CHAPTER

. . SYNTHESIS AND CHARACTERISATION OF POLYSTYRENE-SUPPORTED SCHIFF BASE-METAL COMPLEXES

Synthesis md Chrractmafim ofPdyslyrenesumed SchiIfhe-meld COmpkxes 13

T he study of the metal complexation of polymeric ligands is of great

significance in various branches of chemistry. In a polymeric ligand, the

structural environment of the ligand function is one of the key factors

directing the complexation with metal ions. The characteristics of functional

polymers are not only derived from the macromolecular structure, but

depends to a significant extent on the functional group substitution in the

macromolecules. The chemistry of functional' polymers, their synthesis,

structural modification and application in chemistry and chemical technology

were continued to receive immense attention during the last few decades.'-"

The preparation of crosslinked polystyrene resinsd4 containing various

functionalities is of interest in several extents including the use of polymers as

supports in organic ~ynthesis,~ ion ex~hangers,~ reagent^,^ protecting

groups,lu catalysis,ll immobilising mediafor drugs,'> for the detection of

unstable reaction intermediates,* chelating agents," etc. The attachment of

the low molecular ligands into the insoluble macromolecular matrix can also

solve the problems of lability, toxicity or odour, often experienced with low

molecular weight reagents. In addition, the polymeric matrix can be selected

or tailor-made to provide a specific microenvironment that may induce some

specificity at the reaction site. Because of the possibility of incorporating a

number of functional groups by the nucleophilic displacement of chlorine,

polystyrene is the most commonly used support in reactive polymers.I5

Polymer supported chelating agents form an important group of compounds

for the complexation of metal ions in the separation chemistry.16

Svnfhesis md Chaactriselm of PdysWrenesuwoifed Schiff Beskmefd Complexes 44

The nature of the monomers, chemical nature and extent of

crosslinking, different experimental conditions of polymerisation and finally

the morphology and physicochemical property which governs the

characteristics of a polymer-supported metal complex. Results of studies

toward the realisation of the advantages and illustration of the conceptual

features of the polymeric supports with emphasis on the diverse aspects of

the various macromoiecular characteristics occurring on the insoluble

crosslinked polymer matrix are discussed here.

A number of polymeric Schiff bases have been synthesised and their

ion selective properties are investigated." A renewed interest in this type of

chelating polymers for selective binding of transition and other heavy metal

ions have been observed in recent years.18

T h s section describes the following investigations:

Preparation of EGDMA-, BDDMA-, HDODA-, TTEGDA- and DVB- crosslinked polystyrene resins with varying degree of crosslinking.

'Their functionalisation with Schiff bases.

Complexation of polystyrene-supported Schiff bases with Fe(II),

Fe(IIT), Co(II), Ni(II) and Cu(II) ions.

IR, UV-v~s., EPR and scanning electron micrograph (SEM) analysis of polymeric ligands and their metal complexes.

RESULTS AND DISCUSSION

3.A. Preparation of EGDMA-, BDDMA-, HDODA-, TTEGDA- and DVB- crosslinked Polystyrenes

The physical form of a polymer depends on whether the system is

linear or crosslinked one. In the case of crosslinked systems the morphology

and physical form vary with the nature and extent of crosslinking. The

molecular character, extent of crosslinking and other important determinants

of macromolecular structurelike chemical nature of the monomers, the

polymerisation method and the variables of polymerisation conditions can be

varied systematically to provide model macromolecular systems of diverse

Synthesis md Chrvadekefh of Polyslyrenksuppaled Schiff Base-mdd Cwnpxes 45

physicochemical properties. Depending on the nature of polymer support

and crosslinking agent it exhibit variations in characteristic properties and

reactivity.

Polystyrenes with various tetrafunctional crosslinking agents such as

EGDMA, BDDMA, HDODA, TTEGDA and DVB were prepared by

suspension copolymerisation technique. Various crosslinking agents used are

shown in Scheme 3.1. DVB is perfectly rigid and hydrophobic while

'EGDMA, BDDMA, HDODA and TTEGDA are hydrophilic and flexible.

