Syndiotactic Poly(Substituted Methylene)s with Alkyloxycarbonyl Side Chains: Effects of Side Chain Chirality on the Main Chain Helix and Crystallinity

Syndiotactic poly(substituted methylene)s (st-PMs) with alkyloxycarbonyl side chains form hexagonal columnar liquid crystals (Col(h) LCs), wherein the main chain adopting either right- or left-handed helices is arranged in a 2D hexagonal lattice. This study investigates the main chain conformation for st-PMs with chiral side chains, designated as st-P8(3,7Me)-f(S)S. st-P8(3,7Me)-f(S)S polymers possess 3,7-dimethyloctyloxycarbonyl side chains at different S-enantiomeric fractions, f(S). In chiral st-P8(3,7Me)-f(S)S with an f(S) > 50%, the main chain adopts a one-handed helical conformation along the longer contour with increasing f(S). The f(S) influences the crystallinity of the polymers. Chiral P8(3,7Me)-f(S)S polymers crystallize the Col(h) LCs upon cooling. The crystallite size, melting temperature, and fusion enthalpy increase with f(S). Racemic st-P8(3,7Me)-50S does not crystallize.