Liquid-crystalline side-chain polyacrylates and polymethacrylates I. Variation of the terminal group

Abstract

Liquid-crystalline side-chain polyacrylates and polymethacrylates were prepared having the structure

with X = alkyl, −CH₂CN −CF₃, halogen, −OCH₃, −SCH₃ or the 3,4-methylendioxy group and R = −H or −CH3. The substituent X exerts a strong effect on the properties of the polymer. The influence of the polarizability of X was particularly pronounced; increasing the polarizability raised both the glass transition temperature T _g and to greater extent the clearing point T _cl, and also enhanced the formation of smectic phases. In the polyacrylate series, partial crystallization of the mesogenic side groups as well as a broadening of the two phase liquid crystal-isotropic region were observed with increasing polarizability of X. Polar (e.g. CF₃) and bulky (e.g. tertiary-butyl) substituents increase T _g; non-linear substituents diminish the liquid-crystalline phases. As expected the polyacrylates exhibited lower values of T _g but higher clearing temperatures than the analogous polymethacrylates. The more flexible polyacrylate chain also facilitates the formation of smectic phases.