Synthesis and characterization of H-bonded side-chain liquid-crystalline polysiloxanes

Smectic Liquid-crystalline (LC) polysiloxanes P1 similar to P7 were prepared using cholesteryl 6-undec-10-enoyloxy-naphthalene-2-carboxylate and cholesteryl 3-sulfo-4-undec-10-enoyloxy-benzoate in a one-step reaction with sulfonic acid group contents ranging between 0 and wt4.39%. With an increase of sulfonic acid groups, the glass transition temperature rose slightly; while the temperature of clear point decreased. As sulfonic groups increased, H-bonding interaction strengthened, resulting in an increase of glass transition temperature. On the other hand, aggregates of H-bond derived from sulfonic acids would destroy the homogeneous rigid moieties and the high-ordered structure, resulting in a temperature of clear point decreased. In X-ray measurement, all the polymers displayed sharp strong peaks around 2 theta approximate to 2.6 degrees and broad peaks around 2 theta approximate to 16.6 degrees. The broad peaks at wide-angle are similar, but there is great different at low angles. For the polymer without sulfonic acid, the only one strong peak at low angle indicates high-ordered lamellar structure due to homogeneous rigid moieties. For the polymers containing more sulfonic acid, two sharp peaks appeared at low angles, and the intensities of these two peaks varied. With increase of sulfonic acid groups in the polymer systems, the hydrogen-bonding aggregates in domains would divide the homogeneous rigid mesogens into two kinds of nanophases, that is, one containing non H-bond mesogens and another involving H-bonding aggregated mesogens. These two different nanophases result in different lamellar spacings.