Asymmetric Synthesis of Chiral Polyisocyanides from Achiral Monomers with Living Polymerization in a Liquid Crystal Reaction Field

Abstract

Enzymes and ribosomes play an important role in producing chiral biopolymers with precisely controlled molecular weights and helical properties, taking advantage of the asymmetric environment in the condensed state of a biological cell. This study demonstrates living polymerization in living cell-inspired chiral liquid crystals (LC) as a solvent for preparing preferentially one-handed helical poly(aryl isocyanide)s (PAIs) from achiral monomers with controlled molecular weights and narrow polydispersity. The rod-shaped aryl isocyanide monomers were designed to exhibit high compatibility with chiral host liquid crystal (LC) media. In polymerization, the main chain grows in the manner of living polymerization in the helical matrix by forming a one-handed helical structure. This represents the first-known study on helix sense-selective living polymerization of achiral monomers using cholesteric liquid crystal (CLC) medium as an environmentally structural chiral solvent. Polyisocyanides thus synthesized by the asymmetric living polymerization in cholesteric liquid crystals exhibited a lyotropic twist-bend nematic phase (N_tb), as a form of side chain-type polymer. Magnetic orientation is carried out to obtain a domain-stretched form. Polymerization in the CLC imparts chirality to the resulting PAIs as atropisomers, and the chiral PAIs form an N_tb via LC collective formation. In particular, the main chain forms a predominantly one-handed helical structure as an asymmetric structure, and the side chain drives an N_tb arrangement for the entire shape. Therefore, the LC state of PAIs can be defined as the polymer N_tb. Thus, the CLC as a reaction field has induced the formation of products showing a chiral polymer N_tb. Uniaxially oriented solid polymer films with the N_tb order were obtained using a magnetic field.