Studies on the photodegradation of polarized UV-exposed PMDA-ODA polyimide films

Polarized Fourier transform infrared (FTIR) and ultra violet-visible (UV-VIS) spectroscopy were used to investigate the photodegradation direction of polarized UV (PUV)-irradiated polyimide (PI) films based on pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA). PI films strongly absorb below 350 nm, resulting in a photochemical reaction of the PI. PUV irradiation of the PI film caused a decrease of all existing peaks and formation of new peaks at 3258, 1748, and 1710 cm(-1) in the IR, due to degradation of the PI molecules. The preferential degradation of PI molecules parallel to the PUV irradiation direction results in the predominant orientation of the remaining PI molecules perpendicular to the PUV irradiation direction. But rubbing of the PI films induced orientation of the PI molecules parallel to the rubbing direction. (C) 2002 Wiley Periodicals, Inc.