li X Wu J Kasperczyk and A Marcinkow-ski ldquoSelf-assembled filomicelles prepared from polylactidepoly(ethylene glycol) block copolymers for anticancer drugdeliveryrdquo International Journal of Pharmaceutics vol 485 no1-2 Article ID 14741 pp 357ndash364 2015
[13] H Feng X Lu W Wang N-G Kang and J W MaysldquoBlock copolymers Synthesis self-assembly and applicationsrdquoPolymer vol 9 no 10 article no 494 2017
[14] C Y Zhang Y Q Yang T X Huang et al ldquoSelf-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micellesfor anticancer drug deliveryrdquo Biomaterials vol 33 no 26 pp6273ndash6283 2012
[15] J K Oh ldquoPolylactide (PLA)-based amphiphilic block copoly-mers Synthesis self-assembly and biomedical applicationsrdquoSoft Matter vol 7 no 11 pp 5096ndash5108 2011
[16] L Xiao X Xiong X Sun et al ldquoRole of cellular uptake inthe reversal of multidrug resistance by PEG-b-PLA polymericmicellesrdquo Biomaterials vol 32 no 22 pp 5148ndash5157 2011
[17] V Pertici T Trimaille J Laurin et al ldquoRepair of the injuredspinal cord by implantation of a synthetic degradable blockcopolymer in ratrdquo Biomaterials vol 35 no 24 pp 6248ndash62582014
[18] Z Zhu ldquoEffects of amphiphilic diblock copolymer on drugnanoparticle formation and stabilityrdquo Biomaterials vol 34 no38 pp 10238ndash10248 2013
[19] E Ayano M Karaki T Ishihara H Kanazawa and T OkanoldquoPoly (N-isopropylacrylamide)-PLA and PLA blend nanoparti-cles for temperature-controllable drug release and intracellular
International Journal of Polymer Science 9
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Figure 3 AD as a function of reaction time with different EDA concentrations at 30∘C (a) and different reaction temperatures at an EDAconcentration of 05mmolg
30 35 40 45 50 55 60 6525
20
AD
29
00 3859
ＦＩＡMw
(a)
PDI
0
15
30
45
60
75
2 4 60AD ()
3 4 5 62
2
4
6
13
14
15
16
17
18
19
ETH
times10
3(g
mol
)M
n
Mn０
MnＮＢ
(b)
Figure 4 Evolution of GPC traces (a) and number average molecular weight (119872119899) and molecular weight polydispersity (K = 119872119908119872119899) (b)of the PLA-PEA with aminolysis degree (119860119863)
ETHTheETH decreases with the increasing AD of PLAwith EDAExcept for119872119899GPC the theoretical Mn (119872119899th) of PLA-EDAwas calculated by (2) as shown in Figure 4(b) The 119872119899thvalue is slightly less than the GPC obtained value due tothe different flexibilities of the polymer chains between PLA-EDA and the GPC calibrating standards (PMMA) Howeverthe tendency of119872119899th is in accordance with119872119899GPC
119872119899th =119872119899PLA + AD times119872EDA times119872119899PLA119872PLA1 + AD times119872119899PLA119872PLA
(2)
where 119872119899PLA and 119872PLA are the number average molarmasses of PLA and PLA repeating units respectively119872EDAand AD are the molar mass of EDA and degree of aminolysisrespectively
32 Structure and Characterization of the SynthesizedPLA-Based Block Copolymers
321 Chemical Structure Despite being an eco-friendly bio-plastic with excellent biocompatibility and processability
6 International Journal of Polymer Science
Table 1 Molar weight (Mn) polydispersity (K) of the synthesized PLA-PDMAEMA block copolymers andmass ratio of PDMAEMA blocks(119891PDMAEMA) in the copolymers
Figure 5 Schematic illustration for the preparation of PLA-PDMAEMA block copolymers via RAFT polymerization
PLA is chemically inert without reactive sidechain groupsthereby making its modifications a challenging task [43]After the aminolysis reaction of PLA with EDA the reactivendashNH2 and ndashOH groups can be introduced to the ends of thePLA chains providing opportunity to furthermodify PLA Inthe present work PLA-PDMAEMA block copolymers weresynthesized from PLA segments after aminolysis reaction viaRAFT polymerization Figure 5 shows the fabrication pro-cesses First RAFT agent CDP was immobilized on the reac-tive groups of PLA-EDA via the amide reactionesterificationunder the catalysis ofDCCDMAP inTHFThen the obtainedPLA-CDP was used as the chain transfer agent to regu-late RAFT polymerization of monomers to produce PLA-based block copolymers In the present work a serial ofPLA-PDMAEMA block copolymers were synthesized Themolar weight (Mn) polydispersity (ETH) and mass ratio ofPDMAEMA blocks (119891PDMAEMA) in the copolymers are listedin Table 1
To detect the chemical compositions of the synthesizedPLA-CDP XPS was employed The XPS wide scan andthe elemental mole percentages are shown in Figure 6(a)The peak of S 2p is observed Figure 6(b) shows the 1HNMR spectrum of PLA-CDP The peaks in 425sim413 ppm
range are attributed to the C2H4 protons connected withamide group The peaks of the CH3 protons at (a) and (c)in Figure 2 disappeared These results confirm that PLA-CDP was synthesized successfully It can be used as thechain transfer agent to regulate RAFT polymerization ofDMAEMA
