Synthesis and properties of liquid crystalline polysiloxanes

Most studies on the structure-property relationship of liquid crystalline polysiloxanes are focused on the side-chain-type polymers bearing calamitic or discotic side groups decoupled from the backbone via a flexible spacer. However, main-chain liquid crystalline polymers have been obtained by combining flexible siloxane segments with rigid rod-type mesogens. The synthesis and properties of these two types of liquid crystalline polysiloxanes are examined. One of the most widely used methods of preparation is the hydrosilylation of unsaturated mesogens. However, this reaction is not always as clean and clear-cut as would be necessary for the obtention of polymers with reproducible characteristics. This point is discussed and specific examples of side reactions are given. Some data concerning liquid crystalline polysiloxanes with no mesogenic groups as well as liquid crystalline elastomers are presented. Potential applications of these polymers and future developments are discussed.This review is from the Second International Topical Workshop, Advances in Silicon-Based Polymer Science.