Synthesis and properties of soluble trifluoromethy-substituted polyimides containing laterally attached p-terphenyls

A new fluorinated diamine monomer, 2',5'-bis(4-amino-2-trifluoromethylphenoxy)-p-terphenyl, was synthesized from the chloro-displacement of 2-chloro-5-nitrobenzotrifluoride with the potassium phenolate of 2,5-diphenylhydroquinone, followed by hydrazine palladium-catalyzed reduction. A series of trifluoromethyl-substituted polyimides containing flexible ether linkages and laterally attached side rods were synthesized from the diamine with various aromatic dianhydrides via a conventional two-step process. The inherent viscosities of the poly(amic acid) precursors were 0.84-1.26 dL/g. All the polyimides afforded flexible and tough films. The use of 4,4'-oxydiphthalic anhydride and 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride produced essentially colorless polyimide films. Most of the polyimides revealed an excellent solubility in many organic solvents. The glass-transition temperatures of these polyimides were recorded between 254 and 299 degreesC by differential scanning calorimetry, and the softening temperatures of the polymer films stayed in the range of 253-300 degreesC according to thermomechanical analysis. The polyimides did not show significant decomposition before 500 degreesC in air or under nitrogen. These polyimides also showed low dielectric constants (2.83-3.34 at 1 MHz) and low moisture absorption (0.4-2.2%). For a comparative study, a series of analogous polyimides based on the nonfluorinated diamine 2',5'-bis(4-aminophenoxy)-p-terphenyl were also prepared and characterized. (C) 2004 Wiley Periodicals, Inc.