Side Chain Liquid Crystalline Polypeptides

In side-chain liquid crystalline polymers, the length of the spacer between the backbone and the liquid crystalline mesogen controls its mobility and determines the properties and thermal characteristics of the polymer. The polymers being studied consist of a poly(L-lysine) backbone with side-chain mesogenic groups connected with a flexible spacer of three, five, and ten methylene groups. Characterization of the thermotropic mesogen and of the poly(L-lysine) backbone as separate components is critical in order to understand the thermal dependence of liquid crystal transitions. Circular dichroism studies have shown the secondary structure of the backbone to be alpha helical. Thermal transitions have been determined using differential scanning calorimetry, and polarized optical microscopy is used to identify specific mesophases characteristic of thermotropic liquid crystals. Although the phase behavior of the mesogen is complicated, when coupled with the polypeptide backbone these materials show only a single liquid crystalline phase whose melting temperature is determined by the length of the spacer.