Synthesis of Biomass-Based Linear Aliphatic Polyesters Based on Sebacic Acid and 1,18-Octadecanedioic Acid and Their Thermal Properties and Odd-Even Effect

A series of biomass-based linear aliphatic polyesters are synthesized by combining sebacic acid (SA) (C10 diacid) and 1,18-octadecanedioic acid (OA) (C18 diacid) with a series of diols with varied alkyl chain lengths (C2 to C10 diols). SA and OA are obtainable from castor oil and palm oil, respectively. The reaction extent (polymerization extent) is high (≥96%) in all cases, and the number-average molecular weight (M_n) is 10 000–43 000 g mol⁻¹ after purification. A possible limitation of currently available biomass-derived polyesters is their relatively low melting temperatures (T_m). The polyesters synthesized using OA with a long alkyl chain (C18 chain) in the present work exhibit relatively high T_m values of 78–93 °C, which are rather close to that (105–118 °C) of low-density polyethylene (LDPE), and may serve as biomass-based alternatives to LDPE with respect to thermal properties. Scientifically notably, an odd-even effect is observed in the T_m values. Polyesters with an even total-number of carbon atoms in the repeating unit have higher T_m values than their odd total-number counterparts likely due to their different orientations of dipoles of the polar ester groups along the backbone chain.