Preparation and analyses of stereocomplexes of a polylactide homopolymer and copolymer with poly(ethylene glycol) and urethane capping

Polylactide (PLA) stereocomplexes (SCs) formed by poly(L,L-lactide) (PLLA) and poly(D,D-lactide) (PDLA) are well known, and their derivatives and copolymers have also been reported. However, little research has been conducted on SCs with a combination of one enantiomer of a copolymer and a homopolymer. In this study, we selected a PLA copolymer with poly(ethylene glycol) (PEG) and a urethane capping PLA bearing almost the same molecular weights as PLA segments and prepared various SC samples. Depending on the combination of L-isomers and D-isomers, the SCs were classified as a Homo-SC, Co-SC, and Multi-SC: the Homo-SC had the same polymer chain ends and copolymers, the Co-SC had different polymer chain ends and copolymers, and the Multi-SC had a mixture of various polymer chain ends and copolymers. Depending on the chain end structures, the melting points of the SCs changed in the case of Homo-SC and Co-SC, but Multi-SC showed two broad melting points at ~200 °C. We propose that these findings are the results of the various combinations of polymer–polymer interactions in the case of Multi-SC.