World Applied Sciences Journal 16 (1): 119-125, 2012
ISSN 1818-4952
© IDOSI Publications, 2012
Graft Copolymerization Methacrylamide Monomer onto Carboxymethyl Cellulose
in Homogeneous Solution and Optimization of Effective Parameters
Mohammad Sadeghi, Nahid Ghasemi and Fatemeh Soliemani
Department of Chemistry, Science Faculty, Islamic Azad University, Arak Branch, Arak, Iran
Abstract: PolyMethacrylamide grafted onto Carboxymethyl cellulose (CMC) backbone in a homogeneous
solution using ceric ammonium nitrate(CAN) as an initiator and water as solvent. The structure of pure CMC
and grafted with monomers was characterized by FTIR spectra and TGA analysis. The thermal properties of
pure CMC and grafted with monomers were evaluated with a simultaneous thermal analysis system. The results
showed that the thermal stability of grafted MAAm samples was remarkably improved. The effects of various
reaction conditions such as monomer, polyssacharide, initiator concentration and reaction temperature on the
percentage of conversion (PC%), graft yield (G%) and graft efficiency (GE%) were investigated.
Key words: Carboxymethyl cellulose
Methylmethacrylate
INTRODUCTION
Graft
TGA analysis
resistance of the graft copolymer [5] and also the
subsequent alkaline hydrolysis of the grafting product to
obtain water absorbents [2,6].
The literature survey, however, reveals that few of
the modifications deal with chemical grafting of a premodified polysaccharide such as CMC. Ceric-initiated
grafting of vinyl monomers such as methyl acrylate, ethyl
acrylate and ethyl methacrylate [7,8], AN/methyl
methacrylate mixture [9], acrylamide (AAm) [10,11] and 4vinylpyridine [12,13] onto CMC has been reported.
Dimethylaminoethyl methacrylate (DMAEMA) [14],
AAm/DMAEMA mixture [15], AAm/dimethyloctyl(2methacryloxyethyl)ammonium bromide [16] and
diallyldimethylammonium chloride [17], has been grafted
onto CMC by L.-M. Zhang et al. [15-18]. using different
initiators. Acrylic acid has also been photografted onto
CMC [18]. In addition, N-vinyl-2-pyrrolidone [21] and its
mixture with AA [20] has been graft copolymerized onto
mixtures of CMC/hydroxyethylcellulose to prepare
cellulosic membrane with special biological effects.
However, to the best of our knowledge, no report has
been published on the optimization of MAAm graft
polymerization onto CMC using ceric-saccharide initiating
system. As a part of our research program on
polysaccharide modification, herewith we report the
optimized CAN-induced synthesis of CMC-gpolymethacrylamide under an inert atmosphere.
Cellulose is the most abundant, renewable
biopolymer and a very promising raw material available
at low cost for the preparation of various functional
polymers. Carboxymethylcellulose sodium salt (CMC) is
the first water soluble ionic derivative of cellulose
prepared in 1918 and produced commercially in the early
1920’s in Germany. It has been the most important ionic
cellulose ether with a worldwide annual production of
300,000 tons. It is widely used in pharmaceuticals,
detergents, cosmetics, foods, paper and textile industries
due to its viscosity-increasing and emulsifying properties
[1]. However, it may need to be further modified for some
special applications.
Among the diverse approaches that are possible for
modifying polysaccharides, grafting of synthetic polymer
is a convenient method to add new properties to a
polysaccharide with minimum loss of the initial properties
of the substrate [2]. Graft copolymerization of vinyl
monomers onto polysaccharides using free radical
initiation has attracted the interest of many scientists. Up
to now, considerable works have been devoted to the
grafting of vinyl monomers onto the substrates, specially
cellulose [3]. Of the monomers grafted, acrylonitrile (AN)
has been the most frequently used one, mainly due to its
highest grafting efficiency [2,4], improving the thermal
Corresponding Author: Mohammad Sadeghi, Department of Chemistry, Science Faculty, Islamic Azad University, Arak Branch,
Arak, Iran. Tel: +98-861-3670017, Fax: +98-861-3670017 .
