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

Abstract

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 to micrometers 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.

Surface-initiated ring-opening metathesis polymerization of 5-(perfluorohexyl)norbornene on carbon paper electrodes

“…Fig. 3 shows a dominance of the m pd CF 2 mode, consistent with our observations of pNBF6 films grown from 2-D gold substrates [21].…”

“…The hexadecane droplet was maintained on top of the pNBF6-coated carbon paper for $10 s before the droplet was absorbed, whereas, the droplet was immediately absorbed into untreated, plasmatreated, and PTFE-treated carbon paper. The slower rate of hexadecane absorption is consistent with the CF 3 termini of the pNBF6 side chains, which tend to dominate the surface [21] and represent a more oleophobic surface than the CF 2 composition of PTFE [36].…”

“…Perfluoro-n-hexylnorbornene (NBF6) was synthesized from the Diels-Alder reaction of 1H,1H,2H-perfluoro-1-octene and dicyclopentadiene, as described recently by us [21] and previously by Perez et al [24] SpectraCarb carbon paper (2050-A) and Toray Teflontreated (5 wt.%) carbon paper (TGP-H-30) were purchased from fuelcellstore.com. Deionized water (16.7 MX) was purified using a Modu-Pure filtration system, and 200 proof ethanol was used as received from Aaper.…”

“…A surface-initiated approach is preferred here because presynthesized bulk polymer could be restricted from conformally coating the carbon fibers within the inner dimensions of the carbon paper, leading to underutilized electrochemically active area. We have previously demonstrated surface-initiated growth of poly(5-(perfluoro-n-alkyl)norbornene (pNBFn) films on planar gold electrodes [21]. These films exhibit rapid growth kinetics with lower critical surface energies than PTFE due to the dominance of -CF 3 groups at the surface, while providing an effective barrier to the diffusion of aqueous ions [21].…”

“…We have previously demonstrated surface-initiated growth of poly(5-(perfluoro-n-alkyl)norbornene (pNBFn) films on planar gold electrodes [21]. These films exhibit rapid growth kinetics with lower critical surface energies than PTFE due to the dominance of -CF 3 groups at the surface, while providing an effective barrier to the diffusion of aqueous ions [21]. Here, we employ the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of 5-(perfluorohexylnorbornene) (NBF6), as a route towards ultrathin fluorocarbon-rich polymer coatings on carbon paper substrates.…”