PHOTODEGRADATION OF POLY(STYRENE-CO-METHYLMETHACRYLATE) IN THE SOLID-PHASE

A series of poly(styrene-co-methylmethacrylate) copolymers synthesized by radiation-induced copolymerization of mixtures of the two monomers were photolyzed in the solid phase with light from a medium pressure mercury lamp. The decrease in the viscosity average molecular weight (M OVER BAR v) becomes greater as the methylmethacrylate (MMA) component in the copolymer is increased. It has been found that the formation of polymer radicals and oxygenated products is mainly due to the degradation of the MMA component. The relative number of chain scissions was obtained on the basis of the fact that styrene (St) and MMA are distributed randomly in the copolymer, as shown by pyrolysis-gas chromatography. The degradation of the copolymers is apparently suppressed by St. An estimation of the fraction of photons absorbed by MAA indicates that energy migration from St to MMA occurs to compensate, to some extent, for the light screening effect of St.