The retarding effects and structural evolution of a bio‐based high‐performance polyimide during thermal imidization

ABSTRACT The thermal imidization evolution of a bio‐based high‐performance polyimide, namely adenine‐containing polyimide (API), was investigated by thermogravimetric analysis (TGA), in situ Fourier transform infrared spectroscopy (in situ FTIR), and wide‐angle X‐ray diffraction (WAXD), in contrast to an adenine‐free 4,4′‐oxydiphthalic anhydride (ODPA)/4,4′‐oxydianiline (ODA) PI. The influence derived from adenine was focused. At precursor stage of API (polyamic acid, PAA), the H‐bonding interaction of PAA–PAA type as well as the especial interaction between the secondary amine of adenine and solvent (dimethylacetamide, DMAc) was discovered. Structural evolution of API was traced by in situ FTIR and multistage WAXD from PAA stage to PI stage. Compared with OPI, the retarding effects were found in the process of thermal imidization of API, partly due to the formation of H‐bonding derived from the extra secondary amine of adenine moieties, which complicated the H‐bonding form in API. Finally, a hypothesis of evolution of thermal imidization process about API molecule was proposed in contrast with adenine‐free ODPA ODA PI. Compared with the consistency of both API and ODPA ODA PI in PAA stage, API possessed a more delicate thermal imidization process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46953.