PHYSICAL AND CHEMICAL EVOLUTION OF PMDA-ODA DURING THERMAL IMIDIZATION

The processing of poly(imide) films from poly(amic acid) solutions inv olves the simultaneous loss of solvent and chemical conversion, and ma y involve structural reorganization such as orientation or crystalliza tion. Here, we describe weight loss, solvent sorption. Fourier transfo rm infrared (FTIR), and wide-angle x-ray scattering (WAXS) studies dur ing thermal imidization of the commercially important poly(imide) PMDA -ODA. The results indicate that imidization proceeds nearly to complet ion before significant crystallization occurs. The experimental data a re interpreted in terms of a triangular phase diagram that makes it po ssible to plot the processing pathway during the conversion from poly( amic acid) solution to solid poly(imide). In constructing this triangu lar phase diagram the extent of imidization (i.e., the composition of the poly(amic acid-co-imide) copolymers during conversion) is treated as an independent thermodynamic variable. The form of the triangular p hase diagram can be predicted from the Flory-Huggins lattice theory of mixing. There is inevitably a two-phase region present due to the rel atively poor solubility of the poly(imide) in the poly(amic acid) solv ent (NMP). The specific processing pathway taken depends on the relati ve amount of solvent loss and imidization during conversion. Further d etails about the triangular phase diagrams of poly(imides) will requir e such studies as solvent swelling at intermediate stages of conversio n. (C) 1995 John Wiley and Sons, Inc.