Role of hydrophobicity on structure of polymer-metal complexes

Article abstract of DOI:10.1021/jp002310+

Metal complexation of a series of polymeric gels, with different degrees of ionization, prepared from acrylic acid and acryloyl amino acid monomers (CH₂=CHCONH(CH₂)_nCOOH, where n = 4, 6 and 8), were investigated. The binding of Cu(II) ions to the gels was studied by means of swelling, quantitative determination of the amount of "bound" or complexed Cu(II), and EPR spectroscopy of Cu(II) complexes. Both the amount of Cu(II) and the structure of polymer-Cu(II) complex were influenced by the length of the pendent chain, i.e., "hydrophobicity" of the polymer gels. The metal uptake by the gels increases with increasing "hydrophobicity". Two types of polymer-Cu(II) complexes (monomer and dimer, respectively) were identified by EPR spectroscopy, their concentrations were found to be a function of hydrophilic-hydrophobic balance of the polymer gels.

Full text of DOI:10.1021/jp002310+

5368
J. Phys. Chem. B 2001, 105, 5368-5373
ARTICLES
Role of Hydrophobicity on Structure of Polymer-Metal Complexes
†
†
,†
,‡
Shyni Varghese, Ashish K. Lele, D. Srinivas,* and Raghunath A. Mashelkar*
National Chemical Laboratory, Pune 411008, India, and Council of Scientific and Industrial Research,
Anusandhan BhaVan, New Delhi 110001, India
ReceiVed: June 27, 2000; In Final Form: February 21, 2001
Metal complexation of a series of polymeric gels, with different degrees of ionization, prepared from acrylic
acid and acryloyl amino acid monomers (CH dCHCONH(CH ) COOH, where n ) 4, 6 and 8), were
2 2 n
investigated. The binding of Cu(II) ions to the gels was studied by means of swelling, quantitative determination
of the amount of “bound” or complexed Cu(II), and EPR spectroscopy of Cu(II) complexes. Both the amount
of Cu(II) and the structure of polymer-Cu(II) complex were influenced by the length of the pendent chain,
i.e., “hydrophobicity” of the polymer gels. The metal uptake by the gels increases with increasing
“
hydrophobicity”. Two types of polymer-Cu(II) complexes (monomer and dimer, respectively) were identified
by EPR spectroscopy, their concentrations were found to be a function of hydrophilic-hydrophobic balance
of the polymer gels.
Introduction
ature of thermoreversible gels by subtly modifying the hydro-
phobic-hydrophilic balance.
1
,18
Metal complexation is a process by which certain inorganic
metal ions coordinate with organic functional groups through
ionic bonds, coordination bonds, and ion dipole interactions to
form organometallic hybrids having many interesting properties
and applications. Metal complexation with polymers is used in
The hydrophilic and hydrophobic interactions in the gel also
influence the metal uptake by the gel. Lehto et al.19 found an
enhancement of metal uptake in N-isopropylacrylamide copoly-
mer gels containing ionic comonomers over that of the ho-
20
mopolymer gel. Sasaki et al. showed that the binding efficiency
1
-4
wastewater treatment for selective removal of toxic metal ions
and to improve the thermal properties of polymers.
2
+
of Ca to polyelectrolyte gels increased with an increase in
the hydrophobicity of the gels.
5
-7
An
important application of polymer-metal complexes is in the
area of catalysis. Catalytically active organic polymers can be
obtained through the coordination of certain transition metal
ions with functional groups on the polymers.8 Recently, metal-
complexed stimuli responsive polymer gels have been used to
produce smart catalysts, which combine the advantages of
homogeneous catalysis such as high activity and high selectivity
with those of heterogeneous catalysis such as long life and easy
There are very few reports on the understanding of the
influence of hydrophobic and hydrophilic interactions on the
structure of the polymer-metal complexes. Kruczala et al.21
reported two type of monomeric Cu(II)-poly(acrylic acid)s in
,9
2
+
which Cu was complexed with one or two carboxylic acid
2
2
groups on the polymer chains. El-Sonbati et al. reported the
formation of binuclear Cu(II) complexes with poly(5-vinylsali-
23
cyledene-2-aminopyridine). Schlick et al. reported the forma-
tion of Cu(II)-Cu(II) dimer in Nafion membranes. In this paper
we investigate specifically the influence of hydrophobic interac-
tions in a series of acrylic acid and acryloyl amino acid gels on
the structure of gel-Cu(II) complexes. Our goal is to design
potential organometallic hybrids with varying nuclearity. Ex-
amples of such hybrids include protein-supported copper
complexes, which are well-known catalysts for biological
10-12
separation.
