THERMOTROPIC LIQUID-CRYSTALS IN POLYPEPTIDES WITH MESOGENIC SIDE-CHAINS .1.

We prepared a new type of thermotropic liquid crystalline polypeptide, denoted PLG-BP-64 (see text), in which mesogenic biphenyl moieties are linked to a mesogenic alpha-helical main chain with a flexible spacer. This polymer exhibits transitions at T1 = 143-degrees-C and T2 = 222-degrees-C and forms three distinct phases, the crystalline, the smectic A, and the cholesteric phases. In the crystalline phase below T1, alpha-helical main chains form the layered structure and the biphenyl moieties in the side chains are crystallized in the space between the layers with their long axes perpendicular to the layer. In the temperature range from T1 to T2, the layered structure remains unchanged but the biphenyl moieties are in a liquid crystalline state in which the molten biphenyl groups are located still having the orientational order between the main-chain layers as in the crystalline phase. The structure can be assigned to be the smectic A phase. At the final temperature stage above T2, the layered structure collapses and the biphenyl moieties are randomly dispersed around the main chain, which results in the well-known cholesteric phase based on the alpha-helical mesogenic groups. The thermotropic transition behavior and the mesophase structures are illustrated by considering a coupling effect of main-chain and side-chain mesogenic groups.