POLYIMIDE DERIVED FROM 2,2'-BIS(TRIFLUOROMETHYL)-4,4'-DIAMINOBIPHENYL .1. SYNTHESIS AND CHARACTERIZATION OF POLYIMIDES PREPARED WITH 2,2-BIS(3,4-DICARBOXYPHENYL)HEXAFLUOROPROPANE DIANHYDRIDE OR PYROMELLITIC DIANHYDRIDE

New fluorinated polyimides have been synthesized by the reaction of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) or pyromellitic dianhydride (PMDA). The polyimide 6FDA/TFDB from the reaction of TFDB with 6FDA has high optical transparency and high solubilities in several solvents such as N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), acetone, and ethyl acetate. In addition, it has a low dielectric constant of 2.8 at 1 MHz, a low refractive index of 1.556 at 589.3 nm, and a low water absorption rate of 0.2%. The polyimide PMDA/TFDB prepared from the reaction of TFDB with PMDA has not only a low dielectric constant of 3.2 and a low refractive index of 1.647, but also a low coefficient of thermal expansion (CTE) of -5 x 10(-6) degrees-C-1.