PLA345-PDMAEMA60 block copolymers were character-ized by 1H NMR in CDCl3 and the obtained 1H NMRspectrum is shown in Figure 7(a) The signals in the 519sim514 (A) and 159sim157 ppm range (B) belong to ndashCH andndashCH3 protons of the main chain PLA units The peaks inthe 182 (C) and 091sim106 ppm range (D) are attributed tothe ndashCH2 and ndashCH3 protons of the main chain PDMAEMAunits The signals at 409 (E) and 263 ppm (F) correspondto the ndashCH2 protons connected to the ester and tertiaryamine groups of PDMAEMA respectively The peaks in238sim234 ppm range (G) are attributed to ndashCH3 protonsconnected to the tertiary amine groups In addition FT-IR spectrum of PLA345-PDMAEMA213 block copolymers isshown in Figure 7(b) The peak at around 1758 cmminus1 is thestretching vibration of C=O in ester groups of PLA blocksThe adsorption peaks at about 2823sim2722 and 1730 cmminus1 areascribed to ndashN(CH3)2 and OndashC=O groups of PDMAEMAchains respectively Furthermore the GPC traces of PLA345-PDMAEMA block copolymers with different polymerizationtimes are shown in Figure 7(c) The GPC traces of PLA345-DMAEMA block copolymers exhibit one monomodal distri-butionTheMn of PLA345-PDMAEMA increases from 26300to 58400 gmolwith the increase of polymerization time from1 to 10 h as shown in Table 1 All data indicate that the PLA345-PDMAEMA block copolymers were successfully synthesizedvia RAFT polymerization based on aminolyzed PLA withEDA
322 Kinetic Behavior of the RAFT Polymerization TheRAFT polymerization kinetic behavior of PLA345-PDMAE-MA block copolymers was investigated Conversion andkinetics plots for the RAFT polymerization of the blockcopolymers with increasing polymerization time (1 2 3 4 7and 10 h) are shown in Figure 8 Figure 8(a) further shows thatthe conversion of DMAEMA linearly increases with RAFT
International Journal of Polymer Science 7
Components (mol)C 1s 621O 1s 362S 2p 17
C 1sO 1s
S 2p
164 160168
400 200 0600Binding energy (eV)
(a)
C C
H
O
O NH NHPLA C
O（3
C C SS
S
CN
（3
2（4 12（25
lowast
lowast
6 4 2 08(ppm)
16 151742 4143
(b)
Figure 6 (a) XPS wide scan and elemental mole percentages and (b) 1H NMR spectrum in CDCl3 of PLA345-CDP
＄Ｆ3
8 7 6 5 4(ppm)
3 012
(G) (G)
(G)
(B)
(B)
(C)
(C)
(D)
(D)
(E)
(E)
(A)
(A)
(F)
(F)
O C C
H
nC
C
m
O
O
N
O
（3 （3
（2
(a)
1730
1800 1700
1758minus(（3)2
2000 100030004000
Wavenumbers (＝Ｇminus1)
(b)
(A) (B) (C)
40 44 48 52 5636logMw
(c)
Figure 7 (a) 1HNMR spectrum in CDCl3 and (b) FTIR spectrum of PLA345-PDMAEMA213 block copolymers (c) Evolution of GPC tracesof the synthesized PLA345-PDMAEMA block copolymers with polymerization time of 1 (A) 3 (B) and 10 h (C)
2 4 6 8 100Time (h)
0
20
40
60
Con
vers
ion
()
0
20
40
60
Con
vers
ion
()
1 2 30Time (h)
(a)
0002040608
1 2 30Time (h)
2 4 6 8 100Time (h)
00
02
04
06
08
10
ＦＨ( [M
] 0[
])M
ＦＨ( [M
] 0[
])M
(b)
Figure 8 (a) Conversion and (b) kinetics plots for the RAFT polymerization of PLA-PDMAEMA block copolymers with increasingpolymerization time (1 2 3 4 7 and 10 h)
8 International Journal of Polymer Science
polymerization time in the initial 3 h A pseudo-first-orderkinetics for the RAFT polymerization of PDMAEMA wasdepicted at a low conversion (Figure 8(b)) However the rateof conversion decreases from 3 to 7 h and remains almostunchanged when the polymerization time increases from7 to 10 h These phenomena were mainly attributed to theincreasing viscosity of the reaction solution with the increaseof conversion At higher viscosity the motion of polymerchains becomes more difficult As a result terminationoccurred and the reaction rate decreased
4 Conclusions
PLA undergoes aminolytic degradation with EDA Theaminolysis reaction accelerated at increased EDA concentra-tion and reaction temperature The AD of PLA was rapidlyincreased in the initial stage and then reached a plateauThusthe molar masses of products rapidly decreased in the earlyreaction stage Furthermore ndashNH2 and ndashOH groups wereintroduced to the ends of the produced short PLA chainsThen the RAFT agent was immobilized onto the aminolyzedPLA chains and PLA-PDMAEMA block copolymers weresynthesized via RAFTpolymerization Conversion and kinet-ics plots for the RAFT polymerization of the block copoly-mers with increasing polymerization time were studied Theresults suggested a pseudo-first-order kinetics of the RAFTpolymerization of PDMAEMA at a low conversion Thelength distributions of the PLA and PDMAEMA blocks canbe controlled by controlling the aminolytic reaction andRAFT polymerization degrees in the process
Conflicts of Interest
The authors declare that they have no conflicts of interest
Acknowledgments
The authors are grateful for the financial support of theNational Natural Science Foundation of China (nos 31502213and 51473177) the Central Public-Interest Scientific Institu-tion Basal Research Fund CAFS (no 2018HY-XKQ03-4) andtheOpenFoundation fromFishery Sciences in the First-ClassSubjects of Zhejiang (no 20160014)
References
[1] M Okamoto and B John ldquoSynthetic biopolymer nanocompos-ites for tissue engineering scaffoldsrdquoProgress in Polymer Sciencevol 38 pp 1487ndash1503 2013
[2] N MacKiewicz J Nicolas N Handke et al ldquoPrecise engineer-ing of multifunctional PE gylated polyester nanoparticles forcancer cell targeting and imagingrdquo Chemistry of Materials vol26 no 5 pp 1834ndash1847 2014
[3] I Armentano N Bitinis E Fortunati et al ldquoMultifunctionalnanostructured PLA materials for packaging and tissue engi-neeringrdquo Progress in Polymer Science vol 38 no 10-11 pp 1720ndash1747 2013
[4] S Gupta R Tyagi V S Parmar S K Sharma and R HaagldquoPolyether based amphiphiles for delivery of active compo-nentsrdquoPolymer (UnitedKingdom) vol 53 no 15 pp 3053ndash30782012
