| Abstract: | A bulk PMMA sample was irradiated by gamma rays (0.69 Gy. s−1), and its structural changes were monitored by steric exclusion chromatography, differential scanning calorimetry, dynamic mechanical spectroscopy and dilatometry. The glass transition temperature Tg decreases more than predicted from the molecular weight data, but the corresponding excess of change is not thermoreversible and can be suppressed by annealing. Strong not thermoreversible changes are also observed around the first secondary transition temperature (≈︁ 60°C) as well as in mechanical spectra and in dilatometric curves. Various hypothetical explanations are examined. |
