Nitrile rubber (NBR), poly(acrylonitrile-cobutadiene) or NBR packers, are used to seal oil-well tubing, where they often come into contact with ZnBr2 brines at high temperatures and pressures. Under these conditions, NBR exhibits accelerated chemical degradation, which results in embrittlement and cracking. Although alternative fluoropolymers exhibit excellent chemical resistance, their strength is less than NBR, and replacement of the usual gasket materials with fluoroelastomers is expensive. We have demonstrated that a fluoropolymer surface on a nitrile elastomer provides the necessary chemical resistance while the elastomer retains strength. This can be achieved by direct fluorination, a rather easy and inexpensive process. Samples of NBR O-rings were fluorinated by exposure to F-2 and F-2/HF mixtures at various temperatures. Although fluorination by F-2 produced the desired fluoropolymer layer, fluorination by F-2/HF (hydrofluoric acid) mixtures gave a smoother fluorinated layer at lower temperatures and shorter reaction times. Elemental analysis showed that the fluorinated layer eliminated ZnBr2 diffusion into the NBR polymeric matrix. Surface fluorination also significantly retarded the loss of the mechanical properties of NBR when it was exposed to zinc bromide fluid. (C) 2003 Wiley Periodicals, Inc.