Aqueous Free-Radical Polymerization of Non-Ionized and Fully Ionized Methacrylic Acid

Abstract

Water-soluble, carboxylic acid monomers are known to exhibit peculiar kinetics when polymerized in aqueous solution. Namely, their free-radical polymerization rate is affected by several parameters such as monomer concentration, ionic strength, and pH. Focusing on methacrylic acid (MAA), even though this monomer has been largely addressed, a systematic investigation of the effects of the above-mentioned parameters on its polymerization rate is missing, in particular in the fully ionized case. In this work, the kinetics of non-ionized and fully ionized MAA are characterized by in-situ nuclear magnetic resonance (NMR). Such accurate monitoring of the reaction rate enables the identification of relevant but substantially different effects of the monomer and electrolyte concentration on polymerization rate in the two ionization cases. For non-ionized MAA, the development of a kinetic model based on literature rate coefficients allows us to nicely simulate the experimental data of conversion versus time at a high monomer concentration. For fully ionized MAA, a novel propagation rate law accounting for the electrostatic interactions is proposed: the corresponding model is capable of predicting reasonably well the electrolyte concentration effect on polymerization rate. Nevertheless, further kinetic information in a wider range of monomer concentrations would be welcome to increase the reliability of the model predictions.

PLP-SEC Investigation of the Influence of Electrostatic Interactions on the Radical Propagation Rate Coefficients of Cationic Monomers TMAEMC and MAPTAC

“…As described in the Introduction section, the role of counterions on the overall rate of polymerization as well as on the rate of propagation for ionized monomers has been a matter of interest for many years and remains a current challenge. ,,,, The overall understanding is that counterions increase the rate of polymerization and, as anticipated but not yet systematically studied, increase the k p values by screening the repulsive electrostatic interactions between the positively charged species involving monomers, growing radical chain ends and polymer chains. Figure a,b shows a graphical representation of k p data from Tables and to visualize the dependence of k p on monomer concentration and temperature for both TMAEMC and MAPTAC.…”

Effect of Ionization on Aqueous Phase Radical Copolymerization of Acrylic Acid and Cationic Monomers

“…The group of Buback has successfully measured the additional rate coefficients associated with backbiting for both AA 8,11 and acrylamide (AM) 12 homopolymerizations. It has been demonstrated that the homopolymerization rates of fully ionized methacrylic acid (NaMA) 13 and acrylic acid (NaA) 14 are greatly reduced from those of their nonionized counterparts in aqueous solution, with the relative reduction in the rate of conversion dependent on initial monomer concentration; furthermore, the reaction rate increases in the presence of added salt such as NaCl. PLP-SEC investigations on k p of NaMA 15 and NaA 16 have highlighted the importance of counterions in the screening of monomer-radical electrostatic interactions, with an increase in k p observed with an increased concentration of counterions.…”

Kinetic Measurement of Acrylic Acid Polymerization at High Concentrations under Nearly Isothermal Conditions in a Pendula Slug Flow Reactor

“…Additionally, experimental setups in unstirred batch reactors, for example, NMR tubes, have been performed. 10,11 Solutions consisting of a monomer and initiator are degassed and placed in 5 mm NMR tubes (2 mm NMR tubes for improved heat transfer). Here, the reaction progress is measured by in situ NMR.…”

“…Batch reactors and calorimeters, which are mostly reactor vessels with advanced heat flux management, can be equipped with common online or offline measurement methods. Additionally, experimental setups in unstirred batch reactors, for example, NMR tubes, have been performed. , Solutions consisting of a monomer and initiator are degassed and placed in 5 mm NMR tubes (2 mm NMR tubes for improved heat transfer). Here, the reaction progress is measured by in situ NMR.…”