The Combined Influence of Monomer Concentration and Ionization on Acrylamide/Acrylic Acid Composition in Aqueous Solution Radical Batch Copolymerization

An in situ NMR technique is used to measure the relative monomer consumption rates of acrylamide (AM) and acrylic acid (AA) over a broad range of initial comonomer compositions, initial monomer concentrations (5–40 wt % in aqueous solution), and the complete range of AA ionization. The composition drift with conversion was found not only to be a strong function of AA ionization but also to vary systematically with monomer concentration, with the latter influence increasing at increased degrees of ionization. The coupled effect is captured by expressions developed to represent the monomer reactivity ratios as a function of these two major variables. The proposed correlation, easily implemented into any modeling framework, is based on experimentally measured composition over a much broader range of conditions than examined in previous studies and accurately captures the effect of monomer concentration at low and high degrees of ionization.