Synthesis and properties of hyperbranched aromatic polyimides via thermal self-polycondensation

The thermal self-polycondensation of 4-(3,5-bis(4-aminophenoxy)phenoxy)phthalic acid, an AB2 type monomer, proceeded successfully at 140° C to form a hyperbranched poly(amic acid). The subsequent chemical imidization of the poly(amic acid) afforded hyperbranched aromatic polyimides bearing acetylamide (HBPI-Ac) or imide terminal (HBPI-Im) groups. The formation of high molecular weight polymers was confirmed by gel permeation chromatography measurements using a light scattering detector. The resulting polymers exhibited good solubility and low solution viscosity, which is typical for hyperbranched polymers. The degree of branching of HBPI-Ac was determined to be 0.48. Moreover, the 1H NMR measurement of the model phthalic acid compound at 120° C suggested that the formation of carboxyl anhydride units facilitated the amide bond formation, resulting in the hyperbranched poly(amic acid). HBPI-Im showed the temperature for a 5 % weight loss at 470° C, which was much higher than that of HBPI-Ac (400° C). HBPI-Im film, coated on a glass plate, became insoluble in amide solvents after heating at 280 ° C for 10 min, indicating that it could be applied as a solvent-resistant and thermally stable coating in the microelectronics industry. © 2020 Soc. Mater. Eng. Resour. Japan