PHOTO-OXIDATION OF ELASTOMERIC MATERIALS .3. PHOTOOXIDATION OF ACRYLONITRILE BUTADIENE COPOLYMER

The photo-oxidation of acrylonitrile-butadiene copolymers (NBR) has been investigated for comparison with the photo-oxidation of various polybutadienes (BR) and styrene-butadiene copolymer (SBR) which have been studied recently. Numerous similarities are revealed between these elastomeric materials. Associated hydroperoxides are primarily formed in the allylic position of the butadiene units. Associated unsaturated hydroperoxides are then decomposed into secondary allylic alcohols and αβ unsaturated ketones. The latter absorb at wavelengths longer than 300 nm and are photo-oxidized into saturated acids. The most outstanding feature is associated with the rate of disappearance of double bonds and the rate of formation of photoproducts which becomes zero after 10 h of irradiation. Photo-oxidation stopped after a few hours of irradiation. By the use of micro FTIR analysis, a concentration profile of photoproducts and double bonds has been obtained and a heterogeneous reaction has been revealed. Only two differences have been noticed between the photo-oxidation of BR, SBR and NBR. The first difference is that the presence of acrylonitrile units favours the formation of hydrogen bonds between hydroperoxides and alcohols. The second difference resides in the lower permeability to oxygen of NBR compared with BR and SBR. © 1989.