Synthesis and thermal characterization of poly(butylene terephthalate-co-thiodiethylene terephthalate) copolyesters

1,4-Butanediol-dimethyl terephthalate-thiodiethylene glycol copolymers of various compns. were synthesized and characterized in terms of chem. structure and mol. wt. The thermal behavior was examd. by thermogravimetric anal. and differential scanning calorimetry. All the polymers under investigation show good thermal stability. At room temp. they appear as semicryst. materials: the main effect of copolymn. was a lowering in the amt. of crystallinity and a decrease of melting temp. with respect to homopolymers. A pure cryst. phase has been evidenced at high content of butylene terephthalate or thiodiethylene terephthalate units and Baur's equation was found to describe well the Tm-compn. data. Amorphous samples (contg. 50-100 mol.% of thiodiethylene terephthalate units) showed a monotonic decrease of Tg as the content of sulfur-contg. units is increased, due to the presence of flexible C-S-C bonds in the polymeric chain. Finally, the Fox equation described well the Tg-compn. data.