The catalytic function of polymer-metal com-
plex depends on the structure of the complexes. In this paper
we investigate the role of “hydrophobicity” of polymer gels on
the structure of the metal-gel complexes.
The effect of mono-, di-, and polyvalent metal ions on the
13-16
swelling behavior of gels has been investigated earlier.
The
observed decrease in swelling capacity of polyelectrolyte gels
in the presence of mono- and divalent alkaline earth metal ions
is mainly due to the screening effect. However, the decrease in
swelling of gels in the presence of multivalent transition metal
ions is mainly due to complexation of the ions with the polymer
24
functions. The present study, therefore, would hopefully
provide insight into designing new polymeric catalysts based
on the understanding of the effect of molecular interactions on
the structure of the polymer-metal complex.
1
7
network, which increases its apparent cross-link density.
Transition metal ions also affect the volume transition temper-
Experimental Section
*
Corresponding authors. For D.S.: e-mail, srinivas@cata.ncl.res.in; fax,
Materials. Acrylic acid (AAc) and 8-aminocaprylic acid were
obtained from Aldrich Co. N,N′-methylenebis(acrylamide) (Bis-
Am, cross-linking agent), ammonium persulfate (APS, initiator),
N,N,N′,N′-tetramethylethylenediamine (TEMED, accelerator),
+
5
91-020-5893761. For R.A.M.: e-mail: dgcsir@csir.res.in; fax, +91-020-
893041.
†
‡
National Chemical Laboratory.
Council of Scientific and Industrial Research.
1
0.1021/jp002310+ CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/19/2001

Metal Complexation in Polymer Gels
J. Phys. Chem. B, Vol. 105, No. 23, 2001 5369
prepared by adjusting the pH of the reactants with aqueous
NaOH to 7.6 and 12.1, respectively. In the “partially ionized”
gels some of the carboxyl groups exist in their salt form, i.e.,
-
+
-
COO Na state. However, in the “fully ionized” gel most of
the carboxyl groups are in their salt form. This was verified by
using excess NaOH to ensure complete ionization of the
carboxyl groups and then measuring the swelling capacity of
the gel. Ionization increases the swelling capacity of the gel
due to the electrostatic repulsion between the charges on the
network. After complete ionization of all the carboxyl groups
in the gel, the swelling capacity of the gel remains unchanged.
The un-ionized gels were opaque, the partially ionized gels were
translucent, and the completely ionized gels were transparent.
Figure 1. Structures of the monomers used in the preparation of the
gels.
thionyl chloride, copper chloride (CuCl2), and sodium hydroxide
(NaOH) were all procured from S. D. Fine Chemicals, India.
4
-Aminobutyric acid and 6-aminocaproic acid were obtained
Complexation of Gels with Metal Ions. The complexation
of the gels with Cu(II) ions was carried out by the batch
equilibrium method. Dried gels were placed in CuCl2 solution
and allowed to equilibrate for 72 h. Metal uptake was in-
vestigated using a Shimadzu UV-420 UV-visible spectropho-
tometer. The concentrations of the metal ions before and after
complexation were estimated following the intensity of the d-d
band at 810 nm. For spectrophotometric estimation, standard
solutions of CuCl2 of different concentrations were prepared
and their absorbance was measured to plot a calibration curve.
The concentration of copper uptake by the gels was estimated
using this calibration curve and the copper content in gels is
listed in Table 1.
Swelling Ratio Measurements. Dried gels of known weights
were immersed in CuCl2 solutions (0.1 M) as well as in pure
water for 72 h until equilibrium swelling was achieved. Swelling
ratios of the gels were measured gravimetrically. The swelling
ratio (Q) was defined as the weight of the solvent uptake per
unit mass of the dried polymer.
from SRL, India.
