Poly(butylene succinate)

(PBS1) was irradiated with Co60-γ radiation at various temperatures．The gel fraction of PBS1 irradiated at molten state (100℃) is higher than that of the samples irradiated at lower temperatures with the same dose．Two-step irradiation (irradiation at room temperature and then irradiation at 100℃) yielded the highest gel content as compared with other treatment conditions．It is due to the network structure formed by preirradiation at room temperature and further irradiation at molten state reduce degradation of PBS1．PBS1 prepared by the two-step irradiation was improved in heat distortion resistance because of its higher gel content．Unirradiated PBS1 sheets broke immediately at 11O℃．On the other hand

for samples (gel fraction 50％) irradiated by asing the two-step method

they did not break even at 130℃ for 200 min．