Synthesis and Characterisation of Acrylic Acid-N- Vinyl-2-

Pyrrolidone Copolymers and their Metal Complexes

Synthests and chsrsctensat!on of acrylic acid-N-viioyl-2 pyrolidone copolymers and their metal complexes 73

T he des~gn of

area of both

copolymers wlth specific characteristics has always been an

lndustrlal and academic interest. Great efforts have been

directed toward controlling copolyrner~sations with respect to polydispersity and

molecular wetght uslng, for example, atom transfer radlcal polymerisation

(ATRP) or the r e ~ e r s ~ b l e add~ t~ i in fiagmentatioll chain transfer (RAFT)

140-142 process. These novel techniques also allow one to tailor specific block co-

and terpolymers ot' varlous monomers. For most specialised industrial

applications. the copolymer shouli; contain functional rnonomer units to enable

further chern~cal tnudlfications or to add a specific feature to the polymer.143

Such a monome1 unit I S acryl~c acid Polyacrylic acld is extremely hydrophillc.

But when it I S copolvmer~sed w ~ t h .Z ~1nyl-2-pyrrol1done, the resulting polymer

1s of moderate hvdroph~l~city The 1 copolymer of acryl~c acld and N-vlnyl-2-

pyrrolidone found widespread .ipplication in agriculture, medicine,

pharmaceuticals. paper and food 111dustry. 144-154 Polyacrylic acid and poly

(N-vinyl-2-pyrrolidone) show complexing ability for metal ion^."^^'^^ In our

attempts to synthes~se these polymers and their metal complexes it was very

difficult to handle them because of' their high swelling nature. Hence we

synthesised h e a r and crosslinked copolymers of acrylic acid and N-vinyl-2-

pyrrolidone. The copolymerisation was carried out by solution and suspension

polymerisation techn~que respectively in presence of AIBN as initiator. W e

prepared linear and crosslinked copolymers of acrylic acid and N-vinyl-2-

pyrrolidone wltli 4 rnolo/o TTEGDM.4, BDDMA and NNMBA crosslinking.

These polymers could be synthesisea I C good physical form and were found to be

much superlor to llnear polyacryllc a c ~ d and h e a r poly(N-v1nyl-2-pyrroI1done)

Synthesis and character!salio#i of acrylic a o d - N - w r y / - i pyNoBdone copolymers and their mefai complexes ~ 74

because of thelr bette~ hydrophil~c- hydrophobic balance. 156,157 The properties of

copolymers depend not only on the nature of comonomers and the overall

cornposltlons. but d l ~ o on the dibtr~but~on of the monomer unlts along the

polymer cham 1 5 "

In the present study, the complexation properties of linear and crosslinked

acrylic acid-1V-v1nyl-2-pyrrolidone copolymers (AA-NVP) were carried out

towards various trans~tion metal ions giving emphasis on the effect of the nature

of crosslink~ng agent occurring in tile insoluble crosslinked polymer matrix and

comparison of the complexation behaviour of linear and crosslinked systems

Thls sectlon describes the toliow~ng investigations:

(a) Syntlies~s vl linear and 4 inol% TTEGDMA-, BDDMA- and NNMBA-

crossilnked acrylic aid-:l'-vinyl-2-pyrrolidone copolymers and their

d e r ~ \ ~ t i s a t t o i ~ to sodiutx salt

(b) Complexation of the lineal and crosslinked acrylic acid-N-vinyl-2-

pyrrolidone ci~poiyrners to~v~tl-ds Cr(III), Mn(II), Fe(III), Co(Il), Ni(Il),

CuiIl) and %n(ll) ions.

(c) Swelling studies and physiochem~cal characterisation of polymeric

ligands and their metal complexes using ' 3 ~ - C ~ - ~ ~ ~ NMR, FTIR, UV-

V I S , EPR spectra, nitrogen analysis, TG and SEM.

