OPTICAL-PROPERTIES OF SIDE-CHAIN LIQUID-CRYSTAL COPOLYMERS OF MONOSUBSTITUTED CHOLESTERYL ITACONATE AND A NONCHIRAL MESOGEN

New mono- and disubstituted cholesteryl derivatives of itaconic acid h ave been prepared and their thermotropic liquid crystalline behaviour examined. The monosubstituted derivative has been homopolymerized, and also copolymerized with a non-chiral mesogen 4-cyanophenyl-4'-(6-acry loyl oxyhexyloxy) benzoate. Examination of the series of copolymers pr epared, using differential scanning calorimetry and hot-stage polarizi ng microscopy, showed that when the content of the cholesteryl itacona te was high, both a smectic-A phase (S-A) and a cholesteric phase (N) were present. It was found that the S-A phase could be eliminated by lowering the content of the cholesteryl itaconate in the copolymers, g iving samples that displayed only the N phase over a much wider tempe rature range. The samples in the N phase also exhibited selective ref lection of visible light that changed from short to long wavelengths a s the samples were cooled from the isotropic melt. These colours can b e locked into the glassy state of the polymer by quenching below the g lass transition temperature, but only if the S-A phase is absent. It w as also noted that at high contents of the cholesteryl itaconate the s elective reflection appears to occur in the ultraviolet region.