Thermoresponsive Behavior of Semifluorinated Polymer Brushes

The surface rearrangement of polymer brushes composed of diblock copolymer chains with fluoropolymer blocks has been shown to be readily induced using thermal annealing. Changes in surface composition accomplished by the rearrangement were demonstrated by tensiometry and atomic force microscopy (AFM). Most of the research focused on brushes consisting of a hydrocarbon inner block [either poly(methyl acrylate) or polystyrene] and a fluoropolymer outer block [poly(pentafluorostyrene), poly(heptadecafluorodecyl acrylate), poly(pentafluoropropyl acrylate), or poly(trifluoroethyl acrylate)]. The diblock copolymer brushes were first treated with a block selective solvent for the hydrocarbon block. Rearrangement was complete for all brushes except those in which poly(heptadecafluorodecyl acrylate) was the outer block. Subsequentially, the surfaces were then thermally treated to allow the fluoropolymer to migrate to the surface. The optimal temperature and exposure time for thermal treatment were found to vary with the glass transition temperatures (Tg). The poly(methyl acrylate)-b-poly(pentafluoropropyl acrylate) brush exhibited the most complete surface rearrangement upon solvent treatment and the fastest rearrangement upon thermal treatment. The thermal rearrangement of a poly(2-hydroxyethyl methacrylate)-b-poly(methyl acrylate) brush that was reacted with heptafluorobutyryl chloride via an acylation reaction was also studied. Fluoropolymer-rich surfaces created by thermal rearrangement were rougher than those created by solvent rearrangement.