Influence of the spacer length on the phase behaviors of mesogen-jacketed liquid crystalline polymers with a bulk side-chain

Abstract

A series of mesogen-jacketed liquid-crystalline polymers (MJLCPs) containing two triphenylmethyl (Tr) units in the side chains, named poly{2,5-bis[(triphenylmethoxy-alkyl)oxycarbonyl]-styrenes} (denoted as Pv-m-Tr, m = 2, 4, 6, 8, 10, 12, which is the number of the methylene units between the terephthalate core and Tr moieties in the side chains), were designed and successfully synthesized via free radical polymerization. The chemical structures of the monomers were confirmed by ¹H NMR and mass spectrometry. The molecular characterizations of the polymers were performed with ¹H NMR, GPC and TG analysis. The phase structures and transition temperatures of the polymers were investigated by a combination of techniques including DSC, POM and 1D/2D WAXD. The experimental results revealed that all the polymers exhibited excellent thermal stabilities. The liquid crystalline (LC) phase structures and behaviors of the polymers were strongly dependent on the spacer length (m). With the increase of m, T_g of Pv-m-Tr decreased from 116.7 °C to 11.5 °C because of the alkyl plasticization. When m = 2, 4, 6, 8, 10, the Pv-m-Tr formed a stable columnar nematic (Φ_N) phase above T_g. When m = 12, the Pv-12-Tr presented a re-entrant isotropic phase above T_g and a LC phase at higher temperature. This work provides a new case to understand the structure–property relationships of MJLCPs based on the alkyl spacer and bulk side-chain.