Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2013 Article ID 315917 6 pageshttpdxdoiorg1011552013315917
Research ArticlePreparation of Higher Molecular Weight Poly (l-lactic Acid) byChain Extension
Chenguang Liu Yuliang Jia and Aihua He
Key Laboratory of Rubber-Plastics Ministry of EducationShandong Provincial Key Laboratory of Rubber-PlasticsQingdao University of Science amp Technology Qingdao 266042 China
Correspondence should be addressed to Aihua He aihuaheiccasaccn
Received 7 June 2013 Accepted 18 July 2013
Academic Editor Zhou Yang
Copyright copy 2013 Chenguang Liu et alThis 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
High molecular weight poly (lactic acid) (PLA) was obtained by chain extending with hexamethylene diisocyanate (HDI) Theinfluences of the amount of chain extender reaction time and molecular weight changes of prepolymers on the poly(lactic acid)were investigated PLA prepolymer with a viscosity average molecular weight (119872
120578) of 2 times 104 gmol was synthesized from l-lactide
using stannous octoate as the catalyst After 20min of chain extension at 175∘C the resulting polymer had119872119908of 203 times 104 gmol
and119872119899of 105times 104 gmol Both FT-IR and 1H-NMRverified that the structure of PLAdid not change either before chain extending
or after The optically active characterized that the chain extending-product was left handed DSC and XRD results showed thatboth the 119879
119892and the crystallinity of PLA were lowered by chain-extension reaction The crystalline transformation happened in
PLA after chain extending crystalline 1205721015840 form to 120572 form
1 Introduction
At present plastics waste disposal has become a seriousproblem worldwide There is a strong need to provideplastic materials suitable for packaging which will also bedegradable and result in products that are environmentallysafe [1] Concerning the feasibility of the use of renewable rawmaterials and production process the poly (lactic acid) (PLA)has become a very promising biodegradable polymer [2 3]
High molecular weights are needed for PLA to havegood physical properties Until now high molecular weightPLA was synthesized by ring-opening polymerization of thelactide [4] which is relatively complicated and expensiveDirect polycondensation of lactic acid is a low-cost process toproduce PLA [5] however it is hard to increase themolecularweight enough because of the difficulty of removing thewater from the system A large number of investigationshave been made to improve PLA properties via plasticiza-tion copolymerization and blending with elastomers [6ndash14] Among them low-cost nontoxic HDI as chain extenderis the simplest and most effective way Addition of a chainextender to improve the molecular weight of PLA it can
solve the problemof degradation time of polylactic acid beinguncontrollable [15] But most of the researches were focusedon themolecular weight of the products optical activities andthe transition of crystal form of the products effect of chainextension reaction were ignored
In this paper higher molecular weight PLLA was pro-duced by ring-opening polymerization of lactide followedby chain extension Hexamethylene diisocyanate (HDI) wasused as the chain extender Optical activities and the transi-tion of crystal form of the PLA chain extend with HDI werestudied
2 Materials and Methods
21 Materials l-lactide was synthesized and purified bylaboratory 97 optically pure 119879119898 1008∘C and moisturecontent 190 ppm Stannous octoate was from Sigma Chem-ical Co HDI (+99) was purchased from Shanghai JingchunChemical Co China Toluene was refluxed over sodiumwith benzophenone as an indicator All other chemicals werereagent grade
2 International Journal of Polymer Science
Table 1 The influences of process conditions on poly(lactic acid) after chain extension
22 Synthesis of Polymer The low molecular weight PLAprepolymer was synthesized through lactide ring-openingpolymerization The monomer (l-lactide) was first chargedinto the reactor The catalyst solution was added by a syringewith capillary and polymerization reaction was initiatedThe reactor was heated with an oil bath while stirring andthrough a period of 6 h the temperature was raised to 135∘Cwhile the pressure was reduced to 006MPa After the reac-tion the polymers were dissolved by chloroform precipitatedby alcohol and then dried under vacuum at 40∘C for 48 h
After the ring-opening polymerization the temperaturewas heightened to 175∘C under nitrogen atmosphere andcalculated HDI was added to the reactor while stirring thereaction was taken from 10 to 40min After the reactionthe resulting polymer was dissolved in chloroform andprecipitated in the excess of ethanol The final product wasisolated by filtration and dried in a vacuum at 40∘C for 48 h
23 Characterizations The number average molecularweight and weight average molecular weight of the PLAwere determined by gel permeation chromatography (GPC)on a Waters 1515 HPLC system Tetrahydrofuran was usedas eluent at a flow rate of 10mL sdotminminus1 The temperatureof the columns and detector was 40∘C Calibrationswere fulfilled with narrow molecular weight distributedpolystyrene standards Intrinsic viscosities were determinedin chloroform at (25 plusmn 01)∘C by Ubbelohde viscometer[p] = [2 times (psp minus ln p119903)]
05119862 = 119870119872
120572 119870 = 221 times 10minus4120572 = 077 p119903 = 1199051199050 psp = 1 minus p119903 Optical activities were testedin chloroform at (25plusmn01)∘C by wzz-3 automatic polarimeter(Shanghai Precision Instrument Co) and the measurementconcentration was 90mgmL A Bruker VERTEX 70 FT-IRwas used to scan the FTIT spectrum and the 1H-NMRspectrum was recorded with a Bruker FTAC-80 NMRspectrometer using CDCl3 as a solvent DSC measurementswere performed with a NETZSCH DSC-204F1 scannedat the rate of 10∘Cmin A second-scan DSC spectrumwas recorded after the sample was annealed to 0∘C119883119888 = (9987791198671198989987791198671198980
) times 100 9987791198671198980 = 93 Jg [16] X-ray diffraction patterns were recorded with a Bruker
ADVANCE-D8X X-ray diffractometer scanned from 5∘ to40∘
3 Results and Discussion
31 Polymerization The PLA prepolymer was synthesizedusing stannous octoate as the catalyst according to reaction[17] After chain extending at 175∘C for 10ndash40min thereaction product was collected and analyzed The analysisresults were summarized in Table 1 The molecular weightwas increased several times after chain extension It wassuggested that HDI connects the hydroxyl end group so as todouble grow the molecular weight However the incrementof molecular weight was more than twice as shown in Table 1
Table 1 shows the effect of the dosage of HDI reactiontime and prepolymer molecular weight changes on the chainextension products When the ratio of [NCO] to [OH] is 6after chain extending at 175∘C for 20min119872119908 of 203000 wasobtained FromRun a1 a2 a3 and a4withHDI increased themolecular weight of PLA product growth multiples Whilethe amount of HDI was too much molecular weight ofproducts decreased This is because the excessive HDI isunevenly distributed and then crosslinking or branchinghappened leading to the majority of low molecular weightprepolymer reacting with the remaining chain extenderWhen the ratio of [NCO] to [OH] is 8 119872119908 of 30000 wasobtained and insoluble content reaching 39 indicate thatthe excess amount of the isocyanate groupmay also react withthe other end of PLA molecule to form crosslink and branchstructure according to reaction (3) of Figure 1 Run a3 a5 a6and a4 indicated that long reaction time led to crosslinkingthis was proved by the insoluble content The molecularweight of the prepolymer changing in Run a3 a8 a9 and a10shows that with increasing prepolymer molecular weight themolecular weight of the chain-extended PLA increased whileinsoluble content also increased Optical activity test provedthat the chain-extended product is laevorotary