119
World Appl. Sci. J., 16 (1): 119-125, 2012
Experimental
Materials: CMC sample (DS 0.52) was purched from
Merch Co. Methacrylamide (MAAm, Fluka), was used
after crystallization in acetone. Ceric ammonium nitrate
(CAN, Fluka) was used without purification. All other
chemicals were of analytical grade.
temperature for 48 h. After complete removal of the
homopolymer, the CMC-g-PMAAm was filtered, washed
with methanol and dried in oven at 50°C to reach a
constant weight [26].
Instrumental Analysis: Fourier transform infrared (FTIR)
spectroscopy absorption spectra of samples were taken in
KBr pellets, using an ABB Bomem MB-100 FTIR
spectrophotometer (Quebec, Canada), at room
temperature. Thermogravimetric analyses (TGA) were
performed on a Universal V4.1D TA Instruments (SDT
Q600) with 8-10 mg samples on a platinum pan under
nitrogen atmosphere. Experiments were performed at a
heating rate of 20 °C/min until 600 °C.
Preparation of Hydrogel: CMC solution was prepared in
a one-liter reactor equipped with mechanical stirrer and
gas inlet. CMC was dissolved in degassed distillated
water. In general, 0.50 g of CMC was dissolved in 30.0 mL
of distillated degassed water. The reactor was placed in a
water bath preset at 60°C. then a given volume of freshly
prepared solution of CAN(0.050 g in 2 mL water) as an
initiator was added to CMC solution and was allowed to
stir for 10 min at 60 °C. After adding initiator, variable
amounts of MAAm were added to the CMC solution and
the mixture was continuously stirred for one hour under
argon. The total volume of reaction was 35 mL. After 60
min., the reaction product was allowed to cool to ambient
temperature and methanol-water (500 mL) was added to
the product. After complete dewatering for 24 h, the
product was filtered, washed with fresh methanol (2×50
mL) and dried at 50 °C.
RESULTS AND DISCUSSION
Synthesis and Characterization: PMAAm monomers was
simultaneously grafted onto CMC in a homogenous
medium using CAN as a radical initiator and under an inert
atmosphere.
The mechanism of copolymerization of MAAm onto
CMC in the presence of initiator is shown in Scheme 1. In
the first step, the thermally dissociating initiator, i.e. CAN,
is decomposed under heating (65°C) and Then pair redox
ce3+-ce4+ disconnect C-C bond from the CMC backbones
to form corresponding macroinitiators. These
macroradicals initiate grafting of MAAm onto CMC
backbones leading to a graft copolymer.
Homopolymer Extraction: The graft copolymer, namely
CMC-g-PMAAm, was freed from poly methacrylamide
homopolymer, by pouring 0.50 g of the product in 50 mL
of ethanol solution. The mixture was stirred gently at room
OR
OR
OR
*
O
O
O
HO
OR
(Initiator) - Ce 3+
- H+
O
n*
OH
*
CONH2
MAAm
*
O
n*
(Propagation)
Me
n mol
O
OH
O
OR
(CAN)
.
O
O
Ce 4+
OR
OR
OR
OR
OR
OR
O
OR
O
O
O
HO
O
[
n *CONH2
Me
]
n-m[
Me
*
CONH2
]m
O
OH
O
OR
O
O
OR
O
OR
graft copolymer based on CMC-graft-PolyMAAm
Scheme 1: A brief proposed mechanism for ceric-induced grafting of Methacrylamide onto CMC.
120
n*
OR
World Appl. Sci. J., 16 (1): 119-125, 2012
Fig. 1: FTIR spectra of (a) pure CMC and (b) CMC-g-poly(methacrylamide) copolymer.
