Crystallization-Driven Self-Assembly of Block Copolymers Having Monodisperse Poly(lactic acid)s with Defined Stereochemical Sequences

Abstract

Monodisperse polymers composed of a discrete number of repeating units have attracted considerable interest as model systems to investigate the behavior of polymers having chemical structures without statistical distribution. Herein, we report the crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) built with monodisperse poly(lactic acid) (MPLA) composed of enantiomeric repeating units connected in a defined sequence and poly(ethylene glycol) (PEG). The morphology of self-assembled nanostructures was transformed by a systematic change in the number and the sequence of enantiomeric lactic acid units of MPLA blocks. This effect was more pronounced in the CDSA of a stereocomplex (SC) of a pair of BCPs having MPLA blocks configured in a complementary manner. When the size of the MPLA blocks was mismatched, a pair of the consequent BCPs self-assembled into nanostructures from nanoparticles to two-dimensional (2D) triangles and vesicles. In addition, on mismatching the stereochemical sequences of MPLA blocks forming the SC, the nanostructures of a BCP pair exhibited a transition from ill-defined structures to 2D triangular structures. Our results suggest that the low-dimensional nanostructures created by the crystallization of MPLA-b-PEG could be manipulated by their precisely defined molecular weight and stereochemical sequences.