Properties of stereo multi-block polylactides obtained by chain-extension of stereo tri-block polylactides consisting of poly(L-lactide) and poly(D-lactide)
Stereo multi-block polylactides (multi-sb-PLA) having controlled block sequences of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) were synthesized by chain-extension of stereo tri-block polylacitdes (PLLA-PDLA-PLLA) that were readily synthesized by two-step ring-opening polymerization (ROP) of D- and L-lactides. The weight-average molecular weight of the resultant multi-sb-PLAs reached about 14.3 × 104 Da. These multi-sb-PLAs were found to exclusively form stereocomplex (sc) crystals without homo-chiral (hc) crystallization occurring because the quickly formed sc crystals effectively suppressed the hc crystallization as cross-linkers. Their thermal properties could be tuned by controlling the block lengths of PLLA-PDLA-PLLA in the two-step ROP. Particularly, the multi-sb-PLAs consisting of longer PLLA and PDLA blocks in 1:1 ratio exhibited higher sc crystallinity and thermo-mechanical properties after thermal annealing.
KeywordsPolylactide Ring-opening polymerization Stereo multiblock polylactides Chain extension Stereocomplex crystal
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2015R1D1A1A01056755).