Synthesis and Characterization of a Combined Main-Chain/Side-Chain Liquid-Crystalline Polymer Exhibiting Both Thermotropic and Lyotropic Characteristics and Its Lyotropic Phase Behavior

摘要

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 deg 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 (T_g) of 85 deg C and a nematic-to-isotropic (N-I) transition temperature (T_(NI)) of 172 deg 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 T_g of ca.130 deg C and a TNI of ca.260 deg C,and it undergoes,during isothermal annealing,crystallization at about 240 deg 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 deg 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.