FEATURES OF THE PHASE-BEHAVIOR OF ORIENTE D CROSS-LINKED LIQUID-CRYSTALLINE POLYMERS

A series of oriented cross-linked comblike liquid-crystalline (LC) pol ymers with cyanobiphenyl mesogenic groups in the side chains was synth esized by gamma-irradiation of the samples pre-oriented in magnetic fi eld. Investigations of the samples by methods of wideband H-1 NMR spec troscopy, microcalorimetry, and polarization microscopy showed that tr ansformation of a nematic mesophase of the cross-linked polymer into i sotropic melt is a phase transition of the first kind. The appearance of birefringence in the isotropic melt, the character of temperature v ariation of this parameter, and the conservation of oriented structure of the cross-linked LC polymer upon cooling of the isotropic melt (me mory effect) indicate that the behavior of the cross-linked LC polymer resembles that of a non-cross-linked polymer exposed to an external o rienting field. The observed effects are explained within the framewor k of a structural model of the isotropic melt of oriented cross-linked LC polymer.