SYNTHESIS AND THERMAL TRANSITIONS OF A SOLUBLE, MAIN-CHAIN, NEMATIC LIQUID-CRYSTALLINE POLYMER EXHIBITING A KINETICALLY TRAPPED, DISORDEREDSTRUCTURE

An aromatic copolyester composed of 25 mol % phenyl hydroquinone, 10 m ol % isophthalic acid, 40 mol % chloroterephthalic acid, and 25 mol % t-butyl hydroquinone (PICT) has been synthesized. This amorphous, glas sy polymer is soluble in common organic solvents such as methylene chl oride. Thin, solution-cast films may be prepared which are in a metast able, vitrified, optically isotropic state. On first heating of an iso tropic film at 20 degrees C/ min in a calorimeter, one glass transitio n is observed at low temperature (approximately 49 degrees C) and is a scribed to the glass/rubber transition of the metastable, isotropic po lymer. This thermal event is followed by a small exotherm due to the d evelopment of order during the scan, which results in a second T-g at approximately 125 degrees C. This T-g is associated with the glass/rub ber transition of the ordered polymer. Nematic order can be developed by thermal annealing. The lower T-g increases toward the upper T-g as annealing time is increased. For an initially isotropic film annealed at 90 degrees C, the increase of the lower T-g with annealing time and the increase in birefringence observed by optical microscopy are gove rned by similar kinetics. Isotropization occurs in the temperature ran ge of 250-300 degrees C. The nematic polymer is slightly more dense th an its isotropic analog. No detectable differences between isotropic a nd nematic samples were observed in rotating frame proton spin lattice relaxation times. (C) 1996 John Wiley & Sons, Inc.