SEMICRYSTALLINE AND AMORPHOUS FLUORINE-CONTAINING POLYIMIDES

Semicrystalline and amorphous fluorine-containing polyimides were developed with high transition temperatures and good thermal stability. Polyimides derived from 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF) and pyromellitic dianhydride (PMDA) were semicrystalline and exhibited a melting point of 472-degrees-C as determined by differential scanning calorimetry (d.s.c.). Confirmation of the semicrystalline morphology was provided by wide-angle X-ray scattering (WAXS). Incorporation of 6F dianhydride (2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 6FDA) as a comonomer in the PMDA/4-BDAF BDAF polyimide depressed the melting point to 440-degrees-C. The polyimides based on 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3F diamine, 3FDAM) were soluble and amorphous, probably as a result of the non-coplanar structure. D.s.c. and dynamic mechanical analysis showed a glass transition temperature exceeding 420-degrees-C for the PMDA/3FDAM-based polyimide. These fluorinated polyimide systems are currently under investigation as candidates for high-temperature applications.