Permeation and separation of organic liquid mixtures through liquid-crystalline polymer networks

A side-chain liquid-crystalline polymer (LCP) was synthesized by the addition of the mesogenic monomer to poly (methyl siloxane) in presence of a Pt-catalyst. When an aqueous solution of 10wt% ethanol was permeated through a LCP membrane by pervaporation at various temperatures, the permeation rate increased with increasing temperature and drastically changed at glass-nematic (Tg) and nematic-isotropic (TNI) transition temperatures of the LCP membrane. The LCP membrane exhibited the water-permselectivity in the glassy and liquid-crystalline states. The ethanol concentration in the permeate increased with increasing permeation temperature and the LCP membrane changed from the water-permselectivity to the ethanol-permselectivity around TNI. These results suggested that the permselectivity was influenced by the change of the LCP membrane structure, that is, its state transformation. It was found that a balance of the orientation of mesogenic groups and flexibility of siloxane chains is very important for the permeability and selectivity.