32 FT-IR and 1H-NMR Figure 2 shows the FT-IR spectrumof the PLA prepolymer and the chain-extended product
International Journal of Polymer Science 3
OHO
OHn
OCNNCO
+
Prepolymer HDI
O CO
HO NHO
NHn
O
OO
OHn
HDI
C NH
ONH
O
C NO
NHO
O
Branched structure
Furtherreaction
175∘C
175∘C
Figure 1 The synthesis scheme of the PLA chain extended withHDI
3500 3000 2500 2000 1500 1000
Prepolymer
Run3
Wavenumber (cmminus1)
Figure 2 The infrared spectrum of the PLA prepolymer and thePLA chain extended with HDI (Run3)
with molar ratio at 6 of NCOOH after 20min reactionBoth IR spectra have characteristic ester absorption bandsat 1760 cmminus1 but in the Run3 a shoulder peak appearedat 1691 cmminus1 according to ndashC=O adjoin to ndashNH ThendashNH flexural vibrations absorption peak at 1525 cmminus1 andstretching vibrations absorption peak at 3413 cmminus1 appeared
after the chainextending reaction The weak absorption at720 cmminus1 represents the ndashCH2ndash from HDI With the PLAcrystallization peak at 756 cmminus1 the peak strength weakenedafter the reaction [18]
Figure 3 shows the 1H-NMR (500MHz TMS CDCl3)spectrum of the PLA prepolymer (Figure 3(a)) and thePLA chain extended with HDI (Figure 3(b)) Both spectraexhibited the signal of methine group at 51 ppm (a) and thesignal of methyl group at 16 ppm (c) The signal at 43 ppm(b) in the spectrum shown in Figure 3(a) characteristic of thehydrogen of the methine next to a hydroxyl end group wasfound But the signal at the same shift was not observed inthe spectrum shown in Figure 3(b) because the HDI reactedwith the hydroxyl group The broad signals at 32 ppm (b)and 41 ppm (d) in the spectrum shown in Figure 3(b) wereassigned to the unit of HDI in the PLA polymer chain [15]consistent with the results of FT-IR The intensity ratio ofthe signal corresponding to urethane to the signal of HDIunit was not 1 2 This can be explained by the fact that thehydrogen in the urethane bond reacted with other polymerchain to form branch structure
33 Gel Permeation Chromatography Figure 4 shows theGPC spectra of the PLA chain extender with HDI Fromthe spectra we can comprehend that the distribution has twomodes called a bimodal distributionThe characteristic peaksof low outflow time represent the high molecular weightchain-extending products the peaks of high outflow timepeak for the low molecular weight prepolymer The chainextension reaction successfully happened in prepolymer inthe presence of HDI With the increase of chain extenderreaction time and prepolymer molecular weight the highmolecular weight part content increased in the products
34 DSC Table 2 shows the DSC thermograms of thePLA prepolymer and chain-extended PLA After the chain-extending reaction the melt enthalpies were reducedThe 119879119892and119879119898moved towards lower temperaturesThis suggests thatadding of chain extender had an effect on crystallinity of PLAaccording to the long chain alkane structure unit of the chainextender HDIThe crystallization of the chain-extended PLAis still above 40 yet crystal can be connected to each otherforming throughout the material of the continuous phase Sothe highest used temperature can be increased close to thecrystalline melting point [19]
Figure 5 shows the DSC thermogram of the PLA pre-polymer and the PLA chain extended with different addingamount HDI With the increasing amount of HDI thecrystallinity increased first and then decreased indicatingthat a small amount of HDI was added tomake themolecularchain growth and also to maintain good crystallinity Toomuch HDI makes the product of insoluble matter contentincreased while it also reduces the product crystallinity
Figure 6 shows the DSC thermograms with the time ofthe chain-extending reaction When the reaction time was30min two obvious melting peaks of chain-extending prod-uct appeared suggesting a phase transition process The 119879119892of the PLA chain extended with HDI decreased it suggested
4 International Journal of Polymer Science
Table 2 DSC data of the PLA prepolymer and the chain-extended PLA
Figure 3 1H-NMR spectrum of PLA prepolymer (a) and the PLA chain extended with HDI (Run3) (b)
5 6 7 8 9 10 11
Run a10
Run a9
Run a8
Run a7Run a6Run a5
Run a4Run a3
Run a2
Efflusion time (min)
Run a1
Figure 4 GPC spectrogram of the PLA chain extender with HDI
that the longer reaction time resulted in insoluble mattersincrease Because of the transition of crystal form crystallinepart the melting enthalpy increases and crystallinity of thePLA increased
0 20 40 60 80 100 120 140 160 180 200
Run3
Run2
Prepolymer
ExoRun1
Temperature (∘C)
1635∘C
1645∘C
1613∘C
1703∘C
Figure 5 DSC thermogram of the prepolymer and the PLA chainextended with different adding amount HDI
Figure 7 shows the DSC thermographs of the PLA fromdifferent molecular weight prepolymers With the increase ofmolecular weight of PLA prepolymer transformation of PLAcrystal phenomenon gradually weakened and disappeared
International Journal of Polymer Science 5
0 20 40 60 80 100 120 140 160 180 200
Run3
Run6
Exo
1635∘C
1588∘C
Temperature (∘C)
Figure 6 DSC thermogram of the chain-extended PLA withdifferent chain-extending reaction time
0 20 40 60 80 100 120 140 160 180 200
Run10
Run9
Run8
Run3
Exo
Temperature (∘C)
1645∘C
1641∘C
1635∘C
1635∘C
Figure 7 DSC thermogram of the PLA from different molecularweight prepolymers
The insoluble matter content increased the crystallinitydecreased slightly
35 X-Ray Diffraction Figure 8 shows the X-ray diffractionpattern of the PLA prepolymer and the chain-extended PLAThe PLA prepolymer showed the sharp peak at 2120579 about 165∘(020 reflection) and 188∘ (023 reflection) while the peaks ofthe chain-extended samples were much lower and shifted thepeaks at 2120579 of 168∘and 191∘ The results show that after thechain extender polymerization the crystal type of the PLLAturns 1205721015840 to 120572-crystal type [20 21] consistent with the resultsof DSC
4 Conclusions
Higher molecular weight of poly(l-lactic acid) was preparedby using HDI chain-extending method with the low molec-ular weight PLA as the prepolymer The weight average
10 15 20 25
Prepolymer
Run6
Run10
2120579 (∘)
Figure 8 XRD pattern of the PLA prepolymer and the chain-extended PLA
molecular weight of the chain-extended PLA could reachup to 203 times 104 gmol by GPC measurement Both FT-IRand 1H-NMR tests give a verification of structure and theoptically active characterized that the product was PLLAChain-extended PLLA had lower crystallinity by DSC andX-ray diffraction because of the branched structure TheDSC and X-ray diffraction results both indicated that thecrystalline of product changed from mixed 1205721015840- and 120572-crystalform to 120572-crystal form
Acknowledgments
This work was financially supported by the National KeyTechnology RampD Program of China (2011BAE26B05) theNational Nature Science Foundation of China (No 2117407420774098 51003050 and 51273100) Shandong ProvinceNatural Science Fund for Distinguished Young Scholars(JQ201213) and the Nature Science Foundation of ShandongProvince (ZR2011EMM008)
References
[1] L Yu K Dean and L Li ldquoPolymer blends and composites fromrenewable resourcesrdquo Progress in Polymer Science vol 31 no 6pp 576ndash602 2006
[2] S S Ray and M Bousmina ldquoBiodegradable polymers and theirlayered silicate nanocomposites in greening the 21st centurymaterials worldrdquo Progress in Materials Science vol 50 no 8 pp962ndash1079 2005
[3] B Gupta N Revagade and J Hilborn ldquoPoly(lactic acid) fiberan overviewrdquo Progress in Polymer Science vol 32 no 4 pp 455ndash482 2007
