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Polymer International 47 (1998) 367È374
Copolymer–polyelectrolyte–homopolymer
Associations: Effects of Neighbouring
Comonomer Units and Copolymer
Structure on Interpolymer Complexation
Saroj K. Chatterjee* & Neeti Misra
Department of Chemistry, University of Delhi, Delhi 110007, India
(Received 5 January 1998 ; revised version received 25 February 1998 ; accepted 25 June 1998)
Abstract : Interpolymer interactions between acrylamideÈvinyl alcohol graft
copolymer with poly(ethyleneimine) (PEI) and non-ionic homopolymers, e.g.
poly(vinyl pyrrolidone) (PVP) and poly(ethylene oxide) (PEO), have been studied.
Some blends of binary homopolymer complexes having the same proportion of
interacting units as in copolymer complex have been prepared. Simple binary
complexes of PEI have also been prepared with individual non-ionic homopolymers, e.g. poly(acrylamide) (PAAm), poly(vinyl pyrrolidone) (PVP),
poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA). The stability constant
(K), degree of linkage (h) and related thermodynamic parameters, e.g. standard
free energy change (*GÖ), standard enthalpy change (*HÖ) and standard
entropy change (*SÖ) have been compared for the above three types of complexation systems using OsadaÏs method. The comparative study indicated considerable di†erences in the values of the parameters, which have been interpreted on
the basis of copolymer structure, presence of neighbouring comonomer units and
other non-ionic homopolymers. ( 1998 Society of Chemical Industry
Polym. Int. 47, 367È374 (1998)
Key words : graft copolymer ; poly(ethyleneimine) ; thermodynamic parameters ;
blends
acrylamideÈvinyl
alcohol
(AAm/VA)
with
poly(ethyleneimine) (PEI) and some non-ionic homopolymers, such as poly(vinyl pyrrolidone) (PVP) and
poly(ethylene oxide) (PEO). The thermodynamic
parameters, e.g. standard free energy change (*GÖ),
standard enthalpy change (*HÖ) and standard entropy
change (*SÖ) of the graft copolymer complex have been
compared with an equivalent blend of binary homopolymer complexes, keeping identical and stoichiometric proportions of di†erent interacting units in the
respective systems. Such a comparative study may possibly give an insight into the role of copolymer structure
on the stability and thermodynamic parameters of their
complexes. Also, one could complex individual nonionic homopolymers stoichiometrically with PEI. By
INTRODUCTION
Associations between polyelectrolytes and between
polyelectrolytes and non-ionic homopolymers have
been studied extensively during the last decade.1h8
Interpolymer interaction is an important Ðeld in
polymer science in view of the very wide applications of
these interaction products, particularly medically and
industrially.1,9 There is very little mention in the literature regarding three-component interactions involving
graft copolymer, polyelectrolyte and non-ionic homopolymers. Keeping this in mind, we have studied the
interaction of a typical graft copolymer, e.g.
* To whom all correspondence should be addressed.
367
( 1998 Society of Chemical Industry. Polymer International 0959È8103/98/$17.50
Printed in Great Britain
S. K. Chatterjee, N. Misra
368
comparing the thermodynamic parameters of these
simple binary homopolymer complexes with the
complex of a graft copolymer, it is expected that the
inÑuence of neighbouring comonomer units in the
copolymer chain will be reÑected in interpolymer
complex formation. In this report, an e†ort has been
made to correlate the behaviour of highly complex
three-component systems with simple binary systems of
which the detailed mechanisms of complexation are well
understood.
