Miscibility and morphology of poly(ethylhexylacrylate)/liquid crystal blends prepared under different conditions

A comparative study of the phase diagrams and morphology of blends of poly(2-ethylhexylacrylate) and low molecular weight liquid crystals (LCs) prepared under different conditions is presented. Two LCs are used; one is the 4-cyano-4'-n-pentyl-biphenyl and the other is the eutectic mixture of cyanoparaphenylenes known as E7. Two series of blends are prepared under different conditions. The first series is obtained by the polymerization induced phase separation (PIPS) process under UV curing starting from a monomeric mixture, while the second series is prepared by a combination of the solvent induced phase separation and the thermally induced phase separation process starting from a mixture containing a commercial polymer with known molecular weight. Using gel permeation chromatography, it is found that the polymer molecular weight of the UV-cured systems decreases with the concentration of LC in the precursor mixture. The experimentally obtained phase diagrams of these two series of systems show a miscibility shift at the composition where the molar mass of the polymer in the PIPS/UV blend exceeds that of the commercial polymer. Data are rationalized in terms of the Flory-Huggins theory of isotropic mixing and the Maier-Saupe theory of nematic order. (c) 2006 Wiley Periodicals, Inc.