tert-Butyl, cyclohexyl, n-propyl, and n-dodecyl vinyl ethers have been used as comonomers with styrene and methyl methacrylate using C-13-enriched samples of azobis(isobutyronitrile) and benzoyl peroxide as initiators at 60 degrees C. Examination by C-13-NMR spectroscopy of either ((CH3)-C-13)(2)C(CN)- or (PhCOO)-C-13- end-groups in the products has shown that the vinyl ethers have low reactivities toward the 2-cyano-2-propyl radical but high reactivities toward the benzoyloxy radical.