EXPERIMENTAL
Poly (acrylamide ) (PAAm )10,11
PAAm was prepared from acrylamide by free-radical
polymerization using 2,2@-azoisobutyronitrile (AIBN) as
initiator.10 The polymerization was carried out in
acetone medium in nitrogen atmosphere at 50¡C for
45 min. The polymer was obtained as a while solid that
was removed from the reaction mixture. It was washed
thoroughly with acetone and dried in vacuo. The viscosity average molecular weight (M1 ) of the polymer
g
was obtained from viscosity measurements in aqueous
medium using the equation :11
[g] \ 6É8 ] 10~4M1 0.66,
g
and found to be 1É2 ] 105 g mol~1.
from viscosity measurements in aqueous medium at
25¡C using the relation :15
[g] \ 6É76 ] 10~2M1 0.55
g
and was found to be 2É4 ] 104 g mol~1.
Acrylamide /vinyl alcohol (AAm /VA) graft
copolymer 16
Poly(vinyl alcohol) and acrylamide monomer were
taken in the ratio 1 : 5 (w/w) in aqueous solution, and
graft copolymerization was carried out using a
0É1 mol l~1 solution of cerric ammonium nitrate in 1 M
HNO as initiator. The polymerization was carried out
3
in nitrogen atmosphere at 20¡C for 50 min. The reaction
mixture was poured into an excess of acetone and the
graft copolymer was obtained as a white solid that was
separated, dried and powdered.
The graft copolymer was characterized by means of
electrometric titration with PEI and poly(methacrylic
acid) (PMA) solutions of known concentrations.17 The
composition was found to be 0É55 : 0É45 (i.e. 55 mol% of
AAm units and 45 mol% of VA units).
Solvent
For all experimental measurements twice distilled water
was used as solvent.
pH measurements
Poly (vinyl alcohol ) (PVA )12
PEI was supplied by BDH Chemicals Ltd., Poole, UK,
in the form of 50% viscous water solution. The number
average molecular weight (M1 ) of PEI was determined
n
from osmotic pressure measurements using PoldermanÏs
method13 and found to be 1É5 ] 105 g mol~1.
Measurements of pH were carried out with PTA digital
pH meter using a combination electrode. For thermodynamic studies the solution was taken in a waterjacketed cell and temperature was controlled with in
^0É1¡C by circulating thermostatically controlled
water. The concentration of each polymer solution (in
unit moles per litre) was 1 ] 10~3 um l~1. At these concentrations, the complexes did not precipitate.
For pH titrations, the concentration of graft copolymer and non-ionic homopolymer was taken as
1 ] 10~3 um l~1 and the concentration of titrant
polymer (e.g. PEI) was taken as 1 ] 10~2 um l~1.
Poly (ethylene oxide ) (PEO )
Viscosity
PEO was supplied by Iwai Karu Co. Ltd., Japan, in the
form of white crystalline Ñakes readily soluble in water.
The viscosity average molecular weight (M1 ) was deterg
mined from viscosity measurements14 in aqueous
medium at 25¡C, and was found to be
1É9 ] 104 g mol~1.
Viscosity measurements were carried out at
30 ^ 0É05¡C using an Ubbelohde viscometer for which
the kinetic energy correction was negligible. The concentration of the solutions in viscometer was of the
order of 1 ] 10~4 um l~1 and the concentration of
titrant solution was 1 ] 10~3 um l~1.
Poly (vinyl pyrrolidone ) (PVP )
Infrared spectra
PVP was supplied by Fluka, USA, in the form of a
white crystalline powder readily soluble in water. The
viscosity average molecular weight (M1 ) was determined
g
The infrared spectra of the interpolymer complexes
were recorded with a Perkin Elmer Spectrum 2000
FTIR spectrometer.
PVA was obtained from Fluka, Buchs, Switzerland. The
weight
average
molecular
weight
M1
was
w
1É5 ] 104 g mol~1.
