Sulfonation of Surface-Initiated Polynorbornene Films

We report the sulfonation of surface-initiated polynorbornene with acetyl sulfate to produce ultrathin ionomer films. The complete process consists of exposure of a hydroxyl-terminated self-assembled monolayer (SAM) on gold to a norbornenyl diacid chloride, attachment of Grubbs first generation catalyst, ring-opening metathesis polymerization (ROMP), and sulfonation. Structural and chemical changes in the film upon sulfonation are confirmed by RAIRS, contact angle goniometry, ellipsometry, optical microscopy, and electrochemical impedance spectroscopy. Sulfonation of surface-initiated polynorbomene results in a highly nonuniform surface morphology which can be relaxed to a more uniform film through exposure to dimethyl sulfoxide at room temperature. The sulfonated polynorbornene films have an intermediate surface energy (theta(A)(H2O) approximate to 75 degrees) and a low resistance against proton transport (R-f approximate to 1.6 Omega.cm(2)), which is 6 orders of magnitude lower than that of the original polynorbornene film. The sulfonated films are far more stable than the original polynorbomene films because of a similar to 95% diminution of olefin content within the film. Sulfonated poly(butylnorbornene) films were prepared analogously to demonstrate the versatility of this approach toward ionomer films.