Asymmetric Polymerization-Induced Crystallization-Driven Self-Assembly of Helical, Rod-Coil Poly(Aryl Isocyanide) Block Copolymers

The helical motif is ubiquitous in naturally occurring chemical systems where it confers numerous useful and distinct material properties. Accordingly, a great many synthetic materials have been produced in efforts to mimic biological systems. As an inherently chiral structural feature, the helix provides a modular platform for the creation of chiral nanomaterials exhibiting a diverse range of capabilities. Nonetheless, the development of rapid, scalable methods for production of chiral nanomaterials presents a formidable challenge. However, recent advances in both amphiphilic block copolymer (BCP) synthesis and self-assembly provide tractable means to do just that. In this work, polymerization induced crystallization-driven self-assembly (PI-CDSA) is combined, for the first time, with helical, rod-coil BCP self-assembly to enable scalable and controllable in situ synthesis of chiral nanostructures with variable shape, size, and dimensionality. Herein, we detail the use of newly developed Asymmetric PI-CDSA methodologies in the synthesis and in situ self-assembly of chiral, rod-coil BCPs comprised of poly(aryl isocyanide) (PAIC) rigid-rod and poly(ethylene glycol) (PEG) random-coil components. Using PEG-based Ni(II) macroinitiators, chiral PAIC-BCP nanostructures are constructed in a controlled, scalable fashion forming variable chiral morphologies including 1D twisted nanofibers, 2D hexagonal nanosheets and 3D twisted spirangles (i.e., spirally arranged hexagonal nanosheet stacks). Using seeded, living asymmetric PI-CDSA, the lengths and heights of 1D nanofiber and 3D spirangle nanostructures, respectively, can be selectively tuned via alterations in unimer-to-seed ratios. The formation of these nanostructures is dictated by the liquid crystalline nature of PAIC blocks and the hierarchical assembly of these BCPs, with chirality translated across length scales and in multiple dimensions (i.e., spirangles), led to large amplifications in chiroptical activity with high Kuhn’s dissymmetry factors reaching 0.029.