Assessing the Thermo‐Oxidative Degradation of <scp>6FDA</scp>‐Based Thermosetting Polyimides Using a Combination of Isothermal and Non‐Isothermal <scp>TGA</scp>

ABSTRACT This study investigates and compares the thermal stability of two 6FDA‐based thermosetting polyimide formulations with varied amounts of internal crosslinkers. The baseline formulation is a commercially available polyimide with good resin transfer molding processability and a high glass transition temperature, T g , in the range of 340°C–466°C. The altered formulation has a reduced amount of internal crosslinkers. In the current study, the materials are studied through multiple thermogravimetric analysis (TGA) scans to investigate how the polyimide formulation affects the thermo‐oxidative properties in the cured state. The measurements and the subsequent analyses reveal that the two polyimides have similar thermal oxidation behavior after curing, despite the changes. A combined model‐based approach, utilizing both isothermal and non‐isothermal TGA data, is used for the analysis and to create conversion‐time–temperature diagrams for both materials. The combined method is compared to pure isoconversional and non‐isothermal model‐based methods and shows improvement in the ability to model the degradation of the materials.