Organosilicon mesomorphic polymer systems

This review is devoted to unusual organosilicon polymers exhibiting birefringence due to the formation of mesophase (mu) of the 'condis' (conformationally disordered) type. The polymers (cyclolinear and linear polysiloxanes, polysilanes, poly(oxymultisilanes), polycarbosilanes, their copolymers having organic monomeric units and their networks) are able to form thermotropic mesophases, basically of columnar architecture, although the macromolecules do not incorporate any typical 'rod'- or 'disc'-like mesogenic moieties. Their structure and morphology (if studied), as well as methods of synthesising them are reviewed with particular stress on the effect of polymer composition, molecular weight, and types of side chain substituents on the stability of mesophases and phase transfer temperatures. Most of these polymers show mesomorphic behaviour over a wide temperature range, even at rather elevated temperatures and the isotropisation occurs often only at the decomposition point. It is believed that they may be of importance as relatively simple structures with potential practical applications. (C) 2002 Published by Elsevier Science Ltd.