Lactic and ricinoleic acid based copolyesters stereocomplexation

A systematic study of the synthesis and stereocomplexation Of L-lactic acid and ricinoleic acid based copolyesters is reported. L-lactic acid and ricinoleic acid based copolyesters were synthesized by melt condensation and transesterification of high-molecular-weight poly(lactic acid) (PLA) with ricinoleic acid and repolymerization by condensation to yield random and block copolymers of molecular weights between 3000 and 5000. To correlate between the copolyesters synthesized by polycondensation and transesterification, P(LA-RA)s with different PLA blocks were synthesized. The relative degree of crystallinity of those copolyesters depends directly on PLA block size, which is the only difference between the corresponding polymers. H-1 NMR spectroscopy analysis coupled with information from DSC allowed correlation between the degree of crystallinity and PLA block size. P(L-LA-RA)s and enantiomeric D-PLA were mixed together in acetonitrile solution to form stereocomplexes. Stereocomplex formation was dependent on the size of PLA block in the P(L-LA-RA)s, at least a block length of 10 LA units is required to form a stereocomplex. The formed stereocomplexes exhibited higher melting temperature than the enantiomeric polymers, indicating stereocomplex formulation.