PLP-SEC Study into the Free-Radical Propagation Rate Coefficients of Partially and Fully Ionized Acrylic Acid in Aqueous Solution
✍ Scribed by Igor Lacík; Sabine Beuermann; Michael Buback
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 135 KB
- Volume
- 205
- Category
- Article
- ISSN
- 1022-1352
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✦ Synopsis
Abstract
Summary: 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, α, 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 α = 0 to 13 000 L · mol^−1^ · s^−1^ at α = 1.0. The significant lowering of k~p~ with higher α 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^.
Dependence of apparent k~p~ values on the degree of ionization of acrylic acid (a) and on pH (b) for aqueous polymerizations of acrylic acid.
imageDependence of apparent k~p~ values on the degree of ionization of acrylic acid (a) and on pH (b) for aqueous polymerizations of acrylic acid.