Effects of Annealing Siloxane Side-Chain Liquid Crystalline Polymers in the Biphasic Region

Siloxane-based side-chain liquid crystalline polymers (SCLCP) can be induced to phase separate by annealing near the clearing point in the biphasic region. This has been observed by differential scanning calorimetry (DSC), in which the isotropization endotherm becomes split, and in optical microscopy experiments. The effect was observed in all samples, independent of the chemical structure of the SCLCP synthesized. Only annealing at or below the maximum of the DSC clearing point endotherm was effective in inducing biphasic separation. When the samples were reheated above the clearing point, the demixed phases persisted for varying lengths of time, dependent on the nature of the spacer group covalently linking the mesogen side group to the siloxane backbone. Optical microscopy supports the demixing, which is proposed to be due to the distribution in molecular weight of the siloxane backbone. The effect of annealing in the biphasic region on the crystalline melting point and the glass transition was also examined. The number of precipitations of the SCLCP, which leads to a change in molecular weight distribution, also has an effect on the rate of the separation process.