[5] P Zhang R Tian R Lv B Na and Q Liu ldquoWater-permeablepolylactide blend membranes for hydrophilicity-based separa-tionrdquo Chemical Engineering Journal vol 269 pp 180ndash185 2015
[6] A J R Lasprilla G A R Martinez B H Lunelli A L Jardiniand R M Filho ldquoPoly-lactic acid synthesis for application inbiomedical devices - A reviewrdquo Biotechnology Advances vol 30no 1 pp 321ndash328 2012
[7] L-J Zhu F Liu X-M Yu A-L Gao and L-X Xue ldquoSurfacezwitterionization of hemocompatible poly(lactic acid) mem-branes for hemodiafiltrationrdquo Journal of Membrane Science vol475 pp 469ndash479 2015
[8] A Khoddami O Avinc and F Ghahremanzadeh ldquoImprove-ment in poly(lactic acid) fabric performance via hydrophiliccoatingrdquo Progress in Organic Coatings vol 72 no 3 pp 299ndash304 2011
[9] J Nicolas S Mura D Brambilla N MacKiewicz and PCouvreur ldquoDesign functionalization strategies and biomedicalapplications of targeted biodegradablebiocompatible polymer-based nanocarriers for drug deliveryrdquoChemical Society Reviewsvol 42 no 3 pp 1147ndash1235 2013
[10] Z Ge and S Liu ldquoFunctional block copolymer assembliesresponsive to tumor and intracellular microenvironments forsite-specific drug delivery and enhanced imaging performancerdquoChemical Society Reviews vol 42 no 17 pp 7289ndash7325 2013
[11] M Spasova L Mespouille O Coulembier et al ldquoAmphiphilicpoly(D- or L-lactide)-b-poly(NN-dimethylamino-2-ethylmethacrylate) block copolymers Controlled synthesis char-acterization and stereocomplex formationrdquo Biomacromole-cules vol 10 no 5 pp 1217ndash1223 2009
[12] K Jelonek S Li X Wu J Kasperczyk and A Marcinkow-ski ldquoSelf-assembled filomicelles prepared from polylactidepoly(ethylene glycol) block copolymers for anticancer drugdeliveryrdquo International Journal of Pharmaceutics vol 485 no1-2 Article ID 14741 pp 357ndash364 2015
[13] H Feng X Lu W Wang N-G Kang and J W MaysldquoBlock copolymers Synthesis self-assembly and applicationsrdquoPolymer vol 9 no 10 article no 494 2017
[14] C Y Zhang Y Q Yang T X Huang et al ldquoSelf-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micellesfor anticancer drug deliveryrdquo Biomaterials vol 33 no 26 pp6273ndash6283 2012
[15] J K Oh ldquoPolylactide (PLA)-based amphiphilic block copoly-mers Synthesis self-assembly and biomedical applicationsrdquoSoft Matter vol 7 no 11 pp 5096ndash5108 2011
[16] L Xiao X Xiong X Sun et al ldquoRole of cellular uptake inthe reversal of multidrug resistance by PEG-b-PLA polymericmicellesrdquo Biomaterials vol 32 no 22 pp 5148ndash5157 2011
[17] V Pertici T Trimaille J Laurin et al ldquoRepair of the injuredspinal cord by implantation of a synthetic degradable blockcopolymer in ratrdquo Biomaterials vol 35 no 24 pp 6248ndash62582014
[18] Z Zhu ldquoEffects of amphiphilic diblock copolymer on drugnanoparticle formation and stabilityrdquo Biomaterials vol 34 no38 pp 10238ndash10248 2013
[19] E Ayano M Karaki T Ishihara H Kanazawa and T OkanoldquoPoly (N-isopropylacrylamide)-PLA and PLA blend nanoparti-cles for temperature-controllable drug release and intracellular
International Journal of Polymer Science 9
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Table 1 Molar weight (Mn) polydispersity (K) of the synthesized PLA-PDMAEMA block copolymers andmass ratio of PDMAEMA blocks(119891PDMAEMA) in the copolymers
Figure 5 Schematic illustration for the preparation of PLA-PDMAEMA block copolymers via RAFT polymerization
PLA is chemically inert without reactive sidechain groupsthereby making its modifications a challenging task [43]After the aminolysis reaction of PLA with EDA the reactivendashNH2 and ndashOH groups can be introduced to the ends of thePLA chains providing opportunity to furthermodify PLA Inthe present work PLA-PDMAEMA block copolymers weresynthesized from PLA segments after aminolysis reaction viaRAFT polymerization Figure 5 shows the fabrication pro-cesses First RAFT agent CDP was immobilized on the reac-tive groups of PLA-EDA via the amide reactionesterificationunder the catalysis ofDCCDMAP inTHFThen the obtainedPLA-CDP was used as the chain transfer agent to regu-late RAFT polymerization of monomers to produce PLA-based block copolymers In the present work a serial ofPLA-PDMAEMA block copolymers were synthesized Themolar weight (Mn) polydispersity (ETH) and mass ratio ofPDMAEMA blocks (119891PDMAEMA) in the copolymers are listedin Table 1
To detect the chemical compositions of the synthesizedPLA-CDP XPS was employed The XPS wide scan andthe elemental mole percentages are shown in Figure 6(a)The peak of S 2p is observed Figure 6(b) shows the 1HNMR spectrum of PLA-CDP The peaks in 425sim413 ppm
range are attributed to the C2H4 protons connected withamide group The peaks of the CH3 protons at (a) and (c)in Figure 2 disappeared These results confirm that PLA-CDP was synthesized successfully It can be used as thechain transfer agent to regulate RAFT polymerization ofDMAEMA
