Dégradation photochimique de polymères cétoniques, 2. Etude sur modèles de la photodégradation de copolymères cétoniques à groupes carbonyles en chaǐne

Abstract

AbstractThree linear phenyl ketones, 4‐methyl‐1,7‐diphenyl‐3‐heptanone (6a), 2,8‐diphenyl‐4‐nonanone (6b), and 5‐methyl‐2,8‐diphenyl‐4‐nonanone (6c), and four cyclic ketones, 1‐phenethyl‐2‐(3‐phenylpropionyl)cyclopentane (4a), 1‐(3‐phenylbutyryl)‐2‐(2‐phenylpropyl)cyclopentane (4b) and their cyclohexane homologues (5a and 5b), were synthesized as models of styrene copolymers bearing carbonyl groups in the chain, and their photochemical degradation was studied in various solvants at wavelengths > 280 nm. This study has shown that both Norrish mechanisms, i.e., the type I scission in α‐position of the carbonyl and the type II photoelimination, which occur with the models, take place in a similar fashion with the copolymers. The relative part and the efficiency of each photodegradation depend on the solvent, the linear or cyclic character of the chain, as well as on the substitution. Photodegradation studies of the models have also allowed us to explain the photochemical behaviour of the particular copolymers and especially the faster fragmentation of linear chains, and to elucidate the mechanisms involved in the degradation of these polymers.