Morphological self-control of a phase-separated polymer during photopolymerization in a liquid-crystalline medium

An acrylate monomer having a cyanobiphenyl mesogen (1) was photopolymerized in a liquid-crystalline (LC) ordering field of 4-hexyloxybenzoic acid (2). A blend of (1) and (2) (molar ratio: 1:4), containing a photoinitiator, an inhibitor and a crosslinker, was irradiated with UV light at 120 and 137 °C in order to investigate the effect of an LC phase on the resulting polymer. Here, both temperatures are in the nematic temperature range of the blend, however, the former is in the LC temperature range of the polymer, whereas the latter is in the isotropic temperature range. Scanning electron microscopy of the obtained polymers revealed that the polymer prepared at 120 °C consisted of oriented fine fibers, measuring ca. 400 nm in diameter, while that obtained at 137 °C had a fused bead-like morphology. In addition, we investigated the effect of crosslinking on the morphology by comparing the results from the blends with and without a crosslinker. We found that the LC phase of the phase-separated polymer is one of the necessary conditions for the formation of the fine fiber structures.