PLA345-PDMAEMA60 block copolymers were character-ized by 1H NMR in CDCl3 and the obtained 1H NMRspectrum is shown in Figure 7(a) The signals in the 519sim514 (A) and 159sim157 ppm range (B) belong to ndashCH andndashCH3 protons of the main chain PLA units The peaks inthe 182 (C) and 091sim106 ppm range (D) are attributed tothe ndashCH2 and ndashCH3 protons of the main chain PDMAEMAunits The signals at 409 (E) and 263 ppm (F) correspondto the ndashCH2 protons connected to the ester and tertiaryamine groups of PDMAEMA respectively The peaks in238sim234 ppm range (G) are attributed to ndashCH3 protonsconnected to the tertiary amine groups In addition FT-IR spectrum of PLA345-PDMAEMA213 block copolymers isshown in Figure 7(b) The peak at around 1758 cmminus1 is thestretching vibration of C=O in ester groups of PLA blocksThe adsorption peaks at about 2823sim2722 and 1730 cmminus1 areascribed to ndashN(CH3)2 and OndashC=O groups of PDMAEMAchains respectively Furthermore the GPC traces of PLA345-PDMAEMA block copolymers with different polymerizationtimes are shown in Figure 7(c) The GPC traces of PLA345-DMAEMA block copolymers exhibit one monomodal distri-butionTheMn of PLA345-PDMAEMA increases from 26300to 58400 gmolwith the increase of polymerization time from1 to 10 h as shown in Table 1 All data indicate that the PLA345-PDMAEMA block copolymers were successfully synthesizedvia RAFT polymerization based on aminolyzed PLA withEDA
322 Kinetic Behavior of the RAFT Polymerization TheRAFT polymerization kinetic behavior of PLA345-PDMAE-MA block copolymers was investigated Conversion andkinetics plots for the RAFT polymerization of the blockcopolymers with increasing polymerization time (1 2 3 4 7and 10 h) are shown in Figure 8 Figure 8(a) further shows thatthe conversion of DMAEMA linearly increases with RAFT
International Journal of Polymer Science 7
Components (mol)C 1s 621O 1s 362S 2p 17
C 1sO 1s
S 2p
164 160168
400 200 0600Binding energy (eV)
(a)
C C
H
O
O NH NHPLA C
O（3
C C SS
S
CN
（3
2（4 12（25
lowast
lowast
6 4 2 08(ppm)
16 151742 4143
(b)
Figure 6 (a) XPS wide scan and elemental mole percentages and (b) 1H NMR spectrum in CDCl3 of PLA345-CDP
＄Ｆ3
8 7 6 5 4(ppm)
3 012
(G) (G)
(G)
(B)
(B)
(C)
(C)
(D)
(D)
(E)
(E)
(A)
(A)
(F)
(F)
O C C
H
nC
C
m
O
O
N
O
（3 （3
（2
(a)
1730
1800 1700
1758minus(（3)2
2000 100030004000
Wavenumbers (＝Ｇminus1)
(b)
(A) (B) (C)
40 44 48 52 5636logMw
(c)
Figure 7 (a) 1HNMR spectrum in CDCl3 and (b) FTIR spectrum of PLA345-PDMAEMA213 block copolymers (c) Evolution of GPC tracesof the synthesized PLA345-PDMAEMA block copolymers with polymerization time of 1 (A) 3 (B) and 10 h (C)
2 4 6 8 100Time (h)
0
20
40
60
Con
vers
ion
()
0
20
40
60
Con
vers
ion
()
1 2 30Time (h)
(a)
0002040608
1 2 30Time (h)
2 4 6 8 100Time (h)
00
02
04
06
08
10
ＦＨ( [M
] 0[
])M
ＦＨ( [M
] 0[
])M
(b)
Figure 8 (a) Conversion and (b) kinetics plots for the RAFT polymerization of PLA-PDMAEMA block copolymers with increasingpolymerization time (1 2 3 4 7 and 10 h)
8 International Journal of Polymer Science
polymerization time in the initial 3 h A pseudo-first-orderkinetics for the RAFT polymerization of PDMAEMA wasdepicted at a low conversion (Figure 8(b)) However the rateof conversion decreases from 3 to 7 h and remains almostunchanged when the polymerization time increases from7 to 10 h These phenomena were mainly attributed to theincreasing viscosity of the reaction solution with the increaseof conversion At higher viscosity the motion of polymerchains becomes more difficult As a result terminationoccurred and the reaction rate decreased
4 Conclusions
PLA undergoes aminolytic degradation with EDA Theaminolysis reaction accelerated at increased EDA concentra-tion and reaction temperature The AD of PLA was rapidlyincreased in the initial stage and then reached a plateauThusthe molar masses of products rapidly decreased in the earlyreaction stage Furthermore ndashNH2 and ndashOH groups wereintroduced to the ends of the produced short PLA chainsThen the RAFT agent was immobilized onto the aminolyzedPLA chains and PLA-PDMAEMA block copolymers weresynthesized via RAFTpolymerization Conversion and kinet-ics plots for the RAFT polymerization of the block copoly-mers with increasing polymerization time were studied Theresults suggested a pseudo-first-order kinetics of the RAFTpolymerization of PDMAEMA at a low conversion Thelength distributions of the PLA and PDMAEMA blocks canbe controlled by controlling the aminolytic reaction andRAFT polymerization degrees in the process
Conflicts of Interest
The authors declare that they have no conflicts of interest
Acknowledgments
The authors are grateful for the financial support of theNational Natural Science Foundation of China (nos 31502213and 51473177) the Central Public-Interest Scientific Institu-tion Basal Research Fund CAFS (no 2018HY-XKQ03-4) andtheOpenFoundation fromFishery Sciences in the First-ClassSubjects of Zhejiang (no 20160014)
References
[1] M Okamoto and B John ldquoSynthetic biopolymer nanocompos-ites for tissue engineering scaffoldsrdquoProgress in Polymer Sciencevol 38 pp 1487ndash1503 2013
[2] N MacKiewicz J Nicolas N Handke et al ldquoPrecise engineer-ing of multifunctional PE gylated polyester nanoparticles forcancer cell targeting and imagingrdquo Chemistry of Materials vol26 no 5 pp 1834ndash1847 2014
[3] I Armentano N Bitinis E Fortunati et al ldquoMultifunctionalnanostructured PLA materials for packaging and tissue engi-neeringrdquo Progress in Polymer Science vol 38 no 10-11 pp 1720ndash1747 2013
[4] S Gupta R Tyagi V S Parmar S K Sharma and R HaagldquoPolyether based amphiphiles for delivery of active compo-nentsrdquoPolymer (UnitedKingdom) vol 53 no 15 pp 3053ndash30782012
