PHASE-BEHAVIOR IN HIQ40 LIQUID-CRYSTALLINE POLYMERS

The thermotropic copolyester consisting of 40 mol% p-hydroxybenzoic ac id and 30 mol% isophthalic acid/30 mol% hydroquinone (HIQ40), prepared by two different synthetic routes (''acidolysis'' or ''phenylester'') was studied by differential scanning calorimetry and X-ray diffractio n. All these samples show a glass transition temperature in the range of 125-141 degrees C, dependent on the sample thermal history. A cryst al to nematic transition is observed between 300 and 375 degrees C. Th e samples prepared by the acidolysis route, when compared to those pro duced via the phenylester reaction, have higher crystallinity which is due to the formation of ''IA/HQ'' crystals. The crystallinity can be increased significantly (as much as twice) by annealing the polymers a t 300 degrees C. The heat of fusion (X --> N,crystal to nematic) of th e annealed acidolysis samples is also higher than that of the polymers prepared by the phenylester process. The nematic to isotropic (N --> I) transitions are broad, exhibiting no definite clearing points. Seve ral mesogenic transitions as suggested by X-ray studies and two crysta llization peaks were found for all samples studied. This may be an ind ication that the samples consist of two, distinct polymeric compositio ns or that there are two crystal forms. Furthermore, since the intensi ty ratio of the two crystallization peaks changes as a function of ann ealing, it is clear that the chemical/physical state of the polymer de pends on the thermal history of the samples. Attempts to prepare amorp hous HIQ40 and nematic HIQ40 glass by quenching from the isotropic sta te (480 degrees C and 400 degrees C, respectively) were unsuccessful, however, it can be prepared by precipitation of the acidolysis polymer from solution.