Synthesis and Properties of a Thermotropic Copolyester Based on 4,4'-Dihydroxy-a,a'-Dimethylbenzalazine.

摘要

Thermotropic mesomorphism exhibited by organic compounds has been known and studied extensively for over a century. However, it was not until the mid-1970's that the thermotropic behaviour of polymeric liquid crystals (PLCs) was demonstrated. Since then, there has been an ever increasing interest in this field, reflected by an explosion in publications and patents issued, as well as the commercialisation of several PLCs. Research on thermotropic PLCs can be divided into two broad categories: main chain PLCs and side chain PLCs. The former field has also branched into several different areas largely as a result of the efforts to reduce the usually very high transition temperatures. One of these involves the incorporation of flexible spacers in the main chain, a subject that was recently reviewed by Ober et al. Roviello and Sirigu, first demonstrated thermotropic behaviour in polymers with semi-flexible polyester PLCs based on the mesogen 4,4'-dihydroxy-alpha,alpha'-dimethylbenzalazine. These nematic polyesters had relatively low transition temperatures and were soluble. Among other things, the authors also established that by using two different aliphatic spacers, the melting transition could be lowered significantly while the clearing temperatures remained more or less unchanged. The biggest effect occurred for a 50/50 mole ratio of the spacers.