[4] J Cheng J Sun K Wu et al ldquoRing-opening polymerization ofD L-lacide catalyzed with120573-diketone compleses of Ti and ZrrdquoJournal of Chemical Industry amp Engineering vol 27 no 5 pp5ndash7 2006
[5] J Shu P Wang T Zheng L-Y Tian and B-X Zhao ldquoDirectsynthesis of ploy (L-lactic acid) by melt polycondensationrdquoMaterial Science andTechnology vol 15 no 3 pp 374ndash378 2007
[6] S I Woo B O Kim H S Jun and H N Chang ldquoPolymer-ization of aqueous lactic acid to prepare high molecular weight
6 International Journal of Polymer Science
poly(lactic acid) by chain-extending with hexamethylene diiso-cyanaterdquo Polymer Bulletin vol 35 no 4 pp 415ndash421 1995
[7] Z Wei J Ge Z Gu et al ldquoStudy on biodegradable polymermaterials based on poly(lactic acid)mdashI Chain extending of lowmolecular weight Poly (lactic acid) with methylenediphenyldiisocyanaterdquo Journal of Applied Polymer Science vol 74 pp2546ndash2551 1999
[8] J Tuominen J Kylma and J Seppala ldquoChain extending oflactic acid oligomersmdash2 Increase of molecular weight with 16-hexamethylene diisocyanate and 221015840-bis(2-oxazoline)rdquo Poly-mer vol 43 no 1 pp 3ndash10 2001
[9] R J Feng and W Z Shi ldquoInfluence of polymerization methodsand chain-extension agent on relative molecular weight ofpolylactiderdquo Petrochemical Technology vol 30 no 2 pp 103ndash105 2001
[10] T Yu J Ren S Gu and M Yang ldquoPreparation and charac-terization of biodegradable poly(lactic acid)-block-poly(eopen-caprolactone) multiblock copolymerrdquo Polymers for AdvancedTechnologies vol 21 no 3 pp 183ndash188 2010
[11] D Cohn and A Hotovely Salomon ldquoDesigning biodegradablemultiblock PCLPLA thermoplastic elastomersrdquo Biomaterialsvol 26 no 15 pp 2297ndash2305 2005
[12] J-B Zeng Y-D Li W-D Li K-K Yang X-L Wang and Y-Z Wang ldquoSynthesis and properties of poly(ester urethane)sconsisting of poly(l-lactic acid) and poly(ethylene succinate)segmentsrdquo Industrial and Engineering Chemistry Research vol48 no 4 pp 1706ndash1711 2009
[13] H Li and M A Huneault ldquoEffect of chain extension on theproperties of PLATPS blendsrdquo Journal of Applied PolymerScience vol 122 no 1 pp 134ndash141 2011
[14] B-S Park J C Song D H Park and K-B Yoon ldquoPLAchain-extended PEG blends with improved ductilityrdquo Journal ofApplied Polymer Science vol 123 no 4 pp 2360ndash2367 2012
[15] Z Wang Y Zhao and J Wang ldquoSynthesis of polylactic acidbiodegradable materials through chain extensionrdquo ChineseJournal of Synthetic Chemistry vol 11 pp 106ndash110 2012
[16] M Li T Jiao Y Wang et al ldquoEffect of plasticizer oncrystallization morphology of biodegradable poly(lactic acid)rdquoPlastic Science and Technology vol 39 no 6 pp 55ndash59 2011
[17] W-W Wang Z Yi L Jiang and Y Dan ldquoSynthesis of a poly-lactide macroinitiator via one-step polymerizationrdquo PolymericMaterials Science and Engineering vol 26 no 1 pp 12ndash15 2010
[18] Y Hori M Suzuki Y Okeda et al ldquoA novel biodegradablepoly(urethane ester) synthesized frompoly(3-hydroxybutyrate)segmentsrdquoMacromolecules vol 25 no 19 pp 5117ndash5118 1992
[19] M He Polymer Physics Fudan University Publishing HouseShanghai China 2007
[20] P Pan B Zhu W Kai T Dong and Y Inoue ldquoEffect of crys-tallization temperature on crystal modifications and crystal-lization kinetics of poly(L-lactide)rdquo Journal of Applied PolymerScience vol 107 no 1 pp 54ndash62 2008
[21] J Zhang K Tashiro H Tsuji and A J Domb ldquoDisorder-to-order phase transition andmultiple melting behavior of poly(L-lactide) investigated by simultaneous measurements of WAXDand DSCrdquoMacromolecules vol 41 no 4 pp 1352ndash1357 2008
22 Synthesis of Polymer The low molecular weight PLAprepolymer was synthesized through lactide ring-openingpolymerization The monomer (l-lactide) was first chargedinto the reactor The catalyst solution was added by a syringewith capillary and polymerization reaction was initiatedThe reactor was heated with an oil bath while stirring andthrough a period of 6 h the temperature was raised to 135∘Cwhile the pressure was reduced to 006MPa After the reac-tion the polymers were dissolved by chloroform precipitatedby alcohol and then dried under vacuum at 40∘C for 48 h
After the ring-opening polymerization the temperaturewas heightened to 175∘C under nitrogen atmosphere andcalculated HDI was added to the reactor while stirring thereaction was taken from 10 to 40min After the reactionthe resulting polymer was dissolved in chloroform andprecipitated in the excess of ethanol The final product wasisolated by filtration and dried in a vacuum at 40∘C for 48 h
23 Characterizations The number average molecularweight and weight average molecular weight of the PLAwere determined by gel permeation chromatography (GPC)on a Waters 1515 HPLC system Tetrahydrofuran was usedas eluent at a flow rate of 10mL sdotminminus1 The temperatureof the columns and detector was 40∘C Calibrationswere fulfilled with narrow molecular weight distributedpolystyrene standards Intrinsic viscosities were determinedin chloroform at (25 plusmn 01)∘C by Ubbelohde viscometer[p] = [2 times (psp minus ln p119903)]
05119862 = 119870119872
120572 119870 = 221 times 10minus4120572 = 077 p119903 = 1199051199050 psp = 1 minus p119903 Optical activities were testedin chloroform at (25plusmn01)∘C by wzz-3 automatic polarimeter(Shanghai Precision Instrument Co) and the measurementconcentration was 90mgmL A Bruker VERTEX 70 FT-IRwas used to scan the FTIT spectrum and the 1H-NMRspectrum was recorded with a Bruker FTAC-80 NMRspectrometer using CDCl3 as a solvent DSC measurementswere performed with a NETZSCH DSC-204F1 scannedat the rate of 10∘Cmin A second-scan DSC spectrumwas recorded after the sample was annealed to 0∘C119883119888 = (9987791198671198989987791198671198980
) times 100 9987791198671198980 = 93 Jg [16] X-ray diffraction patterns were recorded with a Bruker
ADVANCE-D8X X-ray diffractometer scanned from 5∘ to40∘
3 Results and Discussion
31 Polymerization The PLA prepolymer was synthesizedusing stannous octoate as the catalyst according to reaction[17] After chain extending at 175∘C for 10ndash40min thereaction product was collected and analyzed The analysisresults were summarized in Table 1 The molecular weightwas increased several times after chain extension It wassuggested that HDI connects the hydroxyl end group so as todouble grow the molecular weight However the incrementof molecular weight was more than twice as shown in Table 1
Table 1 shows the effect of the dosage of HDI reactiontime and prepolymer molecular weight changes on the chainextension products When the ratio of [NCO] to [OH] is 6after chain extending at 175∘C for 20min119872119908 of 203000 wasobtained FromRun a1 a2 a3 and a4withHDI increased themolecular weight of PLA product growth multiples Whilethe amount of HDI was too much molecular weight ofproducts decreased This is because the excessive HDI isunevenly distributed and then crosslinking or branchinghappened leading to the majority of low molecular weightprepolymer reacting with the remaining chain extenderWhen the ratio of [NCO] to [OH] is 8 119872119908 of 30000 wasobtained and insoluble content reaching 39 indicate thatthe excess amount of the isocyanate groupmay also react withthe other end of PLA molecule to form crosslink and branchstructure according to reaction (3) of Figure 1 Run a3 a5 a6and a4 indicated that long reaction time led to crosslinkingthis was proved by the insoluble content The molecularweight of the prepolymer changing in Run a3 a8 a9 and a10shows that with increasing prepolymer molecular weight themolecular weight of the chain-extended PLA increased whileinsoluble content also increased Optical activity test provedthat the chain-extended product is laevorotary
