Synthesis of Combined Main-Chain/Side-Chain Liquid-Crystalline Polymers via Self-Assembly

Abstract

Three combined main-chain/side-chain liquid-crystalline polymers (MCSCLCPs) were prepared via hydrogen bonding or ionic interactions. The first MCSCLCP, PyHQ12−7CNCOOH, was prepared via hydrogen bonding between the pendent nonmesogenic pyridyl group in a main-chain liquid-crystalline polymer (PyHQ12) and the carboxylic acid group (−COOH) in mesogenic 8-[(4-cyano-4‘-biphenyl)oxy]octanoic acid (7CNCOOH). The second MCSCLCP, PABP−AA, was prepared via hydrogen bonding between the nonmesogenic azopyridyl group in the side chain of a main-chain liquid-crystalline polymer (PABP) and the carboxylic acid group (−COOH) in nonmesogenic p-anisic acid (AA). The third MCSCLCP, PABP−TSA, was prepared via ionic interactions between the nonmesogenic azopyridyl group in the side chain of PABP and the sulfonic acid group (−SO3H) in nonmesogenic p-toluenesulfonic acid (TSA). The presence of hydrogen bonds in self-assembled PyHQ12−7CNCOOH and PABP−AA and the presence of ionic interactions in PABP−TSA were confirmed using Fourier transform infrared (FTIR) spectroscopy, the thermal transitions in each MCSCLCP were determined using differential scanning calorimetry (DSC), and the mesophase structures of each self-assembled MCSCLCP were characterized using polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). The following observations have been made. Self-assembled PyHQ12−7CNCOOH (1) has a nematic mesophase as determined by POM, (2) undergoes a glass transition at ca. 54 °C and nematic-to-isotropic transition at ca. 154 °C as determined by DSC and WAXD, and (3) has a significant degree of hydrogen bonding at temperatures even above its clearing temperature as determined by in situ FTIR spectroscopy. Self-assembled PABP−AA (1) has a smectic mesophase as determined by POM and WAXD, (2) undergoes melting at ca. 120 °C and smectic-to-isotropic transition at ca. 161 °C as determined by DSC, and (3) has a moderate degree of hydrogen bonding at temperatures even above its clearing temperature as determined by in situ FTIR spectroscopy. Self-assembled PABP−TSA (1) has a smectic mesophase as determined by POM, (2) undergoes a glass transition at ca. 58 °C, melting at ca. 110 °C, and smectic-to-isotropic transition at ca. 155 °C as determined by DSC, and (3) has strong ionic interactions as determined by in situ FTIR spectroscopy at temperatures even above the clearing temperature.