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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
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