684
Advances in Environmental Biology, 6(2): 684-689, 2012
ISSN 1995-0756
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLE
Modification of Sucrose, S Stracture Via Ceric-Initiated Acrylonitrile Graft
Polymerization
Esmat Mohammadinasab, Mohammad Sadeghi, Fatemeh Shafiei and Fatemeh Soleimani
Chemistry Department, Science Faculty, Islamic Azad University, Arak Branch, Arak, Iran.
Esmat Mohammadinasab, Mohammad Sadeghi, Fatemeh Shafiei and Fatemeh Soleimani;
Modification of Sucrose, S Stracture Via Ceric-Initiated Acrylonitrile Graft Polymerization.
ABSTRACT
Graft copolymerization of acrylonitrile (AN) onto sucrose was carried out under argon atmosphere in a
homogeneous aqueous medium by using ceric ammonium nitrate (CAN) as an initiator. The FTIR spectroscopy
and thermo-gravimetric analysis and solubility characteristics of the products were used for confirming the graft
copolymer formation. A tentative mechanism is proposed to explain the generation of radicals and the initiation.
According to the empirical rates of the polymerization and the graft copolymerization of AN onto sucrose
backbone, the overall activation energy of the graft copolymerization reaction was estimated to be 29.8 kJ/mol.
Key words: Sucrose; acrylonitrile; graft copolymerization; modification.
Introduction
During the past decades, considerable research
was being carried out on the graft copolymerization
of hydrophilic and hydrophobic vinyl monomers
onto polysaccharides [1-5]. These biodegradable and
low cost graft copolymers, with new properties, can
be used in many applications such as textiles, paper
industry, agriculture, medical treatment and also in
petroleum industry as flocculants and thickening
agents[1-3],
[6-9].
Free
radical
graft
copolymerization was usually carried out by using
various initiators such as ammonium persulfate,
benzoyl peroxide and azoisobutyronitrile. Mino and
Kaizerman for the first time utilized ceric ammonium
nitrate (CAN) as a very effective redox initiator[10].
CAN is an efficient oxidizing agent that can create
free radicals capable of initiating graft
copolymerization of vinyl monomers onto
polysaccharides. For example, methyl acrylate was
grafted onto starch using Ce (IV) as an initiator [11,
12]. Ceric ions have been also used to graft
copolymerized some vinyl monomers including
acrylonitrile [13], methyl acrylate and methyl
methacrylate [14], and acrylamide15,16 onto sodium
alginate. In addition, ceric ion was recently used to
graft copolymerization of acrylamide onto
carboxymethyl
starch
[17]
and
carboxymethylcellulose
[18].
Starch-gpoly(methacrylonitrile) [19] and cyanoethylcelluloseg-poly(acrylonitrile)[20] was also prepared by this
method. There have been many investigations
dealing with the grafting of various monomers onto
the most well-known water-soluble cellulose
derivative, i.e., carboxymethylcellulose. But a
literature survey reveals that no paper has been
reported in the case of methacrylonitrile (MAN)
grafting onto this industrial polysaccharide.
Therefore, in the present work, we attempted to
modify CMC by free radical graft copolymerization
of methacrylonitrile. The grafting reaction was
carried out in an aqueous solution by CAN as a redox
initiator in dilute nitric acid solution. The effect of
concentration of CMC, MAN and CAN as well as
the reaction time and temperature on the graft
copolymerization was studied by determining the
grafting parameters.
Experimental:
Materials:
The disaccharide sucrose was purchased from
Merck Chemical Co. (Germany). Polyacrylonitrile
was synthesized through a method mentioned in the
literature [22]. The drug, verapamil hydrochloride,
was received from Aldrich Chemical Co. Double
distilled water was used for the hydrogel preparation
and swelling measurements.
Graft Copolymerization Procedure:
A weighed amount of CMC was dissolved in 50
mL of distilled water in a 100 mL two-necked flask
Corresponding Author
Mohammad Sadeghi, Chemistry Department, Science Faculty, Islamic Azad University, Arak
Branch, Arak, Iran.
E-mail: [email protected] Tel: +98-861-3670017, Fax: +98-861-3670017
685
Adv. Environ. Biol., 6(2): 684-689, 2012
equipped with magnetic stirrer, immersed into a
thermostated water bath, preset at 45oC. An inert gas
(argon) was gently bubbled into the reactor to
remove the oxygen during the graft copolymerization
reaction. After 15 min, various amounts of MAN
monomer were added to the reaction mixture at once,
and the mixture was allowed to stir for 10 min. Then
a given volume of freshly prepared solution of CAN
was added and the graft copolymerization reaction
was conducted for 2 h. Finally, the resulted product
was precipated by pouring the reaction mixture
solution into 250 mL of methanol, and the precipitate
was filtered and repeatedly washed with methanol.
FTIR spectra were measured using an ABB
Bomem MB-100 FTIR spectrophotometer (Quebec,
Canada), at room temperature in the range from 4000
to 500 cm-1, with a resolution of 2 cm-1 and 20 scans.
Samples were prepared by well dispersing the
complexes in KBr and compressing the mixtures to
form disks. 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 oC/min until 600
o
C.