4.1 Synthesis of Linear and 4 mol% TTEGDMA-, BDDMA- and NNMBA- crosslinked Acrylic Acid-N-Vinyl-2-Pyrrolidone Copolymers

4.1.1 Linear copolymer

Llnear copolymer of a c r y l ~ c acid and N-vlnyl-2-pyrrolidone w a s

prepared in w a t e ~ using AIBN as Iiilt~ator at 80-85'C on a water bath using

Synthests and chatactensatloo of acrylic acid-N-nnyl-2- pymlrdone copolymers and then metal complexes - 75

solution p o l y ~ n e ~ i s a t ~ o n technique. The copolymer was obtained in high

yield for 1 I Gomonomer ratio. The polymer is a white solid. It is soluble in

methanol and d~methyl formamide, but insoluble in aliphatic and aromatic

hydrocarbons, ethyl acetate, acetone, dioxane and chloroform. The

experimental detalls are given ln (fhapter 6 .

4.1.2 TTEGDMA-, BDDMA-, and NNMBA-crosslinked copolymers

Copolvmers with 4 mol '~ TTEGDMA, BDDMA and NNMBA

crosslinking were prepared by :suspension polymerisation at 80-8S°C

under nitrogen atmosphere usins A[BN as initiator. Copolymers with 1:1,

1 :2 and 2 I A A l N V P ratios were prepared. The composition of

monomers and the amount oi' crosslinking agents used for the

preparation o t Lai~lous crosslinked systems are described in Chapter 6

(Tables 6.2-6.4)

These copolymers are ~ n s ~ ) l u b l e in almost all solvents since the

polymeric z l la~ns are interconnected to form an infinite network. The

morphology and phys~cal form o f t h e polymers vary with the nature of the

crosslinking agent Depending upon the nature of the crosslinking agent,

the formed copolymer exhibit var~ations in characteristic properties like

swelling. The structure of the monomers, crosslinking agents and a

pictorial representation of the structure of the synthesised crosslinked

copolymers and llnear copolymer are shown in Scheme 4.1

Synthesrs andcharacfensabon of acrylic acid-N-vlnyl 2 Dyrrolldone copolymers andfherr metal complexes -- - 76

Acrylic acid

N N M B A

N N \ H2C\ J1 =O

HE-C H~

N-vinyl-2-py rrolidone

BDDMA TTEGDM A

KT,,"

N V P

Scheme 4.1 Chemical structures of (a) the monomers and (b) crosslinking agents; a pictorial representation of the structure of synthesised (c) linear copolymer and (d) crosslinked copolymer

Synthesis and characterisahon of acrylic acrd-N-vinyl-2 ~yrroiidone copolymers and then metal complexes -- -- 77

4.2 Derivatisation of AA-NVP Copolymers

Because if the c o m p l e x ~ n ~ difficulty of carboxyl groups of the

copolymers, they he re convel-ted to the sodium salt. Derivatisation was effected

at the carboxylate group of the acrylic acid units. For this the linear and

crosslinked copolymers were treated with excess sodium hydroxide solution

(0.2 M) wlth shaking ior 24 h (Scherile 4.2). Carboxyl capacity was estimated by

equlllbratlrig a iiet'~rlltc amoun: of the carboxylate resin with known

concenti-at1011 ut excess l~ydroch lo~~c acid The unreacted hydrochloric acid was

back t~trated \ \ ~ ~ t l st;intiai-d alkali

Scheme 4.2 Preparation of sodium salt of AA-NVP copolymer

The chem~cal reactivity of attached functional groups is governed by their

distribution and access~b~li ty on the polymer backbone. Linear polymers which

can attain homogeneous macromoiecular solutions can provide their functional

groups free in the solution. But in the case of crosslinked polymers due to their

~nsolubility, the accessibility of the functional groups is diffusion-controlled and

penetrant transport causes some sort of molecular relaxation making the

functional group burled deep in the polymer matrix available to low molecular

weight specles I 'iillil, Hence linear copolymer possess high carboxyl capacity

compared to the crosslinked copolymers.

The nature of crosslinking agent in the polymer support exerts a definite

influence on the extent of funct~onalisation. Among the three crosslinked

Synthesrs and characterkabon olacrylrc ecd-N-innyl-2- pynolidons copolymers and then metal complexes -- 78

systems studled the carboxyl capaclty increased with increasing flexibility of the

crosslink~ng agent l ' hus carboxyl capacity decreased in the order: TTEDGMA-

> BDDMA- -. NNMBA-crossl~niced copolymers. The variation of carboxyl

capaclty w ~ t h the nature of c ross l~ r~k~ng agent is depicted in Figure 4.1.

