Photo-oxydation et photolyse de copolymères d'éthylène et d'acétate de vinyle à courte et grandes longueurs d'onde

Analytical and kinetic aspects of the photooxidation and photolysis in the solid state of various ethylene-vinyl acetate (EVA) copolymers (0 300 nm), the photooxidation is independent of the vinyl acetate content. The acetate groups, which are not preferential sites for the photo-induced hydroperoxidation, are photoconverted into chain ketones similar to those formed in the photooxidation of low density polyethylene (LDPE). As the content of monomeric units of vinyl acetate increases, associations between alcohols formed and the acetate groups are observed, based on the appearance of the 3530 cm−1 absorption band. The rate of the formation of vinyl-type insaturations is a decreasing function of the content of monomeric units of vinyl acetate. At short wavelength (λ = 254 nm) direct photolysis of the acetate groups is observed through the formation of alcohols and ketones again similar to those found in LDPE photooxidation. The rate of the EVA photolysis varies linearly with the vinyl acetate content. Oxygen reacts with the primary radicals formed at 254 nm. Alcohols and ketones are formed faster than through photolysis, although no stoichiometry change is observed.