Ternary Stereocomplex and Hetero-Stereocomplex Crystallizability of Substituted and Unsubstituted Poly(lactic acid)s

Abstract

The ternary stereocomplex (TSC) crystallizability of ternary substituted and unsubstituted poly(lactic acid) blends composed of poly(d-2-hydroxy-3-methylbutanoic acid) [P(D-2H3MB)], poly(l-2-hydroxy-3-methylbutanoic acid) [P(L-2H3MB)], and poly(l-2-hydroxybutanoic acid) [P(L-2HB)] or poly(l-lactic acid) (PLLA), together with heterostereocomplex (HTSC) crystallizability of binary blends composed of P(D-2H3MB) and PLLA, were investigated for solvent evaporated and precipitated samples. For the solvent evaporated P(D-2H3MB)/P(L-2H3MB)/P(L-2HB) (50/25/25) (mol/mol/mol) blend, formation of TSC crystallites with a very small amount of P(D-2H3MB) and/or P(L-2H3MB) homocrystallites was observed, whereas in the precipitated P(D-2H3MB)/P(L-2H3MB)/P(L-2HB) (50/25/25) blend, P(D-2H3MB)/P(L-2HB) HTSC crystallites, P(D-2H3MB) and/or P(L-2H3MB) homocrystallites, and P(L-2HB) homocrystallites were formed without formation of TSC crystallites. This is the first report for TSC crystallization of all substituted PLAs with linear and branched side chains. In contrast, in both solvent evaporated and precipitated P(D-2H3MB)/P(L-2H3MB)/PLLA (50/25/25) (mol/mol/mol) blends, P(D-2H3MB)/P(L-2H3MB) homostereocomplex crystallites, P(D-2H3MB) and/or P(L-2H3MB) homocrystallites, and PLLA homocrystallites were formed without crystallization of TSC crystallites. It was confirmed that HTSC between P(D-2H3MB) and PLLA is not formed in both solvent evaporated and precipitated P(D-2H3MB)/PLLA (50/50) (mol/mol) blends. Based on reported and present results, we proposed the rule for TSC and HTSC crystallization of, respectively, binary and ternary substituted and unsubstituted poly(lactic acid)s, wherein all the optically active polymer components are included in the same SC crystalline lattice. The difference in carbon numbers of side chains between the two polymers with different chemical structures and opposite configurations is one.