Fig. 2: TGA thermograms of (A) pure CMC and (B) CMC-g-poly(methacrylamide) copolymer. Heating rate 20 °C/min,
under N2.
121
World Appl. Sci. J., 16 (1): 119-125, 2012
For identification of the hydrogel, infrared
spectroscopy was used. Figure 1 shows the IR
spectroscopy of CMC-g-PAAm hydrogel. The
superabsorbent hydrogel product comprises a CMC
backbone with side chains that carry carboxamide
functional groups that are evidenced by peaks at 1660
cm 1. In fact, In the spectrum of the hydrogel (Fig. 1-b),
new peaks are appeared at 3206 and 1660 cm 1 that may
be attributed to amide NH stretching, asymmetric and
symmetric amide NH bending, respectively [21].
where W3 and W4 are the dried weight of grafted CMC
after extraction and PMAAm homopolymer. Ethanol is a
good solvent for PMAAm as well as a precipitant for pure
CMC or grafted CMC, so the PMAAm homopolymer
could be easily separated from the rough products.
However, it seemed to be difficult to further separate the
unreacted CMC from the products and the right
separation methods are still in progress in my research. In
view of the modification intention, the unreacted CMC is
not very necessary to be separated from the products, so
the blends of unreacted CMC and the graft copolymer
CMC-g-Poly(MAAm) were actually obtained in this
research and their compositions were unknown. In several
studies on the grafting modification of polymer, the
unreacted substrate polymer and graft copolymer were
also not sep-arated from the products [15-17]. If the
unreacted CMC could be separated from the products, the
graft copolymer CMC-g-Poly(MAAm) with higher G%
could be obtained, but the values of PC% and GE% would
not be affected.
Thermogravimetric Analysis: TGA curves for pure CMC
and CMC-g-poly(methacrylamide) copolymer are shown
in Figure 2. The grafted CMC has shown improvement in
thermal stability as clear from TGA curve. The initial
decomposition temperature of the CMC on grafting was
increased from 168 to 402 °C with maximum decomposition
rate at 523 °C, in comparison to original decomposition
temperature of 325 °C of CMC. These observations have
clearly
indicated
that
grafting
of
CMC-gpoly(methacrylamide copolymer has improved the thermal
stability of CMC [24].
Optimization of the Reaction Conditions: In the present
investigation, the effect of concentration of CMC, CAN
and MAAm, along with reaction time and temperature was
studied, to optimize the reaction conditions. It may be
found from the related curves (next figures) that the
trends of the "changes" are similar for grafting parameters
Gr, GE and PC. The reason is the similar concepts applied
for defining the grafting parameters (Eqs. 1-3).
Characteristic andDetermination of Important-Grafting
Parameters: The percentage of conversion (%PC), graft
yield (%Gr) and graft efficiency (%GE) were evaluated
with the following weight-basis expressions as reported
by Fanta [13]:
From the increased weight, the percentage of
conversion (PC%) can be estimated as the following
equation:
PC% = 100 (W2-W0) / W1
Effect of Substrate Concentration: The effect of CMC
amount on the grafting reaction was studied at various
concentrations of CMC. The results are given in Figure 3.
Maximum grafting and the lowest homopolymer formation
was observed at 0.5 g (0.43 wt%) CMC, while others
reactants including, monomer, initiator and temperature
were kept constant. Beyond this value, both grafting yield
and graft efficiency values are considerably reduced. This
behavior is attributed to the availability of more grafting
sites for initiation of graft copolymerization at higher
concentration of the substrate (from 0.22 to 0.43 wt%
CMC). However, upon further increase in the substrate
concentration, increase in the reaction medium viscosity
restricts the movements of macroradicals leading to
decreased grafting ratio and graft efficiency values. It also
may be attributed to deactivation of the macroradical
growing chains (e.g., by transfer reactions, combination
and/or interaction with the primary radicals) soon after
their formation.
