Hierarchical assembly of a series of rod-coil block copolymers: Supramolecular LC phase in nanoenviroment

A series of narrowly distributed rod-coil diblock copolymers, polystyrene-block-(2,5-bis-[4-methoxyphenyl]oxycarbonyl)styrene) (PS-PMPCS), were synthesized by 2,2,6,6-tetramethyl-l-pip-eridinyloxy (TEMPO)-mediated living free radical polymerization. Differential scanning calorimetry, wide-angle X-ray diffraction, small-angle X-ray scattering, polorized light microscopy, and transmission electron microscopy were used to study the phase structure of this series of rod-coil polymers. It was found that the block copolymers microphase separate into ordered structures at temperatures below ca. 240 degreesC. PMPCS blocks form supramolecular columnar nematic phase (phiN) within the microphase-separated block copolymers. LC columnar axes were identified to be parallel to the block copolymer lamellar normal. Two layers of LC columns are confined in each LC domain, and the hierarchical structure resembles the "bilayer smectic A" phase observed in small molecular liquid crystals and rod-coil oligomers.