Preparation and thermal behavior of random copolyesters of thiodipropionicacid

Poly(butylene terephthalate/thiodipropionate) and poly(butylene terephthala te/azelate/thiodipropionate) random copolymers of various compositions were synthesized in bulk and characterized in terms of chemical structure and m olecular weight. The thermal behavior was examined by thermogravimetric ana lysis and differential scanning calorimetry. The copolymers containing low amounts of thiodipropionate units showed a good thermal stability, similar to that of PET, however decreasing with increasing sulfur atom content. All the samples synthesized appear as semicrystalline materials, with fusion t emperatures well correlated to composition by Flory's equation. The T-m(o) and Delta H-u values for the completely crystalline homopolymers poly(butyl ene terephthalate) and poly(butylene azelate) derived using Flory's treatme nt are in good agreement with those reported elsewhere. Due to the high cry stallization rate, the glass transition phenomenon can be detected only for some copolymers with intermediate compositions. As the introduction of S-a toms in the polymeric chain gives rise to a more flexible structure, a decr ease of T-g was observed. (C) 2000 Elsevier Science Ltd. All rights reserve d.