FUNCTIONALIZATION AND METALLIZATION OF FLUOROPOLYMER SURFACES THROUGH REDUCTION

Fluoropolymer films, such as Teflon(TM)-TFE [poly(tetrafluoroethylene)], Teflon(TM)-FEP [copolymer of tetrafluoroethylene and hexafluoropropylene], Teflon(TM)-PFA [copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether)], and PCTFE [poly(chlorotrifluoroethylene)], are reduced by the mild reducing agent benzoin dianion/DMSO, while Teflon(TM)-AF [copolymer of tetrafluoroethylene and perfluoro-2,2-dimethyl-1,3-dioxole] is unreactive. The reduction makes the films adherable toward epoxy resins, the adhesive strength decreasing in the order PCTFE > PFA greater than or equal to FEP > PTFE. Surprisingly, Teflon(TM)-AF films are totally inert except when the TFE content is high, and in these cases, the adhesive strength of Teflon(TM)-AF is close to that of PTFE. The surfaces of PTFE, FEP and PFA films are further modified by first treating these films with the benzoin dianion/DMSO reagent and then with an excess of sodium salts of mercaptans. Reactive PTFE films that are light colored with a metallic luster are formed rather than the dark, metallic color typical of PTFE surface reduction without mercaptan treatment. These films have poor adhesion toward epoxy resins but good adhesion toward gold applied by sputtering. FEP and PFA films behaved similarly. These results are attributed to the incorporation of sulfur onto the reduced surface. Unreduced fluoropolymer films reacted with only sodium mercaptan fail to show C-S bond incorporation. This newly developed method can be used to selectively metallize the fluoropolymer film surface with gold layers and affords very high conductivity of the metallized regions. (C) 1995 John Wiley and Sons, Inc.