Synthesis and characterization of side chain liquid crystalline polymers exhibiting cholesteric and blue phases

Abstract

A series of cyclosiloxane‐based cholesteric liquid crystalline (LC) polymers were synthesized from a cholesteric LC monomer cholest‐5‐en‐3‐yl(3β) 4‐(2‐propenyloxy)benzoate and a nematic LC monomer butyl 4‐[4‐(2‐propenyloxy)benzoxy]benzoate. All the polymers exhibit thermotropic LC properties and show cholesteric phases. Most of the polymers display four types of phase transition behaviour corresponding to glass transition, melting point, cholesteric phase–blue phase transition and clearing point. The mesophase temperature range of the blue phases are as broad as 20°C. The blue phase was confirmed by the apperance of planar textures and cubic packings. With an increase of non‐chiral component in the polymers, the clearing point decreases slightly, while the glass transition and melting temperatures change little. In the reflection spectra of the polymer series the reflected wavelength broadens and shifts to longer wavelength with increase of the non‐chiral component in the polymer systems, suggesting that the helical pitch P lengthens.