Synthesis of ABCBA penta stereoblock polylactide copolymers by two-step ring-opening polymerization of L- and D-lactides with poly(3-methyl-1,5-pentylene succinate) as macroinitiator (C): development of flexible stereocomplexed polylactide materials.

BCB triblock copolymers consisting of poly-L-lactide (PLLA: B) and poly(3-methy-1,5-pentylene succinate) (SA/MPD: C) were first synthesized by ring-opening polymerization (ROP) of L-lactide by using a dihydroxyl-terminated SA/MPD (Mn≈20k) and tin octoate as the macroinitiator and catalyst, respectively. The telechelic dihydroxyl-terminated SA/MPD was readily synthesized by the controlled melt-polycondensation of succinic acid and 3-methyl-1,5-pentandiol (MPD). The resultant triblock copolymers, dihydroxyl-terminated, were subsequently utilized as the macroinitiators in the second-step ROP of D-lactide to obtain ABCBA penta-block copolymers (penta-sb-PLA) consisting of poly-D-lactide (PDLA), PLLA, and SA/MPD as the A, B, and C blocks, respectively. The weight-average molecular weights of the resultant penta-sb-PLAs became higher than 150 kDa. The cast films of these penta-sb-PLAs exhibited flexible nature due to the presence of the SA/MPD soft block as well as excellent heat-stability owing to the easy stereocomplex formation of the neighboring enantiomeric PLLA and PDLA blocks.