MOLECULAR MOBILITY AND STRUCTURE OF LINEA R THERMOTROPIC POLYESTERS WITH MESOGENIC GROUPS IN TRANS-FORM AND CIS-FORM

Dielectric relaxation spectroscopy, optical polarization microscopy, a nd X-ray diffraction were used to study the molecular mobility and str ucture of thermotropic linear polyesters with mesogenic groups showing conformational isomerism. Two forms of local mobility were identified for mesogenic fragments. With the aid of the studies with model compo unds, local motion was found to be associated with the mobility of cen tral and peripheral ester groups in the mesogen, which are not equival ent in terms of internal rotation. The crystalline structure and its e ffect on dielectric behavior of the samples were examined. Different s tructures of the central fragment of mesogenic group (biphenyl, azobip henyl, or diazobiphenyl) had no effect on the glass transition tempera ture, but enhanced the stability of mesomorphic phase. Partial cis-iso merization of the mesogen (20 and 40%) did not affect the intrachain m obility, but hindered the crystallization and reduced the temperature of transition to isotropic state.