Photodegradation behaviors of some glassy polymers as polystyrene (PS), poly(methyl methacrylate) (PMMA), styrene-methyl vinylketone copolymer [P(St-MVK)] and methyl methacrylate-methyl vinylketone copolymer [P(MMA-MVK)] have been investigated in terms of some mechanical proper ties as tensile strength, elongation, flexure strength and flexure strain. The results obtained are as follows. 1) PS and P(St-MVK) have the same photodegradation tendency. However, the photodegra dation of P(St-MVK) is

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... o remarkable as to attain its limitation in about 15 days, while that of PS in about 2 years. The degradation was found to be the decrease of molecular weight by photo reaction because the polymer viscosity lowers in proportion to lowering of mechanical properties. 2) Mercury lamp irradiation is an effective method for the accelerative photodegradation test. 3) Mechanical properties of PMMA and P(MMA-MVK) do not deteriorate in proportion to lowering of molecular weight. 4) Blending of PS homopolymer and MVK copolymer can endow the photodegradabilities and change the photodegradation rate. 5) Photodegradation of MVK copolymer can be adjusted by the addition of the absorbent of ultraviolet rays. 6) The temperature has a great influence on the photodegradation. The activation energy of the degradation for P(St-MVK) is as low as for rubber.