Poly (ethyleneimine ) (PEI )
POLYMER INTERNATIONAL VOL. 47, NO. 3, 1998
CopolymerÈpolyelectrolyteÈhomopolymer associations
RESULTS AND DISCUSSION
An acrylamideÈvinyl alcohol graft copolymer (AAm/
VA) has been prepared and characterized by known
methods, and its interaction with a typical polyelectrolyte, e.g. poly(ethyleneimine) (PEI), and some
non-ionic
homopolymers,
such
as
poly(vinyl
pyrrolidone) (PVP) and poly(ethylene oxide) (PEO),
have been studied. The stability and related thermodynamic parameters e.g. standard free energy change
(*GÖ), standard enthalpy change (*HÖ) and standard
entropy change (*SÖ) of the graft copolymer complex
have been determined using OsadaÏs method.18h20 With
a view to understand the inÑuence of copolymer
structure and neighbouring interacting units in the
copolymer chain on the stability and thermodynamic
parameters of their complexes, it was considered of
interest also to study complex formation of blends of
simple homopolymer complexes of stoichiometry identical to that of graft copolymer complex, e.g.
(PAAm ] PEI) ] (PVP ] PEI) ] (PVA ] PEI) ] (PEO
] PEI). One could also study interpolymer complex
formation involving individual homopolymers (e.g.
PAAm, PVP, PEO and PVA) with PEI. Comparison of
stability constants and thermodynamic parameters of
these three categories of systems, may possibly give an
insight into the role of copolymer structure and neighbouring interacting units in the copolymer chain on
interpolymer complex formation.
The graft copolymer AAm/VA has been found to
have 0É55 unit mole (um) of AAm units and 0É45 um of
VA units. The following complexation systems were
studied :
(I) Graft copolymer complex : 1 um of AAm/VA graft
copolymer ] 2 um PEI ] 0É5 um PVP ] 0É5 um
PEO.
(II) Polymer blend complex : (0É55 um PAAm ] 0É55 um
PEI) ] (0É45 um PVA ] 0É45 um PEI) ] (0É5 um
PVP ] 0É5 um PEI) ] (0É5 um PEO ] 0É5 um
PEI).
(III) Individual binary complexes of homopolymers :
(a) 1 um PAAm ] 1 um PEI
(b) 1 um PVP ] 1 um PEI
(c) 1 um PEO ] 1 um PEI
(d) 1 um PVA ] 1 um PEI
The pairs of interacting units in complexation
systems I and II are identical and are present in the
same stoichiometric proportions in the two systems.
The pairs of interacting units are : AAmÈEI, VAÈEI,
VPÈEI and EOÈEI.
The basic di†erence between complexation systems I
and II is the presence of di†erent pairs of neighbouring
comonomer units in system I, whereas in system II,
which is a blend of several binary homopolymer complexes, the neighbouring comonomer units are identical.
The inÑuence of copolymer structure and pairs of disPOLYMER INTERNATIONAL VOL. 47, NO. 3, 1998
369
similar neighbouring comonomer units could be reÑected if one compares the stabilities and thermodynamic
parameters of the two systems.
The stability constant K and related thermodynamic
parameters, e.g. *GÖ, *HÖ and *SÖ, have been determined for complexation systems I and II, by using the
following equations from OsadaÏs method.18h20 The
method involves determination of the degree of linkage
(h), which is deÐned as the ratio of binding groups to
the total number of potentially interacting groups. The
stability constant K is related to h by :
h \ 1 [ ([H`]/[H`] )2
(1)
0
K \ h/C (1 [ h)2
(2)
0
where C is the initial concentration of graft copolymer
0
(system I) or mixture of homopolymers (e.g.
PAAm ] PVP ] PEO ] PVA) (system II) or individual non-ionic homopolymers (system III) in unit
mol l~1, and [H`] and [H`] are the proton concen0
trations in the above polymer solutions in the presence
and absence of complementary polymers respectively, as
indicated in systems I, II and III.
