Phase Behavior of a Semiflexible Polymer with both Thermotropic and Lyotropic Properties

A semiflexible polymer, comprising rodlike groups connected by spacer groups in alternating succession in the main chain and also rigid side groups attached to each backbone rodlike unit via a spacer, has been found to exhibit both thermotropic and lyotropic behavior. The polymer shows isotropic—nematic biphasic separation over a wide concentration range of 20-100% by volume in the temperature range of 25–268 °C. The resulting phase diagram therefore has a strongly bent chimney shape, in contrast to the nearly vertical chimney obtained with rigid rodlike polymers. Comparison of experimental results with the predictions of Flory and Warner on rodlike molecules with orientation-dependent interactions shows that the spacer groups in the main chain do not behave like free joints. The unique phase behavior is therefore attributed to the strong influence of the degree of flexibility of the spacer groups on the cooperative alignment of neighboring rodlike moieties in the ordered state. © 1989, American Chemical Society. All rights reserved.