Synthesis of Acryloyl Chloride. Acryloyl chloride was
2
5
synthesized by reacting acrylic acid with thionyl chloride. To
a mixture of 40.1 mL of acrylic acid (0.6 M) along with 3 mL
of dimethylformamide and 5 g hydroquinone was added
dropwise 46 mL of freshly distilled thionyl chloride, over a
period of 3 h. After complete addition of thionyl chloride, the
reaction mixture was maintained at 333 K for 6 h with
continuous stirring. Pure acryloyl chloride was distilled out at
3
43 K. Polymerization of the acryloyl chloride was prevented
by adding hydroquinone.
Synthesis of Monomers. The hydrophobic monomers were
synthesized by reacting the respective amino acids with acryl-
2
5
oyl chloride. The structures of the monomers are shown in
Figure 1.
Acryloyl-4-aminobutyric acid (A4ABA). A clear solution
of 4-aminobutyric acid (10.3 g, 0.1 M) in 80 mL of water
containing 4 g of NaOH was prepared, and to this was added
dropwise 9 mL (0.1 M) of acryloyl chloride in 9 mL of
dichloromethane over a period of 1-2 h at 278-283 K. While
adding acryloyl chloride, the pH of the solution was maintained
between 7.5 and 7.8. Dichloromethane and unreacted acryloyl
chloride were removed by extracting with ethyl acetate. The
clear aqueous layer was acidified to pH 5.0-5.5 and extracted
with ethyl acetate. The product in the ethyl acetate layer was
dried using anhydrous sodium sulfate and concentrated. The
concentrate was precipitated in petroleum ether. It was further
purified by dissolving in ethyl acetate and reprecipitating in
petroleum ether.
Q ) weight of the equilibrated gel
(
W )/weight of the dried gel (W )
s
d
EPR Studies. EPR spectra of the complexed gels were
recorded in the temperature range 77-298 K by using a Bruker
EMX spectrometer operating at X and Q-band frequencies. A
field modulation of 100 kHz was used. The microwave
frequency was calibrated with a frequency counter fixed in the
microwave bridge Bruker ER 041 XG-D and the magnetic field
was calibrated using a Bruker ER 035 M NMR Gaussmeter.
Spectral editing and simulations were done by using the Bruker
WINEPR and Simfonia software packages.
Other acryloyl-derivatized amino acids such as acryloyl-6-
aminocaproic acid (A6ACA) and acryloyl-8-aminocaprylic acid
(A8ACA) were synthesized by reacting acryloyl chloride with
respective amino acids as described above.
Synthesis of Gels. AAc, A4ABA, A6ACA, and A8ACA
homopolymer gels were synthesized by free radical polymeri-
zation of the respective monomers in water using Bis-Am as
cross-linker and APS as an initiator in the presence of TEMED
as an accelerator. To a well-stirred aqueous solution of 1 mol
of monomer, 10 mol % of cross-linking agent, and 40 mg of
initiatorwas added 50 µL accelerator. Nitrogen gas was continu-
ously bubbled through the solution. The homogeneous solution
so obtained was poured into glass test tubes and sealed.
Polymerization was carried out at 333 K for 24 h. After
polymerization the gel rods were taken out of the tubes and
immersed in water for 72 h to remove the unreacted reactants.
Fresh water was added frequently during washing. The washed
gels were dried in an oven at 323 K to constant weight. The
pH of this gel (hereafter referred to as “un-ionized gel”) was
Results and Discussion
When a weakly cross-linked gel is immersed in an aqueous
solution of CuCl2 (0.1 M), the Cu(II) ions bind to the polymeric
network and the gel attains a collapsed state, as indicated by
the swelling behavior tabulated in Table 1. The gel that is
equilibrated with the salt solution of the metal ion contains, in
general, two types of metal ions, those complexed with the
polymer chain and those simply osmotically absorbed along with
the solvent (water) in the gel matrix. The metal ions absorbed
by the polymer network can be estimated by assuming that the
concentration of metal ions outside the solution is equal to the
concentration of metal ions inside the gel. We have calculated
the amount of metal ions that are complexed with the polymeric
network by subtracting the absorbed quantity of metal ions from
the total metal uptake. The amount of metal ions absorbed into
the polymer network was calculated using the following
equation.