Linear TTEGDMA BDDMA NNMBA Crosslinking agent

Figure 4.1. Carboxyl capacities of linear and crosslinked AA-NVP copolymers

Amount of monomer in the copolymer has a marked influence on the

carboxyl capac~ty of the copolymers. Thus for TTEGDMA-, BDDMA- and

NNMBA-crosslinked acrylic acid-N-vinyl-2-pyrrolidone copolymers the

carboxyl capac~ty decreased in the order 1 : l > 2:1 > 1:2 AA/NVP ratio.

Irrespective of the nature of crossl~nking agent, maximum yield of copolymer

was obtained for I I copolymer system. The yield dropped down with increasing

amount of N V P and hence a decrease in carboxyl capacity.

4.3 Metal Ion Complexation of Acrylic Acid-N-vinyl-2-pymlidone

Copolymers

The a b ~ l ~ t y of a polymer-supported ligand to form complexes depends on

the nature of the polyrner back bone The matrix effect on ion binding is clearly

Synthesis and characterrsation at acvl!c scrd-N-v,nyc2 oynolidone copolymers and thea metal complexes -- 79

evident when low molecular ligands and their polymeric analogues are compared

as in the case of im~nodiacet~c acid ligand supported on polystyrene and

polyacrylamlde ''I With increasing polarity of the support, the extent of

complexation Increases. The metal uptake by polymeric ligands are varied by the

incorporation of the crosslinking agents which differs in their polarity and

flexibility.

The complexat~on of AA--VVP copolymers in different structural

environments were invest~gated towards Cr(III), Mn(II), Fe(III), Co(II), Ni(II),

Cu(1I) and Znill) ions (0 05M) at their natural pH by batch equilibration method.

In all complexat~on experiments, to 2, definite amount of the polymeric ligand, a

known concentl-atlon irf excess metai salt solution was added and stirred for 7 h.

The decrease in concentration 01' the metal ion solution was determined 118 spectrophotometr~cilllv and volun~etr~cally. The metal uptake by the linear and

various crossl~nked systems 1s given in Table 4.1.

Table 4.1 Metal uptake by linear and 4 mol % TTEGDMA-, BDDMA- and NNMBA- crosslinked AA-NVP copolymers

1 A M ~ Metal ion uotake (meale) 1

.65 lTEGDMA 1 :2 -~ ... .

2 : F . 7 1 ~ --

1:l 1.56

BDDMA --E!T 29

2: 1 1.38 - l : l 1 1.36 105

Synthesjs and charactensarion of acrylic aod-Mvmyl 2- pynohdons copolymers end then metal complexes . - - 80

The hydrophll~c~ty of the polytner support is important in the collection of

metal ions from aqueous solutions. 119,120 In the complexation of AA-NVP

copolymers wlth varlous transition nietal ions the hydrophilicity and flexibility

of the crossllnklng agent determine the diffusion of the aqueous metal salt

solution into the interlor of the polymer networks. The observed trend in metal

uptake is simllar to the variation In the carboxyl capacities of linear and

crosslinked systems Thus the metal uptake by the TTEGDMA-crosslinked

system is h~gher than BDDMA- crosslinked system which is higher than

NNMBA-crosslinked system. in all cases the metal uptake decreased in the

order: Cu(l1) > Cr(l1l) 3 Mn(1I) > C:o(ll) > Fe(II1) > Zn(I1) > Ni(I1).

4.4 Influence of pH on Metal Ion Complexation of AA-NVP Copolymers

The irietal 1011 coniplexatiol; ( i f polymeric ligands is highly dependent on

the equil~brl~lni pH of the mediunr 162-163 The pH dependence of metal ion

complexat~o~i was used f o r the select~ve separation of metal ions from a mixture

of metal ions In the present study, itnce most of the metal ions are prone to

precipitation at h ~ g t i e ~ pH, investlg'itlons were limited upto those pH values

where preclpltatlon was just prevented. Use of buffer solution for adjusting the

pH was avoided due to the undesirable results from the coordination of the ionic

164 species with metal IOIIS. The intei-action of the ligand functions of various

copolymers were Investigated towards Cr(III), Mn(II), Fe(III), Co(II), Ni(II),

Cu(1I) and Zn(l1) Ions in different pH conditions by batch equilibration method.

