| dc.description.abstract | Poly(p-methoxyacrylophenone) (PMAP),
poly{3,4-dimethoxyacrylophenone) (P34DMAP) and
poly(3,5-dimethoxyacrylophenone) (P35DMAP) were exposed in the
form of dilute solutions and thin films to long-wave UV
radiation (see document) under high vacuum at 25 ± 1°C.
Photoreactions of these polymers occurred predominantly from
the carbonyl triplets. In addition, the photophysical
observations were consistent with the formation of low-lying
(see document) triplets which, in turn, was the result of substitution
of the aromatic ketones by electron-donating methoxy groups.
Quenching by both naphthalene and cis-1,3-pentadiene conformed
to Stern-Volmer kinetics. In all cases, methane and ethane
were formed, the quantum yields for their formation being
lower in solution than those observed for the solid state
photolysis. This resulted from methyl radicals formed by O-CH3
fission. The principal photoreaction in solution was a Norrish
type II decomposition which resulted in random chain scission.
The polymers also underwent colouration (yellow), and this was
attributed to the formation of quinonoid entities, their
precursors being the phenoxy radicals formed by O-CH3 fission.
The effects on chain scission of a number of additives with
varying transfer activities were found to be complex as rates
of chain scission decreased but not to the extent that would
be expected if H-transfer alone was occurring. Solvent quality
and polarity were also important. Similarly, the rate of chain
scission decreased with increasing polymer concentration, and this has been attributed, to inhibition of separation of
macrofragments (from the Norrish II reaction) due to polymer
entanglement. | |