14
2
.6. The “un-ionized” gel is the acid form of the gel, which
means that carboxyl groups exist in non-ionized “-COOH”
state. The “partially ionized” and “completely ionized” gels were

5
370 J. Phys. Chem. B, Vol. 105, No. 23, 2001
Varghese et al.
dimeric
TABLE 1: Swelling Behavior of Polyacid Gels in Water and CuCl
2
Solutions
swelling ratio
in water (g/g)
swelling ratio
amt of Cu(II)
complexed (g mol/g)
% COOH groups
complexedb
monomeric
speciesc
a
a
c
gel
AAc(H)
AAc(Na/H)
AAc(Na)
A4ABA(H)
A4ABA(Na/H)
A4ABA(Na)
A6ACA(H)
A6ACA(Na/H)
A6ACA(Na)
A8ACA(Na)
in CuCl
2
(g/g)
species
-
-
-
-
-
-
-
-
-
-
4
3
2
5
4
4
5
4
4
4
4.4
16.3
24.8
1.1
24.9
98.8
1.0
2.3
4.9
4.8
1.0
1.1
1.0
1.0
1.9
1.0
1.0
1.2 × 10
1.7 × 10
1.3 × 10
5.0 × 10
9.3 × 10
9.9 × 10
5.4 × 10
2.4 × 10
9.8 × 10
9.8 × 10
1.6
24
26
1.6
28
30
1.8
32
36
d
d
d
d
d
d
d
d
d
d
d
d
d
d
147.0
230.0
d
d
40
a
b
Swelling measurements made 4 h after immersion in salt solution. % complexation ) 100(gram moles of metal ion compexed)/gram moles
-
c
d
of COO on dry gel. EPR studies. Present.
Figure 2. EPR spectra of Cu(II)-AAc gels as a function of degree of
ionization at 298 K.
AD ) C0V1
(1)
Figure 3. EPR spectra of monomeric Cu(II) species in A6ACA gels
as a function of degree of ionization at 298 K.
where AD is the moles of metal ions absorbed, C0 is the
concentration of the metal solution outside the gel, and V1 is
the amount of water picked up by gel. V1 can be estimated from
the swelling capacities reported in Table 1. In all gel systems it
was observed that a very small amount of metal ions was
absorbed by the polymer network while most of the metal ions
were coordinated with or “adsorbed” on the chains. Evidently,
the gels collapse in the presence of the metal ions, which serve
additional “cross-links” through interchain complexation. The
swelling ratio of the acid form of the gels (i.e., un-ionized gels)
in pure water decreased with the alkyl chain length, as shown
in Table 1. This is expected since the linear polymers having
longer alkyl side chains are more hydrophobic and hence absorb
less water. However, the salt form of the gels (i.e., ionized gels)
showed a reverse trend in that the swelling ratio increased with
the alkyl chain length. This seemingly anomalous swelling
behavior of the salt form of gels could be possibly due to two
reasons: The first reason pertains to the cross-link density of
the gels. Since we do not have direct control over the cross-
link density during polymerization, it is possible that gels with
longer alkyl side chains happen to have lower cross-link density
and hence swell more. The other possible reason could be that
the longer flexible side chains place the ionic charges at a finite
distance away from the main chain, because of which the
polymer chains are forced to adopt a more “open” configuration
2
6

Metal Complexation in Polymer Gels
J. Phys. Chem. B, Vol. 105, No. 23, 2001 5371
TABLE 2: EPR Spin Hamiltonian Parameters of Cu(II)
Complexed Polymer Gel
gel
species
g
II
g
⊥
g
av
A
II (G)
⊥
A (G)
AAc(H)
AAc(Na/H)
M1
M2
M3
M2′
M1
M1
M3
M1
2.356 2.076
2.325 2.082
128.8
a
2.119
2.133
150.5
AAc(Na)
A4ABA(H)
A4ABA(Na/H)
A4ABA(Na)
A6ACA(H)
2.360 2.088
2.358 2.085
2.328 2.083
2.367 2.082
2.264 2.071
2.264 2.065
2.355 2.081
2.352 2.081
125.2
119.8
150.2
119.1
159.7
159.7
119.1
120.1
a
a
a
16.0
12.9
12.9
16.0
a
′
M3
M3
′
A6ACA(Na/H)
A6ACA(Na)
A8ACA(Na)
M1
M1
a
Hyperfine features not resolved.
