Synthesis and properties of fluorinated polyimides, 2. Derived from novel 2,6‐bis(3′‐trifluoromethyl‐p‐aminobiphenyl ether)pyridine and 2,5‐bis(3′‐trifluoromethyl‐p‐aminobiphenyl ether)thiophene

Novel diamine monomers, 2,6‐bis(3′‐trifluoromethyl‐p‐aminobiphenyl ether)pyridine (TABP) and 2,5‐bis(3′‐trifluoromethyl‐p‐aminobiphenyl ether)thiophene (TABT) have been synthesized, which lead to a number of novel fluorinated polyimides by thermal imidization routes when reacted with different commercially available dianhydrides like pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic acid dianhydride (BTDA) or 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane (6FDA). The polyimides ABTP/6FDA and ABTT/6FDA are soluble in several organic solvents such as N,N‐dimethylformamide (DMF), N,N‐dimethylacetamide (DMAc) and tetrahydrofuran (THF). The polyimide ABTP/PMDA is only soluble in N‐methylpyrollidone (NMP) whereas ABTT/PMDA is insoluble in all solvents. The polyimides ABTP/6FDA (2c) and ABTT/6FDA (3c) exhibited number‐average molecular weight 32 940 (polydispersity index (PDI), 1.97) and 24 760 (PDI, 1.87) respectively. These polyimide films have low water absorption rate 0.3–0.9% and low dielectric constant 2.92–3.29 at 1 MHz. These polyimides showed very high thermal stability even up to 532 °C for 5% weight loss in synthetic air and glass transition temperature up to 287 °C (by DSC) in nitrogen. All polyimides formed tough transparent films, with tensile strength up to 115 MPa, a modulus of elasticity up to 2.91 GPa and elongation at break up to 12% depending upon the exact repeating unit structure.

TGA thermograms of the thiophene ring poly(ether imide)s.