Biobased odd–odd poly(propylene dicarboxylate)s

Abstract

Biobased odd–odd poly(propylene dicarboxylate)s, based on 1,3-propanediol and three odd diacids [i.e., glutaric acid (C5), pimelic acid (C7) or azelaic acid (C9)], have been synthesized and analyzed, in order to study the effect of chain length of aliphatic diacids on thermal properties. Crystallization and melting behaviors were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), temperature-modulated differential scanning calorimetry (TMDSC) and polarized optical microscope (POM). DSC results suggested that the crystallization ability increases with the increasing chain length. WAXD patterns of the three polyesters showed a similar crystal structure. In DSC heating curves after isothermal crystallization of the samples, three endothermic peaks for the polyesters at shorter chain length (C5, C7) and at most four endothermic peaks for longer-chain-length polyester (C9) were displayed, and the mechanism of the multiple melting phenomenon was discussed. One or two exothermic peaks can be seen for shorter (C7) or longer (C9) polyester in the non-reversible heat flows of TMDSC, respectively, which evidenced once or twice melting–recrystallization–remelting processes occurring during melting heating. Finally, POM observation indicated that the spherulitic growth rate increases with the increasing chain length. Besides, ring-banded structures were observed in short-chain-length (C5, C7) samples, but C9 aliphatic polyester.