Thermal properties of poly(butylene isophthalate) and its copolyesters with poly(butylene adipate)

Abstract The thermal properties of uniformly random poly(butylene adipate/isophthalate) copolyesters of various composition and different molecular weight were investigated by means of differential scanning calorimetry. All copolymers were partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. The heat of fusion of 100% crystalline poly(butylene isophthalate), estimated by different methods, was found to fall within the range 22–25 kJ · mol−1. Completely amorphous samples, obtained by rapid quenching from the melt, showed a monotonic decrease of the glass transition temperature Tg and a monotonic increase of the heat capacity increment ΔCp with increasing butylene adipate content in the copolymers. The Tg‐composition dependence was found to be well fitted by the Couchman equation with no excess enthalpy correction.