Random terephthalate polyesters based on 1,4-butanediol and bis(hydroxyethyl ether) of bisphenol A: thermal properties and crystallization kinetics

The thermal behavior of poly(butylene-co-2,2-bis[4-(ethylenoxy)-1,4-phenylene]propane terephthalate) copolymers (PBT/BHEEBT) was investigated by thermogravimetric analysis and differential scanning calorimetry. A good thermal stability was found for all the samples. The thermal analysis carried out using DSC technique showed that the Tm of the copolymers decreased with increasing BHEEBT unit content, different from that of Tg, which on the contrary increased. Wide-angle X-ray diffraction measurements permitted to identify the kind of crystalline structure of PBT in all the semi-crystalline samples. The multiple endotherms typical of PBT were also evidenced in the PBT/BHEEBT samples, due to melting and recrystallization processes. By applying the Hoffman–Weeksʹ method, the Tm° of the copolymers was derived. The isothermal crystallization kinetics was analyzed according to the Avramiʹs treatment. The introduction of BHEEBT units decreased the PBT crystallization rate. Values of the exponent n close to 3 were obtained, independently of Tc and composition. Furthermore, the presence of a crystal–amorphous interphase was evidenced.