Chemistry Reference
In-Depth Information
O
O
SO
2
SO
2
h
ν
O
2
S
O
2
S
O
O
O
OH
SO
2
H
O
O
+
O
O
2
S
OH
O
OH
OH
H
O
monomer
SO
2
O
+
O
graft copolymer
O
2
S
OH
O
It is believed that the above dye mono radicals disproportionate to hydroquinones and quinones.
Transfer reactions to solvent lead to formations of homopolymers. This gives high yields of graft
copolymers of methyl methacrylate with cellulose. The same is true of acrylonitrile [
360
]. On
the other hand, only small quantities of graft copolymers form with styrene or vinyl acetate
monomers [
360
].
It is also possible to form graft copolymers on the surface of fibers by coating them with
photoinitiators, like benzophenone together with a monomer and then irradiating them with ultravio-
let light [
414
]. Similar to the action of the anthraquinone dyes shown above, benzophenone in the
excited triplet state mainly abstracts hydrogens and forms radicals on the surface [
415
].
9.6.6 Graft Copolymer Formation with the Aid of High-Energy Radiation
High-energy radiation sources include gamma rays from radioactive elements, electron beams from
accelerators, and gamma rays from nuclear reactors. The energy radiated by these sources is suffi-
ciently high to rupturing covalent bonds. This results in formations of free radicals. Several different
methods are used to form graft copolymers. One of them is
irradiation in open air
. The free radicals
that form scavenge oxygen and form peroxides and hydroperoxides on the polymeric chains. These are
subsequently decomposed in the presence of monomers to form graft copolymers. When they are
decomposed thermally [
361
], the hydroperoxides yield much greater quantities of homopolymers then
do the peroxides. When, however, the decompositions are done at room temperature by redox
mechanisms, formations of homopolymers are reduced [
361
,
362
]. Another method is
irradiation in
vacuum
. This results in formations of trapped radicals on the polymer backbones. After irradiation, the
polymers are heated in the absence of oxygen and in the presence of vinyl monomers. The best results
