EFFECT OF GAMMA-IRRADIATION ON THE ALPHA-RELAXATION IN POLY(METHYL METHACRYLATE) OF VARIOUS MOLECULAR MASSES

The spectra of internal friction in PMMA samples of various molecular masses (M-w > 10(4)) and their dependence on the gamma-irradiation in the dose range 10(3)-10(5) rad were studied by the dynamic mechanical techniques. The exposure to alpha-radiation leads to a triplet splitti ng of the alpha- relaxation peak in the internal friction spectrum int o several loss peaks of different intensities. The splitting is observ ed both on the side of a low-temperature branch of the main alpha-rela xation peak (alpha ''-transition) and on the side of the high-temperat ure branch (alpha'-transition). The losses exhibit redistribution betw een the alpha' and alpha '' peaks, the patterns being different depend ing on the irradiation dose and the molecular mass of PMMA. These phen omena are related to the appearance of new polar groups as a result of the radiolysis and to some insignificant conformational changes in th e macromolecular chains.