Termination kinetics of the free-radical polymerization of nonionized methacrylic acid in aqueous solution

The termination kinetics of free-radical polymerization of nonionized methacrylic acid (MAA) in aqueous solution has been investigated at two MAA concentrations, 30 and 60 wt %, by single-pulse pulsed-laser initiated polymerization carried out in conjunction with mu s time-resolved in-line monitoring of monomer conversion via near-infrared spectroscopy (SP-PLP-NIR). From measured values of k(t)/k(p) for 2000 bar, with the conversion-dependent propagation rate coefficient, k(p), being inferred from literature data, the chain-length-averaged termination rate coefficient, < k(t)>, is deduced as a function of monomer conversion, x. As with methyl methacrylate polymerization, the < k(t)> vs x dependence may be modeled under the assumption that, toward higher degrees of monomer conversion, < k(t)> is successively controlled by segmental diffusion, translational diffusion, and reaction diffusion. For 50 degrees C, 2000 bar, and initial monomer concentrations in water of 30 and 60 wt %, chemically initiated polymerizations have also been carried out. The resulting < k(t)> values are in good agreement with the data from SP-PLP-NIR.