Molecular orientation of rigid-rod polyimide films characterized by polarized attenuated total reflection/Fourier transform infrared spectroscopy

The variations in the molecular orientation of uniaxially drawn rigid-rod polyimide films were systematically characterized in all three dimensions with polarized attenuated total reflection/Fourier transform infrared spectroscopy. The second-order orientation coefficients were directly deduced from the anisotropy in IR absorptions of particular bands. With the draw ratio increasing, the state of the molecular orientation changed from being nearly planar to completely uniaxial via biaxial orientation, and the degree of orientation was much larger than that of a semirigid polyimide having an ether linkage at the same draw ratio, which originated from the rigid-rod structure. In addition, the imide planes were rotationally oriented to the out-of-plane direction of the film geometry. Furthermore, the relationship between the molecular chain orientation and the in-plane birefringence in the biaxial orientation state was examined. The intrinsic birefringence was estimated from biaxial orientation films to be 0.33 at a wavelength of 1307 nm. (C) 2003 Wiley Periodicals, Inc.