[5] P Zhang R Tian R Lv B Na and Q Liu ldquoWater-permeablepolylactide blend membranes for hydrophilicity-based separa-tionrdquo Chemical Engineering Journal vol 269 pp 180ndash185 2015
[6] A J R Lasprilla G A R Martinez B H Lunelli A L Jardiniand R M Filho ldquoPoly-lactic acid synthesis for application inbiomedical devices - A reviewrdquo Biotechnology Advances vol 30no 1 pp 321ndash328 2012
[7] L-J Zhu F Liu X-M Yu A-L Gao and L-X Xue ldquoSurfacezwitterionization of hemocompatible poly(lactic acid) mem-branes for hemodiafiltrationrdquo Journal of Membrane Science vol475 pp 469ndash479 2015
[8] A Khoddami O Avinc and F Ghahremanzadeh ldquoImprove-ment in poly(lactic acid) fabric performance via hydrophiliccoatingrdquo Progress in Organic Coatings vol 72 no 3 pp 299ndash304 2011
[9] J Nicolas S Mura D Brambilla N MacKiewicz and PCouvreur ldquoDesign functionalization strategies and biomedicalapplications of targeted biodegradablebiocompatible polymer-based nanocarriers for drug deliveryrdquoChemical Society Reviewsvol 42 no 3 pp 1147ndash1235 2013
[10] Z Ge and S Liu ldquoFunctional block copolymer assembliesresponsive to tumor and intracellular microenvironments forsite-specific drug delivery and enhanced imaging performancerdquoChemical Society Reviews vol 42 no 17 pp 7289ndash7325 2013
[11] M Spasova L Mespouille O Coulembier et al ldquoAmphiphilicpoly(D- or L-lactide)-b-poly(NN-dimethylamino-2-ethylmethacrylate) block copolymers Controlled synthesis char-acterization and stereocomplex formationrdquo Biomacromole-cules vol 10 no 5 pp 1217ndash1223 2009
[12] K Jelonek S Li X Wu J Kasperczyk and A Marcinkow-ski ldquoSelf-assembled filomicelles prepared from polylactidepoly(ethylene glycol) block copolymers for anticancer drugdeliveryrdquo International Journal of Pharmaceutics vol 485 no1-2 Article ID 14741 pp 357ndash364 2015
[13] H Feng X Lu W Wang N-G Kang and J W MaysldquoBlock copolymers Synthesis self-assembly and applicationsrdquoPolymer vol 9 no 10 article no 494 2017
[14] C Y Zhang Y Q Yang T X Huang et al ldquoSelf-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micellesfor anticancer drug deliveryrdquo Biomaterials vol 33 no 26 pp6273ndash6283 2012
[15] J K Oh ldquoPolylactide (PLA)-based amphiphilic block copoly-mers Synthesis self-assembly and biomedical applicationsrdquoSoft Matter vol 7 no 11 pp 5096ndash5108 2011
[16] L Xiao X Xiong X Sun et al ldquoRole of cellular uptake inthe reversal of multidrug resistance by PEG-b-PLA polymericmicellesrdquo Biomaterials vol 32 no 22 pp 5148ndash5157 2011
[17] V Pertici T Trimaille J Laurin et al ldquoRepair of the injuredspinal cord by implantation of a synthetic degradable blockcopolymer in ratrdquo Biomaterials vol 35 no 24 pp 6248ndash62582014
[18] Z Zhu ldquoEffects of amphiphilic diblock copolymer on drugnanoparticle formation and stabilityrdquo Biomaterials vol 34 no38 pp 10238ndash10248 2013
[19] E Ayano M Karaki T Ishihara H Kanazawa and T OkanoldquoPoly (N-isopropylacrylamide)-PLA and PLA blend nanoparti-cles for temperature-controllable drug release and intracellular
International Journal of Polymer Science 9
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Figure 6 (a) XPS wide scan and elemental mole percentages and (b) 1H NMR spectrum in CDCl3 of PLA345-CDP
＄Ｆ3
8 7 6 5 4(ppm)
3 012
(G) (G)
(G)
(B)
(B)
(C)
(C)
(D)
(D)
(E)
(E)
(A)
(A)
(F)
(F)
O C C
H
nC
C
m
O
O
N
O
（3 （3
（2
(a)
1730
1800 1700
1758minus(（3)2
2000 100030004000
Wavenumbers (＝Ｇminus1)
(b)
(A) (B) (C)
40 44 48 52 5636logMw
(c)
Figure 7 (a) 1HNMR spectrum in CDCl3 and (b) FTIR spectrum of PLA345-PDMAEMA213 block copolymers (c) Evolution of GPC tracesof the synthesized PLA345-PDMAEMA block copolymers with polymerization time of 1 (A) 3 (B) and 10 h (C)
2 4 6 8 100Time (h)
0
20
40
60
Con
vers
ion
()
0
20
40
60
Con
vers
ion
()
1 2 30Time (h)
(a)
0002040608
1 2 30Time (h)
2 4 6 8 100Time (h)
00
02
04
06
08
10
ＦＨ( [M
] 0[
])M
ＦＨ( [M
] 0[
])M
(b)
Figure 8 (a) Conversion and (b) kinetics plots for the RAFT polymerization of PLA-PDMAEMA block copolymers with increasingpolymerization time (1 2 3 4 7 and 10 h)
8 International Journal of Polymer Science
polymerization time in the initial 3 h A pseudo-first-orderkinetics for the RAFT polymerization of PDMAEMA wasdepicted at a low conversion (Figure 8(b)) However the rateof conversion decreases from 3 to 7 h and remains almostunchanged when the polymerization time increases from7 to 10 h These phenomena were mainly attributed to theincreasing viscosity of the reaction solution with the increaseof conversion At higher viscosity the motion of polymerchains becomes more difficult As a result terminationoccurred and the reaction rate decreased
4 Conclusions
PLA undergoes aminolytic degradation with EDA Theaminolysis reaction accelerated at increased EDA concentra-tion and reaction temperature The AD of PLA was rapidlyincreased in the initial stage and then reached a plateauThusthe molar masses of products rapidly decreased in the earlyreaction stage Furthermore ndashNH2 and ndashOH groups wereintroduced to the ends of the produced short PLA chainsThen the RAFT agent was immobilized onto the aminolyzedPLA chains and PLA-PDMAEMA block copolymers weresynthesized via RAFTpolymerization Conversion and kinet-ics plots for the RAFT polymerization of the block copoly-mers with increasing polymerization time were studied Theresults suggested a pseudo-first-order kinetics of the RAFTpolymerization of PDMAEMA at a low conversion Thelength distributions of the PLA and PDMAEMA blocks canbe controlled by controlling the aminolytic reaction andRAFT polymerization degrees in the process
