Photooxidation mechanism of styrene-isoprene copolymer: evolution of the profile of oxidation according to the composition

The photooxidation of styrene-isoprene copolymers is investigated on the ba sis of infrared analysis of irradiated films. The results show that the pol ystyrene segments are stable under irradiation and degradation results only from the photooxidation of the polyisoprene segments. Oxidation of polyiso prene results in chain scissions and generates various carbonylated photopr oducts. A three-dimensional structure is formed by cross-linking reactions resulting from additions on the double bonds and formation of ether linkage . In order to determine the influence of the polyisoprene content on the me chanism and the kinetics of oxidation, different compositions have been tes ted. The extent of degradation is found to be proportional to the polyisopr ene content but the rate of photooxidation is constant whatever the composi tion. The distributions of the oxidation products within the polymer are si milar whatever the composition. This behavior can be attributed to the inco mpatibility between the polyisoprene and the polystyrene segments, which le ads to a phase demixion and the formation of nodules. Each nodule can be co nsidered as an independent photochemical reactor. (C) 1999 Elsevier Science Ltd. All rights reserved.