Figure 5. EPR spectra at Q-band frequency of (a) A6ACA gel and
(b) dimeric copper acetate monohydrate at 298 K.
of Ca2 to the polymer gel increased with the “hydrophobicity”
of the gel. This was attributed to the cooperative effect of
hydrophobicity and metal binding. The complexation of the
metal ions with the carboxylic groups increases the overall
hydrophobicity of the system since the metal-complexed car-
boxyl groups are not available to the water molecule. We have
reported this complexation-induced hydrophobicity and its effect
+
1
8
on volume phase transition in our earlier report. This com-
plexation-induced hydrophobicity drives the polymer chains to
attain a compact conformation and in turn enhances the metal
binding to the polymer chains.
It may also be noted that the percentage of carboxyl groups
involved in complexation is low for the un-ionized gels and
high for completely ionized gels for the same alkyl chain length.
This is simply due to the fact that the ionized carboxyl ions
can coordinate with the Cu(II) ions much more effectively than
the un-ionized carboxyl group.
Figure 4. EPR spectra at 298 K showing the effect of hydrophobic
alkyl chain length on Cu(II) species in the completely ionized Cu(II)
complexed AAc, A4ABA, A6ACA, and A8ACA gels.
We now show that the hydrophobicity also affects the
structure of the polymer-metal complex. X-band EPR spectra
of the complexed poly(acrylic acid) gels of different degrees
of ionization AAc(H), AAc(Na), and AAc(H/Na)) at 298 K are
shown in Figure 2. In general, two types of Cu(II), dimeric and
monomeric, species were detected in the EPR spectra. The
signals denoted by D around 230, 4800, and 6075 G correspond
to dimeric Cu(II) species, while those denoted by M1/M2 in
the region 2690-3600 G are attributed to monomeric species.
The nature of the EPR spectrum, i.e., the intensities of the dimer
signals and the spectral characteristics of the monomeric species,
are dependent on the degree of ionization. The resolved parallel
hyperfine features of the monomeric species in AAc(H) cor-
respond to a distorted molecular geometry for Cu(II). Only an
averaged signal was observed in the complexed gels of AAc-
in order to overcome the electrostatic repulsion; hence the higher
swelling capacity.
The percentage of carboxyl group involved in complexation
is defined as follows:
%
COOH group in complexation )
gram moles of metal ion complexed
100 ×
-
gram moles of COO on dry gel
Our experimental data in Table 1 indicate that as the alkyl
chain length of the gel increases, the percentage of COOH
groups involved in complexation increases. These findings are
similar to those of Sasaki et al.20 who observed that the binding

5372 J. Phys. Chem. B, Vol. 105, No. 23, 2001
Varghese et al.
contained both types of the monomeric species (M1 and M3′).
Hence, the EPR spectra reveal that the structure of the Cu(II)-
complexed gel changes with the degree of ionization.
The spin Hamiltonian parameters for the monomeric species
are listed in Table 2. It is apparent that three types of monomeric
Cu(II) species are formed, one exhibiting an average signal (M2;
gav ) 2.119) and the other two, M1 and M3/M3′, having
distorted molecular geometry.
The length of the pendent chain has a pronounced effect on
the nature of the copper(II) species. Figure 4 reveals this effect
on the EPR spectra of the fully ionized gels as a function of
alkyl chain length. As the alkyl chain length increases, larger
quantities of copper are seen to be present in the dimeric form
(D). The intensity of the dimer signals in the fully ionized gels
increases with the chain length in the order
AAc(Na) <<< A4ABA(Na) <<
A8ACA(Na) < A6ACA(Na)
The gel A6ACA (Na) appears to have an optimal alkyl chain
length to form the maximum amount of dimer species (D).
The spectrum of the dimer species at X-band (ν ) 9.75 GHz)
corresponds to axial symmetry, in which zero field splitting is
larger than the microwave quantum (hν). It is interesting to note
from the Q-band (ν ≈ 35 GHz) spectra that the dimer spectrum
(Figure 5a) matches well with that of dimeric copper acetate,
Cu(CH3COO)2‚2H2O complex (Figure 5b) wherein four acetate
groups bind two Cu(II) ions to form a dimeric copper complex.