DVB EGDMA BDDMA HDODA TTEGD A

Scheme 3.1. Various crosslinking agents used in the present investigation

Polystyrenes with 2-20 1no1% of EGDMA, BDDMA, HDODA; 2 mol%

TTEGDA and DVB crosslinks were prepared by the suspension

polymerisation at 80°C using benzoyl peroxide as initiator and toluene as

diluent. The polymerisation is depicted in Scheme 3.2. The hydrophilic-

hydrophobic balance and nature of the polymeric system like rigidity and

flexibility of polymer chain varied with nature and extent of crosslinking

agent The compositions of' monomers for the preparation of various

tetrafunctional crosslinked systems are described in Chapter 7

(Tables 7.1-7.3).

Synlksis md Chareclemafiw of Pdystyrene-sumed SchiffBase-meld Complexes 46

EGDMA

HDODA

------b

DVB L--+

c - t i - - I Lib- .I{- ? - , &::A Cl I2

Scheme 3.2. Prepurution of EGDM4-, BDDM4-, HDODA-, TTE(;L)A- und 1)VII- crosslinked pohs~renes

Synthesis mi Chasterisdion of Poiyslyremsq+vted Schiff Besefnetd Complexes 47

3.8. Preparation of N,N-bis(salicylidene-2-aminoethyl)aminomethyl Polystyrenes

Styrene based copolymer involve electrophilic substitution at aromatic

ring on functionalisation. The first of the polymer-analogous reaction series

employed for the introduction of the Schiff base function into the polystyrene

matrix is the chloromethylation of the aromatic ring. The reaction was

carried out using chloromethyl methylether with anhydrous stannic chloride

as the Lewis ac~d catalyst (Scheme 3.3). The Volhard's method is used for

determining the chlorine capacity to find out degree of chloromethylation.~Y

The chlorine capacity of all crosslinked systems are shown in Table 3.1.

Scheme 3.3. Chloromethylation of polystyrene

Table 3.1. Chlorine capacities of EGDMA-, BDDMA-, HDODA-, TTEGDA- and DVB (microporous and macroporous)-crosslinkedpulystyrenes

Synthesis md Ch.smteris#h of Polys~renwuppOned Schiff Base-inetd Complexes 48

In the chloromethylation reaction the degree of functionalisation falls

off with increasing crosslink ratio. The lack of efficiency in functionalising

the highly crosslinked resins has been observed in a number of reactions

including chloromethylation20~21 and most recently alkylationZ2 and in

generally attributed in some undefined manner to poor accessibility of

backbone groups. The property of crosslinked polymers totally depends upon

surface area (internal and external), total pure volume and average pore

diameter. Swelling of the resin beads is very important as it brings the

polymer to a state of complete solvation allowing easy permeation of the

reagent molecules through the polymer network. The nature of the

crosslinking agent in the polymer support excerts a definite influence on the

extent of funchonalisation. The capacities of the hydrophobic and rigid DVB-

crosslinked systems are lower when compared to the EGDMA-, BDDMA-,

HDODA- and TTEGDA-crosslinked systems.

The chloromethyl polystyrene resins were treated with Schiff base

derived from salicylaldehyde and diethylenetriamine.z For the preparation

of Schiff bases, 1:2 ratios are used for diethylenetriamine and salicylaldehyde.

rhis leads to the formation of a pentadentate ligand as indicated in

Scheme 3.4. The extent of incorporation of the ligand function was followed

by estimating the residual chlorine content by the modified Volhard's

method. The variation observed in ligand capacity of the EGDMA-,

HDDMA-, HDODA-, TTEGDA- and grossli linked systems are shown in

Figure 3.1. In all the systems 2% crosslinking agents have maximum ligand

capacity. 2% TTEGDA-crosslinked polystyrene systems shows maximum

ligand capacity and DVB systems have minimum ligand capacity (Figure 3.1).

Scheme 3.4. Prepwahahon of pot'ystjvene-supported sulicyluldehyrle- diethylenetriatnine Schiff bases

CROSSUNKING AGENT

Figure 3.1. Ligwrd copwitieu of various 2 mol% crosslinked polystyrene supporied Schiff buses

Synthesis ind CkactenSalic6 of P o f y s t y r e n e ~ u ~ e d Schiff Base-metal Cmpkxes 50

3.C. Complexation Behaviour ' of Various Polystyrene-supported Schiff Bases

The macromolecular structural parameters affecting the

functionalisation of a polymer and the reactivity of attached reactive

functions are the relative rigidity/flexibility of the polymer backbone, the

microenvironment around reactive sites, overall topographical nature of the

polymer matrix, solvation and swelling behaviour and hydrophilic-

hydrophobic balance.14 Thus a functional polymer possesses the combination

of the physical properties of the polymer-support and chemical reactivity of

the attached functional group.

