Gamma irradiation effects on polymethyl methacrylate

The effect of gamma‐irradiation on the structure of polymethyl methacrylate (PMMA) has been investigated. In this study, the PMMA specimens were gamma‐irradiated at doses in the range of 0‐1000 kGy and measured by means of positron annihilation lifetime (PAL) spectroscopy. Irradiation dose dependence of the longest lifetime component (τ3), attributed to ortho‐positronium (o‐Ps) decay, and the intensity of this component (I3) was studied by positron annihilation lifetime spectroscopy (PAL). The two physical quantities were correlated with the size and density of free volume sites in the examined specimens and were compared with the thermal transitions in the material obtained using the DSC technique. It was found that the size and amount of free volume decreases with increasing dose due to irradiation‐enhanced crosslinking. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)