B. Y. Myung, J. J. Kim and T. H. Yoon
A novel dianhydride monomer, 3,6-di[3′,5′-bis(trifluoromethyl)phenyl]pyromellitic dianhydride (12FPMDA), was synthesized via the Suzuki cross-coupling reaction followed by oxidation and cyclodehydration. 12FPMDA was used to prepare polyimides with 1,1-bis(4-aminophenyl)-2,2,2-trifluoroethane and 4,4′-diaminodiphenylether, and the polyimides were designed to have molecular weights of 20,000 g/mol via off-stoichiometry. The resulting polyimides were characterized by Fourier transform infrared, NMR, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis, and their solubility, solution viscosity, water absorption, coefficients of thermal expansion (CTEs), and dielectric constants were also evaluated. The polyimides exhibited excellent solubility even in acetone and toluene, high glass-transition temperatures (>311 °C), good thermal stability (>518 °C in air), and well-controlled molecular weights (19,000–21,000 g/mol). They also provided low CTEs (35–50 ppm/°C), water absorption (1.26–1.35 wt %), and dielectric constants (2.49–2.52).