CHAPTER
Synthesis and Characterisation of FUinyl-2-pyrrolidone-Acrylic Acid Cowolymers and their Metal Complexes
Synthesis and Cnaractensat~o,, of N-Vmy1-Z--pyml~doncAc~~c Acld Copolymers and thea Metal Complexes 77
ecent discoveries using coordination metal complexes show that the R economic potentialities and advantages are greater for the heterogeneous
rather than homogeneous complexes.227 The metal atom immobilised to the
polymeric backbone are found to exhibit characteristic catalytic behaviour, which
are distinctly different from their low molecular weight analogue.52 Synthesis of
metal complex forming polymers has gained considerable interest owing to their
attractive applications in diverse fields such as waste-water treatment,
hydrometallurgy, removal of nuclear waste, catalysis and initiation of
p~l~merisa t ion. '~"~~ l'r oton accepting and proton donating polymers such as
poly(methacry1ic acid) or poly(acrylic acid) form macromolecular complexes with
poly(ethy1ene glycol) or poly(viny1 pyrrolidone).232"36 The y ~nteract ' with each
other in aqueous or organic solvents to form intermacromolecular
complexes.232237 Many interpolymer complexes stabilised by hydrogen bonding
occur in biological systems and represent an appropriate model for studying their
properties and regularities.239~z41 in particular the complex between poly(acylic
acid) and poly(viny1 pyrrolidone) has undergone vey limited investigation,
frequently for compara1:ive purposes.238~ug The 1:l copolymer of acylic acid and
Nvinyl-2-pyrrolidone ibund widespread application in agriculture, medicine,
pharmaceuticals, paper and food
Polyaclylic acid and poly(Nviny1-2-pyrrolidone)~ show complexing ability
for metal i ~ n s . ~ ' ~ ~ ' ~ ' In OUT attempts to synthesise these polymers, it was very
difticult to handle them became of their high swelling nature. Hence, we
synthesised, linear and crosslinked copolymers of polyacrylic acid and
poly(Alviny1-2-pyrrolidone) with 4 mol% DVB, EGDMA and HDODA
crosslinking. These polymers could be synthesised in good physical form and
were found to be much superior to those based on polystyrene because of their
better hydrophilic-hydrophobic The properties of copolymers
synthss ,~ and Chemclsnrabonfil-V~oyl-2-~ymI1done-A~ryI~: Acd Copolymsn and ther Metal Comp@xes 78
depend not only on the nature of the comonomers, and the overall compositions,
but also on the distributbn of the monomer units along the polymer chain.23
In the present sbudy, the complexation properties of linear and different
crosslinked Nvinyl-2-p!molidone and acylic acid (WP-AA) copolymers were
carried out towards various transition metal ions giving emphasis on the effect of
the nature of crosslinking agent occurring in the insoluble crosslinked polymer
matrix and comparison of the complexation behaviour of linear and crosslinked
systems
This chapter describes the following investigations
Preparation of linear, and 4 mol% DVB-, EGDMA- and HDODA-
crosslinked Nvinyl-2-pyrrolidone-acylic acid copolymers, and their
derivatisation.
Complexation of the linear and crosslinked Nvinyl-2-pyrrolidone-acrylic
acid copolymers towards Cr(lll), Mn(ll), Fe(Ill), Co(ll), Ni(ll), Cu(l1) and
Zn(ll) ions.
Physicochemical characterisation of polymeric ligands and metal
complexes using I3C CP-MAS NMR, FTIR, UV-vis, EPR, nitrogen analysis,
TG and SEM. Swelling studies of various polymer systems and their Cu(l1)
complexes.
4.1 Preparation of Linear and 4 mol% DVB-, EGDMA- and HDODA- crosslinked N-Vinyl-2-Pyrrolidone-Acrylic Acid Copolymers
Copolymers of linear and 4 mol% DVB, EGDMA and HDODA crosslinks
were prepared by suspension polymerisation at 80-859C under nitrogen
atmosphere using AlBN as initiator. The composition of monomers used for the
preparation of various crosslinked systems are described in Chapter 6 (Table 6.3).
