HELICAL TWISTING POWER OF CHIRAL SIDE-CHAIN LIQUID-CRYSTAL COPOLYMERS

A series of copolymers, comp rising a chiral mesogen ((S)-(-) -4-metho xyphenyl-4'-(2-acryloyloxy)propoxy benzoate) and a non-chiral mesoenic 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 o f the chiral monomer in the copolymer was greater than 0.2. Films of t hese samples selectively reflect light of wavelength lambda(R) which i s inversely proportional to the mole fraction of chiral monomer in the copolymer. The values of lambda(R) were determined at a fixed reduced temperature T by differential absorption spectrometry and by specula r reflectivity measurements. Plots of (1/lambda(R)) against mole fract ion of the chiral mesogen in the copolymer gave values of the helical twisting power of 5 x 10(-3) mm(-3), which is lower than observed for cholesterol-containing polymers but comparable to or greater than valu es reported for side-chain liquid crystal polymers with alternative ch iral centres. Copyright (C) 1996 Elsevier Science Ltd.