Synthesis and characterization of polyesters derived from succinic acid, ethylene glycol and 1,3-propanediol

Poly(ethylene succinate) (PES), poly(trimethylene succinate) (PTS) and their copolyesters with various compositions were synthesized through a direct polycondensation reaction with titanium tetraisopropoxide as the catalyst. The results of intrinsic viscosity and GPC have proven successful in preparing high molecular weight polyesters. The compositions and the sequence distributions of the copolyesters were determined by analyses of ¹H NMR and ¹³C NMR spectra. The sequence distributions of ethylene succinate units and trimethylene succinate (TS) units were found to be random. Their thermal properties were characterized using differential scanning calorimeter and thermal gravimetric analyzer. All of the copolymers exhibit a single glass transition temperature (T_g). There is no significant difference in the thermal stability among these polyesters. Wide angle X-ray diffractograms (WAXD) were obtained for polyesters which can be crystallized isothermally. The results of thermal analysis and the WAXD patterns indicate that the incorporation of TS units into PES significantly inhibits the crystallization behavior of PES. Additionally, the crystal pattern of PTS is quite different from that of PES. Dynamic mechanical properties of moldable polyesters were investigated using a Rheometer operated at 1 Hz. Below T_g, the incorporation of TS units into PES results in the decline of storage modulus. Above T_g, the effect of crystallinity on the storage modulus can be found.