Poly(propylene/neopenthyl terephthalate) random copolymers (PPT-PNT) and poly(neopenthyl terephthalate) (PNT) were synthesized and subjected to molecular characterization. Afterwards, the polyesters were examined by TGA, DSC, and X-ray. The copolymers, which displayed a good thermal stability, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PPT. XRD measurements allowed the identification of the PPT crystalline structure in all cases. Amorphous samples were obtained after melt quenching, with the exception of PPT-PNT5, and an increment of T-g as the content of NT units is increased was observed due to the effect of the side methylene groups in the polymeric chain. The Wood equation described well T-g-composition data. Lastly, the presence of a rigid-amorphous phase was evidenced in the copolymers, whose amount depended on composition and on thermal treatment. (C) 2007 Wiley Periodicals, Inc.