This observation clearly indicates that on complexation four
strands of the polymer rearrange to form the Cu-Cu dimer
species in the polymer gel. Variable temperature studies on
A6ACA(Na) in the range 77-298 K indicated that the intensity
of dimer signals decreased, as shown in Figure 6, and the
monomeric signals were better resolved and more intense at
lower temperatures. This is in agreement with the antiferro-
magnetic coupling between the two copper(II) ions of the
dimeric species. Tentative structures of different Cu(II) com-
plexed gels are proposed in Figure 7. The spin Hamiltonian
parameters, especially g| ) 2.264 and A| ) 159.7 G, suggest a
distorted geometry around copper with oxygens or amide
nitrogen as the coordinating ligands. However, studies with poly-
(acrylamide) and poly(N-isopropylacrylamide) gels did not
reveal any complexation with Cu(II) ions, indicating that the
amide nitrogen is most probably not involved in complexation.
The formation of dimer species is also dependent on the
Figure 6. EPR spectra of Cu(II)-complexed A6ACA(Na) gels at (a)
98 K and (b) 80 K and (c) dotted portion of (b) in expanded scale.
2
(Na) and AAc(H/Na). In other words, the monomeric species
in AAc(H) (hereafter referred to as M1) has a geometry different
from that in AAc(Na) and AAc(H/Na) (hereafter referred to as
M2). The complexed gels of AAc(H/Na) contain a trace amount
of yet another monomer species M3.
Figure 3 shows the changes in the nature of the EPR spectrum
of the monomer as a function of ionization for A6ACA. The
monomeric species (M3′) in A6ACA(Na/H) is characterized by
g| ) 2.264, g⊥ ) 2.065, A| ) 159.7 G, and A⊥ ) 12.9 G, while
that in A6ACA(Na) (M1) is characterized by g| ) 2.355, g⊥ )
2
.081, A| ) 119.1 G, and A⊥ ) 16.0 G. The gel A6ACA(H)
Figure 7. Structures of monomeric and dimeric Cu(II) species in metal ion complexed gels.

Metal Complexation in Polymer Gels
J. Phys. Chem. B, Vol. 105, No. 23, 2001 5373
degree of ionization. In the case of acrylic acid gels, as shown
in Figure 2, the dimer species is relatively more abundant in
AAc(H) compared to that in gels AAc(H/Na) and AAc(Na).
Cu(II) in AAc(Na) is present mostly as a monomeric species.
Thus, as hydrophobicity decreases, the tendency to form dimeric
species also decreases. In the case of hydrophobic A4ABA gels,
the dimeric Cu(II) species was observed in the un-ionized as
well as in the partially ionized gels. Further, in the case of more
hydrophobic A6ACA gels the dimeric Cu(II) species was found
even in the completely ionized forms. These observations clearly
suggest that an “optimum hydrophobicity” (i.e., a balance of
hydrophilic and hydrophobic interactions) of the polymeric gel
is required to form dimeric species with Cu(II) ions. The data
in Table 1 show that swelling does not determine the structure
of the Cu(II) complexes. For example, both the acid as well as
the salt forms of the Cu(II)-complexed A6ACA gels showed
dimers irrespective of their swelling behavior. Moreover, we
have also observed that A6ACA gels of two different cross-
link densities, viz., 10% and 30%, showed identical EPR spectra
consistent with identical structures of Cu(II) complexes, although
their swelling capacities in water were 230 and 60 g/g,
respectively. Thus, we conclude that the structure of the complex
is not determined by the cross-link density but is certainly influ-
enced by the hydrophobic-hydrophilic balance of the polymer.
Acknowledgment. S.V. acknowledges the Council of Sci-
entific and Industrial Research, New Delhi, for the Senior
Research Fellowship.
References and Notes
(1) Tanaka, T.; Wang, C.; Pande, V.; Grosberg, A. Yu.; English, A.;
Masamune, S.; Gold, H.; Levy, R.; King, K. Faraday Discuss. 1996, 102,
201.
(2) Rivas, B. L.; Maturana, H A.; Molina. M. J.; Gomej-Anton, M.
R.; Rosa, M.; Pierola, I. F. J. Appl. Polym. Sci. 1998, 67, 1109.
