Surface-Initiated Polymerization of 5-(Perfluoro-n-alkyl)norbornenes from Gold Substrates

We report the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of 5-(perfluoro-n-alkyl)norbornenes (NBFn) to grow partially fluorinated polymer films of tunable thicknesses ranging from tens of nanometers tomicrometers on gold substrates. The perfluoroalkyl chains range in length (n) from 4 to 10 carbons, representing 67-83%of the molecular weight of the repeat unit. The growth rate of the film depends on the perfluoroalkyl chain length, with longer chains enabling faster surface-initiated growth and greater ultimate thicknesses. These films exhibit hydrophobic and oleophobic surface properties and provide effective barriers to the diffusion of aqueous ions. The critical surface tensions of the films exhibit a minimum for a fluorocarbon chain of 8 (pNBF8) and range from 9 to 19 mN/m. The morphologies of the pNBFn films consist of densely packed 20-30 nm clusters that differ in the concentration of fluorocarbon chains in the outer few nanometers of the film.