Stereocomplex Crystallization and Homocrystallization of Star-Shaped Four-Armed Stereo Diblock Poly(lactide)s with Different L-Lactyl Unit Contents: Isothermal Crystallization from the Melt.

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.