Crosslinking agents used were same as in the case of polystyrene system and are
shown in Scheme . 3 1
synthesrs and Characfsnsas of N-V!n~2-pymI~done-Acwl!c Acrd Copolymerr and thelr Metal Complexes 79
Scheme4.1. (a) Chemical structures of the monomers used in this study showing the reactive groups Involved in the polymerisation process, (b) A simplified model for the structure of the synthesised crosslinked copolymer, and (c) Linear copolymer
synthesa and Characlensabon of N-Vmnyl.2-pymNdoneAcr)nh Acdd Copolymen and lhea Metal Complexes 80
In the case of taosslinked NVP-AA systems, the morphology and physical
form v a y with the nature of the crosslinking agent. Depending upon the nature
of the polymer support and crosslinking agent the formed polymer exhibit
variations in character~stic properties like swelling.
The structure of the monomers and simplified model of the structures of
linear and crosslinked copolymers are shown in Scheme 4.1.
heparation of sodium salt of NVP-A.4 copolymers
Because of the complexing difficulty of carboxyl groups of the copolymers,
they were converted to the sodium salt. Derivatisation was effected at the
carboxylate group of he acrylic acid units. For this the linear and crosslinked
copolymers were treated with excess sodium hydroxide solution (0.2 M) with
shaking for 24 h (Scheme 4.2). Carboxyl capacity was estimated by equilibrating
a definite amount of the resin with known concentration of excess hydrochloric
acid and is shown in Figure 4.1. The unreacted hydrochloric acid was back
titrated with standard alkali.
24 h $-COOH + NaOH
Room temp. @O.Na+
Scheme 4.2. Preparation of sodium salt of NVP-AA copolymer
The nature of the crosslinking agent in the polymer support exerts a
definite influence on the extent of functionalisation. The carboxyl capacity of the
linear copolyrner is higher than the crosslinked system. Among the various
crosslinked systems the capacity increased with increasing flexibility of the
crosslinking agent. Thus the results can be summarised as: linear > HDODA- >
EGDMA- > DVB-crosslinked copolymers.
synrherls and Characlensatio,r - of N-Viny&2-pymIrdOos-Ac~l;c Acid Copolymen and t.+eir Metel CompbXeS 81
DVB Crasslinking Agent
Figure 4.1. Carboxyl capacities of linear and crosslinked NVP-AA copolymers
4.2 Metal ion complexation of various NVP-AA copolymers
The complexation behaviour of ligand functions supported on polymer is
generally different frorn the corresponding low molecular weight analogue.255257
This variation is corinected with the polymer matrix to which the ligand function
is attached. 'The metal uptake by polymeric ligands varies on the incorporation of
crosslinking agents, which differ in their polarity and flexibilib.
The complexation of the linear and crosslinked copolymers in different
structural environments were investigated towards Cr(lll), Mnlll), Fe(lll), Co(ll),
Ni(ll), Cu(11) and Zn(ll) ions (0.05 M) at their natural pH by batch equilibration
method. In all complexation experiments, to a definite amount of the polymeric
ligand, a known concentration of excess metal salt solution was added and stined
for 8 h. The decrease in concentration of the metal ion solution was determined
spectrophotometrically .and volumetrically. The metal uptake by the linear and
various crosslinked systems are given in Table 4.1.
Synthesis and Charactensat;o,on of N-Vmyl-2-pynoi;done.Ac'yiic Acid Copoiymen and their Metal Complexes 82 -
Table 4.1. Metal uptake by linear and 4 mol% DVB-, EGDMA., and HDODA-crosslinked NVP-AA copolyrnels
In the case of crosslinked polymers due to its insolubility, the accessibility
of the functional groups are diffusion controlled and penetrant transport causes
some sort of molecular relaxation making the functional groups buried in the
polymer matrix available to low molecular weight s p e ~ i e s . ~ ~ ~ , ~ ~ ~ Similarly in the
present study the metal uptake by the linear copolymer is higher than the
crosslinked copolymers. With various crosslinking agents the metal uptake varied
with their relative rigrdity and flexibility. The observed trend is similar to the
variation in the ligand capacities of Linear and crosslinked system. Thus the metal
uptake by the HDODA-crosslinked system is higher than EGDMA-crosslinked
system which is higher than DVB-crosslinked system. In all cases the metal
uptake decreased in (:he order: Cu(ll) > Cr(lll) > Mn(ll) > Co(1l) > Fe(l1l) >
Ni(Il) > Zn(l1).
