The effects of l-lactyl unit content on star-shaped four-armed stereo diblock poly(lactide) (4-LD) polymers and star-shaped four-armed poly(l-lactide) (4-L) on the isothermal crystallization from the melt were investigated. Solely stereocomplex (SC) crystallites were formed in equimolar 4-LD polymer with l-lactyl unit content of about 50%, irrespective of crystallization temperature (Tc) values. 4-L and 4-LD polymers with l-lactyl unit contents of 100 and 93% formed only homocrystallites, regardless of Tc, whereas only SC crystallites with traceable amounts were formed in 4-LD polymers with l-lactyl unit contents of 72 and 31% at a limited narrow Tc range of 110-120 °C, when crystallization was continued for as long as 24 h. About 20% deviation of l-lactyl unit content from 50% dramatically decreased the spherulite growth rate (G) values of SC crystallites, whereas a 7% decrease of l-lactyl unit content from 100% significantly decreased the G values of homocrystallites and largely decreased the overall homocrystallization rates. Branching architecture rather than diblock architecture hindered the simultaneous formation of SC and homocrystallites of non-equimolar 4-LD polymers.

The isothermal crystallization of star‐shaped four‐armed equimolar stereo diblock poly(lactide) (4‐LD) polymers with different molecular weights is investigated. Solely stereocomplex (SC) crystallites are formed in all equimolar 4‐LD polymers, irrespective of molecular weight and crystallization temperature (Tc). The wide‐angle X‐ray diffractometry, differential scanning calorimetry, and polarized optical microscopy results for crystalline species, crystallinity, and maximum radial growth rate of spherulites values indicate that both branching and diblock architectures disturb the SC crystallization and spherulites growth of equimolar 4‐LD polymers, and the disturbance effect is larger for branching architecture than for diblock architecture. The equilibrium melting temperature (Tm0) values are 181.9–266.0 °C, which are comparable with or lower than the value reported earlier (279 °C). The crystallite growth geometries of equimolar of 4‐LD polymers are independent of molecular weight and Tc.

Front Cover: The factors affecting stereocomplex-and homo-crystallization and phase-transition behavior of one-, two-, and four-armed poly(l-lactide)/poly(d-lactide) blends are investigated. Blue, green, and red (or yellow) spherulites are those of one-, two-, and four-armed poly(l-lactide)/poly(d-lactide) blends, respectively. For isothermal crystallization, the transition crystallization temperature ranges below which in addition to stereocomplex crystal-lites, homo-crystallites are formed depended on number-average mole cular weight (M n) per one arm-determining melting temperature or thickness of homo-crystallites. The transition M n ranges above which in addition to stereocomplex crystallites, homo-crystallites are formed are not affected by arm number. Dual wrinkling structure on the surface of uniform-sized biodegradable microparticles is prepared by using blends of hydrophobic poly mer and amphiphilic block copolymer and by introducing dimple-forming organic phase change materials. Both labyrinthine and hexagonal dimple structures are spontaneously formed from the conventional microparticle fabrication procedure of the solvent-emulsion evaporation method.

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