32 FT-IR and 1H-NMR Figure 2 shows the FT-IR spectrumof the PLA prepolymer and the chain-extended product
International Journal of Polymer Science 3
OHO
OHn
OCNNCO
+
Prepolymer HDI
O CO
HO NHO
NHn
O
OO
OHn
HDI
C NH
ONH
O
C NO
NHO
O
Branched structure
Furtherreaction
175∘C
175∘C
Figure 1 The synthesis scheme of the PLA chain extended withHDI
3500 3000 2500 2000 1500 1000
Prepolymer
Run3
Wavenumber (cmminus1)
Figure 2 The infrared spectrum of the PLA prepolymer and thePLA chain extended with HDI (Run3)
with molar ratio at 6 of NCOOH after 20min reactionBoth IR spectra have characteristic ester absorption bandsat 1760 cmminus1 but in the Run3 a shoulder peak appearedat 1691 cmminus1 according to ndashC=O adjoin to ndashNH ThendashNH flexural vibrations absorption peak at 1525 cmminus1 andstretching vibrations absorption peak at 3413 cmminus1 appeared
after the chainextending reaction The weak absorption at720 cmminus1 represents the ndashCH2ndash from HDI With the PLAcrystallization peak at 756 cmminus1 the peak strength weakenedafter the reaction [18]
Figure 3 shows the 1H-NMR (500MHz TMS CDCl3)spectrum of the PLA prepolymer (Figure 3(a)) and thePLA chain extended with HDI (Figure 3(b)) Both spectraexhibited the signal of methine group at 51 ppm (a) and thesignal of methyl group at 16 ppm (c) The signal at 43 ppm(b) in the spectrum shown in Figure 3(a) characteristic of thehydrogen of the methine next to a hydroxyl end group wasfound But the signal at the same shift was not observed inthe spectrum shown in Figure 3(b) because the HDI reactedwith the hydroxyl group The broad signals at 32 ppm (b)and 41 ppm (d) in the spectrum shown in Figure 3(b) wereassigned to the unit of HDI in the PLA polymer chain [15]consistent with the results of FT-IR The intensity ratio ofthe signal corresponding to urethane to the signal of HDIunit was not 1 2 This can be explained by the fact that thehydrogen in the urethane bond reacted with other polymerchain to form branch structure
33 Gel Permeation Chromatography Figure 4 shows theGPC spectra of the PLA chain extender with HDI Fromthe spectra we can comprehend that the distribution has twomodes called a bimodal distributionThe characteristic peaksof low outflow time represent the high molecular weightchain-extending products the peaks of high outflow timepeak for the low molecular weight prepolymer The chainextension reaction successfully happened in prepolymer inthe presence of HDI With the increase of chain extenderreaction time and prepolymer molecular weight the highmolecular weight part content increased in the products
34 DSC Table 2 shows the DSC thermograms of thePLA prepolymer and chain-extended PLA After the chain-extending reaction the melt enthalpies were reducedThe 119879119892and119879119898moved towards lower temperaturesThis suggests thatadding of chain extender had an effect on crystallinity of PLAaccording to the long chain alkane structure unit of the chainextender HDIThe crystallization of the chain-extended PLAis still above 40 yet crystal can be connected to each otherforming throughout the material of the continuous phase Sothe highest used temperature can be increased close to thecrystalline melting point [19]
Figure 5 shows the DSC thermogram of the PLA pre-polymer and the PLA chain extended with different addingamount HDI With the increasing amount of HDI thecrystallinity increased first and then decreased indicatingthat a small amount of HDI was added tomake themolecularchain growth and also to maintain good crystallinity Toomuch HDI makes the product of insoluble matter contentincreased while it also reduces the product crystallinity
Figure 6 shows the DSC thermograms with the time ofthe chain-extending reaction When the reaction time was30min two obvious melting peaks of chain-extending prod-uct appeared suggesting a phase transition process The 119879119892of the PLA chain extended with HDI decreased it suggested
4 International Journal of Polymer Science
Table 2 DSC data of the PLA prepolymer and the chain-extended PLA
Figure 3 1H-NMR spectrum of PLA prepolymer (a) and the PLA chain extended with HDI (Run3) (b)
5 6 7 8 9 10 11
Run a10
Run a9
Run a8
Run a7Run a6Run a5
Run a4Run a3
Run a2
Efflusion time (min)
Run a1
Figure 4 GPC spectrogram of the PLA chain extender with HDI
that the longer reaction time resulted in insoluble mattersincrease Because of the transition of crystal form crystallinepart the melting enthalpy increases and crystallinity of thePLA increased
0 20 40 60 80 100 120 140 160 180 200
Run3
Run2
Prepolymer
ExoRun1
Temperature (∘C)
1635∘C
1645∘C
1613∘C
1703∘C
Figure 5 DSC thermogram of the prepolymer and the PLA chainextended with different adding amount HDI
Figure 7 shows the DSC thermographs of the PLA fromdifferent molecular weight prepolymers With the increase ofmolecular weight of PLA prepolymer transformation of PLAcrystal phenomenon gradually weakened and disappeared
International Journal of Polymer Science 5
0 20 40 60 80 100 120 140 160 180 200
Run3
Run6
Exo
1635∘C
1588∘C
Temperature (∘C)
Figure 6 DSC thermogram of the chain-extended PLA withdifferent chain-extending reaction time
0 20 40 60 80 100 120 140 160 180 200
Run10
Run9
Run8
Run3
Exo
Temperature (∘C)
1645∘C
1641∘C
1635∘C
1635∘C
Figure 7 DSC thermogram of the PLA from different molecularweight prepolymers
The insoluble matter content increased the crystallinitydecreased slightly
35 X-Ray Diffraction Figure 8 shows the X-ray diffractionpattern of the PLA prepolymer and the chain-extended PLAThe PLA prepolymer showed the sharp peak at 2120579 about 165∘(020 reflection) and 188∘ (023 reflection) while the peaks ofthe chain-extended samples were much lower and shifted thepeaks at 2120579 of 168∘and 191∘ The results show that after thechain extender polymerization the crystal type of the PLLAturns 1205721015840 to 120572-crystal type [20 21] consistent with the resultsof DSC
4 Conclusions
Higher molecular weight of poly(l-lactic acid) was preparedby using HDI chain-extending method with the low molec-ular weight PLA as the prepolymer The weight average
10 15 20 25
Prepolymer
Run6
Run10
2120579 (∘)
Figure 8 XRD pattern of the PLA prepolymer and the chain-extended PLA
molecular weight of the chain-extended PLA could reachup to 203 times 104 gmol by GPC measurement Both FT-IRand 1H-NMR tests give a verification of structure and theoptically active characterized that the product was PLLAChain-extended PLLA had lower crystallinity by DSC andX-ray diffraction because of the branched structure TheDSC and X-ray diffraction results both indicated that thecrystalline of product changed from mixed 1205721015840- and 120572-crystalform to 120572-crystal form
Acknowledgments
This work was financially supported by the National KeyTechnology RampD Program of China (2011BAE26B05) theNational Nature Science Foundation of China (No 2117407420774098 51003050 and 51273100) Shandong ProvinceNatural Science Fund for Distinguished Young Scholars(JQ201213) and the Nature Science Foundation of ShandongProvince (ZR2011EMM008)
References
[1] L Yu K Dean and L Li ldquoPolymer blends and composites fromrenewable resourcesrdquo Progress in Polymer Science vol 31 no 6pp 576ndash602 2006
[2] S S Ray and M Bousmina ldquoBiodegradable polymers and theirlayered silicate nanocomposites in greening the 21st centurymaterials worldrdquo Progress in Materials Science vol 50 no 8 pp962ndash1079 2005
[3] B Gupta N Revagade and J Hilborn ldquoPoly(lactic acid) fiberan overviewrdquo Progress in Polymer Science vol 32 no 4 pp 455ndash482 2007
