Composition design and properties investigation of BPDA/PDA/TFDB co‐polyimide films with low dielectric permittivity

Aiming at fabricating the polyimide (PI) films with low permittivity and excellent comprehensive properties, 2,2 '-bis-(trifluoromethyl)-4,4 '-diaminobiphenyl was incorporated into the polyimide backbone composed of 3,3 ',4,4 '-biphenyltetracarboxylic dianhydride and p-phenylenediamine. The introduction of trifluoromethyl (-CF3) groups led to a substantial reduction of the PI's permittivity (3.42-2.96). Meanwhile, as-prepared co-PI films showed excellent mechanical performance (217.13-238.20 MPa for strength and 3.49-4.90 GPa for modulus), as well as good thermal stability (high glass transition temperature over 354 degrees C, whereas low thermal expansion coefficient below 10 ppm/K). Structure-property relationship of the PI samples was further established through molecular simulations (MS), which suggested the crucial effects of polarizability per unit volume (alpha/V-vdw) and free volume on PI permittivity. The computational results were highly consistent with the experimental findings, meaning that MS technique is of guiding importance in copolymer design. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47989.