Poly(propylene isophthalate) (PPI), poly(propylene succinate) (PPS), and poly(propylene isophthalate/succinate) (PPI-PPS) random copolymers were synthesized and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by TGA and DSC. All the polymers showed a good thermal stability. At room temperature, they appeared as semicrystalline materials, except 20PPI-PPS and 30PPI-PPS: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of T-m with respect to homopolymers. A crystalline phase of PPI and PPS was evidenced at high content of PI or PS units, respectively. Amorphous samples were obtained after melt quenching and an increment of T-g, with the increment of PI units, was observed. This behavior was explained as due to the presence of stiff phenylene groups. The Wood equation described well T-g-composition data. Lastly, the presence of a rigid-amorphous phase was evidenced in copolymers, differently from the two homopolymers. (c) 2006 Wiley Periodicals, Inc.