[4] J Cheng J Sun K Wu et al ldquoRing-opening polymerization ofD L-lacide catalyzed with120573-diketone compleses of Ti and ZrrdquoJournal of Chemical Industry amp Engineering vol 27 no 5 pp5ndash7 2006
[5] J Shu P Wang T Zheng L-Y Tian and B-X Zhao ldquoDirectsynthesis of ploy (L-lactic acid) by melt polycondensationrdquoMaterial Science andTechnology vol 15 no 3 pp 374ndash378 2007
[6] S I Woo B O Kim H S Jun and H N Chang ldquoPolymer-ization of aqueous lactic acid to prepare high molecular weight
6 International Journal of Polymer Science
poly(lactic acid) by chain-extending with hexamethylene diiso-cyanaterdquo Polymer Bulletin vol 35 no 4 pp 415ndash421 1995
[7] Z Wei J Ge Z Gu et al ldquoStudy on biodegradable polymermaterials based on poly(lactic acid)mdashI Chain extending of lowmolecular weight Poly (lactic acid) with methylenediphenyldiisocyanaterdquo Journal of Applied Polymer Science vol 74 pp2546ndash2551 1999
[8] J Tuominen J Kylma and J Seppala ldquoChain extending oflactic acid oligomersmdash2 Increase of molecular weight with 16-hexamethylene diisocyanate and 221015840-bis(2-oxazoline)rdquo Poly-mer vol 43 no 1 pp 3ndash10 2001
[9] R J Feng and W Z Shi ldquoInfluence of polymerization methodsand chain-extension agent on relative molecular weight ofpolylactiderdquo Petrochemical Technology vol 30 no 2 pp 103ndash105 2001
[10] T Yu J Ren S Gu and M Yang ldquoPreparation and charac-terization of biodegradable poly(lactic acid)-block-poly(eopen-caprolactone) multiblock copolymerrdquo Polymers for AdvancedTechnologies vol 21 no 3 pp 183ndash188 2010
[11] D Cohn and A Hotovely Salomon ldquoDesigning biodegradablemultiblock PCLPLA thermoplastic elastomersrdquo Biomaterialsvol 26 no 15 pp 2297ndash2305 2005
[12] J-B Zeng Y-D Li W-D Li K-K Yang X-L Wang and Y-Z Wang ldquoSynthesis and properties of poly(ester urethane)sconsisting of poly(l-lactic acid) and poly(ethylene succinate)segmentsrdquo Industrial and Engineering Chemistry Research vol48 no 4 pp 1706ndash1711 2009
[13] H Li and M A Huneault ldquoEffect of chain extension on theproperties of PLATPS blendsrdquo Journal of Applied PolymerScience vol 122 no 1 pp 134ndash141 2011
[14] B-S Park J C Song D H Park and K-B Yoon ldquoPLAchain-extended PEG blends with improved ductilityrdquo Journal ofApplied Polymer Science vol 123 no 4 pp 2360ndash2367 2012
[15] Z Wang Y Zhao and J Wang ldquoSynthesis of polylactic acidbiodegradable materials through chain extensionrdquo ChineseJournal of Synthetic Chemistry vol 11 pp 106ndash110 2012
[16] M Li T Jiao Y Wang et al ldquoEffect of plasticizer oncrystallization morphology of biodegradable poly(lactic acid)rdquoPlastic Science and Technology vol 39 no 6 pp 55ndash59 2011
[17] W-W Wang Z Yi L Jiang and Y Dan ldquoSynthesis of a poly-lactide macroinitiator via one-step polymerizationrdquo PolymericMaterials Science and Engineering vol 26 no 1 pp 12ndash15 2010
[18] Y Hori M Suzuki Y Okeda et al ldquoA novel biodegradablepoly(urethane ester) synthesized frompoly(3-hydroxybutyrate)segmentsrdquoMacromolecules vol 25 no 19 pp 5117ndash5118 1992
[19] M He Polymer Physics Fudan University Publishing HouseShanghai China 2007
[20] P Pan B Zhu W Kai T Dong and Y Inoue ldquoEffect of crys-tallization temperature on crystal modifications and crystal-lization kinetics of poly(L-lactide)rdquo Journal of Applied PolymerScience vol 107 no 1 pp 54ndash62 2008
[21] J Zhang K Tashiro H Tsuji and A J Domb ldquoDisorder-to-order phase transition andmultiple melting behavior of poly(L-lactide) investigated by simultaneous measurements of WAXDand DSCrdquoMacromolecules vol 41 no 4 pp 1352ndash1357 2008
Figure 1 The synthesis scheme of the PLA chain extended withHDI
3500 3000 2500 2000 1500 1000
Prepolymer
Run3
Wavenumber (cmminus1)
Figure 2 The infrared spectrum of the PLA prepolymer and thePLA chain extended with HDI (Run3)
with molar ratio at 6 of NCOOH after 20min reactionBoth IR spectra have characteristic ester absorption bandsat 1760 cmminus1 but in the Run3 a shoulder peak appearedat 1691 cmminus1 according to ndashC=O adjoin to ndashNH ThendashNH flexural vibrations absorption peak at 1525 cmminus1 andstretching vibrations absorption peak at 3413 cmminus1 appeared
after the chainextending reaction The weak absorption at720 cmminus1 represents the ndashCH2ndash from HDI With the PLAcrystallization peak at 756 cmminus1 the peak strength weakenedafter the reaction [18]
Figure 3 shows the 1H-NMR (500MHz TMS CDCl3)spectrum of the PLA prepolymer (Figure 3(a)) and thePLA chain extended with HDI (Figure 3(b)) Both spectraexhibited the signal of methine group at 51 ppm (a) and thesignal of methyl group at 16 ppm (c) The signal at 43 ppm(b) in the spectrum shown in Figure 3(a) characteristic of thehydrogen of the methine next to a hydroxyl end group wasfound But the signal at the same shift was not observed inthe spectrum shown in Figure 3(b) because the HDI reactedwith the hydroxyl group The broad signals at 32 ppm (b)and 41 ppm (d) in the spectrum shown in Figure 3(b) wereassigned to the unit of HDI in the PLA polymer chain [15]consistent with the results of FT-IR The intensity ratio ofthe signal corresponding to urethane to the signal of HDIunit was not 1 2 This can be explained by the fact that thehydrogen in the urethane bond reacted with other polymerchain to form branch structure
33 Gel Permeation Chromatography Figure 4 shows theGPC spectra of the PLA chain extender with HDI Fromthe spectra we can comprehend that the distribution has twomodes called a bimodal distributionThe characteristic peaksof low outflow time represent the high molecular weightchain-extending products the peaks of high outflow timepeak for the low molecular weight prepolymer The chainextension reaction successfully happened in prepolymer inthe presence of HDI With the increase of chain extenderreaction time and prepolymer molecular weight the highmolecular weight part content increased in the products
34 DSC Table 2 shows the DSC thermograms of thePLA prepolymer and chain-extended PLA After the chain-extending reaction the melt enthalpies were reducedThe 119879119892and119879119898moved towards lower temperaturesThis suggests thatadding of chain extender had an effect on crystallinity of PLAaccording to the long chain alkane structure unit of the chainextender HDIThe crystallization of the chain-extended PLAis still above 40 yet crystal can be connected to each otherforming throughout the material of the continuous phase Sothe highest used temperature can be increased close to thecrystalline melting point [19]
Figure 5 shows the DSC thermogram of the PLA pre-polymer and the PLA chain extended with different addingamount HDI With the increasing amount of HDI thecrystallinity increased first and then decreased indicatingthat a small amount of HDI was added tomake themolecularchain growth and also to maintain good crystallinity Toomuch HDI makes the product of insoluble matter contentincreased while it also reduces the product crystallinity
Figure 6 shows the DSC thermograms with the time ofthe chain-extending reaction When the reaction time was30min two obvious melting peaks of chain-extending prod-uct appeared suggesting a phase transition process The 119879119892of the PLA chain extended with HDI decreased it suggested
4 International Journal of Polymer Science
Table 2 DSC data of the PLA prepolymer and the chain-extended PLA
Figure 3 1H-NMR spectrum of PLA prepolymer (a) and the PLA chain extended with HDI (Run3) (b)
5 6 7 8 9 10 11
Run a10
Run a9
Run a8
Run a7Run a6Run a5
Run a4Run a3
Run a2
Efflusion time (min)
Run a1
Figure 4 GPC spectrogram of the PLA chain extender with HDI
that the longer reaction time resulted in insoluble mattersincrease Because of the transition of crystal form crystallinepart the melting enthalpy increases and crystallinity of thePLA increased