(1)
where W0, W1 and W2 designate the weight of CMC
substrate, MAAm monomer in feed and total weight
product (copolymer and homopolymer) respectively. In
this study, the value of W1 was fixed at 0.5 g. The rough
products were extracted by ethanol in a Soxhlet apparatus
at least 48 h for the complete removal of the homopolymer.
The graft yield (G%) and graft efficiency (GE%) are
estimated as follows [13]:
or
G% = 100 (W3-W0) / W0
(2)
GE% = 100 (W3-W0) / (W2-W0)
(3)
GE% = 100 (W3-W0) / (W4+ W3-W0)
122
World Appl. Sci. J., 16 (1): 119-125, 2012
Fig. 3: Effect percent weight of CMC on the grafting
parameters.
Reaction conditions: CAN 0.065 M, MAAm
0.50 mol/L, temperature 45°C, time 120 min.
Fig. 5: Effects of MAAm concentration on the graft
copolymerization.
Reaction conditions: CMC 0.43 wt%,CAN 0.06 M,
temperature 45°C, time 120 min.
Fig. 4: Effects of initiator concentration on the graft
copolymerization.
Reaction conditions: CMC 0.43 wt%, MAAm 0.50
mol/L, temperature 45°C, time 120 min.
Fig. 6: Effects of reaction temperature on the graft
copolymerization.
Reaction conditions: CMC 0.43 wt%,CAN 0.06 M,
MAAm 0.3 M, time 120 min
This observation is in close agreement with the
results obtained by other investigators [26-27].
Effect of MAAm Concentration: The copolymerization
of grafting MAAm onto CMC was carried out at
different Methacrylamide concentrations ranging
from 0.05 molL 1 to 0.5 molL 1. The effect of MAAm
concentration on the graft copolymerization is shown
in Figure 5. the increase in GE% is due to the fact
that more MAAm monomers are present to react with
CMC macroradicals with initially increasing MAAm
concentration, but with the further increase of
MAAm concentration after a critical value being
reached, the homopolymerization probability of
Methacrylamide increased, usually resulting in the
decrease of GE%. G% is a function of GE%, PC% and
monomer weight in feed (W 1). From the eqns (1), (2) and
(3), the relationship between G% and GE%, PC%, W 1 can
be deduced as the following equation:
Effect of Initiator Concentration: The grafting
dependence on CAN concentration can be concluded
from Figure 4. The highest grafting yield (417%) was
achieved at 0.06 mol/L of CAN where graft efficiency
content was 133%. Increased CAN concentration resulted
in more radical sites on the polysaccharide backbone that
in turn led to higher grafting yield and graft efficiency
values and lower homopolymer formation. However, since
the CAN initiator solution is used as dilute HNO3, at CAN
concentration higher than 0.06 mol/L, a more acidic pH
probably causes partially termination of the macroradicals
on CMC. As a result, increased free radicals on CMC are
compensated by partial termination of the macroradicals.
Thus G%r and GE% values were diminished at higher
amounts of the initiator [27].
G%=100 (W 1× PC × GE) / W 0
123
(4)
World Appl. Sci. J., 16 (1): 119-125, 2012
Enmasse the decrease of %G and %Ge with further
increase in the MAAm concentration may be explained as
follows: (a) preferential homopolymerization over graft
copolymerization, (b) increasing the viscosity of reaction
medium, which hinders the movement of free radicals and
(c) increase in the chance of chain transfer to monomer
molecules. Similar observations have been reported for
the grafting of ethyl acrylate onto cellulose [22] and
methyl acrylate onto starch [23].
2.
3.
4.
Effect of Reaction Temperature: The effect of reaction
temperature on the graft copolymerization was carried out
at different temperatures between 30 and 70°C and
keeping the other variables constant. As shown in
Figure 6, it is found that %G and %GE increase initially
and then decrease to some extent with further increase in
temperature. This is attributed to the fact that increasing
the temperature favours the activation of macroradicals as
well as accelerates the diffusion and mobility of the
monomers from the aqueous phase to the backbone.
