Simultaneous stereocomplex cocrystallization from coexisting two types of stereocomplexationable poly(lactide) systems

Abstract

Crystallization behavior of coexisting two types of stereocomplexationable poly(lactide) (PLA) systems, i.e., star-shaped four-armed stereo diblock poly(lactide) (4-LD) and linear one-armed poly(L-lactide) and poly(D-lactide) (1-L and 1-D, respectively) having molecular weights similar to that of 4-LD [higher molecular weight 1-L(H) and 1-D(H)] and that of one block of 4-LD [lower molecular weight 1-L(L) and 1-D(L)] was investigated at different 4-LD content [X(4-LD)] values from 100 to 0 wt% fixing 1-L/1-D (w/w) = 50/50. The present article reports for the first time the simultaneous stereocomplex (SC) cocrystallization from coexisting two types of stereocomplexationable PLA systems (4-LD and 1-L/1-D blends). Solely SC crystallites were formed in 4-LD/1-L&1-D blends as well as unblended 4-LD or 1-L/1-D blends during crystallization from the melt, excluding 4-LD/1-L&1-D(H) with X(4-DL) = 25% at T_c ≤ 120 °C and 4-LD/1-L&1-D(H) blends with X(4-DL) = 0% [i.e., 1-L(H)/1-D(H) only] at T_c ≤ 140 °C, wherein both SC and homo-crystallites were formed. The SC melting temperature values of 4-LD/1-L&1-D blends in the ternary blends indicate that 4-LD and 1-L&1-D cocrystallized simultaneously to form SC crystallites by the intersystem interaction between the PLLA block of 4-LD and 1-D or the PDLA block of 4-LD and 1-L, irrespective of molecular weights of 1-L and 1-D and T_c. Interestingly, the SC crystallinity [X_c(S)] values of 4-LD/1-L&1-D were higher than those expected from the X_c(S) values of 4-LD and 1-L/1-D blends, indicating that blending star-shaped four armed stereo diblock 4-LD and linear one-armed 1-L and 1-D facilitated SC crystallization. The radial growth rate of spherulites decreased with an increase in X(4-DL) and the crystalline growth mechanism was altered depending on X(4-DL).