0 20 40 60 80 100 120 140 160 180 200
Run3
Run2
Prepolymer
ExoRun1
Temperature (∘C)
1635∘C
1645∘C
1613∘C
1703∘C
Figure 5 DSC thermogram of the prepolymer and the PLA chainextended with different adding amount HDI
Figure 7 shows the DSC thermographs of the PLA fromdifferent molecular weight prepolymers With the increase ofmolecular weight of PLA prepolymer transformation of PLAcrystal phenomenon gradually weakened and disappeared
International Journal of Polymer Science 5
0 20 40 60 80 100 120 140 160 180 200
Run3
Run6
Exo
1635∘C
1588∘C
Temperature (∘C)
Figure 6 DSC thermogram of the chain-extended PLA withdifferent chain-extending reaction time
0 20 40 60 80 100 120 140 160 180 200
Run10
Run9
Run8
Run3
Exo
Temperature (∘C)
1645∘C
1641∘C
1635∘C
1635∘C
Figure 7 DSC thermogram of the PLA from different molecularweight prepolymers
The insoluble matter content increased the crystallinitydecreased slightly
35 X-Ray Diffraction Figure 8 shows the X-ray diffractionpattern of the PLA prepolymer and the chain-extended PLAThe PLA prepolymer showed the sharp peak at 2120579 about 165∘(020 reflection) and 188∘ (023 reflection) while the peaks ofthe chain-extended samples were much lower and shifted thepeaks at 2120579 of 168∘and 191∘ The results show that after thechain extender polymerization the crystal type of the PLLAturns 1205721015840 to 120572-crystal type [20 21] consistent with the resultsof DSC
4 Conclusions
Higher molecular weight of poly(l-lactic acid) was preparedby using HDI chain-extending method with the low molec-ular weight PLA as the prepolymer The weight average
10 15 20 25
Prepolymer
Run6
Run10
2120579 (∘)
Figure 8 XRD pattern of the PLA prepolymer and the chain-extended PLA
molecular weight of the chain-extended PLA could reachup to 203 times 104 gmol by GPC measurement Both FT-IRand 1H-NMR tests give a verification of structure and theoptically active characterized that the product was PLLAChain-extended PLLA had lower crystallinity by DSC andX-ray diffraction because of the branched structure TheDSC and X-ray diffraction results both indicated that thecrystalline of product changed from mixed 1205721015840- and 120572-crystalform to 120572-crystal form
Acknowledgments
This work was financially supported by the National KeyTechnology RampD Program of China (2011BAE26B05) theNational Nature Science Foundation of China (No 2117407420774098 51003050 and 51273100) Shandong ProvinceNatural Science Fund for Distinguished Young Scholars(JQ201213) and the Nature Science Foundation of ShandongProvince (ZR2011EMM008)
References
[1] L Yu K Dean and L Li ldquoPolymer blends and composites fromrenewable resourcesrdquo Progress in Polymer Science vol 31 no 6pp 576ndash602 2006
[2] S S Ray and M Bousmina ldquoBiodegradable polymers and theirlayered silicate nanocomposites in greening the 21st centurymaterials worldrdquo Progress in Materials Science vol 50 no 8 pp962ndash1079 2005
[3] B Gupta N Revagade and J Hilborn ldquoPoly(lactic acid) fiberan overviewrdquo Progress in Polymer Science vol 32 no 4 pp 455ndash482 2007
[4] J Cheng J Sun K Wu et al ldquoRing-opening polymerization ofD L-lacide catalyzed with120573-diketone compleses of Ti and ZrrdquoJournal of Chemical Industry amp Engineering vol 27 no 5 pp5ndash7 2006
[5] J Shu P Wang T Zheng L-Y Tian and B-X Zhao ldquoDirectsynthesis of ploy (L-lactic acid) by melt polycondensationrdquoMaterial Science andTechnology vol 15 no 3 pp 374ndash378 2007
[6] S I Woo B O Kim H S Jun and H N Chang ldquoPolymer-ization of aqueous lactic acid to prepare high molecular weight
6 International Journal of Polymer Science
poly(lactic acid) by chain-extending with hexamethylene diiso-cyanaterdquo Polymer Bulletin vol 35 no 4 pp 415ndash421 1995
[7] Z Wei J Ge Z Gu et al ldquoStudy on biodegradable polymermaterials based on poly(lactic acid)mdashI Chain extending of lowmolecular weight Poly (lactic acid) with methylenediphenyldiisocyanaterdquo Journal of Applied Polymer Science vol 74 pp2546ndash2551 1999
[8] J Tuominen J Kylma and J Seppala ldquoChain extending oflactic acid oligomersmdash2 Increase of molecular weight with 16-hexamethylene diisocyanate and 221015840-bis(2-oxazoline)rdquo Poly-mer vol 43 no 1 pp 3ndash10 2001
[9] R J Feng and W Z Shi ldquoInfluence of polymerization methodsand chain-extension agent on relative molecular weight ofpolylactiderdquo Petrochemical Technology vol 30 no 2 pp 103ndash105 2001
[10] T Yu J Ren S Gu and M Yang ldquoPreparation and charac-terization of biodegradable poly(lactic acid)-block-poly(eopen-caprolactone) multiblock copolymerrdquo Polymers for AdvancedTechnologies vol 21 no 3 pp 183ndash188 2010
[11] D Cohn and A Hotovely Salomon ldquoDesigning biodegradablemultiblock PCLPLA thermoplastic elastomersrdquo Biomaterialsvol 26 no 15 pp 2297ndash2305 2005
[12] J-B Zeng Y-D Li W-D Li K-K Yang X-L Wang and Y-Z Wang ldquoSynthesis and properties of poly(ester urethane)sconsisting of poly(l-lactic acid) and poly(ethylene succinate)segmentsrdquo Industrial and Engineering Chemistry Research vol48 no 4 pp 1706ndash1711 2009
[13] H Li and M A Huneault ldquoEffect of chain extension on theproperties of PLATPS blendsrdquo Journal of Applied PolymerScience vol 122 no 1 pp 134ndash141 2011
[14] B-S Park J C Song D H Park and K-B Yoon ldquoPLAchain-extended PEG blends with improved ductilityrdquo Journal ofApplied Polymer Science vol 123 no 4 pp 2360ndash2367 2012
[15] Z Wang Y Zhao and J Wang ldquoSynthesis of polylactic acidbiodegradable materials through chain extensionrdquo ChineseJournal of Synthetic Chemistry vol 11 pp 106ndash110 2012
[16] M Li T Jiao Y Wang et al ldquoEffect of plasticizer oncrystallization morphology of biodegradable poly(lactic acid)rdquoPlastic Science and Technology vol 39 no 6 pp 55ndash59 2011
[17] W-W Wang Z Yi L Jiang and Y Dan ldquoSynthesis of a poly-lactide macroinitiator via one-step polymerizationrdquo PolymericMaterials Science and Engineering vol 26 no 1 pp 12ndash15 2010
[18] Y Hori M Suzuki Y Okeda et al ldquoA novel biodegradablepoly(urethane ester) synthesized frompoly(3-hydroxybutyrate)segmentsrdquoMacromolecules vol 25 no 19 pp 5117ndash5118 1992
[19] M He Polymer Physics Fudan University Publishing HouseShanghai China 2007
[20] P Pan B Zhu W Kai T Dong and Y Inoue ldquoEffect of crys-tallization temperature on crystal modifications and crystal-lization kinetics of poly(L-lactide)rdquo Journal of Applied PolymerScience vol 107 no 1 pp 54ndash62 2008
[21] J Zhang K Tashiro H Tsuji and A J Domb ldquoDisorder-to-order phase transition andmultiple melting behavior of poly(L-lactide) investigated by simultaneous measurements of WAXDand DSCrdquoMacromolecules vol 41 no 4 pp 1352ndash1357 2008
Figure 3 1H-NMR spectrum of PLA prepolymer (a) and the PLA chain extended with HDI (Run3) (b)
5 6 7 8 9 10 11
Run a10
Run a9
Run a8
Run a7Run a6Run a5
Run a4Run a3
Run a2
Efflusion time (min)
Run a1
Figure 4 GPC spectrogram of the PLA chain extender with HDI
that the longer reaction time resulted in insoluble mattersincrease Because of the transition of crystal form crystallinepart the melting enthalpy increases and crystallinity of thePLA increased
0 20 40 60 80 100 120 140 160 180 200
Run3
Run2
Prepolymer
ExoRun1
Temperature (∘C)
1635∘C
1645∘C
1613∘C
1703∘C
Figure 5 DSC thermogram of the prepolymer and the PLA chainextended with different adding amount HDI
Figure 7 shows the DSC thermographs of the PLA fromdifferent molecular weight prepolymers With the increase ofmolecular weight of PLA prepolymer transformation of PLAcrystal phenomenon gradually weakened and disappeared
International Journal of Polymer Science 5
0 20 40 60 80 100 120 140 160 180 200
Run3
Run6
Exo
