The effect of Lewis acids (AlCl3 and Sc(OTf)(3)) on the reactivity ratios for (meth)acrylate/1-hexene and methacrylate/norbornene radical copolymerizations was investigated. The reactivity ratio r(1) for both methyl acrylate and methyl methacrylate decreases in the presence of Lewis acids; I-alkene reactivity ratio r(2) is close to zero. The substantial decrease in r(1) values and an increased polymerization rate demonstrate that Lewis acids promote (meth)acrylate cross-propagation significantly more than self-propagation, especially for methyl acrylate. The alkenes do not undergo self-propagation under our conditions. Furthermore, due to (a) enhanced binding of the Lewis acid to the carbonyl group on the monomer compared to those on the polymer and (b) the facile exchange of the Lewis acid between the monomer and the polymer, only a catalytic amount to Lewis acid is required to strongly influence alkene uptake and copolymerization rate.