CRYSTALLIZATION KINETICS OF A THERMOTROPIC LIQUID-CRYSTALLINE POLYIMIDE DERIVED FROM 1,3-BIS[4-(4'-AMINOPHENOXY) CUMYL] BENZENE

We have studied the nonisothermal and isothermal crystallization kinet ics of an aromatic thermotropic liquid crystalline polyimide synthesiz ed from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA) and 1,3-bis[ 4-(4'-aminophenoxy) cumyl] benzene (BACB) by means of differential sca nning calorimetry (DSC). Polarized light microscopy (PLM) and wide-ang le X-ray diffraction (WAXD) results confirm that this polyimide exhibi ts a smectic texture. Nonisothermal crystallization showed two strong and one weak exothermic peaks during cooling. The phase transition fro m isotropic melt to liquid crystalline state is extremely fast which c ompletes in several seconds. The mesophase transition has a small Avra mi parameter, it, of approximate 1. The isothermal crystallization of 253-258 degrees C has been examined. The average value n is about 2.6 and the temperature-dependent rate constant k changes about two orders of magnitude in the crystallization temperature range of 6 degrees C. The slope of In k versus 1! (T-c Delta T) is calculated to be -2.4 x 10(5), which suggests nucleation control, via primary and/or secondary nucleation for the crystallization process. During the annealing proc ess, a new phase (slow transition) is induced, which grows gradually w ith annealing time. At lower annealing temperatures (220-230 degrees C ), the slow transition process seems not to be influenced by the cryst als formed during cooling process and its Avrami parameter n is ca. 0. 3-0.4. However, the slow transition was hindered by the crystals forme d during cooling process when annealed at higher temperature (230-240 degrees C). (C) 1998 John Wiley & Sons, Inc.