Chemistry Reference
In-Depth Information
Scheme 3.9
Reaction scheme of grafting of starch with vinyl monomers in bromate/cyclohexa-
none redox system
graft copolymerisation, which explains that oxidation degree of starch decides the
grafting ability. The graft mechanism of acrylonitrile onto starch under the initia-
tion of potassium permanganate was investigated [
41
]. The relationships of the
grafting rate and the concentrations of potassium permanganate, acrylonitrile and
starch, as well as the reaction temperature, were established.
3.2.5
Initiation by Bromate/Cyclohexanone Redox System
Bromate/cyclohexanone redox system was investigated as a novel initiator for graft
copolymerisation of
N
-vinyl formamide onto pregelled starch [
42
]. It is assumed
that in the presence of sulphuric acid, during the oxidation of cyclohexanone by
bromate ion, the free radicals like
•
C
6
H
4
O,
•
OH and Br
•
are produced. These
radicals abstract hydrogen atom from pregelled starch molecules producing
pregelled starch macroradical. The monomer molecules, which are in the close
vicinity of reaction sites, accept starch macroradicals, resulting in chain initiation
and thereby themselves become free radical donor to neighbouring molecules
leading to the propagation. These grafted chains are terminated by coupling to
