Upon the addition of an equimolar amount of 2,20-bipyridine, a cationic Pd-diimine complex capable of facilitating ‘‘living’’ ethylene polymerization is switched to catalyze ‘‘living’’ alternating

copolymerization of 4-tertbutylstyrene and CO. This unique chemistry is thus employed to synthesize a range of well-defined treelike (hyperbranched polyethylene)-b-(linear polyketone) block polymers.