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 µs 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 °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.