Synthesis and properties of polyimides from a diamine containing side diphenylphosphine oxide and trifluoromethyl groups

A fluorinated diamine, (2,5-bis(4-amino-3-trifluoromethylphenoxy)phenyl)diphenyl-phosphine oxide (2), was synthesized via Williamson reaction and hydrogenation. A series of polyimides with side diphenylphosphine oxide and trifluoromethyl groups were prepared by the high-temperature one-pot polymerization of diamine 2 with several commercial aromatic dianhydrides. The resulting PIs exhibit excellent solubility in common organic solvents (i.e., tetrahydrofuran, trichloromethane etc.) and are easily processed into light color transparent films (thickness: 20 ± 1 μm) through the blade-coating method. The transmittance of PI films is above 86% in the visible light region (400—760 nm). They also show good thermal stability with the glass transition temperatures from 246 to 286 °C. The limiting oxygen index values of them exceed 38.3%. At the same time, they display the low water absorption (0.89—1.32%) and good mechanical properties (tensile strength: 72.3—153.24 MPa, Young’s modulus: 1.4—2.3 GPa, elongation at break: 6.9—12.5%). They are promising candidates for advanced flame-retardant and optical film materials.