The thermal, mechanical and viscoelastic properties of poly(butylene succinate-co-terephthalate) (PBST) copolyesters with high content of BT units

Poly(butylene succinate-co-terephthalate) (PBST) copolyesters, with rigid butylene terephthalate (BT) units varying from 50 to 70 mol%, were synthesized via direct esterification route. The chemical structure and comonomer composition were characterized by (1)H NMR. The weight-average molecular weights (M (w) ) of the prepared products measured by GPC spanned a range of 1.39 x 10(5)-1.93 x 10(5) with corresponding M (w) /M (n) value of 2.23-2.42. Based on the WAXD analysis, PBST copolyesters were identified to have the same crystal structure as that of poly(butylene terephthalate) (PBT). The researches on the thermal properties showed that the melting temperature and decomposed temperature of PBST copolyesters increased with the increasing content of rigid BT units through DSC and TGA measurement. Furthermore, the tensile test results presented that the copolyester with higher content of BT units had higher initial modulus, higher breaking strength but lower elongation at break. Additionally, the viscoelastic properties of the prepared PBST films were analyzed by DMA measurement. It was found that both storage modulus (E') and loss modulus (EaEuro(3)) corresponding to the peak tended to heighten with the increase of BT units, indicating the copolyester with higher BT units content had the more prominent viscoelasticity. The peak of loss factor (tan delta) curve shifted to higher temperature as the content of rigid BT units increased due to the increasing of the glass transition temperature (T (g)).