Molecular Engineering of Surface-Initiated Polymer Films to Prepare Highly Fluorinated Coatings

G. Kane Jennings

Assistant Professor of Chemical Engineering

Vanderbilt University

Fluorocarbon polymer films expose low-energy surfaces and are potentially useful as corrosion-resistant barrier films, lithographic resists, and lubricating coatings. Nonetheless, the difficulty of processing fluorocarbons into ultra thin films has limited their application in advanced materials processing. We have developed a new method to prepare partially fluorinated ultra thin films on metal surfaces by acylation of surface-initiated poly(2-hydroxyethyl methacrylate) (PHEMA) films with perfluorinated alkyl (C₃F₇COCl and C₇F₁₅COCl) and aryl (C₆F₅COCl) acid chlorides. PHEMA films with thicknesses of ~250 nm are first prepared by water-accelerated atom-transfer-radical polymerization (ATRP) from an initiator-terminated monolayer on gold substrates. The hydroxyl side chains of the PHEMA film are then acylated with a fluorinated acid chloride to produce partially fluorinated polymer films that exhibit well-defined structures, extremely low critical surface tensions (9 – 15 mN/m), and dramatic improvements in barrier properties. In the talk, I will discuss the effect of fluorocarbon side chain length, composition, and overall reaction conversion on the properties of polymer films. Especially important is determining the appropriate fluorocarbon content to provide the surface properties and barrier protection of purely fluorocarbon films. We are currently exploiting the instability of these films to basic conditions to create uniquely patterned polymer structures and films. This method to prepare partially fluorinated polymer films is straightforward and results in properties similar to and even superior to those of traditional fluoropolymer films with greatly improved processibility. I will also compare the performance of these partially fluorinated films with those prepared from hydrocarbon acid chlorides. Of particular importance is the side chain length of hydrocarbon required to create a densely packed outer methyl surface. Fundamental information gained from these studies can impact the molecular-level design of customized coatings.