Side-chain polycarbosilane-based liquid crystals

Side-chain liquid crystal polycarbosilanes can be obtained by ring-opening polymerization of silacyclobutanes bearing mesogenic substituents or, alternatively, silacyclobutanes can be polymerized to linear polymers with reactive Si-H moieties, and the latter polycarbosilanes are used in the hydrosilylation of mesogenic alkenes subsequently. A 'one-pot' synthesis makes their preparation more efficient, while application of silyl-modified polyethylenes leads to liquid crystalline materials with properties similar to the traditional polycarbosilanes, but at lower cost. Polycarbosilanes, a novel group of organosilicon liquid crystals, have a unique regularity in their pendent mesogenic groups, the 'density' of which can be varied to meet particular requirements. The best known organosilicon side-chain liquid crystals, based on the polysiloxane main chain, have T-g and mesophase transition temperatures that are typically 60-100 degrees C lower than their acrylate or methacrylate analogues. The intermediate flexibility of the polycarbosilane main chain allows us to cover the temperature gap for the generation of a mesophase, that exists between these organic and inorganic liquid crystal polymers.