The optlmum pH of the medium for maximum uptake of metal ion depend only

on the nature of the metal ion and 1s Independent of the type of crosslinking. The

effect of pH on the complexation of various metal ions with the crosslinked AA-

NVP(1: 1) copolymers are depicted in Figure 4.2.

Synthesis and chaiactensaiioii of aclyfrc and-N-vin ,I-i pyrmlidone copolymers and the,rmefal complexes -- 8 1

Figure 4.2 Effect of pH on the metal ion complexation of 411101% (a) TTEGDMA-, (b) BDDMA-, and (c) NNMBA-crosslinked AA-NVP (1:i) copolymers

The optimum pH for the complexation of various metal ions are Cr(II1)

2.6, Mn(I1) 4.4, Fe(1II) 2.2, Co(I1) 5.6, Ni(I1) 5 . 1 , Cu(I1) 4.5 and Zn(I1) 5.3. The

complexation behaviour of copolymers with AANVP ratio 1:2 and 2:l was

similar to that of 1 : 1 copolymers.

Synthss,~ and charactensatron of acrylic scrd-N-v,ny&Z- pyno1,done copolymers and then metal complexes 82

4.5 Swelling Studies of Various Crosslinked Acrylic Acid-N-Vinyl-2-

Pyrrolidone Copolymers

The complexatlon of a metal Ion with a polymer-supported ligand which

occurs in an aqueous environment I > decided by the extent of swelling of the

165 - crosslinked polymer In water. rhe design and development of crosslinked

copolymers w ~ t h opttmum hydroph~lic-hydrophobic balance is of paramount

importance in synthetic and biomedical fields.166 Hydrogels are polymeric

materials whlch are able to swell in water and retain a significant fraction of

water within the~r macromolecular structure but do not completely dissolve in

water. This IS due to the existence of crosslinks which at least in water bind

macromolecules or the11 segments elther by permanent bonds or through more

extensively organ~sed regions which can be considered to be formed from

molecular assoclatlons, usually hydrogen bonds. During the preparation of the

polymers, alteration of the iatio of hydrophilic monomer and

hydrophiliclhydrophob~c crosslinker .illows the degree of hydrophilicity of the

copolymer to be varred. The effects of molecular weight, crosslinks and

plasticisers on the water sorption bei-lavlour of poly(methy1 methacrylate) have

been studied by T U I - n e ~ er ~ 1 ' " ~ ' ~ ~ A:tempts have been made by various groups

to understand the water sorption beha\ lour of synthetic hydrogels and to evaluate

the kinetlcs and mechanism of sorption. 169-171 The delineation of the

interdependence of molecular paramt-ters on the physicochemical properties of

macromolecular systems 1s of contemporary interest. 172-178

The maln focus of t h ~ s study IS to determine the equlllbrlum water content

(EWC) of the crossl~nked acryl~c ac1d-N-v1nyl-2-pyrrolldone copolymers and to

correlate the effects of molecular parameters such as the nature of crosslinking

Synthesis and cnaracrensaNoo of aciyllc and-N-v~r i / I -~ pyriolldone copoiymers and their melai complexes - 83

agent on theil- water sorption and water binding behaviour. At a given

composition. the HWC' of a cop~~lyrner depends on the balance between

contributing polar and steric effects. The polar contribution arises mainly from

the amide groups and to a lesser extent from the ester groups. EWC of NNMBA-

crosslinked copolymer is higher than BDDMA- and TTEGDMA-crosslinked

copolymers due to the possibility of H-bonding through the amide linkage

whereas TTEGDMA and BDDMA possess ester linkages. Moreover, a steric

effect arises from the combined cclntribution of the a-methyl groups, methylene

groups and the polyethylene groups of the TTEGDMA crosslinks. Hence EWC

of the various copolymer decreased in the order NNMBA- > BDDMA- >

TTEGDMA-crosslinked copolymer. The decrease in EWC on complexation is

maximum for TTEGDMA-crosslinked copolymer indicating the high flexibility

of this crosslinked system. EWC of various crosslinked AA-NVP copolymers,

their derivatives and copper complexes are given in Figure 4.3.