The thermodynamic parameter *HÖ can be calculated for the interpolymer complexes from the temperature dependence of K by using eqn (4). K was
calculated at a given temperature by using eqn (2), and
by substituting the value obtained in eqn (3), the corresponding value of *GÖ could be found. The values of
*HÖ and *GÖ at a given temperature calculated as
mentioned above, could be substituted in eqn (5) to
obtain *SÖ
*GÖ \ [RT ln K
d(ln K)/d(1/T ) \ [*HÖ/R
*SÖ \ [(*GÖ [ *HÖ)/T
(3)
(4)
(5)
where *GÖ is the change in the standard free energy
and R is the molar gas constant. Values of the stability
constant K calculated on the basis of OsadaÏs eqns (1
and 2) for complexation systems I, II and III, indicated
the following trend at all temperatures :
ln K(graft copolymerÈPEI complex)
System I
[ ln K (blend of binary complexes)
System II
[ ln K (homopolymerÈPEI complex)
System III
The above trend was observed for most of the
homopolymerÈPEI complexes, except in the case of
PAAmÈPEI complex, where it was observed only above
45¡C. The following trends were observed by comparing
the stability constants of various homopolymerÈPEI
complexes :
370
S. K. Chatterjee, N. Misra
Below 40ÄC : ln K(PAAmÈPEI complex) [
ln K(PVAÈPEI complex) [ ln K(PVPÈPEI complex)
[ ln K(PEOÈPEI complex).
Above 40ÄC : ln K(PAAmÈPEI complex) [
ln K(PVPÈPEI complex) [ ln K(PVAÈPEI complex)
[ ln K(PEOÈPEI complex).
The reversal of trend above 40¡C between PVPÈPEI
complex and PVAÈPEI complex, could possibly be
attributed to greater hydrophobic interactions of VP
units at higher temperatures.
Interestingly, the relative complexation ability of different non-ionic homopolymers with respect to PEI is
di†erent from that observed with respect to PMA, e.g.
PAAm [ PVA [ PVP [ PEO with respect to PEI but
PAAm [ PVP [ PEO [ PVA with respect to PMA.
The trend with respect to PMA was observed by Tsuchida and co-workers,21 and they interpreted it on the
basis of a speciÐc mechanism between the units of the
interacting pair. Therefore, one can infer that the
mechanism of interactions between the units in the case
of PEI could be di†erent. This will be taken up in a
subsequent discussion in the later part of this paper.
The stability of the graft-copolymerÈPEIÈnon-ionic
homopolymer complex (System I) was relatively higher
than the stability of blend complex (System II). This
trend was di†erent from the trend observed in the
systems involving complex of graft copolymer with only
PEI and its corresponding blend of binary homopolymer complexes,17 where the graft copolymerÈPEI
complex was found to be less stable than its corresponding blend. Therefore, it is obvious that introduction of non-ionic homopolymers (e.g. PVP, PEO)
imparts more stability to the graft copolymer complex
as compared to the blend complex. This could probably
be due to the fact that PVP and PEO interactions with
PEI are fairly strong and secondly the hydrophobicity
of PVP units is contributing to the total stability of the
complex. Moreover, the structure of graft copolymer
complex is more interpenetrating as three dissimilar
units are getting attached to PEI, whereas in the blend
of homopolymer complexes, identical units in a
sequence are likely to be attached to the PEI chain.
Therefore, one would expect some neighbouring group
inÑuence on the interaction between units in the graft
copolymer complex. The greater stability of the graft
copolymer complex could also be attributed to the
entanglement of interacting units in the branched chains
of graft copolymer (AAm/VA).
The standard enthalpy and entropy changes for the
complexation systems I and II have been calculated at
several temperatures using the equations mentioned
earlier. The plots of *HÖ versus T and *SÖ versus T
for complexes I and II are depicted in Figs 1 and 2,
respectively. Complex I showed three distinct maxima
in both *HÖ versus T and *SÖ versus T curves (cf.
curves 1 of Figs 1 and 2), whereas complex II showed
Fig. 1. Temperature dependence of standard enthalpy change
*HÖ for complexation systems I (curve 1) and II (curve 2).
only two maxima in the respective curves. The values of
the di†erent maxima observed for complexes I and II
are tabulated in Table 1.