1635∘C
1588∘C
Temperature (∘C)
Figure 6 DSC thermogram of the chain-extended PLA withdifferent chain-extending reaction time
0 20 40 60 80 100 120 140 160 180 200
Run10
Run9
Run8
Run3
Exo
Temperature (∘C)
1645∘C
1641∘C
1635∘C
1635∘C
Figure 7 DSC thermogram of the PLA from different molecularweight prepolymers
The insoluble matter content increased the crystallinitydecreased slightly
35 X-Ray Diffraction Figure 8 shows the X-ray diffractionpattern of the PLA prepolymer and the chain-extended PLAThe PLA prepolymer showed the sharp peak at 2120579 about 165∘(020 reflection) and 188∘ (023 reflection) while the peaks ofthe chain-extended samples were much lower and shifted thepeaks at 2120579 of 168∘and 191∘ The results show that after thechain extender polymerization the crystal type of the PLLAturns 1205721015840 to 120572-crystal type [20 21] consistent with the resultsof DSC
4 Conclusions
Higher molecular weight of poly(l-lactic acid) was preparedby using HDI chain-extending method with the low molec-ular weight PLA as the prepolymer The weight average
10 15 20 25
Prepolymer
Run6
Run10
2120579 (∘)
Figure 8 XRD pattern of the PLA prepolymer and the chain-extended PLA
molecular weight of the chain-extended PLA could reachup to 203 times 104 gmol by GPC measurement Both FT-IRand 1H-NMR tests give a verification of structure and theoptically active characterized that the product was PLLAChain-extended PLLA had lower crystallinity by DSC andX-ray diffraction because of the branched structure TheDSC and X-ray diffraction results both indicated that thecrystalline of product changed from mixed 1205721015840- and 120572-crystalform to 120572-crystal form
Acknowledgments
This work was financially supported by the National KeyTechnology RampD Program of China (2011BAE26B05) theNational Nature Science Foundation of China (No 2117407420774098 51003050 and 51273100) Shandong ProvinceNatural Science Fund for Distinguished Young Scholars(JQ201213) and the Nature Science Foundation of ShandongProvince (ZR2011EMM008)
References
[1] L Yu K Dean and L Li ldquoPolymer blends and composites fromrenewable resourcesrdquo Progress in Polymer Science vol 31 no 6pp 576ndash602 2006
[2] S S Ray and M Bousmina ldquoBiodegradable polymers and theirlayered silicate nanocomposites in greening the 21st centurymaterials worldrdquo Progress in Materials Science vol 50 no 8 pp962ndash1079 2005
[3] B Gupta N Revagade and J Hilborn ldquoPoly(lactic acid) fiberan overviewrdquo Progress in Polymer Science vol 32 no 4 pp 455ndash482 2007
[4] J Cheng J Sun K Wu et al ldquoRing-opening polymerization ofD L-lacide catalyzed with120573-diketone compleses of Ti and ZrrdquoJournal of Chemical Industry amp Engineering vol 27 no 5 pp5ndash7 2006
[5] J Shu P Wang T Zheng L-Y Tian and B-X Zhao ldquoDirectsynthesis of ploy (L-lactic acid) by melt polycondensationrdquoMaterial Science andTechnology vol 15 no 3 pp 374ndash378 2007
[6] S I Woo B O Kim H S Jun and H N Chang ldquoPolymer-ization of aqueous lactic acid to prepare high molecular weight
6 International Journal of Polymer Science
poly(lactic acid) by chain-extending with hexamethylene diiso-cyanaterdquo Polymer Bulletin vol 35 no 4 pp 415ndash421 1995
[7] Z Wei J Ge Z Gu et al ldquoStudy on biodegradable polymermaterials based on poly(lactic acid)mdashI Chain extending of lowmolecular weight Poly (lactic acid) with methylenediphenyldiisocyanaterdquo Journal of Applied Polymer Science vol 74 pp2546ndash2551 1999
[8] J Tuominen J Kylma and J Seppala ldquoChain extending oflactic acid oligomersmdash2 Increase of molecular weight with 16-hexamethylene diisocyanate and 221015840-bis(2-oxazoline)rdquo Poly-mer vol 43 no 1 pp 3ndash10 2001
[9] R J Feng and W Z Shi ldquoInfluence of polymerization methodsand chain-extension agent on relative molecular weight ofpolylactiderdquo Petrochemical Technology vol 30 no 2 pp 103ndash105 2001
[10] T Yu J Ren S Gu and M Yang ldquoPreparation and charac-terization of biodegradable poly(lactic acid)-block-poly(eopen-caprolactone) multiblock copolymerrdquo Polymers for AdvancedTechnologies vol 21 no 3 pp 183ndash188 2010
[11] D Cohn and A Hotovely Salomon ldquoDesigning biodegradablemultiblock PCLPLA thermoplastic elastomersrdquo Biomaterialsvol 26 no 15 pp 2297ndash2305 2005
[12] J-B Zeng Y-D Li W-D Li K-K Yang X-L Wang and Y-Z Wang ldquoSynthesis and properties of poly(ester urethane)sconsisting of poly(l-lactic acid) and poly(ethylene succinate)segmentsrdquo Industrial and Engineering Chemistry Research vol48 no 4 pp 1706ndash1711 2009
[13] H Li and M A Huneault ldquoEffect of chain extension on theproperties of PLATPS blendsrdquo Journal of Applied PolymerScience vol 122 no 1 pp 134ndash141 2011
[14] B-S Park J C Song D H Park and K-B Yoon ldquoPLAchain-extended PEG blends with improved ductilityrdquo Journal ofApplied Polymer Science vol 123 no 4 pp 2360ndash2367 2012
[15] Z Wang Y Zhao and J Wang ldquoSynthesis of polylactic acidbiodegradable materials through chain extensionrdquo ChineseJournal of Synthetic Chemistry vol 11 pp 106ndash110 2012
[16] M Li T Jiao Y Wang et al ldquoEffect of plasticizer oncrystallization morphology of biodegradable poly(lactic acid)rdquoPlastic Science and Technology vol 39 no 6 pp 55ndash59 2011
[17] W-W Wang Z Yi L Jiang and Y Dan ldquoSynthesis of a poly-lactide macroinitiator via one-step polymerizationrdquo PolymericMaterials Science and Engineering vol 26 no 1 pp 12ndash15 2010
[18] Y Hori M Suzuki Y Okeda et al ldquoA novel biodegradablepoly(urethane ester) synthesized frompoly(3-hydroxybutyrate)segmentsrdquoMacromolecules vol 25 no 19 pp 5117ndash5118 1992
[19] M He Polymer Physics Fudan University Publishing HouseShanghai China 2007
[20] P Pan B Zhu W Kai T Dong and Y Inoue ldquoEffect of crys-tallization temperature on crystal modifications and crystal-lization kinetics of poly(L-lactide)rdquo Journal of Applied PolymerScience vol 107 no 1 pp 54ndash62 2008
[21] J Zhang K Tashiro H Tsuji and A J Domb ldquoDisorder-to-order phase transition andmultiple melting behavior of poly(L-lactide) investigated by simultaneous measurements of WAXDand DSCrdquoMacromolecules vol 41 no 4 pp 1352ndash1357 2008
Figure 6 DSC thermogram of the chain-extended PLA withdifferent chain-extending reaction time
0 20 40 60 80 100 120 140 160 180 200
Run10
Run9
Run8
Run3
Exo
Temperature (∘C)
1645∘C
1641∘C
1635∘C
1635∘C
Figure 7 DSC thermogram of the PLA from different molecularweight prepolymers
The insoluble matter content increased the crystallinitydecreased slightly
35 X-Ray Diffraction Figure 8 shows the X-ray diffractionpattern of the PLA prepolymer and the chain-extended PLAThe PLA prepolymer showed the sharp peak at 2120579 about 165∘(020 reflection) and 188∘ (023 reflection) while the peaks ofthe chain-extended samples were much lower and shifted thepeaks at 2120579 of 168∘and 191∘ The results show that after thechain extender polymerization the crystal type of the PLLAturns 1205721015840 to 120572-crystal type [20 21] consistent with the resultsof DSC
4 Conclusions
Higher molecular weight of poly(l-lactic acid) was preparedby using HDI chain-extending method with the low molec-ular weight PLA as the prepolymer The weight average
10 15 20 25
Prepolymer
Run6
Run10
2120579 (∘)
Figure 8 XRD pattern of the PLA prepolymer and the chain-extended PLA
molecular weight of the chain-extended PLA could reachup to 203 times 104 gmol by GPC measurement Both FT-IRand 1H-NMR tests give a verification of structure and theoptically active characterized that the product was PLLAChain-extended PLLA had lower crystallinity by DSC andX-ray diffraction because of the branched structure TheDSC and X-ray diffraction results both indicated that thecrystalline of product changed from mixed 1205721015840- and 120572-crystalform to 120572-crystal form