U B e f o r e der ivat ieat ion - A f t e r deriuatiaaTion

120 Ocu(11) complex I "

60

40

20

I (1 -

TTEGDMA BDDMA NNMBA Croislinklng agent

Figure 4.3 Swelling characteristics of various AA-NVP (1:l) copolymer, their sodium salts and Cu(ll) complexes

Synthesrs and chaiscrsnsatron of acvjyirc sod-N-vlnyl 2. jiynohdone copolymers end their metsl complexes -- 84

4.6 Characterisation of Polymeric Ligands and Derived Polymer- Metal

Complexes

4.6.1 FT-IR spectra

The FT-IR spectra of linear and crosslinked AA-NVP copolymers showed

the characterlst~c absorption of an amide carbonyl (>C=O) of NVP at

1725-1750 c m ' A band found ai. 2327-2950 cm.' range is attributed to -C-H

stretching uf'the poiymer~c back bone. A broad band at 3300-3500 cm-I region

was due to the --0-H b~bratlon The carboxyl group of the AA-NVP copolymer

showed a strong absorption band a: 1624 cm-I and weak one at 1455 cm-'

corresponding to >C=O group On metal Ion complexat~on it IS shifted to

1594 cm-' Metal Ion complexat~on weakens the double bondlng character of the

carboxylate group 179-1x1 owing to the coordinate bond between oxygen atom of

the carboxyl group with metal ion. ln addition to these, the TTEGDMA- and

BDDMA-crosslinked copolymers showed the absorption of ester carbonyl group

at 11 16 cm-' and 1740 cm-I respecti~ely. NNMBA-crosslinked copolymer gave

an absorption at 1625 cm-I corresponding to the >NH bending of amide group.

Fine structure observed on the long wavelength side of the broad -OH band

represented overtones and combinat~on tones of fundamental bands. The FTIR

spectrum of 4 mol % NNMBA-crosslinked AA-NVP copolymer is given in

Figure 4.4

Synthesrs and chaiactensst~o~~ of vcryiic and-N-nny,-i-pyrroiidone copolymers and therr metal complexes 81

4000 3000 2000 1000 Wave number (cm-')

Figure 4.4 FTlR spectra of 4 mol% NNMBA-crosslinked (a) AA-NVP (1:l) copolymer, and (b) Cu(ll) complex

4.6.2 13C CP-MAS NMR spectra

l3C CP-MAS NMK spectrurn was used to probe the chemical composition

of linear and crosslinked copolymer\ "C CP-MAS NMR spectra of 1:l linear

and 4 mol % TTEGDMA-, BDDMA-. and NNMBA-crosslinked copolymers are

depicted in Figure 4.5 & 4.6. Linear and 4 mol% TTEGDMA-, BDDMA- and

NNMBA-crosslinked copolymers gave an intense peak at 180-182 ppm

corresponding to >C'-0 of the carhoxylic acid. The peak at 44-46 ppm is

responsible for the methyiene carbon of the polymer backbone. The ring carbon

of the pyrrolidone ring appeared as a small peak at 21-23 ppm. The tertiary

carbons in the polymer backbone gave a peak at 34-36 ppm region. A small peak

in the 64-70 ppm region in crosslinked copolymers was due to the crosslinking

agent and was absent in the NMR spectrum, of linear copolymers.

. '00 100 0 6 PPm

Figure 4.5 13C CP-MAS NMR spectrum of linear AA-NVP copolymer

Figure 4.6 '3C CP-MAS NMR spectra of (a) TTEGDMA-, (b) BDDMA-, and (c) NNMBA- crosslinked AA-NVP (1:l) copolymers

Synlhes,~ and chsraste~hehon ofacwiic acid-N-vmi/-2- pynolidone copolymsm and their metal complexes - 8 2

4.6.3 Ni trogen analysis

In the PI-esent study the elenlental analysis was limited to the estimation

of nltrogen ~ v l i ~ c h I> t l o l r ~ the N\ 'P part of the copolymer. This is an additional

evidence that '1 ~opolyrner of AA-NVP is being formed (Table 4.2). Further the

percentage of n~trogen decreases on :ierivatisation followed by its complexation

with Cu(l1) Ions

Table 4.2 Percentage of nitrogen content in 4 mol% TTEGDMA-crosslinked copolymer, sodium salt and Cu(ll) complexes

r --r ---- - Nitrogen content (%)

A ratio Copolymer-Cu

I I !