Because of the nature of secondary binding forces the
destabilization of various pairs of interacting units is
Fig. 2. Temperature dependence of standard entropy change
*SÖ for complexation systems I (curve 1) and II (curve 2).
POLYMER INTERNATIONAL VOL. 47, NO. 3, 1998
CopolymerÈpolyelectrolyteÈhomopolymer associations
371
TABLE 1. The maximum values of DH Ö and DS Ö observed for complexation systems I and II
Maxima observed in DH Ö (kcal molÉ1)
Complexation
systems
DH
Ia
IIb
DH
1
É6·42
(22·5¡C)
37·05
(27·5¡C)
DH
2
3·45
(32·5¡C)
22·39
(42·5¡C)
Maxima observed in DS Ö (cal molÉ1 KÉ1)
DS
3
21·98
(42·5¡C)
DS
1
19·25
(22·5¡C)
148·24
(27·5¡C)
DS
2
50·92
(32·5¡C)
97·62
(42·5¡C)
3
109·94
(42·5¡C)
a (1·0 um graft cop. AAm/VA) ½ (2·0 um PEI ½ 0·5 um PVP ½ 0·5 um PEO).
b Í0·55 um PAAm ½ 0·55 um PEIË ½ Í0·45 um PVA ½ 0·45 um PEIË ½ Í0·5 um PVP ½ 0·5 um PEIË ½ Í0·5 um
PEO ½ 0·5 um PEIË
likely to occur at di†erent temperatures. Thus, the
maxima observed at di†erent temperatures could be
assigned to the destabilization of di†erent pairs of interacting units. Because the number of pairs of interacting
units is four (see above) in both complexation systems I
and II, it is obvious that destabilizations of some pairs
of interacting units overlap and thus are indicated by
one maximum. On the basis of the observed trend in
stability constants of the various complexes, it may be
possible to assign the Ðrst maximum (*HÖ at 22É5¡C) to
the destabilization of relatively weaker pairs of interacting units, e.g. VPÈEI and EOÈEI. The second and
third maxima observed at 32É5¡C and 42É5¡C may similarly be assigned to destabilization of VAÈEI and
AAmÈEI pairs, respectively (see curve 1 of Fig. 1).
However, in the case of polymer blend complex II, only
two distinct maxima were observed at 27É5¡C and
42É5¡C. In this system where several binary complexes
are mixed, destabilizations of three interacting pairs
VAÈEI, VPÈEI and EOÈEI) seem to overlap and are
possibly indicated by the steep maximum at 27É5¡C.
The second maximum observed at 42É5¡C, may be
assigned to the destabilization of the strongest interacting pair AAmÈEI. These assignments have been
carried out on the basis of temperatures at which
maxima have been observed in the two systems I and
II. Further evidence will be given in the later part of
this discussion by comparing *HÖ or *SÖ versus T
curves of individual binary homopolymer complexes
(system III) with the corresponding curves of complexes I and II. The corresponding *SÖ versus T curves
for both systems I and II showed the same features
as *HÖ versus T curves (compare curves 1 and 2 of
Figs 1 and 2).
Figures 3 and 4 show the *HÖ and *SÖ versus T
curves for the four individual binary systems PEIÈ
PAAm, PEIÈPVP, PEIÈPEO and PEIÈPVA. In each of
these curves two distinct maxima are observed. The
absolute values of *HÖ or *SÖ of the various
maximum and the corresponding temperatures at which
they were observed are tabulated in Table 2. Obviously,
a two-stage destabilization of complexes is indicated.
The multi-stage complexation of PEI with various nonionic homopolymers could be attributed to the
branched structure of PEI.22 Although linear PEI contains almost only secondary amine groups with coordination number two, branched PEI contains, in addition
to secondary groups, signiÐcant fractions of primary
terminal groups and tertiary amine groups on the
branched points, so that ionizable groups have coordination numbers one, two and three. It should be
pointed out that these multi-stage interactions could be
observed only in the case of individual non-ionic homopolymers.