Conflicts of Interest
The authors declare that they have no conflicts of interest
Acknowledgments
The authors are grateful for the financial support of theNational Natural Science Foundation of China (nos 31502213and 51473177) the Central Public-Interest Scientific Institu-tion Basal Research Fund CAFS (no 2018HY-XKQ03-4) andtheOpenFoundation fromFishery Sciences in the First-ClassSubjects of Zhejiang (no 20160014)
References
[1] M Okamoto and B John ldquoSynthetic biopolymer nanocompos-ites for tissue engineering scaffoldsrdquoProgress in Polymer Sciencevol 38 pp 1487ndash1503 2013
[2] N MacKiewicz J Nicolas N Handke et al ldquoPrecise engineer-ing of multifunctional PE gylated polyester nanoparticles forcancer cell targeting and imagingrdquo Chemistry of Materials vol26 no 5 pp 1834ndash1847 2014
[3] I Armentano N Bitinis E Fortunati et al ldquoMultifunctionalnanostructured PLA materials for packaging and tissue engi-neeringrdquo Progress in Polymer Science vol 38 no 10-11 pp 1720ndash1747 2013
[4] S Gupta R Tyagi V S Parmar S K Sharma and R HaagldquoPolyether based amphiphiles for delivery of active compo-nentsrdquoPolymer (UnitedKingdom) vol 53 no 15 pp 3053ndash30782012
[5] P Zhang R Tian R Lv B Na and Q Liu ldquoWater-permeablepolylactide blend membranes for hydrophilicity-based separa-tionrdquo Chemical Engineering Journal vol 269 pp 180ndash185 2015
[6] A J R Lasprilla G A R Martinez B H Lunelli A L Jardiniand R M Filho ldquoPoly-lactic acid synthesis for application inbiomedical devices - A reviewrdquo Biotechnology Advances vol 30no 1 pp 321ndash328 2012
[7] L-J Zhu F Liu X-M Yu A-L Gao and L-X Xue ldquoSurfacezwitterionization of hemocompatible poly(lactic acid) mem-branes for hemodiafiltrationrdquo Journal of Membrane Science vol475 pp 469ndash479 2015
[8] A Khoddami O Avinc and F Ghahremanzadeh ldquoImprove-ment in poly(lactic acid) fabric performance via hydrophiliccoatingrdquo Progress in Organic Coatings vol 72 no 3 pp 299ndash304 2011
[9] J Nicolas S Mura D Brambilla N MacKiewicz and PCouvreur ldquoDesign functionalization strategies and biomedicalapplications of targeted biodegradablebiocompatible polymer-based nanocarriers for drug deliveryrdquoChemical Society Reviewsvol 42 no 3 pp 1147ndash1235 2013
[10] Z Ge and S Liu ldquoFunctional block copolymer assembliesresponsive to tumor and intracellular microenvironments forsite-specific drug delivery and enhanced imaging performancerdquoChemical Society Reviews vol 42 no 17 pp 7289ndash7325 2013
[11] M Spasova L Mespouille O Coulembier et al ldquoAmphiphilicpoly(D- or L-lactide)-b-poly(NN-dimethylamino-2-ethylmethacrylate) block copolymers Controlled synthesis char-acterization and stereocomplex formationrdquo Biomacromole-cules vol 10 no 5 pp 1217ndash1223 2009
[12] K Jelonek S Li X Wu J Kasperczyk and A Marcinkow-ski ldquoSelf-assembled filomicelles prepared from polylactidepoly(ethylene glycol) block copolymers for anticancer drugdeliveryrdquo International Journal of Pharmaceutics vol 485 no1-2 Article ID 14741 pp 357ndash364 2015
[13] H Feng X Lu W Wang N-G Kang and J W MaysldquoBlock copolymers Synthesis self-assembly and applicationsrdquoPolymer vol 9 no 10 article no 494 2017
[14] C Y Zhang Y Q Yang T X Huang et al ldquoSelf-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micellesfor anticancer drug deliveryrdquo Biomaterials vol 33 no 26 pp6273ndash6283 2012
[15] J K Oh ldquoPolylactide (PLA)-based amphiphilic block copoly-mers Synthesis self-assembly and biomedical applicationsrdquoSoft Matter vol 7 no 11 pp 5096ndash5108 2011
[16] L Xiao X Xiong X Sun et al ldquoRole of cellular uptake inthe reversal of multidrug resistance by PEG-b-PLA polymericmicellesrdquo Biomaterials vol 32 no 22 pp 5148ndash5157 2011
[17] V Pertici T Trimaille J Laurin et al ldquoRepair of the injuredspinal cord by implantation of a synthetic degradable blockcopolymer in ratrdquo Biomaterials vol 35 no 24 pp 6248ndash62582014
[18] Z Zhu ldquoEffects of amphiphilic diblock copolymer on drugnanoparticle formation and stabilityrdquo Biomaterials vol 34 no38 pp 10238ndash10248 2013
[19] E Ayano M Karaki T Ishihara H Kanazawa and T OkanoldquoPoly (N-isopropylacrylamide)-PLA and PLA blend nanoparti-cles for temperature-controllable drug release and intracellular
International Journal of Polymer Science 9
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
polymerization time in the initial 3 h A pseudo-first-orderkinetics for the RAFT polymerization of PDMAEMA wasdepicted at a low conversion (Figure 8(b)) However the rateof conversion decreases from 3 to 7 h and remains almostunchanged when the polymerization time increases from7 to 10 h These phenomena were mainly attributed to theincreasing viscosity of the reaction solution with the increaseof conversion At higher viscosity the motion of polymerchains becomes more difficult As a result terminationoccurred and the reaction rate decreased
4 Conclusions