4.6.4 UV-vis. s p e c t r a

The actual pos~tion of the band maxima observed in the electronic spectra

is a function of the geometry and the strength of the coordinating ~i~and.'~"he

structure and geometry of the resulting polymer metal complex are largely

determined by the mlcro environments around the polymer domain.'82 Although

the band mamma for each class transitions for the differently crosslinked

Synthests and charactersation of aciyBc sod-N-vriryl-l- pyrrolidane copolymen and thev me181 complexes - 88

polymers are in the same range, the) d~ffer depending on the nature and extent of

crossllnklng in the polyrner matrix

The UV-v~s~b le spectra of Cr(III), Mn(II), Fe(III), Co(Il), Ni(I1) and

Cu(I1) complexes of h e a r and 4 mol% TTEGDMA-, BDDMA- and NNMBA-

crosslinked AA-NVP copolymers were recorded. The typical transitions of

metal con~plexes of i~near and crosslinked AA-NVP copolymers are given in

Tables 4.3-4.6.

Table 4.3 Details of the electronic spectra of linear AA-NVP copolymer-metal complexes

Metal complex Band assignment (cm-I) 1 Type of t rans~t~on I T- -- -

I Cr(l1I) 17152

Mn(I1) ! +--- 2423 1

18117'7

Fe(ll1) 2879t1 -

1785''

Co(I1) I I

32894 ~

1470'5 Ni(1l)

! 25000 -. -~ ~- --

15077

Cu(l1) 253 1 ( .

4 Azg - Yzg

6 ~ 1 , - 4 ~ , 4 ~ 1 ,

6 AI, - 4T~g

6 ~ 1 , - 4 T ~ g

4 ~ ~ g - 9 2 g

4 T ~ , - 4 T ~ g (P)

3 Aze - 'TI, (F)

3 - 3 ~ 1 g (P)

2 E,- z T,,

Synthesis and characterisahon of acviic yi,csnd-N-vinyb2- pynolidone copolymers and their metal complexes 89

Table 4.4 Details of the electronic spectra of 4 mol% TTEGDMA-crosslinked AA-NVP copolymer-metal complexes

AAbJVP feed ratio

Metal complex 1 Band assignment Type of transition

I (cm-')

24875

- 32786 Azg - 3 ~ 1 g (P)

25125

33003

Synthes,~ and characterrsation of acry1,c aod-N-vmyl-2- pyrralrdone copolymets and thsrr metal complexes - YO

Table 4.5 Details of the electronic spectra of 4 mol% BDDMA-crosslinked AA-NVP copolymer metal complexes

l i

- C - - I 32768 ' ~ 2 ~ - ' ~ 2 , (P)

4- -

-- AA/NVP f e e d - r ~ e t a l complex Band assignment

ratlo (cm-I) Type of transition

Synthesm and charactensahon of acryl,s acrd-N-vmnyl-2- pynolrdons copolymers end t h e ~ m e t a l complexes 9 L

Table 4.6 Details of the electronic spectra of 4 mol% NNMBA-crosslinked AA-NVP copolymer.metal complex

Synthss,~ and cheractensatran a /acryl~c acrd-N-vmyf-2- oynolrdone copolymers end their metal complexes 92

The electron~c transit~ons of Cr(II1) lead to an octahedral geometry for

Cr(II1) complex. Mn(1l) complex has a broad band which is supposed to be the

combinatton of two tratnsitions in h ~ g h spin octahedral geometry. For Fe(lI1)

complexes. spirt transltlons suggesting an octahedral geometry are observed.

Polymet ancho~ed i ' ~ ) ( l l ) compicx exhibits two transitions in an octahedral

Seometry l \ \ o tralisitioiis are obseived for polymer anchored Ni(I1) complex

w ~ t h a neal octahctl~al Zeometr.; 111 the case of polymer anchored Cu(1l)

complex, duc to LI" conf i~ura t~on Jahn Teller distortion make a distorted

octahedral~scluate planar geometry In polymer anchored Zn(l1) complex, the

spectrum obta~ned 1s ligand related and no d-d transition occurs. Therefore it

would have a tetrahedral geometrq The UV-vis. spectra of various metal

complexes of TTEGDMA- crossl~nked copolymer are given in Figure 4.7.

