Kinetics and Modeling of Free-Radical Batch Polymerization of Nonionized Methacrylic Acid in Aqueous Solution

Abstract

The batch free-radical polymerization of nonionized methacrylic acid (MAA) in aqueous solution has been investigated at 50 °C and initial monomer concentrations up to 30 wt % MAA. The rate of conversion increases as the initial weight fraction of MAA decreases, a result explained by the dependence of the propagation rate coefficient, k p , on monomer concentration. The conversion profiles measured at different MAA and initiator levels are represented by a polymerization model with conversion-dependent k p taken from literature, and the termination rate coefficient, k t , represented by a function including terms for segmental diffusion, translational diffusion, and reaction diffusion. The model includes chain transfer to monomer and is capable of representing polymer molecular weight averages and distributions, with the better fit obtained assuming that the transfer rate coefficient also varies with monomer concentration.

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

“…After about 60 min, an increase of the slope is noticeable, which is a sign of diffusion limitations to termination (gel effect). This is fully consistent with the experimental results of Buback et al [23], who ran their reactions at larger initiator concentrations (5 mmol/L, equivalent to ca. 0.12 wt %).…”

“…For the repetition of the reaction with 10 wt % MAA ( Figure S4), the difference in the slope above 40% conversion is a bit larger. Since this discrepancy (of similar size) at the same reaction conditions has already been reported in the literature [23], we consider this accuracy to be sufficient. A kinetic model suitable for evaluating the reaction rate and number average molecular weight of the active chains has been developed.…”

“…The kinetics of methacrylic acid (MAA) has been the subject of several studies by pulsed-laser polymerization (PLP), which have been focused especially on the estimation of propagation [12,20] and termination [21,22] rate coefficients. In addition, some attempts of characterizing and modeling the polymerization kinetics of MAA have been carried out recently, in some cases together with the analysis of the molar masses and of the effect of chain transfer reactions [23][24][25]. Nevertheless, the majority of the existing studies are focused on non-ionized MAA and limited to medium-large monomer concentrations.…”

Kinetics of the Aqueous-Phase Copolymerization of MAA and PEGMA Macromonomer: Influence of Monomer Concentration and Side Chain Length of PEGMA

“…The effect of the solids content on the conversion indicates that the dependence of the polymerization rate on the monomer conversion is not first order for any of the two monomers. This has been reported for the aqueous solution homopolymerization of MAA [19][20][21]25,42]. It has been found that the propagation rate coefficient of MAA was a function of the concentration of the monomer in the aqueous phase and of the ionization degree.…”

“…In addition to the effect of the monomer concentration on the k p , the ionization degree also affects the kinetics of acidic water-soluble monomers like AA and MAA. For instance, for MAA, one of the monomers used in this work, Lacík et al [19][20][21]25] have determined the effect of the ionization degree (from non-ionized to fully ionized conditions) and found that the k p significantly reduces on going from non-ionized form to the fully ionized form, and that this decrease diminishes as MAA concentration increases.…”