Diamines, i.e., compounds which contain two primary amino (--NH.sub.2) groups, constitute an important class of organic monomers. Diamines are particularly important because the two primary amino groups can be reacted with a variety of electrophiles to prepare polymers such as polyureas, polyamides and polyimides. In fact, one of the most commercially important polymers, i.e., "Nylon 66," is prepared from the reaction of hexamethylene diamine with adipoyl chloride. Moreover, due to the higher reactivity of the amino group as compared to the hydroxy group, diamines are finding increased use in commercial processes such as reaction injection molding (RIM).
Fluorinated diamines, in particular, are important because they have certain properties that make them valuable for a variety of applications. Fluorocarbon segments are generally incorporated into a polymer matrix to impart favorable dielectric, water-repellency, thermal, soil release and fouling release properties. Moreover, incorporation of fluorine also lowers the coefficient of friction and refractive index of the polymer system. These properties make fluorinated materials useful for diverse applications ranging from non-stick frying pans to water repellant clothing to drag-reducing coatings. Although the hydrocarbon analogs of telechelic diamines are well known, very few fluorinated diamines having useful properties are known to date.
Perfluorinated diamines, i.e., H.sub.2 N(CF.sub.2).sub.n NH.sub.2, are known, but they are unstable and readily eliminate hydrofluoric acid to form dinitriles. Due to the instability of these materials, no attempts have been made to isolate these diamines, or to incorporate them into a polymer matrix. Fluorinated diamines in which the amine functionality is separated from the fluorinated segment by one intervening methylene group are also known. Such fluorinated diamines have been prepared by the hydrogenation of the corresponding dinitrile derivatives (see, e.g., U.S. Pat. No. 2,515,246 issued to E. T. McBee and P. A. Wiseman (1950)), or by a three-step process from the corresponding fluoroalcohols T. F. Bell and R. N. Henrie, OPPI Briefs, 21(2): 245 (1989); and U.S. Pat. No. 4,020,176 issued to R. B. Greenwald (1977)). The use of these diamines in the synthesis of polymers, however, has been somewhat limited due to their low nucleophilicity, resulting primarily from the presence of a strongly electron-withdrawing perfluoroalkyl group on the neighboring carbon atom.
Synthesis of fluorinated diamines in which the amine functionality is separated from the fluorinated segment by two intervening methylene groups, i.e., NH.sub.2 --CH.sub.2 CH.sub.2 --(CF.sub.2).sub.n --CH.sub.2 CH.sub.2 --NH.sub.2, was recently described by Malik, et al., (see, J. Org. Chem., 56: 3043 (1991)). These diamines were prepared by a three-step process involving free radical addition of perfluoroalkyl iodide to ethylene, displacement of the iodo groups with azide, and reduction of the diazide to diamine. Although these compounds are more reactive than fluorinated diamine analogs with one intervening methylene group, their reactivity is still much lower than that of the hydrocarbon analogs.
One of the major applications of specialty fluoropolymers is in the area of surface coatings. In order to prepare polymers with good surface properties, it is important to have fluorine in the side chain and not in the polymer backbone. (See, e.g., Hopken, J. and M. Moeller, Macromolecules, 25: 1461 (1992); Zisman, W. A., "Contact Angle, Wettability and Adhesion," Advances in Chemistry Series, American Chemical Society, vol. 43 (1964); and Kobayashi, H. and M. J. Owen, Macromolecules, 22: 2951 (1989)). When the currently available fluorinated diamines are incorporated into a polymer matrix, the fluorinated segments are buried in the bulk with the rest of the backbone, which contains polar groups such as urethane and urea linkages. Unfortunately, the presence of these polar groups increases the surface energy of the coatings and give materials with poor surface properties.
In view of the foregoing, there remains a need in the art for fluorinated diamines which overcome the disadvantages associated with the currently available fluorinated diamines. Quite surprisingly, the present invention remedies this need by providing such fluorinated diamines.