Effect of chemical structures and environmental factors on the thermal degradation mechanism of polyimide: Experiments and molecular dynamics simulations

The impact of chemical structure and environment on the thermal stability of polyimide (PI) was examined, and the degradation mechanism was determined using a combination of experiments and molecular simulations. Changes in mechanical properties and thermogravimetric analysis (TGA) were used to characterize the thermal stability of PI. Pyrolysis gas chromatography mass spectrometry (Py-GCMS) and thermogravimetric-infrared spectroscopy (TG-IR) were used to analyze the degradation products both qualitatively and quantitatively. Molecular simulation was employed to analyze the primary bond breakage and thermal degradation pathways of PI, as well as to investigate the effects of the chemical structure, atmosphere, and temperature on degradation properties. The findings indicated that p-benzene-structured 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (PDA) has the best thermal stability, whereas weak bonds like C–O–C in 4,4′-oxydianiline (ODA) and C–N in the 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) imidazole group decrease thermal stability. The formation path of low molecular weight products (CO2, CO, HCN, and NH3) and the potential degradation mechanism of PI were proposed. The process of PI thermal degradation accelerated by oxygen and high temperature was observed at the atomic level. Taken together, this work offers the possibility of monitoring the structural evolution of PI degradation process in real-time.