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.