Figure

-

f-4.

(b)

i; i

(d)

. L 4

(4 /--

-- - 2(lO W.ivelength (nm) 1100

The UV v~s . spectra of varlous metal complexes of TTEGDMA. crosslinked AA-NVP copolymer (a) Cr(lll), (b) Mn(ll), (c) Fe(lll), (d) Co(ll), (e) Ni(ll), and (f) Cu(ll) complex

Synthesa and charactensatron of aciylrc acrd-N.v,nyl 2 pymalrdone copolymem and thev metel complexes -- - 93

4.6.5 EPR spectra

EPR studies of paramagnetic transition metal ion yield a great deal of

information about the magnetic properties of the unpaired electrons.lS3 The

molecular orbltal approach has proved most successful in the illustration of

complex hyperfine structure that found in EPR spectra of covalently bonded

metals.'x4 Due to the presence of dramagnetic polymeric back bone, the metal

centres in polymer-supported complexes represented ideal magnetically dilute

systems and gave reasonably good EPR spectra in polycrystalline solids in the

absence of a dlarnagnetlc diluent.'"

The E P K spectr ,~~ of Cu(l l ) complexes of linear and crosslinked

copolymers of acrvllc a c ~ d and .4'-~1nyl-2-pyrrolidor1e are given in Figure 4.8

and 4.9. The spectra of paramagnet^,: Cu(I1) complexes were Influenced by the

number of coord~natlng ligands as well as geometry of the complex. 130,131 The

EPR parameters of varlous Cu(I1) complexes are summarised in Table 4.7. The

values are in agreement with the d~storted octahedral geometry of the Cu(I1)

complex. The g,, values calculated almost coincide with the values of 2.3,

indicating the covalent character of metal-ligand bond. The value of gil >

shows that the unpalred electron localised in dx2 - 1.2 orbital of Cu(I1) ion and

spectral character~stlcs of axial symmetry."2

Synthesis and chatactensatlorr of dc'yltc and-N-vinyl 2 byrrohdone copolymen and Me,r met01 complexes -- - 94

Figure 4.8 EPR spectrum of Cu(ll) complex of linear AA-NVP copolymer

Figure4.9 EPR spectra of the Cu(ll) complexes of 4 mol% (a) TTEGDMA-, (b) BDDMA-, and (c) NNMBA-crosslinked AA-NVP(1:I) copolymers

Synfhesis and characfansation of acrylic acid-N-vhyl-2- pynobdone copolymers and their metal EompleXss - - 95

Table 4.7 EPR parameters of Cu(ll) complexes of linear and 4 mol% TTEGDMA-, BDDMA-, and NNMBA-crosslinked AA-NVP copolymer

-- --

Linear 2 32 2.07 154.00 30.00 0.80 ~

Crosslinked I TTEGDMA 1

I NNMBA

4.6.6 Thermogravimetric analysis

The thermal stability gained by polymer-metal complexes on .c 4

complexat~on and thelr i - lecornpos~t~~~n patter$ were studied using dynamic

thermogravimetrlc analys~s Polymer science and technology is an area where

thermoanalyttcal methods are extensively used. This analytical technique is made

Synthesa and chaiactensaiio!~ or i iclyl~c and-N-vmjl-2- pyrrolidane copolymers and lhelr metal cornpieves 96 -.

use of in solving a number of application-oriented problems and fundamental

aspects of polyn~er structure, degradation, stability and reactivity. The

thermogravimetric studies of the 4 mol% NNMBA-crosslinked copolymer, its

derivatised resin and Cu(I1) iornplex were carried out in air and the

corresponding TG curves are given in Figure 4.10.

