In nonpolar media LiCB11Me12 catalyzes the radical copolymerization of ethyl acrylate with isobutylene. The reaction is initiated by azo-tert-butane at 75-80 degrees C or with UV-irradiated di-tert-butyl peroxide at room temperature. Nonalternating copolymers with novel somewhat branched structures were produced and characterized by NMR Isobutylene incorporation (up to 56 mol %) depends on the comonomer ratio, and a copolymerization mechanism is proposed.