Fluorinated polyimides based on 3,3-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]phthalide

A novel fluorinated diamine monomer, 3,3-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]phthalide (II), was prepared through the nucleophilic substitution reaction of 2-chloro-5-nitrobenzotrifluoride with phenolphthalein in the presence of potassium carbonate to yield the intermediate dinitro compound 1, followed by catalytic reduction with hydrazine and Pd/C. Polyimides V were synthesized from diamine II and various aromatic dianhydrides IIIa-f via thermal or chemical imidization of poly(amic acid)s. These polymers had inherent viscosities ranging from 0.63 to 0.95 dL/g and were soluble in a variety of organic solvents. Va-f films had tensile strengths of 105-125 MPa, elongations to break of 9-12%, and initial modulus of 2.35-2.65 GPa. The glass transition temperatures of these polymers were recorded 259-320 degreesC, and no significant weight loss was observed below a temperature of 500 degreesC in nitrogen or in air. Compared with nonfluorinated homologues VI, V showed better solubility and lower color intensity, dielectric constant (2.70-3.11 at 1 MHz), and moisture absorption (0.12-0.27 wt %). In particular, Vc-f afforded lightly colored films, which had cutoff wavelengths lower than 380nm and yellowness index (b* values) ranging from 9 to 25. On comparing thermal imidized polymers with chemical imidized ones, films Va-f (C) showed a lower color intensity than Va-f(H) did.