Preparation and thermal behavior of random copolyesters of thiodipropionic acid

Poly(butylene terephthalate/thiodipropionate) and poly(butylene terephthalate/azelate/thiodipropionate) random copolymers of various compositions were synthesized in bulk and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. The copolymers containing low amounts of thiodipropionate units showed a good thermal stability, similar to that of PBT, however decreasing with increasing sulfur atom content. All the samples synthesized appear as semicrystalline materials, with fusion temperatures well correlated to composition by Flory’s equation. The T0m and ΔHu values for the completely crystalline homopolymers poly(butylene terephthalate) and poly(butylene azelate) derived using Flory’s treatment are in good agreement with those reported elsewhere. Due to the high crystallization rate, the glass transition phenomenon can be detected only for some copolymers with intermediate compositions. As the introduction of S-atoms in the polymeric chain gives rise to a more flexible structure, a decrease of Tg was observed.