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 T-m of the copolymers decreased with increasing BHEEBT unit content, different from that of T-g, 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-Weeks' method, the T-m(o) of the copolymers was derived. The isothermal crystallization kinetics was analyzed according to the Avrami's treatment. The introduction of BHEEBT units decreased the PBT crystallization rate. Values of the exponent n close to 3 were obtained, independently of T-c and composition. Furthermore, the presence of a crystal-amorphous interphase was evidenced. (C) 2003 Elsevier Science Ltd. All rights reserved.