Degree of Polymerization-Regulated Chirality of the Helical Nanopatterns Assembled by Polypeptide Block Copolymers on Homopolymer Nanorods

Chiral polymer self-assembly represents a powerful strategy for constructing chiral nanostructures; however, the mechanism underlying the evolution of chirality from molecular polymers to nanostructures is still not well understood. Especially, regulating the chirality of assemblies under external conditions without changing the chirality of the polymers attracts increasing attentions. In this work, we demonstrate that the degree of polymerization (DP) of the building polymers can effectively modulate the chirality of the nanostructures. It was found that for the nanopatterns assembled by poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) block copolymers on rod-like templates formed by PBLG homopolymers, a chirality transition from left-handed to right-handed is observed upon decreasing the DP of either the PBLG homopolymers, the PBLG blocks, or the PEG blocks. It is revealed that the chirality of the nanopatterns is governed by the chiral arrangement of the pendant phenyl groups of PBLG. Decreasing the DP of PBLG homopolymers or PBLG blocks weakens the dipolar attractions between PBLG chains and the solvents, whereas decreasing the DP of PEG blocks enhances the chain crowding between adjacent PBLG blocks. Both of these effects alter the arrangement of the pendant phenyl groups from an extended right-handed form to a contracted left-handed form, thereby inducing observed chirality inversion in the nanopatterns. This study offers a novel approach to control the chirality of polymer nanostructures through tuning the DP of building polymers and advances our understanding of chirality evolution from polymers to nanostructures.