PLA undergoes aminolytic degradation with EDA Theaminolysis reaction accelerated at increased EDA concentra-tion and reaction temperature The AD of PLA was rapidlyincreased in the initial stage and then reached a plateauThusthe molar masses of products rapidly decreased in the earlyreaction stage Furthermore ndashNH2 and ndashOH groups wereintroduced to the ends of the produced short PLA chainsThen the RAFT agent was immobilized onto the aminolyzedPLA chains and PLA-PDMAEMA block copolymers weresynthesized via RAFTpolymerization Conversion and kinet-ics plots for the RAFT polymerization of the block copoly-mers with increasing polymerization time were studied Theresults suggested a pseudo-first-order kinetics of the RAFTpolymerization of PDMAEMA at a low conversion Thelength distributions of the PLA and PDMAEMA blocks canbe controlled by controlling the aminolytic reaction andRAFT polymerization degrees in the process
Conflicts of Interest
The authors declare that they have no conflicts of interest
Acknowledgments
The authors are grateful for the financial support of theNational Natural Science Foundation of China (nos 31502213and 51473177) the Central Public-Interest Scientific Institu-tion Basal Research Fund CAFS (no 2018HY-XKQ03-4) andtheOpenFoundation fromFishery Sciences in the First-ClassSubjects of Zhejiang (no 20160014)
References
[1] M Okamoto and B John ldquoSynthetic biopolymer nanocompos-ites for tissue engineering scaffoldsrdquoProgress in Polymer Sciencevol 38 pp 1487ndash1503 2013
[2] N MacKiewicz J Nicolas N Handke et al ldquoPrecise engineer-ing of multifunctional PE gylated polyester nanoparticles forcancer cell targeting and imagingrdquo Chemistry of Materials vol26 no 5 pp 1834ndash1847 2014
[3] I Armentano N Bitinis E Fortunati et al ldquoMultifunctionalnanostructured PLA materials for packaging and tissue engi-neeringrdquo Progress in Polymer Science vol 38 no 10-11 pp 1720ndash1747 2013
[4] S Gupta R Tyagi V S Parmar S K Sharma and R HaagldquoPolyether based amphiphiles for delivery of active compo-nentsrdquoPolymer (UnitedKingdom) vol 53 no 15 pp 3053ndash30782012
[5] P Zhang R Tian R Lv B Na and Q Liu ldquoWater-permeablepolylactide blend membranes for hydrophilicity-based separa-tionrdquo Chemical Engineering Journal vol 269 pp 180ndash185 2015
[6] A J R Lasprilla G A R Martinez B H Lunelli A L Jardiniand R M Filho ldquoPoly-lactic acid synthesis for application inbiomedical devices - A reviewrdquo Biotechnology Advances vol 30no 1 pp 321ndash328 2012
[7] L-J Zhu F Liu X-M Yu A-L Gao and L-X Xue ldquoSurfacezwitterionization of hemocompatible poly(lactic acid) mem-branes for hemodiafiltrationrdquo Journal of Membrane Science vol475 pp 469ndash479 2015
[8] A Khoddami O Avinc and F Ghahremanzadeh ldquoImprove-ment in poly(lactic acid) fabric performance via hydrophiliccoatingrdquo Progress in Organic Coatings vol 72 no 3 pp 299ndash304 2011
[9] J Nicolas S Mura D Brambilla N MacKiewicz and PCouvreur ldquoDesign functionalization strategies and biomedicalapplications of targeted biodegradablebiocompatible polymer-based nanocarriers for drug deliveryrdquoChemical Society Reviewsvol 42 no 3 pp 1147ndash1235 2013
[10] Z Ge and S Liu ldquoFunctional block copolymer assembliesresponsive to tumor and intracellular microenvironments forsite-specific drug delivery and enhanced imaging performancerdquoChemical Society Reviews vol 42 no 17 pp 7289ndash7325 2013
[11] M Spasova L Mespouille O Coulembier et al ldquoAmphiphilicpoly(D- or L-lactide)-b-poly(NN-dimethylamino-2-ethylmethacrylate) block copolymers Controlled synthesis char-acterization and stereocomplex formationrdquo Biomacromole-cules vol 10 no 5 pp 1217ndash1223 2009
[12] K Jelonek S Li X Wu J Kasperczyk and A Marcinkow-ski ldquoSelf-assembled filomicelles prepared from polylactidepoly(ethylene glycol) block copolymers for anticancer drugdeliveryrdquo International Journal of Pharmaceutics vol 485 no1-2 Article ID 14741 pp 357ndash364 2015
[13] H Feng X Lu W Wang N-G Kang and J W MaysldquoBlock copolymers Synthesis self-assembly and applicationsrdquoPolymer vol 9 no 10 article no 494 2017
[14] C Y Zhang Y Q Yang T X Huang et al ldquoSelf-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micellesfor anticancer drug deliveryrdquo Biomaterials vol 33 no 26 pp6273ndash6283 2012
[15] J K Oh ldquoPolylactide (PLA)-based amphiphilic block copoly-mers Synthesis self-assembly and biomedical applicationsrdquoSoft Matter vol 7 no 11 pp 5096ndash5108 2011
[16] L Xiao X Xiong X Sun et al ldquoRole of cellular uptake inthe reversal of multidrug resistance by PEG-b-PLA polymericmicellesrdquo Biomaterials vol 32 no 22 pp 5148ndash5157 2011
[17] V Pertici T Trimaille J Laurin et al ldquoRepair of the injuredspinal cord by implantation of a synthetic degradable blockcopolymer in ratrdquo Biomaterials vol 35 no 24 pp 6248ndash62582014
[18] Z Zhu ldquoEffects of amphiphilic diblock copolymer on drugnanoparticle formation and stabilityrdquo Biomaterials vol 34 no38 pp 10238ndash10248 2013
[19] E Ayano M Karaki T Ishihara H Kanazawa and T OkanoldquoPoly (N-isopropylacrylamide)-PLA and PLA blend nanoparti-cles for temperature-controllable drug release and intracellular
International Journal of Polymer Science 9
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
uptakerdquoColloids and Surfaces B Biointerfaces vol 99 pp 67ndash732012
