Effects of gamma radiation on two aromatic polysulfones. II. A comparison of irradiation at various temperatures in air-vacuum environments

The aromatic polysulfone poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyleneisopropylidene-1,4-phenylene) (I) showed no change in flexural yield strength after doses of γ-radiation up to 600 Mrad in vacuum at 35, 80, and 1250C(T/sub g = 1900C). However, the flexural strength decreased markedly with doses above 100 Mrad on irradiation in air, to 40 to 60% of the initial value after 200 to 400 Mrad, depending on the sample and the irradiation conditions. Chain crosslinking was predominant over scission for irradiation in vacuum at all temperatures; G(X), G(S), and G(S)/G(X) increased with the irradiation temperature, but G(S)/G(X) decreased to zero above T/sub g/. Poly-(oxy-1,4-phenylenesulfonyl-1,4-phenylene) (II) behaved similarly, except that the flexural strength was found to be very dependent on the thermal treatment of the sample. This polymer showed a remarkable retention of its mechanical properties on irradiation up to 2000C(T/sub g/ = 2300C) in the absence of air, the flexural strength being retained up to 500 Mrad. Radiation annealing occurred at 350C in vacuum and air and combined radiation and thermal annealing at 125 and 2200C. Progressive removal of surface layers from flexural test bars of I irradiated in air showed that the decrease in flexural strength with dose could be explained by a decrease in the molecular weight towards the surface resulting from radiation-oxidation reactions