4.2.1 Influence of pH on metal ion complexation of NVP-AA copolymers
The interaction of the ligand functions of various copolymers were
investigated towards C:r(lll), Mn(ll), Fe(lll). Co(Il), Ni(ll), Cu(l1) and Zn(l1) ions in
different pH conditions by batch equilibration method. The optimum pH of the
medium for maximum uptake of metal ion depends only on the nature of the
metal ion and is independent of the type of crosslinking. The results of the pH
SYnlhesls and Chamctensa& of N-V~nfl-2-P~noit~e-AcwItc And Capolymem and the,, ~ e t ~ l complexes *-,
dependence of 4 mol% DVB-, EGDMA- and HDODA-crosslinked systems are
represented in Figure 4.2. In all cases the upper limit of pH was just below the
precipitation. The optimum pH for the complexation of various metal ions are
Cr(I1l) - 2.68, Mn(I1) - 4.5, Fe(I1Ii - 2.2, Co(11) - 5.5, Ni(I1) - 5.2, Cu(ll) -
4.31, and Zn(li) 5.39
Figure 4.2. Effect of pH on the metal ion complexation of 4 mol% (a) DVB-, (b) EGDMA-, and (c) HD0DA.crosslinked NVP-AA copolymen
Synthesrs and Characlensatrm - of N-Vt'myl-2-pyrmlrdone-AclyIjc Acld Copolymen and therr Mefal Complexes 84
4.3 Characteristion of Polymeric Ligands and Derived Polyrner- Metal Complexes
4.3.1 13C CP-MAS NMR Spectra
The 13C CP-MAS NMR spectra of linear and 4 mol% DVB-, EGDMA- and
HDODA-crosslinked PNP-AA copolymers gave an intense peak at 180.64 ppm
corresponding to -C=O of the carboxylic acid; and a small peak at 68.58 ppm
corresponding t i , the crosslinking agent
300 ZOO 100 0 -100
Figure 4.3. 'IC CP-MAS NMR spectra of (a) HDODA-, (b) EGDMA-, (c) DVB-crosslinked and (d) linear NVP-AA copolymers
s~,,(,,~~~ and maraclense~on ~ - Y l o y C 2 - ~ ~ - A C ' y l i c Acid Copolymers and their Mdal Complexes 85
The peaks at M.83 and 34.568 ppm conespond to the polymer
backbone. The ring carbon of the pynolidone ring appears as a small ~ e a k at
21.32 ppm. In the case of EGDMA-crosslinked copolymer the characteristic
peaks are at 180.507 ppm for -C=O of carboxylic acid, 66.545 ppm for
crosslinking agent, 45.439 and 37.783 ppm, for polymer backbone and
21.15 ppm for ring carbon. In the case of DVB-crosslinked system, the peaks
conesponding to cr83sslinking agent are seen at 147.42 and 131.42 ppm; and for
linear NVP-AA systern, peak due to crosslinking agent is absent. The typical
13C CP-MAS NMR spectra of 4 mol% HDODA-, EGDMA- and DVB-crosslinked
copolymers and linear NVP-AA copolymers are given in Figure 4.3.
4.3.2 FTIR Spectra
The R I R spectra of the polymeric ligands and metal complexes are of
considerable value for determining the chemical nature and also in the location of
binding sites in the metal c ~ m p l e x e s . ~ ~ ~ ~ ~ ~ The bTIR spectra of linear and
crosslinked NVP-A/\ copolymers showed the characteristic absorption of an
amide carbonyl (C=O) of NVP at 1725 cm-' (Figure 4.4). A band found at
2971 cm ! is attributed to C-H stretching vibration. A broad band at 3491 cm.'
indicated intramolecular hydrogen bonding resulting from the lowering of -0-H
vibration. The carboxylate ion gives rise to a strong asymmetrical stretching band
st 1657 cm', and weak symmetrical stretching band at 1450 cm.'. In addition to
these the DVB-cn>sslinked copolymer showed the characteristic absorption of
benzene ring at 86'0 cm.'. EGDMA- and HDODA-crosslinked copolyme~s showed
the absorption of ester carbonyl at 1720 cml. FTlR spectra of HDODA-
crosslinked NVP-AA copolymer, and its Cu(l1) complex are given in Figure 4.5.