Chelating resins have been widely applied as metal ion acceptor in the

environmental chemistry and chemical industry.25 Polymer-supported

complexes have found numerous application recently as catalysts in organic

synthesis as well as in model r eac i t i~ns .~~ ,~~ The complexing power of

macromolecular ligand depends upon the arrangement of functional groups

relative to the main chain. The shorter the distance between them, lower the

efficiency of complex formation because of steric hindrance. The complexing

characteristics of insoluble macromolecules are also strongly influenced by

the extent of crosslinking in the ligancl. The metal ion adsorption capacities

of the chelating resins were determined by batch equilibrium procedure in

the presence of excess metal ions. Polystyrene- supported Schiff base resins

readily forms metal complexes with various transition metal ions.

Tlus sechon ~llustrates the conlplexation of the different Schiff base

functions supported on crosslinked polystyrenes in different structural

environments towards Fe(E), Fe(IIl), Co(II), Ni(II) and Cu(1I) ions at their

natural pH. The coordination pattern of N,N-bis(salicy1idene-2-

aminoethy1)aminomethyl polystyrene is shown in Scheme 3.5. A definite

amount of metal solution of known concentration was added to this

polymeric ligand and stirred for 6 h. The difference in the concentration of

Svnthesis ind Chaactensalrw of PWstyremesuppxfed SctRBase-meld Complexes 51

the metal ion solubons before and after metal ion binding were determined

spectrophototnrh~cally.

Scheme 3.5 Coordination p&n of N,N-bis(salicyli&ne-2-wnin(~thy1) aminomethyl polystyrenes

3.C.1 Effect of the nature and extent of crosslinking agent on complexation

Crosslinked polymer exhibits consider difference in properties

depending on the degree of crosslinking and the method of preparation. The

nature and extent of crosslinking agent in the polymer matrix influence the

complexing ability and hence the extent of complexation of the polymer

ligand varies with the metal ions. Complexation is significantly slow in

aqueous medium presumably due to the hydrophobic character of the

polymer matrix. This hinders the effective interaction of the metal ions in the

aqueous phase and the ligand sites in the dense hydrophobic polystyrene

matrix.

The complexation of polystyrene-supported diethyleneh-iamino-

salicylaldehyde Schiff base of EGDMA-, BDDMA-, HDODA-, TTEGDA- and

DVB (microporous and macroporous)-crosslinked resins were investigated

using Fe(lI), Fe(III), Co(lI), Ni(I1) anti Cu(1I) ions at their natural pH. The

influence of the nature and degree of crosslinking agent on metal ion

complexation ot different systems are :given in Table 3.2.

Synlhesa and C h m l m d m of Pdysfymwuppxfed Scluff i f f e t d Complexes 52

Table 3.2. Metal ion uptake by EGDMA-, BDDMA-, HDODA-, TTEGDA- ~11d DVB-o-osslit~ked po2ysiyrene-supported Schiff bases

Cross- Crosslink Ligand linking density capacity -

agent (mol%) (mrnol/g)

The complexation of 2 mol% 1TEGDA-crosslinked polystyrene Schiff

base resin is h g h when compared with 2% DVB (microporous,

macroporous), 2% EGDMA, BDDMA and HDODA systems (Figure 3.2). The

high metal ion complexation of TTECiDA-crosslinked polystyrene-supported

Schiff base is due to the high flexibility of TTEGDA crosslinks. With rigid and

Svnthesis ivld Ch&clensaf&m of P o l y s f y m n e s u ~ e d Sct~iffBesemeta' Comp/exes 53

hydrophobic DVB crosslinks the polystyrene systems become totally rigd

and hydrophob~c. This increased hydrophobicity is the reason for the less

complexation behaviour. The DVB-.crosslinked polystyrene (microporous)

systems showing high complexation, compared with macroporous system

because of higher surface area associated with it.

