THE MOLECULAR-STRUCTURE OF POLY(BIPHENYL DIANHYDRIDE-P-PHENYLENEDIAMINE) POLYIMIDE THIN-FILMS BY INFRARED-SPECTROSCOPY - THICKNESS DEPENDENCE OF STRUCTURE IN THE NANO-METER TO MICROMETER RANGE

The molecular structure of poly[biphenyl dianhydride-p-phenylenediamin e] (BPDA-PDA) polyimide in ultrathin (3-300 nm) films on silicon has b een characterized by polarized infrared spectroscopy in conjunction wi th ellipsometry and X-ray reflectivity measurements. In spite of the h igh degree of crystalline packing of the polymer chains, the results s how that an unexpected and significant content of imide rings exhibit local structural perturbations, including out-of-plane twisting. Furth er, the fraction of perturbed rings increases with increasing film thi ckness while, in contrast, the high degree of in-plane uniaxial film s ymmetry and planar stacking of the chains remain constant with thickne ss. These results reveal a new structural aspect of localized ring dis order that arises within the otherwise well-ordered, chain-stacked str ucture of BPDA-PDA polyimide films. (C) 1998 John Wiley & Sons, Inc.