Chemistry Reference
In-Depth Information
where, X• represents a free-radical fragment from a photoinitiator.
With gamma radiation, there is no need for any additives [
104
,
105
]. Here, the mechanism of
isomerization is believed to involve direct excitation of the
-electrons of the double bonds to anti-
bonding orbitals where free and geometric interconversions are possible. In benzene solutions, energy
transfers take place from excited benzene molecules to the polymer double bonds.
When 1,4-polyisoprene films are irradiated with light [
122
],
p
isomerizations occur. In the
process, the quantities of 1,4-unsaturations decrease. Also, vinyl and vinylidene double bonds and
cyclopropyl groups form. This can be illustrated as follows:
cis-trans
hn
isomerization
hydrogen shift
and
+
+