Figure 3.2. Eflect of the nature of crosslinking on the Cu(I1) complexutio~n of 2mol% EGDMA-, EDDMA-, HDODA-, TTEGDA- und DVII (micopororous, macroporous)-crosslinked pobstyrene-supporied Schiff bases

Depending on the nature of metal ion, there is appreciable difference

in amount of metal Ion complexed for all crosslinked systems suggesting that

even at high crosslinking the matrix has a definite influence on the spatial

requirements ot the metal ion complexation. Decrease in metal uptake at

higher crosslinking is due to the lower accessibility of the reactive site for

complexation.

Synthesrs and Charwf~n- * ' f r v a' P~fvstyrenesupporfed Schif Basemetal Comp/exes 5.1 -

4 8 12 20

CROSSLINKING DENSITY

Figure .?.3. Ef' .r.t nf the degree of crosslinking on tlre Cu(11) ccompl~ution r,f ' . - ' . mr,l"h D M - , BDDMA- and tfI)OI>A-crosslinked poi ~ ~ t t ~ r ~ ~ r r ~ - . u p p o e d Schiff bases

In t ! ~ <.,>',, P' i:GDMA-, BDDMA- and HDODA-crosslinked svstenis

the nmour-it i,l a-..,!.i: ton complexed decreased as the degree of crosslinking

incrcasod . t . ~ ~ ~ - . - ; ~ l , ~ ~ : ! in Figure 3.3. With increasing degree of crosslinkings

the l ipnc' F:rol:!~s an, getting buried into the polymer matrix. But this

variatiorl \vi'!i ' r of crosslinking is less in the HDODA-crosslinked

s\stem. 111 f h ~ q C , ! W alqo lightly crosslinked systems have high ligand capacity

a n m i I uptake. Complexation of EGDMA and BDDMA

pol\,st\,rc.iv> i i- '>i ' i ~ , < i > resins is less compared with TTEGDA crosslinks, due

to the Ir.5~ !!t . i ih' , ,,.>!~irt' of EGDMA and BDDMA.

Synthesis and Characterisalion of Polyslyrene-supported Schiff Basemela1 Complexes 55

3.C.2 Influence of equilibrium pH on metal uptake o f diethylenetriamino- salicylaklehyde Schfi base resins

The chelation of metal ions by a polymeric ligand highlv depends

upon the equilibrium pH of the mediurn.w.31 Generally, the metal ion

selectivity varies with pH. Polystyrene-salicylaldehyde-Schiff base resin is

used for this investigation. The studies were carried out by batch

equilibration technique. Since most of the metal ions are prone to

precipitation at higher pH, investigations were limited to those pH where

precipitation is just prevented.

The complexation of 2% DVB-c-crosslin ked macroporous

diethylenetriarnine-salicylaldehyde supported polystyrene resins were

studied towards Fe(II), Fe(III), Co(LI), Ni(I1) and Cu(II) ions a t various pH. By

varying pH of the metal solutions selectivity of the metals changed. Most of

the rnetal ions exhibited tendency to precipitate at higher pH. For 2% DVB-

crosslinked macroporous diethylenetriarnine-salicylaldehyde polystyrer~e

resins maximum metal uptake was observed for Cu(Q ions as shown in

Figure 3.4. In diethylenetriarnine-salicy Laldehyde y olystyrene resins metal

uptake decreased in the order: Cu(II) > Co(II) > Fe(III) > Fe(1I) > Ni(1l).

Figure 3.4. pH dependence on the metal binding .of 2 mol% D VI2-c:rosslinkcd polystyre~e-supported diethylenetriumine-saltc~~lal~ieI~~~de SclzifJ'huse

3.0. Characterisation of Polymeric Ligands and their Metal Complexes

3.0.1 Infrared spectra

Standard elemental analysis with supporting infrared absorption

spectra generally provides satisfactory evidence for chemical modification

and allows calculation of degree of substitution or functionalisation of a

polymer species, quoted in rnilliequivalents per gram of polymer. The IR

spectrum of the crosslinked polystyrene-supported Schiff base ligand showed

cliarac.ter~st~c nosorption band of benzene ring, ester and oxide groups. A

band at 3200 cnl~l attribute to OH-vibrations. Another band found at 2900 cm-

I indicated intramolecular hydrogen bonding resulting from the lowering of

OH-vibration.'. 'The bands appearing between 1020-1250 cm-I are attributed

to aliphatic N and the band a t 1615 cm-I can be assigned to C=N vibration.

