Curing Kinetics of Ultrahigh-Temperature Thermosetting Polyimides Based on Phenylethynyl-Terminated Imide Oligomers with Different Backbone Conformations

A series of phenylethynyl-terminated imide (PETI) oligomers with varying chemical backbones and calculated number-average molecular weights were successfully synthesized via chemical imidization. These PETI oligomers exhibited exceptional solubility (>50 wt %) in both the high-boiling-point solvent N-methyl-2-pyrrolidinone (NMP) and low-boiling-point solvents tetrahydrofuran (THF) and 1,4-dioxane (dioxane). The curing reactivities of the PETI oligomers were assessed based on the dianhydride structure using a nonisothermal differential scanning calorimetry (DSC) method. Kinetic parameters, including the preexponential factor (A), activation energy (E-a), reaction order (n), and reaction rate constant (k), were determined using Kissinger, Ozawa, Crane, and Arrhenius equations. All PETI oligomers followed a first-order kinetic reaction model below 90% conversion. The curing process was characterized by two distinct stages: initiation and propagation. PETI oligomers containing electron-donating linkages (-O-) exhibited the lowest curing reactivity. In contrast, despite its slower initiation, the PETI oligomer containing electron-withdrawing groups (-CF3) exhibited the highest curing reactivity. Thermally cured resin derived from 2,3,3 ',4 '-biphenyltetracarboxylic dianhydride and 2,2 '-bis(trifluoromethyl)benzidine is expected to exhibit excellent processability and thermal stability due to their high solubility, relatively low T-m (237.4-263.1 degrees C), and remarkable T-d5% of 595.3 degrees C. This study provides a comprehensive understanding of the properties of PETI oligomers, enabling informed material selection for high-performance resin-based composite applications.