Thermotropic and Lyotropic Mesomorphism in a Polymeric Network with Low Cross-Link Density

The synthesis and the phase properties of a cross-linked polymer are reported. The cross-linkedpolymer exhibits thermotropic nematogenic behavior with isotropization temperature and enthalpy not very much lower than measured for the linear polymer. Swelling in o-dichlorobenzene produces an optically anisotropic material containing 73.7% (mass) solvent at room temperature. Its X-ray diffraction pattern is consistent with a noncrystalline structure. The swollen polymer undergoesa thermotropic transition (peaked around 84-87 "C) to an optically isotropic phase. If the phase transition takes place in the presence of free solvent, further swelling occurs. The transition enthalpy per unit mass of pure polymer is considerably larger than found for the isotropization of the pure polymer itself. Seemingly, some ordering of the solvent molecules is involved.