Correlation Between Side-Chain Arrangement and Main-Chain Helix Conformation in Liquid Crystalline Syndiotactic Poly(Substituted Methylene)s Bearing Cyanobiphenyl Mesogens

This study focuses on the helical conformation of the main chain of syndiotactic poly(substituted methylene)s with 4-cyanobiphenyl (CB) moieties incorporated at the ends of the alkyloxycarbonyl side chains. The polymers are designated as PCBn, where n is the number of methylene units in the spacer between the main chain and CB. PCB6 and PCB8 assemble the side chains into layers without positional order within the layers. Meanwhile, PCB10 and PCB12 assemble the side chains into layers with a short-range positional order. Each CB moiety at a side chain end is bonded to a carbon atom, which is arranged along the helical main chain contour, and its position correlates with that of the carbon atom. As the temperature increases, PCB10 undergoes a phase transition, losing the positional order of the side chains within a layer, which alters the main chain conformation. Consequently, the positions of the side-chain CB moieties affect the helical conformation of the main chain. In contrast, PCB12 maintains the main chain conformation when undergoing a phase transition similar to that of PCB10. PCB12 with the longer spacer allows the main chain to adopt a helix conformation, which is independent of the positions of side-chain CB moieties. Syndiotactic poly(substituted methylene)s bearing 4-cyanobiphenyl (CB) moieties at the side-chain end, designated as PCBn, form smectic structures by assembling side-chain CBs into layers with short-range positional ordering. The main-chain carbon atom positions along the helical chain contour correlate with the side-chain positions. image