Synthesis and Charactensat;oo of N-Wnyl-2-pynolWone-Aqlk Ac;d Copdymes and their Metal Complexes 86 -
Figure 4.4. FTlR spectra of linear (a) NVP-AA copolymer, and (b) Cu(ll) complex
The conversion of the carboxylic acid to the sodium salt of carboxylate ion
is evidenced by the shift to 1663 cm' and on metal ion complexation this shift
further to 1638 cm '. Metal ion complexation weakens the double bonding
character of the carboxylate group owing to the coordinate bond between oxygen
atom of the carboxylate group with metal
splnes,r and Characrensanoo olN-VinykZ-pyrmlidooe-Acwlic Acrd Capolymers and their Metal Complexes 87
Wavenumber (cm-')
Flgure4.5. FTiR spectra of HDODA.crosslinked NVP-AA copolymers (a) before functionaiisation, (b) after functlonalisation, and (c) Cu(ll) complex
4.3.3 W-visible Spectra
The structure and geometry of a polymer-metal complex is largely
determined by the niicroenvironment of the polymer domain.2M The actual
position of the band maxima observed in the electronic spectra is a function of
the geometry and the strength of the coordinating ligand.I9'
The UV-visible spectra of Cr(lll), Mn(ll), Fe(lll), Co(II), Ni(ll) and Cu(I1))
complexes of linear and 4 mol% DVB-, EGDMA- and HDODA-crosslinked
sodium salt of NVP-AA copolymers were recorded and their typical transitions are
summarised in Tables 4.2-4.7. The UV-vis. spectra of the various metal
complexes of 4 mol% HDODA-crosslinked copolymer are given in Figure 4.6.
Synlhesis and Charactenratron of N-Vmyl-2-pym~~dodooe-Ac~I~c Acid Copolymem and thew Metal Complexes 88 --
Figure 4.6. UV.visible spectra of the various metal complexes of HDDDA.crosslinked NVP- AA copoiymar: (a) Fe(lll), (b) Co(ll), (c) Mn(ll), (dl Cr(ll), (a) Cu(ll), and (9 Cr(lll)
Table 4.2. Details of the electronic spectra of various Cu(ii) complexes of NVP-AA copolymer.
Band assignments (cm-') Crosslinking agent
- -~
~. . ~ 14,705
EGDMA . -- 13,869
HDODA 13,037
1 01, - >E,
25,316
25,906
26,455
25,641
Syntheslr and Characletisatioi7 of N-Viny-2-pyrnlidone-Ac'yI,c Acid Co~dymerr and lhsir Metal Complexes 89
In the case of polymer anchored Cu(ll) complexes d9 configuration due to
Jahn-Teller distortion made a distorted octahedraVsquare planar symmetry.265
The usually broad visible band contain xy-(xy) and xz,yz-(xZ$) transition shift to
blue regron (Table 4.3).
Table4.3. Details of the eledronic spectra of various Co(ll) complexes of NVP-AA copolymers
Band asslgnments (cm ') Crossllnklng agent
V d F ) - 'T,g(P)
- . -- -- ~p
EGDMA 33,003
HDODA ~
34,322
Polymer anchored Co(l1) complexes exhibits bands in the region 17,857-
18,726 cm' and 32,617-34,322 cm' due to 'TI, - 'T,,(F) (v,) and 4T1g(F) -
'T,,(P) (v,) transitions in an octahedral geometry (Table 4.3).
Table4.4. Details of the electronic spectra of various Cr(lll) complexes of NVP-AA copolymeo
The electronic spectra of Cr(ll1) complex has A,, between 17,152-
17,361 cm' ['A,, - 'T,,(I')I and 23,529-24,213 cm-' ['A,, - 7,,(F)] (Table 4.4).
These transitions lead to an octahedral geometry for Cr(ll1) complex.
- - - -
Crossi~nk~ng agent
Llnear -- DVB
EGDMA -- HDODA 17,361 23,752
Band asslgnments (cm I)
<A2, - 7 2 , F )
17,152
17,331
17,301
4 A,, - T'g(F)
23,529
23,696
24,213
Synlhess and Cnaradensatml of N-Vmyl-2-pym~~done-AcwI~c Awd Copalymen and thetr Metal Complexes 90 -- ---
Table4.5. Details of the electronic spectra of various Mn(ll) complexes of NVP-AA copolymers
~- -- - Band assignment (cm-')
Crosslinking agent -- .. 6Aig - +rZQ(F) (GI
Linear ~-
21,231
DVB -- --- -
23,529 +
Mn(l1) complexes has a broad band in the region 20,000-25,000 cm-'
which is supposed to be the combination of the two transitions 6A,, - 4T2g(G) and
'A,, - 'Eg(G) in high spin octahedral geometry (Table 4.5).267
Table4.6. Details of the electronic spectra of various Ni(ll) complexes of NVP-AA copolymers
~ -.-A
~- ~~ ~-
Linear L . .
EGDMA .- --.A- 24,380
HDODA 13,280
The typical ilV.visible absorption of polymer anchored Ni(ll) complexes
gave two spin allowed h.ansitions 3A,g - 3Tlg(P) (13,280-14,705 cm-') and
34g -3Tig(F) (24,330-25,000 cm.') give near octahedral geometry (Table 4.6).
