Free-Radical Polymerization of N-Vinylimidazole and Quaternized Vinylimidazole in Aqueous Solution

Aqueous-phase free-radical batch polymerizations of N-vinylimidazole (NVI) and quaternized N-vinylimidazole (QVI) are conducted with varying initial monomer and initiator concentrations at 70 and 85 degrees C. The polymerization rate of NVI is very slow at the natural pH of 9 due to degradative radical addition to monomer. The rates are increased by lowering the pH, wherein the degradative addition to NVI monomer is partially (at pH 4) and completely (at pH 1) hindered, with the polymerization rate matching that of QVI at pH 1. The initial rates of polymerization for both NVI and QVI are independent of temperature. A kinetic model developed in Predici that includes the pH-dependent side reactions can reasonably represent both QVI and NVI polymerization.