However, in the case of graft copolymerÈPEI interactions, or in the case of blends of binary homopolymer
TABLE 2. The maximum values of DH Ö and DS Ö observed for complexation system III
Complexation system
Maxima observed in DH Ö (kcal molÉ1)
DH
1·0 um PAAm ½ 1·0 um PEI
1·0um PVP ½ 1·0 um PEI
1·0 um PEO ½ 1·0 um PEI
1·0 um PVA ½ 1·0 um PEI
1
É22·68
(22·5¡C)
13·68
(22·5¡C)
5·8
(22·5¡C)
19·6
(17·5¡C)
POLYMER INTERNATIONAL VOL. 47, NO. 3, 1998
DH
2
18·65
(42·5¡C)
53·55
(37·5¡C)
38·64
(32·5¡C)
É3·66
(32·5¡C)
Maxima observed in DS Ö (cal molÉ1 KÉ1)
DS
1
É47·05
(22·5¡C)
68·37
(22·5¡C)
33·36
(22·5¡C)
90·32
(17·5¡C)
DS
2
85·86
(42·5¡C)
193·54
(37·5¡C)
141·09
(32·0¡C)
10·39
(32·5¡C)
372
S. K. Chatterjee, N. Misra
Fig. 3. Temperature dependence of standard enthalpy change
*HÖ for the systems PAAm ] PEI (curve 1), PVA ] PEI
(curve 2), PVP ] PEI (curve 3) and PEO ] PEI (curve 4).
Fig. 4. Temperature dependence of standard entropy change
*SÖ for systems PAAm ] PEI (curve 1), PVA ] PEI (curve
2), PVP ] PEI (curve 3) and PEO ] PEI (curve 4).
systems, these multi-stage interactions of PEI with the
respective units were not observed, perhaps because of
the presence of other comonomer units or interacting
units in complexes I and II. Because di†erent EI units of
PEI, are destabilized at di†erent temperatures, it is
likely that the multi-stage interactions observed in the
case of individual homopolymers may merge in the
presence of di†erent comonomer units. However, some
correlations could be seen by comparing the *HÖ
versus T curves of individual homopolymer complexes
with those of the complexes of graft copolymer and
polymer blend. In other words, this assignment of
various maxima to destabilizations of di†erent interacting pairs at speciÐc temperatures substantiates the
evidence obtained from the observed maxima at the
same temperatures for complexes of PEI with individual
non-ionic homopolymers.
It must be admitted that although these interpretations look reasonable there still exists some uncertainty
regarding the variations of *HÖ or *SÖ versus T . The
observed variations have been found to be much greater
than the calculated experimental error in such measurements. Some unequivocal evidence as to whether these
interpretations will hold good or not could possibly be
provided from measurements of some independent
physical properties during complex formation, and
these are presented in the subsequent part of this discussion.
Figures 5 and 6 show the variations of pH and
reduced viscosity (g /c) of the individual homopolymer
sp
solutions PAAm, PVP, PEO and PVA with increasing
addition of PEI solution expressed in unit mole ratios
(umr). In each of these curves, distinct breaks have been
observed at 0É25 : 1É0, 0É5 : 1É0, 0É75 : 1É0, 1É0 : 1É0 unit
mole ratios of [PEI] : [homopolymer] which could be
related to speciÐc stoichiometries of the complex, i.e.
1 : 4, 1 : 2, 3 : 4 and 1 : 1 complexes between PEI and
the respective homopolymers. The excellent correlation
of the di†erent stages of interaction between component
polymers observed from these two independent physical
properties, could provide unequivocal evidence of the
interaction between the units. The interaction of PEI
with di†erent non-ionic homopolymers in distinct steps
as observed from these two independent physical
properties, once again indicates that the branched PEI
chains have primary, secondary and tertiary amine
structures which may be responsible for the multi-stage
interaction of non-ionic homopolymers with PEI.
