Novel side-chain liquid-crystalline polyimide for film materials

A novel side-chain liquid-crystalline polyimide (SLCPI) was prepared via copolycondensation from 3,5-diamino-benzonic-4′-biphenyl ester, 4,4′-diamino- biphenyl ether, and 3,3′,4,4′-oxydiphthalic dianhydride. The energy-minimized structure and liquid crystallinity of SLCPI were investigated by molecular modeling, differential scanning calorimetry (DSC), wide-angle X-ray scattering, and polarized optical microscopy, respectively. The results indicated that this polyimide (PI) with side-chain mesogenic units exhibited a nematic NI phase. Because of the in situ self-reinforcement of side-chain mesogenic units, the improved tensile strength and modulus of PI films reached 270% and 300%, respectively. The coefficient of thermal expansion of films decreased by 40%. DSC and thermogravimetric analyses indicated that the phase-transition temperature of SLCPI was above 240 °C, and the 5% weight-loss temperature was above 520 °C. Moreover, copolycondensation of two diamines with dianhydride and incorporation of pendent mesogenic units diminished the regularity and symmetry of main chains; as a result, SLCPI exhibits good film processability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 554–559, 2003