Photodegradation of High Polymers in Solution. Part 3. Poly(Methyl Methacrylate)

摘要

The photodegradation of poly(methyl methacrylate) in solution in the presence and absence of air under 2537A irradiation at about 25C was investigated, primarily by means of viscosity measurements. Random scission is confirmed as the major chain-breaking process. Quantum yields for scission in degassed solutions are solvent dependent; for methylene chloride, dioxane, and ethyl acetate, the quantum yields are 0.15, 0.17, and 0.38, respectively. In methylene chloride the quantum yield is nearly independent of polymer concentration and decreases slightly with increasing absorbed radiation intensity. Small amounts of benzene tend to increase the quantum yields, but carbon tetrachloride has relatively small effect and does not sensitize the degradation. In any of the solvents in the presence of air the quantum yields are approximately half of those found in the absence of air. Adventitious peroxides appear not to play a role in the degradation, but an oxygenated sample which probably contains peroxides acts initially as a sample would in air. The results can be interpreted in terms of possible electronic energy transfer processes. (Author)