Results and Discussion
Homopolymer Extraction:
Evidence Of Grafting:
The graft copolymer, namely sucrose-gPolyAcrylonitrile, was freed from polyacrylonitrile
(PAN) homopolymer, by pouring 0.80 g of the
product in 50 mL of dimethylformamide solution.
The mixture was stirred gently at room temperature
for 48 h. After complete removal of the
homopolymer, the sucrose-g-PolyAcrylonitrile was
filtered, washed with methanol and dried in oven at
50˚C to reach a constant weight.
Instrumental Analysis:
Infrared Spectroscopy:
The existence of PolyAN grafting was
confirmed by the difference between FTIR spectra of
the grafted and non-grafted products (Figure 1). An
additional sharp characteristic peak in the graft
copolymer at 2251 cm-1 (Fig. 1b) which is attributed
to –CN stretching absorption can be used for
confirming the grafting of PolyAN onto the
substrate, sucrose.
Fig. 1: KBr FT-IR spectra [transmittance versus wave number (cm-1)] of (a) pure sucrose and (b) the
homopolymer-free sucrose -g-PolyAN.
Thermogravimetric Behavior:
The grafting was also supported by
thermogravimetric analysis (Fig.1). TGA of pure
sucrose (Fig. 2a) shows a weight loss in two distinct
stages. The first stage ranges between 15 and 120 oC
and shows about 17% loss in weight. This may
correspond to the loss of adsorbed and bound
water.17 No such inflexion was observed in the TGA
curve of sucrose -g-PolyAN. This indicated that the
grafted copolymers were resistant to moisture
absorption. The second stage of weight loss starts at
330 oC and continues up to 440 oC during which
there was 60% weight loss due to the degradation of
sucrose. Grafted samples, however, show almost
different behavior of weight loss between 15 and 550
o
C (Fig. 2b). The first stage of weight loss starts at
205 oC and continues up to 330 oC due to the
degradation of sucrose. The second stage from 370 to
480 oC may contribute to the decomposition of
different structure of the graft copolymer. The
appearance of these stages indicates the structure of
sucrose chains has been changed, which might be
due to the grafting of PolyAN chains. In general, the
copolymer had lower weight loss than sucrose. This
means that the grafting of sucrose increases the
thermal stability of sucrose in some extent.
Solubility Test:
The simplest method to prove the formation of
sucrose-g-PolyAN is based on the solubility
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Adv. Environ. Biol., 6(2): 684-689, 2012
difference of the graft copolymer and the non-grafted
homopolymer. sucrose and PolyAN are soluble in
water and DMF, respectively. When a reaction
product was extracted with DMF and alternatively
with water for 48 h, an insoluble solid still remained.
A physical mixture of sucrose and PolyAN was
treated in the same way and was found to dissolve
completely. Therefore, it is obvious that the resulted
graft copolymer was not a simple physical mixture,
but some chemical bonds must exist between the
sucrose substrate and PolyAN macromolecules.
Synthesis, Mechanism And Reaction Rate:
Duke and coworkers have shown that ceric salts
form complexes with alcohols, and these complexes
are disproportionate via single electron transfer with
the formation of free radicals on the reducing agent.
On the other hand, it has been shown that the
anhydroglucose units are predominantly oxidized
through C2–C3 bond cleavage induced by Ce (IV)
ions [23]. Therefore, a general reaction mechanism
for graft copolymerization reaction, in analogy with
that previously mentioned[24] may be as follows
(Scheme 1): the first step of the mechanism is a
complex formation of the Ce4+ ion with the oxygen
atom at the C-2 position and the hydroxyl group at
the C-3 position. This CMC-Ce4+ complex are then
reduced to a Ce3+ ion and consequently a free radical
is formed onto CMC backbone. These radicals are
responsible for the initiation of methacrylonitrile
grafting onto polysaccharide backbone.
The rates of polymerization (Rp) and graft
copolymerization (Rg) may be evaluated as measures
of the rate of monomer disappearance by using the
following equations25:
Rp mol. s1.m3  
Weight of total polymerformed
3
Molecular weight of monomer [rection time (s)]volume (m)
(1)
Weight ofgraftedpolymer
(2)
Rg mol.s1.m3 
3
Molecularweight ofmonomer [rectiontime(s)]volume(m)
The calculation of Rp values may be of
significant importance in confirming a proposed
reaction mechanism and kinetics. Therefore, we
investigated the relation between rate of graft
copolymerization and concentration of CAN, AN and
sucrose. Figures 2-4 show that the plots of Rp versus
the monomer concentration, [AN], half-order of the
initiator
concentration,
[Ce+4]1/2
and
the
polysaccharide concentration, [sucrose]1/2, are linear.
This is in agreement with a modified kinetic scheme
recently explored for CAN-initiated methacrylate
grafting onto sago starch26. The statement of rate of
polymerization according to the scheme is as
follows:
Rp = kp (K kd / kt )1/2 [sucrose]1/2 [ Ce+4 ]1/2 [ AN ] (3)
The coefficient K is the equilibrium constant, kp,
kd, and kt are the rate constants for propagation,
sucrose–ceric complex dissociation, and termination
reactions, respectively. Therefore, we preliminarily
conclude that the CAN-initiated grafting of
acrylonitrile onto sucrose is also fitted with this kind
of rate statement.