[20] X Y Xiong L Guo Y C Gong et al ldquoIn vitro in vivotargeting behaviors of biotinylated Pluronic F127poly(lacticacid) nanoparticles through biotinavidin interactionrdquo EuropeanJournal of Pharmaceutical Sciences vol 46 no 5 pp 537ndash5442012
[21] H Moroishi C Yoshida and Y Murakami ldquoA free-standingsheet-shaped ldquohydrophobicrdquo biomaterial containing poly-meric micelles formed from poly(ethylene glycol)-poly(lacticacid) block copolymer for possible incorporationrelease ofldquohydrophilicrdquo compoundsrdquo Colloids and Surfaces B Biointer-faces vol 102 pp 597ndash603 2013
[22] QWu CWang D Zhang X Song F Verpoort and G ZhangldquoSynthesis and micellization of amphiphilic biodegradablemethoxypolyethylene glycolpoly(dl-lactide)polyphosphateblock copolymerrdquo Reactive and Functional Polymers vol 71 no9 pp 980ndash984 2011
[23] X Zhang D Chen S Ba et al ldquoPoly(l-histidine) based triblockcopolymers PH induced reassembly of copolymer micelles andmechanism underlying endolysosomal escape for intracellulardeliveryrdquo Biomacromolecules vol 15 no 11 pp 4032ndash40452014
[24] E K Efthimiadou L-A Tziveleka P Bilalis and G KordasldquoNovel PLA modification of organic microcontainers basedon ring opening polymerization Synthesis characterizationbiocompatibility and drug loadingrelease propertiesrdquo Interna-tional Journal of Pharmaceutics vol 428 no 1-2 pp 134ndash1422012
[25] M A Kryuchkov C Detrembleur and C G Bazuin ldquoLinearamphiphilic diblock copolymers of lactide and 2-dimethylami-noethyl methacrylate using bifunctional-initiator and one-potapproachesrdquo Polymer (United Kingdom) vol 55 no 10 pp2316ndash2324 2014
[26] D Rasselet A Ruellan A Guinault G Miquelard-Garnier CSollogoub and B Fayolle ldquoOxidative degradation of polylactide(PLA) and its effects on physical and mechanical propertiesrdquoEuropean Polymer Journal vol 50 no 1 pp 109ndash116 2014
[27] M-L Cairns G R Dickson J F Orr D Farrar K Hawkinsand F J Buchanan ldquoElectron-beam treatment of poly(lacticacid) to control degradation profilesrdquo Polymer Degradation andStability vol 96 no 1 pp 76ndash83 2011
[28] MCKimandTMasuoka ldquoDegradation properties of PLAandPHBV films treated with CO2-plasmardquo Reactive and FunctionalPolymers vol 69 no 5 pp 287ndash292 2009
[29] D VanCong THoang N V Giang N THa T D Lam andMSumita ldquoA novel enzymatic biodegradable route for PLAEVAblends under agricultural soil of Vietnamrdquo Materials Scienceand Engineering C Materials for Biological Applications vol 32no 3 pp 558ndash563 2012
[30] M Karamanlioglu A Houlden and G D Robson ldquoIsolationand characterisation of fungal communities associated withdegradation and growth on the surface of poly(lactic) acid(PLA) in soil and compostrdquo International Biodeterioration ampBiodegradation vol 95 pp 301ndash310 2014
[31] M Karamanlioglu and G D Robson ldquoThe influence of bioticand abiotic factors on the rate of degradation of poly(lactic)acid (PLA) coupons buried in compost and soilrdquo PolymerDegradation and Stability vol 98 no 10 pp 2063ndash2071 2013
[32] Y-X Weng L Wang M Zhang X-L Wang and Y-Z WangldquoBiodegradation behavior of P(3HB4HB)PLA blends in real
soil environmentsrdquo Polymer Testing vol 32 no 1 pp 60ndash702013
[33] P E Le Marec L Ferry J-C Quantin et al ldquoInfluence of meltprocessing conditions on poly(lactic acid) degradation Molarmass distribution and crystallizationrdquo PolymerDegradation andStability vol 110 pp 353ndash363 2014
[34] J Li W Zheng L Li Y Zheng and X Lou ldquoThermaldegradation kinetics of g-HAPLA compositerdquo ThermochimicaActa vol 493 no 1-2 pp 90ndash95 2009
[35] Y Zhu Z Mao and C Gao ldquoAminolysis-based surface modifi-cation of polyesters for biomedical applicationsrdquoRSCAdvancesvol 3 no 8 pp 2509ndash2519 2013
[36] Z Yang M Zhengwei S Huayu and G Changyou ldquoIn-depth study on aminolysis of poly(120576-caprolactone) Back to thefundamentalsrdquo SCIENCE CHINA Chemistry vol 55 no 11 pp2419ndash2427 2012
[37] Y Zhu C Gao X Liu T He and J Shen ldquoImmobilizationof Biomacromolecules onto Aminolyzed Poly(L-lactic acid)toward Acceleration of Endothelium Regenerationrdquo TissueEngineering Part A vol 10 no 1-2 pp 53ndash61 2004
[38] F J Xu X C Yang C Y Li and W T Yang ldquoFunctionalizedpolylactide film surfaces via surface-initiated ATRPrdquo Macro-molecules vol 44 no 7 pp 2371ndash2377 2011
[39] GMoad Y K Chong A Postma E Rizzardo and S HThangldquoAdvances in RAFT polymerization the synthesis of polymerswith defined end-groupsrdquo Polymer Journal vol 46 no 19 pp8458ndash8468 2005
[40] L Zhu F Liu X Yu and L Xue ldquoPoly(Lactic Acid) He-modialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive Prepara-tion Characterization and Performancerdquo ACS Applied Materi-als amp Interfaces vol 7 no 32 pp 17748ndash17755 2015
[41] A Mittal R K Soni K Dutt and S Singh ldquoScanning electronmicroscopic study of hazardous waste flakes of polyethyleneterephthalate (PET) by aminolysis and ammonolysisrdquo Journalof Hazardous Materials vol 178 no 1-3 pp 390ndash396 2010
[42] L Wang Y Cui N Wang et al ldquoAminolytic depolymerizationof polyarylsulfonesrdquo PolymerDegradation and Stability vol 103no 1 pp 69ndash74 2014
[43] R M Rasal A V Janorkar and D E Hirt ldquoPoly(lactic acid)modificationsrdquo Progress in Polymer Science vol 35 no 3 pp338ndash356 2010
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