Figure 4.10 TG curves of 4 mol% NNMBA-crosslinked (a) copolymer (b) sodium salt, and (c) Cu(ll) complex

The degradation of AA-NVP copolymer occurred in three stages. About

25% water is lost from the polymer from 30-239OC due to the evolution of

adsorbed and coordinated water molecules. The second stage decomposition

occurred (239-4 1 S°C) with a weight loss of 48%. This may be due to the rupture

of crosslinking and breaking of polymeric linkage. From 415OC onwards the

whole substance was converted to gaseous products with a weight loss of 27% at

715OC.

Synthesa and charactensstion 01 dcryl!c acrd-N-wnpl-2- pymlrdane copolymers and t h e ~ m e t a l complexes - 97

In the case of ' derlvatised resin the first stage decomposition occurred

(42.73" to 308'C) wlth a total weigh! loss of 32% due the evolution of adsorbed

and coordinated water molecule. The second stage decomposition (308 -353'C)

occurred w ~ t h a welyht loss of about 38% due to the rupture of polymeric

llnkages and crossl~nku~lgs. The third stage decomposition with a weight loss of

about 16% occurred from 352'C lo 45083OC due to the evolution of C02 and

other vaporisable gases. About 14041 NazO remained at 60OoC.

Since the water uptake capaclty of the copper complex is less, the first

stage decompos~t~on occurred from 59°C to 249'C with a weight loss of about

14%. The second stage decomposlt~un occurred during 249'C to 42S°C with a

weight loss of 37% This may be due the rupture of polymer-copper coordinate

bonds. As a continuat~on of this, the I upture of crosslrnking agent and polymeric

linkages occurred with a weight loss of 39% from 42S°C to 663'C. After that

the weight ot'the res~duc I . e_ cupric oxide remained constant (10.3%).

4.6.7 Scanning electron microscopy

The physlcai property and molecular architecture of the polymer support

can be ~llustrated b y using scannlng electron microscopy. Guyout et al. used

SEM technique extensively for studying the morphological features and the

mechanism of format~on of beaded polymers. 135,136 Some rare investigations also

proceed in crosslinked p o l y m e r s . l x ~ ~ ~ has been used as a tool for the

determination of functional group distribution in the polymer matrix by Grubbs

et al. 13' The SEM plctures of 4 mol O/b TTEGDMA-crosslinked polymer and its

copper complex are g~ven in Figure 4.11.

Synlhesrs and diaiudelr3r nii of a:ry!c and-N-vinv 2 >yirolrdane copolymers and therrmetal complexes - - - - - 98

Figure 4.11 Scanning Electron Micrographs of (a) 4 mol% TTEGDMA-crosslinked AA.NVP copolymer, and (5) Cu(ll) complex

Thc .;LII.!':ICC i , ! ' the uncc~m:~lexed resin is smoother than that of

complexetl resin. The rough surface appeared because of the rearrangement

of the polymer chains for comple.ta~ion with Cu(I1) ions. The voidslchannels

present in the cr.ixz!inketi poly~ner matrix are responsible for the swelling of

the polymcl- a t i i l tlic re,lctivity PI' the active sites buriecl within the three

dimensional cr.cv;linketl polymer matrix. The voids disappeared on

complexation t l w 1 0 he cooperative contribution of the ligands for metal ion

complexation rc.;r~!rins: in the contq-action of the polymer matrix.

Linear a n ~ l irosslinked copolymers of acrylic acid and N-vinyl-2-

pyrrolidone \r;il!i tlif?'?i.ent crosslinking agents were synthesised. EWC values

were calculnted in i>t.drl. 10 study tlir swelling characteristics of the polymer,

its sodium sai l :rnt ('~(11) c o n ~ p l i . ~ . The formation of 'copolymer' was

Synthesrs and charaCtensalion of aciylic acrd-N.vmi/ i pynolidone copolymers and their metal complexes - -- --- -- 9 9

confirmed bg cieterm~n~ng the c~~rboxy l capacity and nitrogen content values,

whlch came from -\.4 and NVP part of the respective copolymer. FTIR and

"C CP-MAS N M R studies gave an insight into the characteristic groups

through w h ~ c h metal coordination occurred and L'V visible spectra revealed

the geometry of the complexes Covalent nature of ligand-metal bond was

confirmed by EPR spectra of the Cu(l1) complex of the respective copolymer.

The disorder~ng of the polymer surface on met.al ion complexation was

supported by SEM