1070-4272/03/7612-1978 $25.00 C 2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 12, 2003, pp. 1978!1982. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 12, 2003,
Original Russian Text Copyright + 2003 by Nud’ga, Petrova, Lebedeva.
AND POLYMERIC MATERIALS
Effect of Allyl Substitution in Chitosan on the Structure
of Graft Copolymers
L. A. Nud’ga, V. A. Petrova, and M. F. Lebedeva
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received July 4, 2003
Abstract-The kinetics of graft polymerization of vinyl acetate on allyl chitosan samples with varied content
of allyl groups, initiated with ammonium peroxodisulfate, was studied.
Graft polymerization of vinyl monomers on poly-
saccharides allows preparation of hybrid copolymers
combining the properties of natural and synthetic
polymers, e.g., biocompatibility and thermoplasticity.
Such copolymers show promise as biomaterials.
Graft polymerization of vinyl acetate (VA) on
chitosan in acetic acid solution, initiated with ammo-
nium peroxodisulfate, yielded self-stabilized emul-
sions. The process kinetics was studied; it was found
that the reaction rate only weakly depends on the con-
centrations of chitosan and initiator and is propor-
tional to the VA concentration. An examination of the
thermomechanical properties of the copolymers with
different degrees of grafting showed that, at longer
grafting time, partially cross-linked structures are
obtained. Alkaline treatment of the grafted polyvinyl
acetate resulted in transfer of the copolymer into solu-
tion or its transformation into a gel (in the case of the
cross-linked copolymer) through hydrolysis of acetate
groups. The hydrolysis kinetics was studied. The final
product was a copolymer of chitosan with polyvinyl
alcohol . Despite the 100% conversion of the mono-
mer and high degree of grafting, the grafting efficien-
cy did not exceed 50%, i.e., grafting and homopoly-
merization of VA occurred at different rates. It has
been shown previously that the use of cellulose ethers
with a small content of allyl groups sharply enhances
the efficiency of grafting of vinyl monomers and
the content of grafted chains .
In this study we examined the effect of allyl sub-
stituents in chitosan on the parameters of graft poly-
merization of VA and structure of the resulting co-
Allyl chitosan (ACAN) with the degrees of allyl
, of 4, 9, 25, and 38 was prepared as
described in .
Vinyl acetate was distilled twice; the fraction with
bp 72.5372.8oC was used. Ammonium peroxodisul-
fate (APS) was recrystallized from water.
Graft polymerization of VA was performed as fol-
lows. A calculated amount of water was added to
a definite portion of a 4% solution of ACAN in 2%
acetic acid to obtain the required ACAN concentra-
tion. The mixture had pH 3.6. Then a definite amount
of VA was added; the mixture was vigorously stirred
to obtain an emulsion and heated to 60oC. The calcu-
lated amount of APS was added, with the stirring
being continued. This instant of time was considered
to be the start of the reaction. Samples of the reac-
tion mixture were taken at regular intervals; the reac-
tion in these samples was stopped by adding acetone.
The precipitate was filtered off on a Schott filter
placed in a Soxhlet apparatus. The homopolymer was
separated from the precipitate by exhaustive extrac-
tion with acetone, followed by solvent evaporation in
a rotary evaporator. The copolymer yield was deter-
mined by weighing the filter with the precipitate after
drying in a vacuum at 60oC.
The degree of grafting, C (%), was calculated by
] 0 100,
is the ACAN weight in the sample, and
, the copolymer weight in the sample.