Acknowledgments
This work was financially supported by the National KeyTechnology RampD Program of China (2011BAE26B05) theNational Nature Science Foundation of China (No 2117407420774098 51003050 and 51273100) Shandong ProvinceNatural Science Fund for Distinguished Young Scholars(JQ201213) and the Nature Science Foundation of ShandongProvince (ZR2011EMM008)
References
[1] L Yu K Dean and L Li ldquoPolymer blends and composites fromrenewable resourcesrdquo Progress in Polymer Science vol 31 no 6pp 576ndash602 2006
[2] S S Ray and M Bousmina ldquoBiodegradable polymers and theirlayered silicate nanocomposites in greening the 21st centurymaterials worldrdquo Progress in Materials Science vol 50 no 8 pp962ndash1079 2005
[3] B Gupta N Revagade and J Hilborn ldquoPoly(lactic acid) fiberan overviewrdquo Progress in Polymer Science vol 32 no 4 pp 455ndash482 2007
[4] J Cheng J Sun K Wu et al ldquoRing-opening polymerization ofD L-lacide catalyzed with120573-diketone compleses of Ti and ZrrdquoJournal of Chemical Industry amp Engineering vol 27 no 5 pp5ndash7 2006
[5] J Shu P Wang T Zheng L-Y Tian and B-X Zhao ldquoDirectsynthesis of ploy (L-lactic acid) by melt polycondensationrdquoMaterial Science andTechnology vol 15 no 3 pp 374ndash378 2007
[6] S I Woo B O Kim H S Jun and H N Chang ldquoPolymer-ization of aqueous lactic acid to prepare high molecular weight
6 International Journal of Polymer Science
poly(lactic acid) by chain-extending with hexamethylene diiso-cyanaterdquo Polymer Bulletin vol 35 no 4 pp 415ndash421 1995
[7] Z Wei J Ge Z Gu et al ldquoStudy on biodegradable polymermaterials based on poly(lactic acid)mdashI Chain extending of lowmolecular weight Poly (lactic acid) with methylenediphenyldiisocyanaterdquo Journal of Applied Polymer Science vol 74 pp2546ndash2551 1999
[8] J Tuominen J Kylma and J Seppala ldquoChain extending oflactic acid oligomersmdash2 Increase of molecular weight with 16-hexamethylene diisocyanate and 221015840-bis(2-oxazoline)rdquo Poly-mer vol 43 no 1 pp 3ndash10 2001
[9] R J Feng and W Z Shi ldquoInfluence of polymerization methodsand chain-extension agent on relative molecular weight ofpolylactiderdquo Petrochemical Technology vol 30 no 2 pp 103ndash105 2001
[10] T Yu J Ren S Gu and M Yang ldquoPreparation and charac-terization of biodegradable poly(lactic acid)-block-poly(eopen-caprolactone) multiblock copolymerrdquo Polymers for AdvancedTechnologies vol 21 no 3 pp 183ndash188 2010
[11] D Cohn and A Hotovely Salomon ldquoDesigning biodegradablemultiblock PCLPLA thermoplastic elastomersrdquo Biomaterialsvol 26 no 15 pp 2297ndash2305 2005
[12] J-B Zeng Y-D Li W-D Li K-K Yang X-L Wang and Y-Z Wang ldquoSynthesis and properties of poly(ester urethane)sconsisting of poly(l-lactic acid) and poly(ethylene succinate)segmentsrdquo Industrial and Engineering Chemistry Research vol48 no 4 pp 1706ndash1711 2009
[13] H Li and M A Huneault ldquoEffect of chain extension on theproperties of PLATPS blendsrdquo Journal of Applied PolymerScience vol 122 no 1 pp 134ndash141 2011
[14] B-S Park J C Song D H Park and K-B Yoon ldquoPLAchain-extended PEG blends with improved ductilityrdquo Journal ofApplied Polymer Science vol 123 no 4 pp 2360ndash2367 2012
[15] Z Wang Y Zhao and J Wang ldquoSynthesis of polylactic acidbiodegradable materials through chain extensionrdquo ChineseJournal of Synthetic Chemistry vol 11 pp 106ndash110 2012
[16] M Li T Jiao Y Wang et al ldquoEffect of plasticizer oncrystallization morphology of biodegradable poly(lactic acid)rdquoPlastic Science and Technology vol 39 no 6 pp 55ndash59 2011
[17] W-W Wang Z Yi L Jiang and Y Dan ldquoSynthesis of a poly-lactide macroinitiator via one-step polymerizationrdquo PolymericMaterials Science and Engineering vol 26 no 1 pp 12ndash15 2010
[18] Y Hori M Suzuki Y Okeda et al ldquoA novel biodegradablepoly(urethane ester) synthesized frompoly(3-hydroxybutyrate)segmentsrdquoMacromolecules vol 25 no 19 pp 5117ndash5118 1992
[19] M He Polymer Physics Fudan University Publishing HouseShanghai China 2007
[20] P Pan B Zhu W Kai T Dong and Y Inoue ldquoEffect of crys-tallization temperature on crystal modifications and crystal-lization kinetics of poly(L-lactide)rdquo Journal of Applied PolymerScience vol 107 no 1 pp 54ndash62 2008
[21] J Zhang K Tashiro H Tsuji and A J Domb ldquoDisorder-to-order phase transition andmultiple melting behavior of poly(L-lactide) investigated by simultaneous measurements of WAXDand DSCrdquoMacromolecules vol 41 no 4 pp 1352ndash1357 2008
poly(lactic acid) by chain-extending with hexamethylene diiso-cyanaterdquo Polymer Bulletin vol 35 no 4 pp 415ndash421 1995
[7] Z Wei J Ge Z Gu et al ldquoStudy on biodegradable polymermaterials based on poly(lactic acid)mdashI Chain extending of lowmolecular weight Poly (lactic acid) with methylenediphenyldiisocyanaterdquo Journal of Applied Polymer Science vol 74 pp2546ndash2551 1999
[8] J Tuominen J Kylma and J Seppala ldquoChain extending oflactic acid oligomersmdash2 Increase of molecular weight with 16-hexamethylene diisocyanate and 221015840-bis(2-oxazoline)rdquo Poly-mer vol 43 no 1 pp 3ndash10 2001
[9] R J Feng and W Z Shi ldquoInfluence of polymerization methodsand chain-extension agent on relative molecular weight ofpolylactiderdquo Petrochemical Technology vol 30 no 2 pp 103ndash105 2001
[10] T Yu J Ren S Gu and M Yang ldquoPreparation and charac-terization of biodegradable poly(lactic acid)-block-poly(eopen-caprolactone) multiblock copolymerrdquo Polymers for AdvancedTechnologies vol 21 no 3 pp 183ndash188 2010
[11] D Cohn and A Hotovely Salomon ldquoDesigning biodegradablemultiblock PCLPLA thermoplastic elastomersrdquo Biomaterialsvol 26 no 15 pp 2297ndash2305 2005
[12] J-B Zeng Y-D Li W-D Li K-K Yang X-L Wang and Y-Z Wang ldquoSynthesis and properties of poly(ester urethane)sconsisting of poly(l-lactic acid) and poly(ethylene succinate)segmentsrdquo Industrial and Engineering Chemistry Research vol48 no 4 pp 1706ndash1711 2009
[13] H Li and M A Huneault ldquoEffect of chain extension on theproperties of PLATPS blendsrdquo Journal of Applied PolymerScience vol 122 no 1 pp 134ndash141 2011
[14] B-S Park J C Song D H Park and K-B Yoon ldquoPLAchain-extended PEG blends with improved ductilityrdquo Journal ofApplied Polymer Science vol 123 no 4 pp 2360ndash2367 2012
[15] Z Wang Y Zhao and J Wang ldquoSynthesis of polylactic acidbiodegradable materials through chain extensionrdquo ChineseJournal of Synthetic Chemistry vol 11 pp 106ndash110 2012
[16] M Li T Jiao Y Wang et al ldquoEffect of plasticizer oncrystallization morphology of biodegradable poly(lactic acid)rdquoPlastic Science and Technology vol 39 no 6 pp 55ndash59 2011
[17] W-W Wang Z Yi L Jiang and Y Dan ldquoSynthesis of a poly-lactide macroinitiator via one-step polymerizationrdquo PolymericMaterials Science and Engineering vol 26 no 1 pp 12ndash15 2010
[18] Y Hori M Suzuki Y Okeda et al ldquoA novel biodegradablepoly(urethane ester) synthesized frompoly(3-hydroxybutyrate)segmentsrdquoMacromolecules vol 25 no 19 pp 5117ndash5118 1992
[19] M He Polymer Physics Fudan University Publishing HouseShanghai China 2007
[20] P Pan B Zhu W Kai T Dong and Y Inoue ldquoEffect of crys-tallization temperature on crystal modifications and crystal-lization kinetics of poly(L-lactide)rdquo Journal of Applied PolymerScience vol 107 no 1 pp 54ndash62 2008
[21] J Zhang K Tashiro H Tsuji and A J Domb ldquoDisorder-to-order phase transition andmultiple melting behavior of poly(L-lactide) investigated by simultaneous measurements of WAXDand DSCrdquoMacromolecules vol 41 no 4 pp 1352ndash1357 2008
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