Investigation of thermal decomposition of bulk-polymerized polysterene after small-dose γ-irradiation

A study has been made of the kinetics and composition of products of thermal decomposition of block polystyrene (PS) designed for medical purposes and which has been gamma-irradiated with a dose of 2.5 Mrad. Methods of pyrolytic gas chromatography and infrared spectroscopy have been used. Studies have been conducted at 375 and 400 deg C. Thermal decomposition is shown to occur via two stages with different activation energies and two parallel routes: depolymerization and thermal destruction. In the case of irradiation in air, radiation-induced oxidation processes which develop in polymers lead to an appreciable increase in the rate of depolymerization and destruction. In the case of pyrolysis of polystyrene irradiated in air, the effective activation energy of destruction at the initial stage remains the same as in the case of the specimens non-irradiated or irradiated in vacuum, the activation energy of depolymerization at the initial stage increases from 24.6 kcal/mole up to 33 kcal/mole. At the second stage for the PS specimens irradiated in air the effective activation energy of depolymerization falls down to 23 kcal/mole, while the effective activation energy of thermal destruction is 30 kcal/mole. An explanation is given for these variations