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 characterized in terms of their mesomorphic properties. These monomers can be photopolymerized in situ in an appropriate ratio of vinyl and mercapto groups to form highly ordered liquid-crystalline main-chain polymers. During polymerization in the nematic phase the appearance changes from clear in the highly aligned birefringent state to opaque. This effect is probably due to scattering which is caused by the disturbance of the macro alignment as a result of the polymerization shrinkage and/or phase separation. In some cases, the reaction mixtures pass from the nematic to the crystalline state which results in a reduction in the degree of conversion and also in a change in the microcrystalline state. Crystallization can be suppressed by promoting asymmetry of the molecular structure which leads to a higher degree of conversion.