Table4.7. Details of the electronic spectra of various Fe(lll) complexes of NVP-AA copolymers
~-
Crosslinking agent -- - -- I Linear . ~-
DVB - ~~
EGDMA .- .
HDODA .~
Band Assignment (cm")
6 ~ , p - 7lg(G)
12,077
11,778
12,033
11,737
6A~g - +T>g(G)
18,796
17,953
18,691
18,903
syothesis and Charactensal,on of N-Vmyl-2-pyrmitdone.Ac'yI~c Acd Capolyrnen and fhsr Metal Cornpiexes 9 1
For Fe(ll1) complexes two spin transitions are observed, i.e., 11,737-
12,077 cm ' 'A,, - 'Tj9(G) and 17,953-18,903 cm-' 6Al, - 4T2g(G) suggesting an
octahedral coordination geometry (Table 4.7).
4.3.4 EPR Spectra
EPR spectroscopy can provide direct information on the structure,
property and concentration of fiee The EPR spectral pattern of
paramagnetic Cu(ll] complexes is influenced by the number of coordinating
ligands as well as geometry of the complex.269~270 The spectra obtained at liquid
nitrogen temperatun? are given in Figure 4.7. The spectra obtained are clearly
anisotropic and which can be the case in which the metal ions are bound directly
to the polymeric ligancl. The EPR parameters of various Cu(ll) complexes are
summarised in Table 11.8. The value of g , > g, showed that the unpaired
electron is in the dx2-y' orbital of Cu(ll) ion and spectral characteristics of axial
symmetry2" The bonding parameters (aZCu), of the Cu(l1) complexes, which is
the measure of the covalency of the in plane o-bonding of the ligand group with
the coordinating metal ion, was calculated by the expression given by Kivelson
and Neimen. The expression is based on the Cu(ll) hyperfine tensor A l l asZo8
For covalent bonding aZCu is in between 0.75 to 0.80 and for ionic it
approaches 1. The values supports distorted octahedral geomeby for Cu(l1)
complexes.
Figure 4.7. EPR S P ~ N . of b CU(II) complexes of 4 mol% (a) HOODA-, (b) EGDU(., (c) DVB-crosslinked, and (d) linear NVP-AA copolymer-Cu(ll) complexes
4"' EpR panmeten of CU(11) COmpIe~es of linear and 4 mol% OM., EDOW and HDOOA-crosslinked NVP-AA copolymen
-- AII
-%-
2.078 154.00
- - 160.00 EGDMA - 156.67 HDODA 2.26
---- 2.043 , 155.00
A,
30.00
43.00
38.33
43.33
a2Cu
0.8006
0.7581
0.7489
0.7456
Synthesis and Charactematran of NVmyl-2-~mllbone-Acwlic Add Copolymen and the$ Metal Complexes 93
4.3.5 Nitrogen Analysis
From the elemental analysis the degree of incorporation of ligand function
can be followed. In the present study the analysis was limited to the estimation
of nitrogen which originates from the NVP part of the copolymer. This is an
additional evidence that a copolymer of NVP-AA is being formed (Table 4.9).
Further the percentage of nitrogen decreases on derivatisation followed by its
complexation with Cu ions.
4.3.6 Themogravimetric Analysis
To study the thermal stability and decomposition patterns of the crosslinked
copolymers, dynamic thermogravimetric analysis was ~nder taken.~ '~ The TG
curves of the HDODA-crosslinked copolymer, its functionalised resin and Cu(l1)
complex were carried out in air. The TG curves of NVP-AA copolymer, its
sodium salt, and Cujll) complex are shown in Figure 4.8.
TaMe4.9. Percentage of nitrogen content in 4 mol% DVB-, EGDMA and HDODA- crosslinked copolymer, sodium salt, and Cu(l1) complexes
- - r- I Nitrogen content (%)
Crosslinking agent -
Polymer alone i - 3.20
-
--
EGDMA 4.35 . - +--
HDODA 5.20 ~- ~~ -~
Derivatised polymer
2.94
4.08
4.94 -
Cu complex
2.68
3.84
4.61
SynIhesls and Characfensa11000 of N-Vmnyb2-pymlrdodaoe-Acwl~c Acd Copolymers and tnen Metal Compkxes 94
Temperature ("C)
Figure4.8. TG curves of HDODAcrosslinked NVP-AA copolymer (a) before functionalisation, (b) after functionalisation, and (c) Cu(ll) complex
The degradation of NVP-AA copolymer occurred in three stages. The first
stage is due to the 10s; of adsorbed water. Both NVP and acrylic acid are highly
hygroscopic. About 16% water is lost from the polymer from 30-100°C and the
second stage of deconlposition of the polymer matrix starts at 239°C. The third
stage decomposition stops at 473°C and thereafter TG curves remains constant.
