SYNTHESIS AND POLYMERIZATION OF LIQUID-CRYSTALS CONTAINING VINYL AND MERCAPTO GROUPS

Liquid-crystalline monomers containing two vinyl groups, two mercapto groups, or a 1:1 combination of the two have been synthesized and char acterized in terms of their mesomorphic properties. These monomers can be photopolymerized in situ in an appropriate ratio of vinyl and merc apto groups to form highly ordered liquid-crystalline main-chain polym ers. During polymerization in the nematic phase the appearance changes from clear in the highly aligned birefringent state to opaque. This e ffect is probably due to scattering which is caused by the disturbance of the macro alignment as a result of the polymerization shrinkage an d/or phase separation. In some cases, the reaction mixtures pass from the nematic to the crystalline state which results in a reduction in t he degree of conversion and also in a change in the microcrystalline s tate. Crystallization can be suppressed by promoting asymmetry of the molecular structure which leads to a higher degree of conversion.