In Situ Analysis of Chain Orientation Behavior in Thin Film Aromatic Polyimides by Variable Temperature pMAIRS during Thermal Imidization

摘要

A variable-temperature p-polarized multiple-angle incidence resolution spectroscopy (VT pMAIRS) technique is developed that enables the in situ analysis of the evolution of molecular orientation in polymer thin films induced by a wide range of temperature changes involving phase transition, chemical reaction, and so on. This technique is used to analyze variations in chain orientation during the thermal curing of thin films (<300 nm) composed of various aromatic polyimides (PIs) on Si substrates. The orientation mechanisms in these thin films are found to be significantly different from those of the corresponding thick films because of lower levels of residual solvent and low shrinkage during solvent evaporation and imidization. Furthermore, the orientation behavior strongly depends on chemical structure; for pyromelliric anhydride-based PIs, planar orientations of the PI segments spontaneously form with eliminating perpendicularly oriented precursor segments, while those of 3,3',4,4'-biphenyltetracarboxylic dianhydride-based PI segments occur in the film as a result of large tensile stresses induced by the imidization reactions. VT pMAIRS is a powerful tool for the analysis of complex behavior in multicomponent thin films involving morphological changes, chemical reactions, as well as molecular orientations.