The sharp decrease in intensity of the band around 3400 cm-I and at 2900 cm~l

supports t h r involvement of the phenolic oxygen in metal ion coordination.

The distortion of C=N shifts towards lower frequency in the spectra of the

polymer-metal complexes is due to the involvement of azomethine group in

metal ion complexation (Figure 3.5).

Figure 3.5. IK spectra of (a) chloromethylated polystyrene, (b) polystyrene- supported diethylenetrimine-salicylaldehyde Schiff base and (c) polystyrene-supported diethylenetriamine-salicylaldehyde Cu(l1) compler

Svnthesis and Chivacfensalim of Pdvsfvrene-sumed Schiff BsremeftJ Complexes 57

3.0.2 UV-visible spectra

Electroni~ spectra provide an accurate and simple method for

determining the geometry around the transition metal ion in the complexes of

chelating resins As the flexibility of the matrix increases the geometry of the

resulting polymer-metal complex tend to be most favourable for satisfying

the electronic requirements of the central metal ion. Although the band

maxima for each class transitions for the differently crosslinked polymers are

in the same range, they differ depending on the nature and extent of

crosslink~ng in the polymer matrix. The structure and geometry of the

resulting polymer-metal complex are largely determined by

microenvironmc~nt of the polym&&$+dn.~ .., The actual position of the band ., - . ,

maxlma obserbed in the electronic spectra is a funchon of the geometry and

strength of the, corresponding ligand.34 The absorphon maxima around

40000 cm ' 1s due to the azomethine chromophore (n-n') transition. In the

complexes the band due to this transition is shifted to (40160-40223 cm-1)

indicating the) .~~ornr thyl coordination to metal ion. Thc polvnier-anchored

Co(I1) complexes exhibit band in the region 15432-19380 cm-I due to the

4 A ~ + 4T~(P) transltlon ~ndicating a near tetrahedral geometry. The polymer

anchored Co(l1) complexes of 2 mol% TTEGDA, DVB (m~croporous,

macroporous), I-IDODA, BDDMA and EGDMA are given in Table 3.3.

For the HDODA-crosslinked system, with increase in the extent of

crosslinklng thtsre is not much influence on the band maxima probably due to

the less distort~on from the regular structure. This minimum distortion is

due to the increased flexibility of the HDODA-crosslinked system. But

considering other BDDMA- and EGDMA-crosslinked systems there is not

much influence of the crosslinking agent on the band maxima indicating its

flexible nature. Comparing all of these systems, HDODA has flexible nature.

When the crosslinking is flexible the geomeby and the structure of the

complex will tK, the one that satisfy the electronic requirement of the central

metal ion. As the rigidity of the crosslinking increases the deviation from the

most stable coordination geometry takes place.

Synthesis and Chw&tensalron of Pdysfyrene-su@ed Schiff Base-metal Complexes 58 --

Polvmer anchored Ni(1I) complexes exhibit band in the region

15160-16367 cm due to the 3T~(F) + 3T~(P) transition indicating a near

tetrahedral geolnetrv.

Table 3.3. 1)etaiIs of the electronic spectra of various polystyrene-supporled di~thvlenetriumine-saIiqIaIdehyde Schiff base-Co(II) complc:~e.v

-~ ~~ -~

~lgellt ~vilyity iX2 + 4 T ~ (1') (cm~')

Synfhess end Cthwacfensdron of Pdysfyren~uppffed Schiff Basemetal Complexes 59

As the flexlbllity of the matrix increases the geometry of the resultrng

Table 3.4. 1I)etuils (4 the electronic .specha of ~~urious polystyrene-supported diethylenetriamine-salicyluldehyde Schiff hase-Ni(I1) compleres

polymer metal complex tends to be more favourable for satisfying the

electronic. requirements of the central metal ion. The band maxima also

STI(F)-+"TI(P) (cm-')

13889

~~ - -- ~ ~

Crosslinking agent

shows changes in the nature and extent of crosslinking agent. This is due to

Crosslink density (mol%)

