Synthesis of new fluorinated polyimides

Two monomers 1,2-bis(meta-aminophenyl)hexafluorocyclobutane (1), and 1,2-bis(para-aminophenyl)hexafluorocyclobutene (2), were prepared from meta- or para-nitroiodobenzenes. Palladium-catalyzed coupling reaction of trifluorovinylzinc reagents with nitroiodobenzenes gave the corresponding nitrotrifluorovinylbenzenes, which dimerized at 130–150°C to give hexafluorocyclobutane derivatives. Reduction of 1,2-di(meta-nitrophenyl)hexafluorocyclobutane with NaBH4 and SnCl2 afforded the diamine 1 in high yield. Upon treatment of 1,2-di(para-nitrophenyl)hexafluorocyclobutane with NaBH4 and SnCl2, reduction–defluorination occurred to give 2. Diamines, 1 or 2, polymerized with pyromellitic anhydride (A), 3,3,4,4-biphenyltetracarboxylic dianhydride (B), and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (C), to give the corresponding poly(amic acids), which were imidized at above 250°C to give thermally stable and amorphous polyimide films.