Preparation and thermal behavior of random poly(butylene terephthalate/azelate) copolyesters

Poly(butylene terephthalate), poly(butylene azelate), and poly(butylene ter ephthalate/butylene azelate) random copolymers of various compositions were synthesized in bulk using the well-known two-stage polycondensation proced ure, and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differ ential scanning calorimetry. As far as the thermal stability is concerned, it was found to be rather similar for all copolymers and homopolymers inves tigated. All the copolymers were found to be partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallin ity and a decrease of melting temperature with respect to pure homopolymers . Flory's equation was found to describe the T-m-composition data and permi tted to calculate the melting temperatures (T(m)degrees) and the heats of f usion (Delta H-u) of both the completely crystalline homopolymers. Owing to the high crystallization rate, the glass transition was observable only fo r the copolymers containing from 30 to 70 mol % of the terephthalate units; even though the samples cannot be frozen in a completely amorphous state, the data obtained confirmed that the introduction of the aromatic units gav e rise to an increase of T-g, due to a chain stiffening. (C) 1999 John Wile y & Sons, Inc.