The miscibility of poly(butylene succinate) (PBS)/poly(butylene thiodiglycolate) (PBTDG) blends was investigated by DSC technique. PBS and PBTDG were completely immiscible in as blended-state, as evidenced by the presence of two Tgs at -34 and -48 degrees C, respectively. The miscibility changes upon mixing at elevated temperature: the original two phases merged into a single one because of transesterification reactions. Poly(butylene succinate/thiodiglycolate) block copolymers, prepared by reactive blending of the parent homopolymers, were studied to investigate the effects of transesterification reactions on the molecular structure and solid-state properties. 13C-NMR analysis evidenced the formation of copolymers whose degree of randomness increased with mixing time. Thermal characterization results showed that all the samples were semicrystalline, with a soft rubbery amorphous phase and a rigid crystal phase whose amount decreased by introducing BTDG units into the PBS chain (20 = ?c = 41). Lastly, the mechanical properties were found strictly related to crystallinity degree (?c), the random copolymer, exhibiting the lowest elastic modulus (E = 61 MPa) and the highest deformation at break (eb (%) = 713). (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012