Solid-state amidization and imidization reactions in vapor-deposited poly(amic acid)

摘要

The condensation polymerization of 4,4'-oxydianiline with pyromellitic dianhydride for the formation of poly(amic acid) and the subsequent imidization for the formation of polyimides were investigated for films prepared with vapor-deposition polymerization techniques. Fourier transform infrared spectroscopy, thermal analysis, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of films at different temperatures indicated that additional solid-state polymerization occurred before imidization. The experiments revealed that, upon vapor deposition, poly(amic acid) oligomers formed that had a number-average molecular weight of about 1500 Da. Between 100-130 degreesC, these chains underwent an additional condensation reaction and formed slightly higher molecular weight oligomers. Calorimetry measurements showed that this reaction was exothermic [enthalpy of reaction (DeltaH) similar to -30 J/g] and had an activation energy of about 120 kJ/mol. The experimental DeltaH values were compared with results from ab initio molecular modeling calculations to estimate the number of amide groups formed. At higher temperatures (150-300 degreesC), the imidization of amide linkages occurred as an endothermic reaction (DeltaH similar to +120 J/g) with an activation energy of about 130 kJ/mol. The solid-state kinetics depended on the reaction conversion as well as the processing conditions used to deposit the films. (C) 2004 Wiley Periodicals, Inc.