The Ru(II)-mediated living radical copolymerization of styrene and methyl methacrylate (MMA) led to novel ABC-type "block-random" copolymers that consist of three segments each of which is a copolymer of the two monomers with a composition differing from each other. Thus, a styrene/MMA mixture (3/1 mole ratio) was polymerized with CH3CH(Ph)Br/RuCl2(PPh3)(3)/Al(OiPr)(3), and two portions of MMA were sequentially added at varying styrene conversions. The final products are living copolymers with narrow molecular weight distributions ((M) over bar(W)/(M) over bar(n) similar to 1.5) where the styrene/MMA sequential compositions from the alpha- to the omega-ends are about (3/1)-(1/1)-(1/4). Therefore, in the particular example two end segments are rich in either styrene or MMA unit, while the mid segment contains both units at a comparative composition. The basis of this new reaction is that independent of feed composition, both monomers polymerize at nearly the same rates to give virtually "azeotropic" random copolymers that are also living or long-lived and thus possess controlled molecular weights and narrow distributions.