I. Lacik, S. Beuermann, M. Buback
PLP-SEC Study into the Free-Radical Propagation Rate Coefficients of Partially and Fully Ionized Acrylic Acid in Aqueous Solution
Macromol. Chem. Phys. 205, 1080-1087 (2004)

Propagation rate coefficients, k_p, for acrylic acid (AA) polymerization at 6°C in aqueous solution were measured via pulsed laser polymerization (PLP) with the degree of ionization, , varied over the entire range between 0 and 1. These measurements were carried out in conjunction with aqueous-phase size-exclusion chromatography (SEC). Strictly speaking, the reported k_p's are apparent propagation rate coefficients deduced from the PLP-SEC data under the assumption that the local monomer concentration at the radical site is identical to overall monomer concentration. At an AA concentration of 0.69 mol · L^-1, the apparent k_p decreases from 111 000 L · mol^-1 · s^-1 at  = 0 to 13 000 L · mol^-1 · s^-1 at  = 1.0. The significant lowering of k_p with higher is attributed to the repulsion between both monomer molecules and macroradicals becoming negatively charged. Addition of up to 10 mol-% (with respect to AA) sodium hydroxide to the fully ionized aqueous AA solution leads to an enhancement of k_p up to 57 000 L · mol^-1 · s^-1.