Critically evaluated rate coefficients for free-radical polymerization Part 6: Propagation rate coefficient of methacrylic acid in aqueous solution (IUPAC Technical Report)

Critically evaluated propagation rate coefficients, k p, for free-radical polymerization of methacrylic acid, MAA, in aqueous solution are presented. The underlying k p values are from two independent sources, which both used the IUPAC-recommended technique of pulsed-laser-initiated polymerization (PLP) in conjunction with molar mass distribution (MMD) analysis of the resulting polymer by size-exclusion chromatography (SEC). Different methods of measuring the MMD of the poly(MAA) samples have, however, been used: (i) direct analysis via aqueous-phase SEC and (ii) standard SEC with tetrahydrofuran as the eluent carried out on poly(methyl methacrylate) samples obtained by methylation of the poly(MAA) samples from PLP. Benchmark k p values for aqueous solutions containing 15 mass % MAA are presented for temperatures between 18 and 89 °C. The Arrhenius pre-exponential and activation energy of k p at 15 mass % MAA are 1.54 × 106 L mol-1 s-1 and 15.0 kJ mol-1, respectively. Also reported are critically evaluated k p values for 25 °C over the entire MAA concentration range from dilute aqueous solution to bulk polymerization.