Molecular Design for Preparation of Hexagonal-Ordered Porous Films Based on Side-Chain-Type Liquid-Crystalline Star Polymer

Fabrication of regularly porous films by the breath-figure method has attracted much attention. The simple, low-cost technique uses the condensation of water droplets to produce these structures, but the phenomenon itself is complex, requiring control over many interacting parameters that change throughout the process. Developing a unified understanding for the molecular design of polymers to prepare ordered porous films is challenging, but required for further advancements. In this article, the effects of the chemical structure of polymers in the breath-figure technique were systematically explored using side-chain-type liquid-crystalline star polymers. The formation of porous films was affected by the structure of the polymers. Although the entire film surface of poly­(11-[4-(4-cyanobiphenyl)­oxy]­undecyl methacrylate) (<b>P11CB</b>) had a hexagonal ordered porous structure over a certain <i>M</i>_n value, regularly arranged holes did not easily form in poly­(methyl methacrylate) (<b>PMMA</b>), even though the main chain of <b>PMMA</b> is similar to that of <b>P11CB</b>. A comparison of <b>P11CB</b> and poly­(11-[(1,1′-biphenyl)-4-yloxy]­undecyl methacrylate) (<b>P11B</b>) (<b>P11CB</b> without cyano groups) showed that the local polar groups in hydrophobic polymers promoted the formation of ordered porous films. No holes were formed in poly­(4-cyanobiphenyl methacrylate) (<b>P0CB</b>) (<b>P11CB</b> without alkyl spacers) films due to its hydrophilicity. The introduction of alkyl chains in <b>P0CB</b> allowed the preparation of honeycomb-structured films by increasing the internal tension. However, alkyl chains in the side chain alone did not result in a porous structure, as in the case of poly­(undecyl methacrylate) (<b>P11</b>). Aromatic rings are also required to increase the <i>T</i>_g and improve film formability. In the present study, suitable molecular designs of polymers were found, specifically hydrophobic polymers with local polar groups, to form a regularly porous structure. Development of clear guidelines for the molecular design of polymers is the subject of our current research, which will enable the fabrication of porous films using various functional polymers