2

the difference in stereochemistry depending on the microenvironment

around the meial Ion. The characteristic absorptions for 2-20 mol% EGDMA-,

BDDMA- and HDODA- and 2 mol% TTEGDA-, DVB (microporous,

macroporous)-8. rossl~nked Cu(II) complexes are given in Table 3.5. The bands

obtained in the range 17036-18832 cm~' supported the square planar

geometry

Table 3.5. 1)etails of the electronic spectra of various polystyrene-supported diethyleneh'mine-saliqlaldehyde Schiff base-Cu(Z9 complexes

I Crosslinking agent I Crosslink density I Band maximum (mol%) (cm-') I

EGDMA 1 8 1 17153 1

HDODA

1 TTEGDA I 2 I 18587 I

The polymer anchored Fe(I1) complex exhibit bands in the region

18382-19379 cm-I, 'TI, + lTzg transition showing a near octahedral geometry.

The bands obta~ned for 2-20 mol% EGDMA-, BDDMA- and HDODA and

2 mol% TTEGDA-, DVB (microporous, macroporous)-crosslinked Fe(I1)

complexes are glven in Table 3.6.

Synthesis am Che%iensatw of Pdyslyrene-supported Schiff Bm.tnetd Cwnplexes 6 1

Table 3.6. Details of the electronic spectra of various polystyrene-supported cliethylenehiamine-sdicylddehyde Schijjf base-Fe(I9 complexes

HDODA

I TTEGDA I 2 I 18657 I I DVB (microporous) I 2 1 18529 I

The polvmer anchored Fe(II1) complexes exhibit bands at

23753-24938 cm due to 6A~, --t (Tzg and 6 A ~ g --t 4Eg in a near octahedral field.

The band max~nium observed for different crosslinking agents of various

crosslink degrees are gven in Table 3.7.

DVB (macroporous) 2 18382

Table 3.7. Details 4 the electronic spectra of various polystyrene-supported diethylenetn'mine-salicyI&yde Schiff base-Fe(ll1) complexes

EGDM \

HDODA

Synthesis md Ch~~cfenSation of P d y s l y m u p p d e d SMBasemetd Comprexes 63

3.D.3 EPR spectra of Cu(l1) complexes of diethyleneb5amine-salkflaMehyde polystyrene Schiff base resins

EPR spectral studies of paramagnetic transition metal ions yield a

great deal of information about the magnetic properties of the unpaired

electron. The molecular orbital approach has proved most successful in the

illustration of complex hyperfine structure that found in EPR spectra of

covalently bounded metals. Due to the presence of diamagnetic polymeric

backbone, the metal centres in polymer-supported complexes represent ideal

magnetically dilute system and gave reasonably good EPR spectra in

polycrystalline solids in the absence of a diamagnetic diluent The large size

of the polymer frame work keeps the metal centres considerably separated

and as a result dipolar broadening does not occur. The appreciable distance

between two funchonal groups leads to a magnetically dilute situation for

each metal atoms as the path way for dimer formation with M-M interaction

is blocked. However, when the polymer chains get twisted and overlapped

some of the reachve groups may come nearer to one another and as a result

M-M interachon may takes place.

The molecular orbital approach has proved most successful in the

explanation of EPR spectra. The bliinri'ing parameter (a2) was calculated by

the expression glven by Kivelson and Neiman."

The EPR spectra of Cu(I1) complexes with differently crosslinked

polystyrene-supported Schiff bases are given in Table 3.8. The values are in

agreement with the square plannar geometry of Cu(1I) complex. The gll

values almost coincide with the values of 2.3, indicating the covalent

character of metal ligand bond, i.e., 811 < 2.3 for covalent character and gll> 2.3

for ionic character. The value of gll> shows the unpaired electron localised

Synthesm imd Ch~~dctensb?~cf~ ofPolysfyrene-suppcded Schiff Basemetd Cwnplexes 64

in dx2-y2 orbital of Cu(II) ions and spectral characteristics of axial symmetry

(Figures 3.6-3.9). The values of a2 Cu observed in the range of 0.4722-0.5555

support the covalent character. The spectra of Cu(Q complexes of polymeric

ligand showed hvo g values, (gll = 2.1890 to 2.2120 and g, = 2.1110 to 2.1040)

indicative of a square planar type symmetry about Cu(Q ions. The EPR data

showed that gll . g, and All > AL are indicative of the presence of unpaired

electron in dx2-y' orbital.

