PLP-SEC study into the free-radical propagation rate coefficients of partially and fully ionized acrylic acid in aqueous solution

Propagation rate coefficients, kappa(p), for acrylic acid (AA) polymerization at 6 degreesC in aqueous solution were measured via pulsed laser polymerization (PLP) with the degree of ionization, alpha, varied over the entire range between 0 and 1. These measurements were carried out in conjunction with aqueous-phase size-exculsion chromatography (SEC). Strictly speaking, the reported kappa(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 kappa(p) decreaes from 111 000 L.mol(-1).s(-1) at alpha = 0 to 13 000 L.mol(-1).s(-1) at alpha = 1.0. The significant lowering of kappa(p) with higher alpha 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 kappa(p) up to 57 000 L.mol(-1).s(-1).