Molecular orientation in polyimide films

Abstract

Molecular orientation in polyimide thin films has been characterized using Fourier transform infrared spectroscopy, FT-IR. Biaxial orientation in these films has been characterized using attenuated total reflection, ATR spectroscopy with polarized radiation as well as by transmission spectroscopy with and without polarization. The polyimides studied were PMDA-ODA, PMDA-PDA and BPDA-PDA. The samples were prepared by spin casting from solution onto NaCl, germainium and quartz substrates. The samples were then cured to the polyimide using various temperature profiles. Initial investigations were of a uniaxilly deformed sample of PMDA-ODA polyamic acid. Polarized spectra of this sample are given. From these spectra it is clear that the C-N stretching vibration at 1500 wavenumbers has a transition moment which is parallel to the stretching direction. This is consistent with the axis of the polymer chains being oriented into the direction of stretch. In a study of the effect of the initial cure temperature on the degree of orientation, it was found that samples which were rapidly cured to 400 C were less oriented than samples cured initially at 200 C then ramping up to 400 C.