Novel soluble polyimides derived from 2,2′-bis[4-(5-amino-2-pyridinoxy)phenyl]hexafluoropropane: Preparation, characterization, and optical, dielectric properties

Two novel aromatic diamine monomer, 2,2′-bis[4-(5-amino-2-pyridinoxy)phenyl] hexafluoropropane (6FBAPDP) and 2,2′-bis[4-(5-amino-2-pyridinoxy)phenyl] propane (BAPDP), were successfully synthesized. Aimed at clarifying the structure-property relationships of pyridine-containing high-performance polymers, a series of novel fluorinated polyimides PI-(1–4) were prepared from 6FBAPDP with various commercially aromatic anhydrides, and polyimide (PI-5) was synthesized derived from BAPDP and 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) via a two-stage process with heating imidization method. The fluorinated polyimides PI-(1–4) exhibited good solubility in strong polar solvents, such as N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, m-cresol, and could afford flexible, tough and transparent films with an UV–visible absorption cut-off wavelength at 342–393 nm. The glass transition temperatures of these polyimides were recorded between 239 and 306 °C by differential scanning calorimetry, and the 5% weight loss occurred at temperatures above 498 and 490 °C, in nitrogen and air, respectively. The polyimide films had the in-plane coefficients of thermal expansion (CTE) that ranged from 54 to 74 ppm °C−1. Moreover, the fluorinated polyimide films showed low moisture absorptions of 0.51–0.82% and outstanding mechanical properties with the tensile strengths of 75–100 MPa, tensile moduli of 3.2–4.0 GPa and elongation at break of 5.5–10.3%, good dielectric properties with low dielectric constants of 2.71–2.92 at 1 MHz.