The alternating polymerization of cyclobutene 1-carboxylic esters and cyclohexene derivatives with the precatalyst [(H2IMes)(3-Br-pyr)(2)Cl2Ru=CHPh] is described. This reaction is synthetically accessible and provides (AB)(n) heteropolymers with an alternating backbone and alternating functionality. The regiocontrol of heteropolymer formation derives from the inability of the cyclobutene ester and cyclohexene monomers to undergo homopolymerization in combination with the favorable kinetics of cross polymerization.