Preparation and characterization of novel polyimide films containing amide groups

A novel diamine monomer 4-amino-N-(4-amino-phenyl)-benzamide (DABA) containing amide group was introduced to modify the polyimide of pyromellitic dianhydride (PMDA) and 4, 4′-oxydianiline (ODA) by copolymerization. A series of homo- and co-polyamic acid were synthesized by DABA and ODA in different molar ratio with PMDA, and polyimide films were obtained by thermal imidization. The films were characterized by tensile testing, dynamic mechanical analysis (DMA), thermal gravimetry analysis (TGA), fourier transform infrared (FTIR) and wide x-ray diffraction (WAXD). All of the obtained polyimide films show excellent mechanical properties and thermal stability. With the content of DABA increasing from 0% to 100%, the tensile strength and initial modulus are highly improved from 124.72 MPa and 4.70 GPa to 286.46 MPa and 22.06 GPa respectively. The polyimides have 5% weight loss temperature in the range of 530.0–555.5 °C. The glass transition temperatures are in the range of 387.90–409.16 °C and the tanδ values decrease from 0.3721 to 0.08316. The results of WAXD and FTIR indicate that the introduction of DABA containing amide group can improve the order degree of macromolecule and form hydrogen bonds between the main chains, which results in the improvement of mechanical properties.