PLP-SEC Studies into the Propagation Rate Coefficient of Acrylamide Radical Polymerization in Aqueous Solution

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• 作者：Igor Lacík ; Anna Chovancová ; Lucia Uhelská ; Calista Preusser ; Robin A. Hutchinson ; Michael Buback
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：May 10, 2016
• 年：2016
• 卷：49
• 期：9
• 页码：3244-3253
• 全文大小：562K
• 年卷期：0
• ISSN：1520-5835

文摘

Acrylamide (AAm) is an important water-soluble monomer. Pulsed-laser polymerization in conjunction with size-exclusion chromatography (PLP-SEC) has been employed to measure the propagation rate coefficient, k_p, in aqueous solution at monomer concentrations from 1 to 30 wt % and temperatures between 5 and 70 °C. Laser pulse repetition rate has been extensively varied, from 25 up to 500 Hz, to check for consistency of the measured k_p values, which increase toward larger water content, e.g., by 50% upon lowering AAm concentration from 30 to 5 wt %. Variation of pH, up to pH 11, and addition of up to 1 mol L^–1 NaCl to the polymerizing system do not significantly affect k_p. The activation energy, E_A(k_p), of about 18 kJ mol^–1 stays more or less constant within the monomer concentration range under investigation, which indicates that the changes of k_p are primarily of entropic origin. The pre-exponential factor, A(k_p), increases from 5.7 × 10⁷ to 7.7 × 10⁷ L mol^–1 s^–1 upon lowering the AAm concentration from 30 to 10 wt %. These high A(k_p) numbers demonstrate the fluidizing action of water on the transition state structure for propagation and on the barrier toward internal rotation with AAm being lower than with acrylates.