Helical twisting power of chiral side-chain liquid crystal copolymers

A series of copolymers, comprising a chiral mesogen ((S)-(-)-4-methoxyphenyl-4'-(2-acryloyloxy)propoxy benzoate) and a non-chiral mesogenic comonomer (4-cyanophenyl-4'-(6-acryloyloxy) benzoate), was prepared, and each sample characterized physically and optically. The copolymers were found to exhibit a chiral nematic phase when the mole fraction of the chiral monomer in the copolymer was greater than 0.2. Films of these samples selectively reflect light of wavelength ?_R which is inversely proportional to the mole fraction of chiral monomer in the copolymer. The values of ?_R were determined at a fixed reduced temperature T* by differential absorption spectrometry and by specular reflectivity measurements. Plots of (1/?_R) against mole fraction of the chiral mesogen in the copolymer gave values of the helical twisting power of 5 × 10^-3 mm^-1, which is lower than observed for cholesterol-containing polymers but comparable to or greater than values reported for side-chain liquid crystal polymers with alternative chiral centres. Copyright © 1996 Elsevier Science Ltd.