Photochemical Behavior in Copolymers of 2(2-Hydroxy-5-vinylphenyl)2H-benzotriazole and Methyl Methacrylate: Photochemical Processes in Polymeric Systems. 6

Abstract

The photochemical behavior of poly[2(2-hydroxy-5-vinylphenyl)2H-benzotriazole)]-co-methyl methacrylate was studied by spectroscopic and analytical techniques; no degradation of this copolymer occurred when the bulk polymer was exposed for several thousand hours of accelerated aging by ultraviolet irradiation. However, by the end of the period, surface deterioration became noticeable. Picosecond flash photolysis on copolymer solutions demonstrated that the lowest energy excited singlet state undergoes rapid internal conversion with little or no triplet yield. The observed short singlet lifetime (∼25 ps) is undoubtedly responsible for the photostability of this copolymer system. Analysis of the surface exposed to ultraviolet irradiation indicates some photooxidative degradation of the methyl methacrylate portion of the copolymer, but the surface 2(2-hydroxy-5-vinylphenyl)2H-benzotriazoles of the macromolecules remain unchanged.