Table 3.8. EPR parameters of various crosslinked polystyrene-supported diethylenehiamine-salcylddehyde Schiff base-Cu(II) compleres

S y M s md Ch6f~~fenSilM of Pdyslymm.su@ed Schiff Basmeld ~ o m p k f f 65

#

I I

2MM 3000 35M)

GAUSS

Figure 3.6. EPR spectra of 2 mol% DVB (a) macroporous-, (b) microporous- and (c) TTECDA-crosslinked polystyrene Schiff base-Cu(I9 compleres

GAUSS

Figure 3.7. EPR spectra of 2-20 mol% ECDMA-crosslinked polystyrene Schiff buse-Cu(I1) compleres

Figure 3.8.

2000 I

3000 3500

GAUSS

EPR spectra of 2-20 mol% BDDM-crosslinked polystyrene Schiff cu (11) complexes

base-

GAUSS

Figure 3.9. EPR spectra of 2-20 m d % HDODA-crosslinked polysiyrene Schiff base-Cu(II) complews

From these results, Cu(II) complexes of the differently crosslinked

polystyrene-supported Schiff base systems, maximum covalent character is

exhibited in low crosslinked systems compared to high crosslinked system

irrespective of the crosslinking agent HDODA, EGDMA, TTEGDA, BDDMA

and DVB. The tuncbonal groups are frequently and statistically distributed

over the macromolecular ligand so that both the more favourable and the less

favourable conformahons would occur.

3.0.4 Scanning electmn micmscopy

The physical property and niolecular architecture of the polymer

support can be illustrated by using scanning electron microscopy. Guyout

et al. used SEM techtuque extensively for studying the morphological features

and the mechanism of formation of beaded polymers.",% Some rare

investigations also proceed in crosslinked polymer^.^^-^^ SEM has been used . .

as a tool for the determination of functional group distribution in the polymer ... , . . . . , . .

matrix by Grubbset ~ 1 . 4 4 ~.

The SEM pic&&. of 2 ntol%, DVB-crosslinked macroporous and . ( L , , . . , "<..

microporous polystyrene ~chi f f base resin and its complexes are given in

Figures 3.10 and 3.1 1. The macroporous resins have large pores and cavities

compared with microporous resins. The 2 mol% TTEGDA-crosslinked

polystyrene-Schiff base resins is given in Figure 3.12. In all cases the surface

of the uncomplexed bead is smoother than that of complexed resins. The

rough surface of the beads appeared because of the rearrangement of the

polymer chains on complexation with metal ions.

Synthesis and Characferisefion of Polystyrene-supporfed SchiRBase-mefal Complexes 68

. .

Figure 3.1 0. ~i&nning electron micrographs of D VB (m ncroporous)-crosslin ked chloromethylated: (a) polystyrene, (b) polystyrene S c h w base and (c) polystyrene SchiJf base complek:

Synthesis and Characterisation of Polysfyrene-supported Schiff Basemeld Complexes 0 9

Figure 3.11. canning electron 3nicrogruphs oj D VB (microporous)-crosslinked dJoromethylated: (a) polystyrene, (b) polystyrene Schvf buse and (C)pbIVstj'r;ene Sfhi / / buse complcr .

Synthesis and Chmcierisetion of Polystyrenesuppo~ed Schiff Base-meld Complexes 70

-' ; .Figure 3.12. Scanning electron rnicrograplt s of ked , , ch lorornethylut~d~~~:~{u) polystyrene Sihiff base and (b) polystyrene

... . ,Schi/f b&e complex

References

1. R. B. Me*field, J. Am. Clrerri. Soc., 85,2149 (1963).

: 2. r. Hodge and. D. -C. Sherrington, (Eds.), P o l y ~ w Srlppwted Renctions in br@nic . . . ~ ~ i i N ~ c ~ i ~ , . ~ . i l e ~ , . . . New . York, 1980.

3. N. K. Mathur, C.'K. %rang, R. E. W i l l i a m s , Polylrrer as Aids ir~ Orgnnlc CLmi~by, Academic Press, ~ e w : ~ o r k , 1980.

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