Phase behaviour of copolymers containing cholesterol and 4-methoxybiphenyl as mesogenic groups

Abstract

Liquid crystalline side group copolymers containing cholesterol and methoxybiphenyl were synthesized and investigated by size exclusion chromatography, ¹H NMR, polarization microscopy, X-ray diffraction, differential scanning calorimetry and additionally by measuring the birefringence and the optical reflection of the cholesteric phase. This cholesteric phase could be obtained by copolymerization of two monomers whose homopolymers exhibit only smectic phases. The cholesteric phase exists over a broad range of copolymer composition. For the cholesterol containing homopolymer an S_A2 bilayer phase was observed, whereas the methoxybiphenyl homopolymer shows a highly ordered E phase below an S_A1 monolayer phase. The layer periods of the S_A phases of the copolymers depend on the composition. By measuring the birefringence the order parameter in the cholesteric phase could be determined.