Stereo multiblock poly(lactic acid)s (PLA)s and stereo diblock poly(lactic acid) (DB) with a wide variety of block length of 15.4-61.9 lactyl units are synthesized, and the effects of block length sequence on crystallization and spherulite growth behavior are investigated at different crystallization temperatures, in comparison with neat poly(L-lactide) (PLLA), poly(D-lactide) (PDLA), and PLLA/PDLA blend. Only stereocomplex crystallites as crystalline species are formed in the stereo multiblock PLAs and DB, irrespective of block length and crystallization temperature. The maximum crystallinities (33-61%), maximum radial growth rate of spherulites (0.7-56.7 lm min À1 ), and equilibrium melting temperatures (182.0-216.5 C) increased with increasing block length but are less than those of PLLA/PDLA blend (67 %, 122.5 lm min À1 , and 246.0 C). The spherulite growth rates and overall crystallization rates of the stereo multiblock PLAs and DB increased with increasing block length and are lower than that of PLLA/PDLA blend.

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Stereo multiblock PLAs with different block lengths are synthesized by melt polycondensation of low‐molecular‐weight poly(L‐lactic acid)/poly(D‐lactic acid) blends with a wide variety of $\overline {M} _{{\rm w}} $ in the range of 1.1–5.2 × 103 g · mol–1. The average block length (νav) of the stereo multiblock PLAs increases with increasing $\overline {M} _{{\rm w}} $ of the blend and with the reaction temperature, whereas $\overline {M} _{{\rm w}} $ and PDI of the stereo multiblock PLAs increases with increasing $\overline {M} _{{\rm w}} $ of the blend, the reaction time, and the temperature. Stereo multiblock PLAs with νav > 7 are crystallizable to form stereocomplex crystallites, and the crystallinity and melting temperature of the stereo multiblock PLAs increases with increasing νav and $\overline {M} _{{\rm w}} $ of the stereo multiblock PLAs. magnified image