Critically evaluated rate coefficients for free-radical polymerization. Part 6: Propagation rate coefficient of methacrylic acid in aqueous solution

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 degrees C. The Arrhenius pre-exponential and activation energy of k(P) at 15 mass % MAA are 1.54 x 10(6) L mol(-1) s(-1) and 15.0 kJ mol(-1), respectively. Also reported are critically evaluated k(P) values for 25 degrees C over the entire MAA concentration range from dilute aqueous solution to bulk polymerization.