Selective modification of 4-methylstyrene polymers

We report on the selective oxidative functionalization of polymers incorporating 4-methylstyrene. Cobalt(II) acetate/bromide serves as oxidation catalyst in the presence of air to convert 4-methyl groups into aldehyde and carboxylic acid. Cerium(IV) ammonium nitrate (CAN) and cobalt(III) acetate are used as stoichiometric oxidants under nitrogen to convert 4-methyl groups into acetoxymethyl, trichloroacetoxymethyl, and chloromethyl groups. In 4-methylstyrene homopolymers, and especially in copolymers with sterically demanding α-substituted comonomers such as α-methylstyrene and alkylmethacrylates, we exploit the steric hindrance of the backbone to achieve selective modification of the 4-methyl group, with only limited or no oxidation on the backbone methane (tertiary benzylic site). The resulting functional polymers have useful properties, and may help clarify the mechanism of metal-mediated oxidation of alkylbenzenes.