Synthesis and Characterization of a Combined Main-Chain/Side-Chain Liquid-Crystalline Polymer Exhibiting Both Thermotropic and Lyotropic Characteristics and Its Lyotropic Phase Behavior
journal contributionposted on 15.11.2005 by Ming Zhou, Chang Dae Han
Any type of content formally published in an academic journal, usually following a peer-review process.
A combined main-chain/side-chain liquid-crystalline polymer (PSHQ4−7CNCOOH), which is composed of poly[(phenylsulfonyl-p-phenylenene 1,4-tetramethylene bis(oxybenzoate)] (PSHQ4) as the main-chain backbone and 8-[(4-cyano-4‘-phenyl)oxy]octanoic acid (7CNCOOH) as the side-chain mesogenic groups, has been synthesized. It has been found that 7CNCOOH has a clearing temperature of 150 °C and exhibits nematic mesophase, and PSHQ4−7CNCOOH exhibits both thermotropic and lyotropic characteristics. The thermotropic characteristics of PSHQ4−7CNCOOH have been investigated using differential scanning calorimetry (DSC), fiber and powder patterns of wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). It has been found that in the thermotropic state PSHQ4−7CNCOOH has a glass transition temperature (Tg) of 85 °C and a nematic-to-isotropic (N−I) transition temperature (TNI) of 172 °C, and it is a glassy polymer. Interestingly, PSHQ4−7CNCOOH is found to exhibit lyotropic characteristics, undergoing isotropic-to-nematic biphasic separation over a wide range of concentrations in m-dibromobenzene, o-dichlorobenzene, and tetrachloroethane, enabling us to construct a phase diagram. The thermal transitions and phase structures of the main-chain backbone of PSHQ4−7CNCOOH, PSHQ4, were compared with those of PSHQ4−7CNCOOH. It has been found that PSHQ4 has a Tg of ca. 130 °C and a TNI of ca. 260 °C, and it undergoes, during isothermal annealing, crystallization at about 240 °C as determined from DSC. Both the fiber and powder patterns of WAXD indicate that PSHQ4 is a semicrystalline polymer, which is consistent with the findings from DSC. It has been found that, in contrast to PSHQ4−7CNCOOH, PSHQ4 does not exhibit lyotropic characteristics. Both the very large decrease (about 90 °C) in TNI after the attachment of side-chain mesogenic groups (7CNCOOH) onto the main-chain backbone (PSHQ4) and the lyotropic characteristics of PSHQ4−7CNCOOH are attributable to the significant increase in the bulkiness of PSHQ4−7CNCOOH, which apparently cannot pack well, giving rise to a glassy state.