Fluorinated surfaces are ideal for a wide range of applications, as they offer low surface energy, superior corrosion resistance, and extremely low coefficients of friction. However, polymers with these desirable properties can be difficult to form, and even more difficult to form as even coatings that adhere to complex surfaces. Two recent reports highlight the use of surface-initiated ring-opening metathesis polymerization (SI-ROMP) for generation of partially-fluorinated films (non-fluorinated backbone with fluorinated alkyl pendant groups) bound to the substrate surface. Metathesis polymerization allows for rapid generation of these polymer films under mild reaction conditions.
The Jennings group of Vanderbilt University presented a series of partially-fluorinated polymer films generated by SI-ROMP of norbornenes bearing perfluorinated carbon chains (NBFn).1 Mercaptobutanol-treated gold substrates were combined with norbornene dicarbonyl chloride to create metathesis-active initiators. These initiators were activated by second generation Grubbs catalyst, and exposed to solutions of NBFn monomer to give rapid growth of dense films (NBFn). Film thickness increased linearly with monomer concentration (from 0.005M to 1.0 M NBFn), suggesting the ability to produce films from 50nm to 1.5μm with a 15-minute metathesis polymerization reaction. These thick pNBFn films offered increased electrical resistance, decreased capacitance, improved polymer stability, and low critical surface energies.
Feng Zhou and colleagues at the Lanzhou Institute of Chemical Physics reported the use of a catecholic initiator to anchor the SI-ROMP of pentadecafluorooctyl-5-norbornene-2-carboxylate (NCA-F15) to a range of metals and metal oxides.2 TiO2 nanotubes and alumina nanowires were modified by the metathesis-active catechol, activated by first generation Grubbs catalyst, and exposed to 0.25M solutions of NCA-F15 for two hours to generate polymer films of 10-15 nm. These partially-fluorinated films created super-repellant surfaces with water-droplet contact angles greater than 160°. Similar films were generated with copper, silver, iron, zinc, aluminum, and titanium planar substrates.
These reports demonstrate that metathesis chemistry holds great potential for future developments in surface modifications.
1 “Surface-Initiated Polymerization of 5-(Perfluoro-n-alkyl)norbornenes from Gold Substrates,” Christopher J. Faulkner, Remington E. Fischer, G. Kane Jennings. Macromolecules 2010 43 (3), 1203-1209
2 “Surface-Initiated Ring-Opening Metathesis Polymerization of Pentadecafluorooctyl-5-norbornene-2-carboxylate from Variable Substrates Modified with Sticky Biomimic Initiator,” Qian Ye, Xiaolong Wang, Shaobai Li, Feng Zhou. Macromolecules 2010 43 (13), 5554-5560