EFFECTS OF GAMMA-RADIATION ON 2 AROMATIC POLYSULFONES .2. COMPARISON OF IRRADIATION AT VARIOUS TEMPERATURES IN AIR-VACUUM ENVIRONMENTS

The aromatic polysulfone poly(oxy‐1,4‐phenylenesulfonyl‐1,4‐phenyleneoxy‐1,4‐phenyleneiso‐propylidene‐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 125°C (Tg = 190°C)). However, the flexural strength decreased markedly with doses above 100 Mrad on irradiation in air, to 40–60% of the initial value after 200–400 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 Tg. 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 200°C (Tg = 230°C) in the absence of air, the flexural strength being retained up to 500 Mrad. Radiation annealing occurred at 35°C in vacuum and air and combined radiation and thermal annealing at 125 and 220°C. 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. Copyright © 1979 John Wiley & Sons, Inc.