A novel series of styrene‐based liquid crystal monomers displaying either nematic or chiral nematic phases

Abstract

A new series of liquid crystalline styrene‐based monomers is described. These monomers are prepared by the DCC‐mediated esterification reaction between 4‐[11‐(4‐vinylphenoxy)undecyloxy]benzoic acid and a range of phenols chosen due to their proven utility in the synthesis of liquid crystals. Most members of the series display thermally stable (enantiotropic) nematic phases, although a few give only monotropic nematic phases. By incorporating the (S)‐2‐methylbutyl side chain, monomers that exhibit the chiral nematic phase can be obtained. Predictably, monomers derived from phenols containing an additional ring as substituent (e.g. 4‐cyano‐4′‐hydroxybiphenyl) display relatively high transition temperatures. In contrast, monomers derived from simple 4‐n‐alkylphenols possess a nematic phase, which is accessible at moderate temperatures. In addition, a eutectic mixture derived from these monomers has a melting point only just above room temperature, which is an advantage for the fabrication of robust films via the in situ photopolymerization process. Standard free radical polymerization of a number of these monomers provides side chain liquid crystal polymers, SCLCPs, with mesophases that are stable over a wide temperature range. For a homologous series of SCLCPs containing a terminal n‐alkyl chain on the mesogenic group, an unexpected but distinct odd–even effect is observed.