Lactic acid and ricinoleic acid based copolyesters

Copolyesters based on purified ricinoleic (RA) and lactic (LA) acids with different RA:LA ratios were synthesized by thermal polycondensation and by transesterification of high molecular weight poly(lactic acid) (PLA) with ricinoleic acid and repolyesterification. Thermal polycondensation resulted in random P(LA-RA) copolyesters of molecular weights between 2000 and 8000 with the polymers containing 20% or more RA were liquid at room temperature. Transesterification of high molecular weight PLA with pure ricinoleic acid and repolymerization of those oligomers by condensation resulted in multiblock P(PLA-RA) copolyesters of molecular weights between 6000 and 14000. Polymers containing 50% RA were liquid at room temperature. H-1 NMR spectroscopy analysis coupled with information from DSC allowed determination of the polymer structure. Polymers prepared by thermal polycondensation are random copolymers (h > 1), while the copolymers prepared by transesterification have a multiblock character (h < 1). The LA number-average sequence length (L-LA) decreased from 12 to 4 for the LA-RA 9:1 and 5:5 copolymers prepared by thermal polycondensation and from 50 to 17 for the corresponding LA-RA copolymers prepared by transesterification. Thermal analysis by DSC revealed crystalline structure for polyester synthesized by transesterification. For polyesters synthesized by random condensation only P(LA-RA) 90:10 w/w contained crystalline domains.