Figure 7, shows the variations of pH of graft copolymer and a mixture of non-ionic homopolymers of two
di†erent compositions upon the addition of PEI solution in small instalments. These curves reveal distinct
breaks at speciÐc stoichiometries, but in the mixtures of
POLYMER INTERNATIONAL VOL. 47, NO. 3, 1998
CopolymerÈpolyelectrolyteÈhomopolymer associations
373
Fig. 6. Variation of g /c with unit mole ratio (umr) of [PEI]/
sp
[PAAm] (curve 1), [PEI]/[PVP] (curve 2) and [PEI/PEO]
(curve 3).
Fig. 5. Variation of pH with unit mole ratio (umr) [PEI]/
[PAAm] (curve 1), [PEI]/[PVA] (curve 2), [PEI]/[PVP]
(curve 3) and [PEI]/[PEO] (curve 4).
non-ionic homopolymers it was difficult to distinguish
between the stages corresponding to PEOÈPEI and
PVAÈPEI interactions. The unit mole ratios (umr) at
which these distinct breaks were observed and the cor-
responding stoichiometries assigned to them are summarized in Table 3. This provides, once again
unequivocal evidence for the interactions of di†erent
pairs of units.
Additional evidence of the involvement of various
functional group during complex formation could be
provided by comparing the IR spectrum of the PAAmÈ
PEI complex with the spectra of its pure components.
The l
frequency for PEI observed at 1580 cm~1,
NhH
shifted to 1620 cm~1 for the complex. The l
(str.)
C/O
TABLE 3. Breaks observed in pH versus umr curves and probable stoichiometries
assigned to complexation systems I and II
Complexation system
Breaks observed (umr)
Probable stoichiometries
1·0 um graft cop. AAm/VA ½ 2·0 um
PEI ½ 0·5 um PVP ½ 0·5 um PEO
½ X’s PEO
0·28
0·55
1·00
2·00
2·50
AAm : EI (2 : 1)
AAm : EI (1 : 1)
VA : EI (1 : 1)
Excess PEI (1 um)
VP : EI (1 : 1)
Í0·55 um PAAm ½ 0·45 um PVA ½
0·5 um PVP ½ 0·5 um PEOË ½
(2·0 um ½ X’s) PEI
0·14
0·28
0·52
1·00
AAm : EI (2 : 1)
AAm : EI (1 : 1)
VP : EI (1 : 1)
VA : EI (1 : 1) ½ EO : EI (1 : 1)
Í0·55 um PAAm ½ 0·50 um PVA ½
0·70 um PVP ½ 0·25 um PEOË ½
(2·0 um ½ X’s) PEI
0·14
0·28
0·63
1·00
AAm : EI (2 : 1)
AAm : EI (1 : 1)
VP : EI (1 : 1)
VA : EI (1 : 1)
VA : EI (1 : 1) ½ EO : EI (1 : 1)
POLYMER INTERNATIONAL VOL. 47, NO. 3, 1998
S. K. Chatterjee, N. Misra
374
Fig. 7. Variation of pH with unit mole ratio (umr) for complexation systems I (curve 1) and II (curve 2).
frequency of PAAm observed at 1680 cm~1 shifted to
1660 cm~1 for the 1 : 1 complex. The distinct shift in
group frequency unequivocally indicates the involvement of various functional groups during complex formation.
In conclusion, it can be said that the graft copolymer
AAm/VA forms a relatively more stable complex than
both binary homopolymer complexes and blends of
homopolymer complexes. This is attributable to the
neighbouring groups inÑuence, the speciÐc structural
e†ect of the copolymer, and the presence of non-ionic
homopolymers.
ACKNOWLEDGEMENT
The authors are grateful to CSIR, India for providing
Neeti Misra with a research fellowship.
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POLYMER INTERNATIONAL VOL. 47, NO. 3, 1998
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