Étude par spectroscopie ESR de la photodégradation de la poly(vinyl‐2 pyridine) et des copolymères vinyl‐2 pyridine/méthacrylate de méthyle

Irradiation of films of poly(2‐vinylpyridine), (poly[1‐(2‐pyridyl)ethylene]), and poly(4‐vinylpyridine), (poly[1‐(4‐pyridyl)ethylene]) at wavelengths λ > 300 nm gives rise to the corresponding vinylpyridinyl and azabenzyl radicals, the concentrations of which do not exceed 1015 spins/g. Introduction of naphthyl substituents into the polymer chain enhances appreciably the rate of radical formation from the copolymer. Irradiation at 254 nm of poly(methyl methacrylate), (PMMA) and its copolymers containing various amounts of 2‐vinylpyridine monomeric units shows that the presence of pyridyl groups along the chain of PMMA reduces the rate of accumulation of radicals. This result is ascribed to the screening effect of pyridine. The photoprotection by the pyridyl ring is likewise observed in the phenanthrene sensitized photolysis at λ > 300 nm of the various 2‐vinylpyridine/methyl methacrylate copolymers and its mechanism is discussed.