In functionalised copolymer, the final product is NaO, which is unstable whereas
in Cu(ll) complex, a stable metallic oxide (CuO) was formed after 663°C.
4.3.7 Scanning Electron Microscopy
Guyout e t d . used SEM technique extensively for studying the
morphological features and mechanism of formation of beaded p ~ l y r n e r s . ~ ~ ~ ~ ~ ~ '
SEM has been used as a tool for the determination of functional group
distribution in the polymer matrix by Grubbs eta/273 Morphological features of
the various crosslinked polymer supports have been investigated by using this
technique. The change in morphology of polymeric ligands with complexation
have also been investigated in some ~ a s e s . ~ "
Synlhesis and Charactensahon of N-Vinyl-2-pyrrolidone-Ac~ylic Ac~d Copolymers and Ihefr Metal Complexes 95 --
(a) (b)
Flgure 4.9. Scanning electron micrographs of HDODA-crosslinked NVP-AA copolymer: (a) before functionalisation, (b) after functionalisation, and (c) Cu(ll) complex
HDODA-crosslinked NVP-AA copolymer before derivatisation, sodium salt
of NVP-AA and Cu(1l) complex of NVP-AA are shown jn Figure 4.9. The surfnce
became disordered on derivatisation followed by complexation. On metal ion
complexation, the surface becomes rough, resulting from the rearrangement of
the already-orderly arranged macromolecular chains from their normal positions
for complexation with metal ions."5
4.4 Swelling Studies of Various Crosslinked NVP-AA Copolymers
For a crosslinked polymer the extent of swelling depends on the solvent-
polymer interactions which is determined not only by the nature of the solvent
Swhesls and C h a r a c t e n ~ ~ ~ o l N - V 1 n y I ~ 2 ~ p ~ m I ~ n e - A c v l c Acld Copolymen and then Metal Compk,xes 96
and polymer matrix E~ut also by the active groups introduced into the polymer
matrix. The presence of hydrophobidhydrophilic crosslinking agents would Led to
the formation of crosslinked systems with vaving solvation and swelling
characteristics. In the present study, the extent of swelling of polymer in water is
represented as
Weight of wet resin- Weight of dry resin Equilibrium water content = - x I00
Weight of wet resin
The EWC of the unfunctionalised copolymer, functionalised copolymer
and the Cu(1l) complexes are given in Figure 4.10. The swelling of the
functionalised resin is higher than the respective crosslinked copolymers. In the
metal ion complexed state, the ligand groups are less amenable for binding with
water, and hence the reduction in EWC values. The complexation with metal ions
will act as add~tional crosslinking. Generally the swelling characteristics increased
on changing the crosslinking DVB to EGDMA to HDODA. On metal ion
complexation, this decrease in EWC is highest in the HDODA-crosslinked system.
" DVB EGDMA HDODA
FIgure 4.10. Swelling chaacteristlcs of various NVP-AA copolymers and their Cu(ll) complexes
synrhes!s and Characlensabon of N-V!nyl-2-pyml~done-A~'yI~~ Acld Copolymers and therr Metal Complexes 97 ----
Suspension polymerisation of NVP-AA with different crosslinking agents
were prepared 'T CCP-MAS NMR measurement was carried out to ensure the
incorporation of all the monomers, acrylic acid, N-vinyl-2-pyrrolidone and the
respective crosslinkirlg agent, in the linear and crosslinked copolymer. The
polymers and corresponding metal complexes were characterised by FTIR. The
UV-vis. spectra studies suggest a octahedral geomehy for Cr(lII), Mn(ll) and Fe(ll)
complexes and distorted octahedrausquare planar geomehy Cu(1l) complexes.
Co(ll) and Ni(ll) were assigned to have near octahedral geometries. The EPR
spectra of the CuZ' complexes showed that it is more covalent in nature.
Nitrogen analysis is an additional evidence that the copolymer was being formed.
Thermal studies were also carried out. The swelling characteristics of the
complexes are lower than the derived sodium salt of NVP-AA system. The
scanning electron microscopy supports the disordering of the surface of the
polymer-matrix on metal ion complexation.