Comparative study on the effects of incorporating poly(d,l-lactide) and solvent on stereocomplex crystallization and homocrystallization in unconstrained and constrained poly(l-lactide)/poly(d-lactide) systems

The effects of incorporating poly(d,l-lactide) (PDLLA) and solvent on the stereocomplex (SC) crystallization and homocrystallization of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) chains were explored using linear one-armed PLLA (1-L)/PDLA (1-D) and linear one-armed PDLLA (1-DL) as an unconstrained system and using branched four-armed PLLA-b-PDLA (4-L-D) and linear one-armed 1-DL as a constrained system. In the unconstrained 1-L/1-D/1-DL blends, both SC crystallites and homocrystallites formed in the absence of PDLLA or solvent, whereas only SC crystallites formed in the presence of PDLLA (75 and 50 wt.% at crystallization temperatures of 100 and 140 °C, respectively) or solvent. The SC crystallinity and total crystallinity increased, and the homocrystallinity decreased due to the presence of PDLLA and solvent. In the constrained 4-L-D/1-DL blends, SC crystallites formed without homocrystallites, even in the absence of PDLLA and solvent. SC crystallinity slightly increased due to the presence of PDLLA; however, the presence of both PDLLA and solvent somewhat decreased the SC crystallinity. In summary, the dilution effects of PDLLA and solvent enhanced SC crystallization and suppressed homocrystallization, with the exception of the constrained 4-L-D/1-DL blends in the presence of both PDLLA and solvent.