The overall activation energy (Ea) of the graft
polymerization reaction was calculated by using of
the Eq. (2) and the slope of the plot LnRg versus1/T
(Fig. 5) based on Arrhenius relationship [kp=Aexp(Ea/RT)].
Therefore,
Ea
for
the
graft
copolymerization was found to be 29.8 kJ/mole. In a
previous work, we estimated similarly the overall
activation energy to be 39.7 kJ/mol for the grafting
of acrylonitrile onto sucrose [17].
Fig. 2: TGA of grafted and ungrafted polymer: Pure sucrose (a) and grafted sucrose (b).
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Adv. Environ. Biol., 6(2): 684-689, 2012
Fig. 3: Plot of Rp versus monomer (AN) concentration.
Fig. 4: Plot of Rp versus [Ce 4+]1/2.
Fig. 5: Plot of Rp versus [sucrose]1/2.
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Adv. Environ. Biol., 6(2): 684-689, 2012
Fig. 6: Plot of LnRg versus 1/T.
Scheme. 1: General reaction mechanism for graft copolymerization of acrylonitrile onto Sucrose backbone in
the presence of ceric (IV) ion.
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Adv. Environ. Biol., 6(2): 684-689, 2012
Conclusion:
8.
Novel graft copolymer were synthesized by
grafting of methacrylonitrile onto sucrose in the
presence of cerium (IV) ammonium nitrate as an
efficient initiator in acidified aqueous medium, under
inert atmosphere. Empirical polymerization rate
showed a first-order dependence on the monomer
concentration and a half-order dependence on the
initiator concentration. According to the slope of
LnRg versus 1/T, the overall activation energy for
graft copolymerization reaction was estimated to be
29.8 kJ/mol.
9.
10.
11.
12.
13.
14.
References
15.
1.
2.
3.
4.
5.
6.
7.
Fanta, G.F., 1973. In "Block and Graft
Copolymerization", R.J. Cerasa (Ed.), Wiley,
London.
Hebeish, A., J.T. Guthrie, 1981. In "The
Chemistry and Technology of Cellulosic
Copolymers", Springer-Verlag, Berlin.
Athawale, V.D., S.C. Rathi, 1999. J. Macromol.
Sci.-Rev. Macromol. Chem. Phys. C., 39(3): 445.
Sun, T., P. Xu, Q. Liu, J. Xue, W. Xie, 2003.
Eur. P. J., 39: 189.
Cao, Y., X. Qing, J. Sun, F. Zhou, S. Lin, 2002.
Eur. Polym. J., 38, 1921.
Singh, R.P., 1995. In "Polymers and Other
Advanced Materials, Emerging Technologies
and Business Opportunities", P.N. Prasad, J.E.
Mark, T.J. Fal (Eds), Plenum, New York, pp:
227.
Bicak, N., D.C. Sherrington, B.F. Senkal, 1999.
React. Func. Polym. 41, 69.
16.
17.
18.
19.
20.
21.
22.
23.
24.
Zhang, L.M., B.W. Sun,1999. J. Appl. Polym.
Sci., 74, 3088.
Lee, W.F., G.Y. Haung, 1996. Polymer, 37,
4389.
Mino, G., S. Kaizerman, 1958. J. Polym. Sci.,
31(122) 212.
Patil, D.R., G.F Fanta, 1993. J. Appl. Polym.
Sci., 47, 1765.
Rahman, L., S. Silong, W.M. Zin, M.Z.A.
Rahman, M. Ahmad, J. Haron, 2000. J. Appl.
Polym. Sci., 76, 516(2000).
Shah, S.B., C.P. Patel, H.C. Terivedi, 1992.
High Perform. Polym., 4(3): 151.
Shah, S.B., C.P. Patel, H.C. Terivedi, 1995.
Carbohydr. Polym., 26, 61.
Tripathy, T., R.P. Singh, 2000. Eourp. Polym.
J., 36, 1471.
Tripathy, T., N.C. Karmakar, Singh, R.P., 2001.
J. Appl. Polym. Sci., 82(2): 375.
Cao, Y., X. Qing, J. Sun, F. Zhou, S. Lin, 2002.
Eur. Polym. J., 38, 1921.
Tripathy, T., N.C. Karmakar, R.P. Singh, 2000.
Int. J. Polym. Mater., 46, 81.
Athawale, V.D., V. Lele, 2000. Carbohydr.
Polym., 41, 407.
Nada, A.M.A., M.L. Hassan, 2000. Polym.
Degrad. Stab., 67, 111.
Duke, F.R., A.A. Froist, 1949. J. Am. Chem.
Soc., 71, 2790.
Duke, F.R., A.A. Froist, 1951. J. Am. Chem.
Soc., 73, 5179.
Doba, T., C. Rodehed, B. Ranby, 1984.
Macromolecules, 17, 2512.
Berlin, A.A., V.N. Kislenco, 1990. Prog. Polym.
Sci., 17, 765.