Polyolefins are important commodity plastics, yet their lack of functional groups limits their applications. The functionalization of C-H bonds holds promise for incorporating functionalities into polymers of ethylene and linear alpha-olefins. However, the selective functionalization of polyolefins derived from branched alkenes, even monobranched, 1,1-substituted alkenes, has not been achieved. These polymers are less reactive, due to steric effects, and they are prone to chain scission that degrades the polymer. We report the chemoselective and regioselective oxidation of a commercially important polymer of a branched olefin, polyisobutene. A polyfluorinated ruthenium-porphyrin catalyst incorporates ketone units into polyisobutene at methylene positions without chain cleavage. The oxidized polymer is thermally stable, yet it undergoes programmed reactions and possesses enhanced wetting properties.