Synthesis and Characterisation Pyrrolidone Copolymers...
Transcript of Synthesis and Characterisation Pyrrolidone Copolymers...
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