However, a further increase in temperature decreases %G
and %GE parameters, which can be ascribed both to the
acceleration of termination reaction and to the increased
chance of chain transfer reaction, accounting for the
increase in the amount of homopolymers. This
observation indicates that the optimal reaction
temperature is 55°C. Similar behavior was observed in the
case of grafting of acrylic acid onto methyl cellulose [24]
and acrylamide onto xanthan gum [25].
5.
6.
7.
8.
9.
CONCLUSION
PolyMethacrylamide Groups were successfully
grafted onto the CMC backbone using CAN as an initiator
in water-HNO3 solution. The structural characterizations
by FTIR spectra have indicated the presence of PMAAm
units in the products. The study of FTIR spectra and
thermogravimetric analysis provide that the graft
copolymerization takes place. The main factors affecting
the grafting parameters, including concentration of the
initiator, monomer and CMC, reaction temperature was
studied in detail. The optimum reaction conditions were
found to be CAN 0.006 mol/L,MAAm 0.3 mol/L,CMC 0.43
%wt, reaction temperature 55°C. Under the optimized
conditions the grafting parameters were calculated to be
%G 632, %GE 164 and %PC 91.8 %.
10.
11.
12.
13.
REFERENCES
1.
14.
Heinze,
T.
and
T.
Liebert,
2001.
Unconventional
Methods
in
Cellulose
Functionalization. Prog. Polym. Sci., 26: 1689-1762.
124
Athawale, V.D. and S.C. Rathi, 1997. Role and
Relevance of Polarity and Solubility of Vinyl
Monomers in Graft Polymerization onto Starch. React.
Func. Polym., 34: 11-17.
Sandle, N.K., O.P.S. Verma and I.K. Varma, 1987.
Thermal Characterization of Starch-g-Acrylonitrile
Copolymers. Thermochim. Acta, 115: 189-198.
Athawale, V.D.
and
S.C.
Rathi, 1999.
Graft Polymerization: Starch as a Model Substrate.
J. Macromol. Sci. Rev. Macromol. Chem. Phys.,
C39(3): 445-480.
Hebeish, A. and J.T. Guthrie, 1981. The Chemistry
and Technology of Cellulosic Copolymers,
Springer: Berlin.
Okieimen, F.E. and D.E. Ogbeifun, 1996.
Graft Copolymerizations of Modified Cellulose:
Grafting of Methyl Acrylate Ethyl Acrylate and
Ethyl Methacrylate on Carboxymethyl Cellulose. Eur.
Polym. J., 32(3): 311-315.
Okieimen, F.E., 1998. Graft Copolymerization
of Vinyl Monomers on Cellulosic Materials. Angew.
Makromol. Chem., 260(1): 5-10.
Okieimen, F.E. and D.E. Ogbeifun, 1996.
Graft Copolymerizations of Modified Cellulose:
Grafting of Acrylonitrile and Methyl Methacrylate on
Carboxymethyl Cellulose. J. Appl. Polym. Sci.,
59: 981-986.
Deshmukh, S.R., K. Sudhakar and R.P. Singh, 1991.
Drag-Reduction Efficiency, Shear Stability and
Biodegradation Resistance of Carboxymethyl
Cellulose-Based and Starch-Based Copolymers.
J. Appl. Polym. Sci., 43: 1091-1101.
Okieimen, F.E., 2003. Preparation, Characterization
and Properties of Cellulose-Polyacrylamide Graft
Copolymers. J. Appl. Polym. Sci., 89: 913-923.
Leza, M.L., I. Casinos and G.M. Guzman, 1989.
Graft Copolymerization of 4-Vinylpyridine onto
Cellulosics: Effect of Temperature. Eur. Polym. J.,
25(12): 1193-1196.
Fanta, G.F. and W.M. Doane, 1986. Grafted Starches.
