Fluorinated polymer films from acylation of ATRP surface-initiated poly(hydroxyethyl methacrylate)

We report a new strategy to prepare partially fluorinated polymer films by utilizing surface-initiated films of poly(2-hydroxyethyl methacrylate) (PHEMA) grown onto gold surfaces via atom transfer radical polymerization (ATRP). Hydroxyl side chains of PHEMA were reacted with perfluoroalkyl. (C3F7 and C7F15) and perfluoroaryl (C6F5) acid chlorides to yield partially fluorinated surface-initiated polymer films with conversions ranging from similar to70 to 85%. The resulting fluorinated PHEMA films dramatically altered surface and barrier properties, particularly lowering the critical surface tension to as low as 9 mN/m and boosting film resistance by as much as 5 orders of magnitude compared to that of PHEMA. Film properties depend on the chemical composition and length of the fluorinated side chains. The longer C7F15 fluoroalkyl chain structured the film to a greater extent than the shorter C3F7 chain and yielded improved barrier properties and lower critical surface tension. The C7F15 groups are oriented nearly normal to the surface at the air-film interface and predominantly parallel to the surface in the bulk. Modification of PHEMA with the fluoroaryl side chain produced the best barrier properties of the three side chains investigated.