Stereocomplex Crystallization of Star-Shaped Four-Armed Stereo Diblock Poly(lactide) from the Melt: Effects of...

Star-shaped four-armed stereo diblock poly(lactide) (4-LD) and linear one-armed PLLA or PDLA (1-L or 1-D) having a molecular weight similar to that of 4-LD [higher molecular weight 1-L(H) or 1-D(H)] and that of one block of 4-LD [lower molecular weight 1-L(L) or 1-D(L)] were synthesized, and the effects of incorporated 1-L or 1-D on the isothermal and nonisothermal crystallization of 4-LD blends from the melt were investigated. Solely stereocomplex crystallites were formed in unblended 4-LD and 4-LD blends incorporated with 1-L or 1-D during isothermal and nonisothermal crystallization. Incorporated 1-L or 1-D increased normalized stereocomplex crystallinity and accelerated cold nonisothermal crystallization and isothermal crystallization. The accelerating effect became higher with decreasing the molecular weight of 1-L or 1-D. The crystalline growth mechanism was not altered by the incorporation of 1-L and 1-D, whereas the crystalline growth geometry changed from line to sphere or circle, depending on the type of sample and T_c. The difference in crystallization half time and cold crystallization temperature between 4-LD/1-L(H) and 4-LD/1-D(H) blends or 4-LD/1-L(L) and 4-LD/1-D(L) blends was explained by the difference in radial growth rate and spherulite density, which was further discussed considering the non-interpenetrating and interpenetrating models.