Random copolymers of poly(butylene terephthalate) - Effect of thiodiethylene terephthalate units on melting behaviour and crystallization kinetics

The melting behavior and the crystallization kinetics of poly(butylene terephthalate/thiodiethylene terephthalate) copolymers were investigated by DSC technique. The multiple endotherms were influenced both by T-c and composition. By applying the Hoffman-Weeks' method, the of the copolymers was derived. The isothermal crystallization kinetics was analyzed according to the Avrami's treatment. Values of the exponent n close to 3 were obtained, independently of T-c and composition. The introduction of thiodiethylene terephthalate units decreased the PBT crystallization rate. DeltaH(m) was correlated to Deltac(p) for samples with different degree of crystallinity and the results were interpreted on the basis of the existence of an interphase.