(3) Tiera, M. J.; De Oliveira, V. A.; Burrows, H. D.; Da Graca Miguel,
M.; Neumann, M. G. Colloid Polym. Sci. 1998, 276, 206.
(4) Thompson, J. A.; Jarvinen, G. Filter. Sep. 1999, 36, 28.
(
5) Siyam, T.; Ashour, A. H.; Youssef, H. A. Polym. Int. 1999, 48,
799.
(
6) Bekturov, E. A.; Mammutbekov, G. K. Macromol. Chem. Phys.
1
997, 198, 81.
(
(
(
7) Jose, L.; Pillai, V. N. R. Macromol. Chem. Phys. 1996, 197, 2089.
8) Naoki, T. Shokubai 1998, 40, 536.
9) Yakura, N.; Kashiwada, T.; Hirai, H. Kobunshi Ronbunshu 1998,
55, 415.
(10) Bergbreiter, D. E.; Case, B. L.; Liu Y.-S.; Caraway, J. W.
Macromolecues 1998, 31, 6053.
11) Case, B. L.; Franchina, J G.; Liu, Y.-S.; Bergbreiter, D. E. Chem.
Ind. 1998, 75, 403.
(
(12) Bergbreiter, D. E. Catal. Today 1998, 42, 389.
(13) Starodoubtsev, S. G.; Khokhlov, A. R.; Sokolov, E. L.; Cho, B.
Macromolecules 1995, 28, 3930.
Conclusions
(14) Lee, W. F.; Hsu, C.-H. J. Appl. Polym. Sci. 1998, 69, 229.
(15) Liu, X.; Tong, Z.; Hu, O. Macromolecules 1995, 28, 3813.
We have investigated the effect of alkyl chain length on metal
complexation using a series of homopolymer gels having
different alkyl chain lengths varying from zero to seven. The
nature of the Cu(II) complexes and the number of COOH groups
involved in complexation were strongly dependent on alkyl
chain length or hydrophobicity of the gel. The EPR analysis
showed two types of complexes, dimeric and monomeric. The
present work gives an insight into the role of the hydrophobic-
hydrophilic balance on the molecular structure of the Cu(II)
complexed polyacids. It is known that encapsulation of copper
(
16) Budtova, T. V.; Belnikevich, N. G.; Suleimenov, I. E.; Frenkel, S.
Ya. Polymer 1993, 34, 5154.
(17) Budtova, T. V.; Navard, P. Macromolecules 1998, 31, 8845.
(
18) Varghese, S.; Lele, A. K.; Srinivas, D.; Mashelkar, R. A. J. Phys.
Chem. B 1999, 103, 9530.
19) Lehto, J.; Vaaramaa, K.; Vesterinen, E.; Tenhu, H. J. Appl. Polym.
(
Sci. 1998, 68, 355.
(20) Sasaki, S.; Yataki, K.; Maeda, H. Langmuir 1998, 14, 796.
(21) Kruczala, K.; Schlick, S. J. Phys. Chem. B 1999, 103, 1934.
(22) El-Sonbati, A. Z.; El-Binadary, A. A.; Diab, M. A.; El-Ela, M. A.;
Mazrouh, S. A. Polymer 1994, 35, 647.
(23) Schlick, S.; Alonso-Amigo, M. G.; Eaton, S. S. J. Phys. Chem.
27
acetate in zeolite cavities enhances the catalytic activity. Here
we present another innovative way of encapsulating metal
complexes within the polymer matrix. In principle, by this
method one should be able to design new catalysts for enhanced
catalytic activities. These gels could also find applications in
water purification, wherein the ability of the gels to form
complexes with the divalent metal ions, such as Pb(II), could
be used effectively.
1
989, 93, 7906.
(24) Solomon, E. I.; Tuczek, F.; Root, D. E.; Brown, C. A. Chem. ReV.
1994, 94, 827.
(25) Badiger, M. V.; Lele, A. K.; Bhalerao, V. S.; Varghese, S.;
Mashelkar, R. A. J. Chem. Phys. 1998, 109, 1175.
(
26) Varghese, S.; Lele, A. K.; Mashelkar, R. A. J. Chem. Phys. 2000,
12, 3063.
27) Chavan, S.; Srinivas, D.; Ratnasamy, P. Top. Catal. 2000, 11/12,
359.
1
(