In Modified Starches: Properties and Uses;
O.B. Wurzburg, Ed.; CRC Press: Boca Raton (Florida),
pp: 149-178.
Leza, M.L., I. Casinos and G.M. Guzman, 1990.
Graft Copolymerization of 4-Vinylpyridine onto
Cellulosics: Effects of Stirring and Inorganic Salts.
Brit. Polym. J., 23: 341-346.
Zhang,
L.M.
and
Y.B.
Tan, 2000.
Graft Copolymerization of 2-(Dimethylamino)ethyl
Methacrylate onto Carboxymethylated Cellulose.
Macromol. Mater. Eng., 280/281: 59-65.
World Appl. Sci. J., 16 (1): 119-125, 2012
15. Tan, Y., L. Zhang and Z. Li, 1998. Synthesis and
Characterization of New Amphoteric Graft Copolymer
of Sodium Carboxymethylcellulose with Acrylamide
and Dimethylaminoethyl Methacrylate. J. Appl.
Polym. Sci., 69: 879-885.
16. Zhang, J., L.M. Zhang and Z.M. Li, 2000.
Synthesis and Aqueous Solution Properties of
Hydrophobically Modified Graft Copolymer of
Sodium Carboxymethyl Cellulose with Acrylamide
and Dimethyloctyl(2-methacryloxyethyl)ammonium
Bromide. J. Appl. Polym. Sci., 78: 537-542.
17. Zhang, L.M., 2000. Modification of Sodium
Carboxymethylcellulose
by
Grafting
of
Diallyldimethylammonium Chloride. Macromol.
Mater. Eng., 280/281: 66-70.
18. Kuwabara, S. and H. Kuboka, 1996. Water-Absorbing
Characteristics
of
Acrylic
Acid-Grafted
Carboxymethyl
Cellulose
Synthesized
by
Photografting. J. Appl. Polym. Sci., 60: 1965-1970.
19. Ibrahim, M.M., E.M. Flefel and W.K. El-Zawawy,
2002. Cellulose Membranes Grafted with Vinyl
Monomers in Homogeneous System. J. Appl. Polym.
Sci., 84: 2629-2638.
20. Flefel, E.M.
and
M.M.
Ibrahim, 2002.
W.K. El-Zawawy and Ali, A.M. Graft
Copolymerization of N-vinylpyrrolidone and
Acrylamide
on
Cellulose
Derivatives:
Synthesis, Characterization and Study of Their
Biological Effect. Polym. Adv. Technol., 13: 541-547.
21. Berlin, A.A. and V.N. Kislenco, 1992. Kinetics and
Mechanism of Radical Graft Polymerization of
Monomers onto Polysaccharides. Prog. Polym. Sci.,
17: 765-825.
22. Pourjavadi, A. and M.J. Zohuriaan-Mehr, 2002.
Modification of Carbohydrate Polymers via
Grafting in Air. 1. Ceric-Induced Synthesis of
Starch-g-Polyacrylonitrile in Presence and Absence
of Oxygen. Starch/Starke, 54: 140-147.
23. Doyle, C.D., 1961. Estimating Thermal Stability
of
Experimental
Polymers
by
Empirical
Thermogravimetric
Analysis.
Anal.
Chem.,
33(1): 77-79.
24. Athawale, V.D. and V. Lele, 2000. Thermal Studies on
Granular Maize Starch and its Graft Copolymers with
Vinyl Monomers, Starch/Starke, 52: 205-213.
25. Zohuriaan, M.J., A. Pourjavadi and M. Sadeghi, 2005.
Modified CMC. 1. Optimized Synthsis of
Carboxymethylcellulose-g-Polyacrylonitrile, iranian
polymer journal, 14(2): 131-138.
26. Mohammad, S. and H. Hossein, 2010. Studies on graft
copolymerization of 2-hydroxyethylmethacrylate onto
kappa-carrageenan initiated by ceric ammonium
nitrate, Journal of The Chilean Chemical Society,
55, N0 4.
125