Effect of transesterification reactions on the crystallization behaviour and morphology of poly(butylene/diethylene succinate) block copolymers

The melting behaviour, the crystallization kinetics and the morphology of block poly(butylene/diethylene succinate) copolymers (PBSPDGS) were investigated by means of differential scanning calorimetry and hot stage optical microscopy. Multiple endotherms were evidenced in the PBSPDGS samples, due to melting and recrystallization processes, similarly to PBS. By applying the Hoffman-Weeks’ method, the of both the homopolymer and the copolymers was derived. The isothermal crystallization kinetics was analyzed according to the Avrami’s treatment. The copolymers with long PBS blocks are characterized by a very similar behaviour with respect to pure poly(butilene succinate), indicating that PBS macromolecular folding is not affected by the presence of non-crystallizable diethylene succinate blocks. On the contrary, the copolymers characterized by very short PBS block length were found to crystallize at a slower rate than the homopolymer. As a matter of fact, a higher value of the work of chain folding was also derived on the basis of Hoffman-Lauritzen nucleation theory. Anyway, in all cases the crystallization mechanism (heterogeneous nucleation and three-dimensional growth) was found to be the same.