Microemulsion Polymerization. 2. Influence of Monomer Partitioning, Termination, and Diffusion Limitations on Polymerization Kinetics

Abstract

We investigate the polymerization kinetics of microemulsions prepared with the cationic surfactant dodecyltrimethylammonium bromide and the hydrophobic monomers n-butyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, and styrene. Our previous model for microemulsion polymerization kinetics cannot account for the kinetics of these systems. Using the results of smallangle neutron scattering monomer partitioning studies and an extended kinetic model to analyze the data, the failure of the original kinetic model is shown to be due to a combination of nonlinear monomer partitioning, nonnegligible bimolecular termination, and, in some cases, diffusion limitations to propagation.

Size Shrinkage of Methacrylate-based Terpolymer Latexes Synthesized by Free Radical Polymerization: Kinetics and Influence of Main Reaction Parameters

“…The reaction of a primary free radical with a first monomer is indeed reported in the literature to occur very rapidly, essentially in the diffusion-limited regime. 15 The conversion of MMA was obtained from the weight of PMMA contained in the reaction mixture according to the method already presented in the Experimental Section. Figure 2 presents monomer conversion as a function of reaction time.…”

Microstructure, Kinetics, and Transport in Oil‐in‐Water Microemulsion Polymerizations

“…Deviations of measured microemulsion polymerization kinetics from the Morgan model have been directly related to monomer solubility and the initial microemulsion composition through the introduction of expressions for non-linear monomer partitioning and biradical termination. [15][16][17] A significant development in the modeling of microemulsion polymerization kinetics was the ability to measure monomer partitioning by small angle neutron scattering (SANS). [16] SANS experiments confirmed that when the concentration of monomer does not decrease linearly as a function of conversion, the conversion at which the maximum rate of polymerization occurs moves away from 39%.…”

“…[16] SANS experiments confirmed that when the concentration of monomer does not decrease linearly as a function of conversion, the conversion at which the maximum rate of polymerization occurs moves away from 39%. [15] The transport and partitioning of monomer throughout a microemulsion polymerization introduces complications in the design of block copolymers and in extending the polymer chain length by semi-continuous polymerization. [18,19] Further understanding of semi-continuous microemulsion polymerization is critical in order to reduce the ratio of surfactant to polymer and thereby allow microemulsion polymerization to be commercially feasible.…”

“…The Morgan model for the rate of microemulsion polymerization provides a single rate equation that is able to predict the polymerization kinetics a priori. [14,15] Valuable information about the impact of monomer partitioning and biradical termination, which are directly related to monomer solubility and microemulsion composition, can be obtained from the comparison of microemulsion polymerization kinetics with the Morgan model predictions. The fundamental rate equation for microemulsion polymerization is first order in both the concentration of monomer and propagating radicals,…”

“…Several monomers demonstrate rate maxima at conversions less than the 39% conversion predicted by the Morgan model, most notably styrene [15,29,31,[33][34][35][36] and vinyl acetate. [37][38][39][40][41] DeVries et al have studied the deviations of the rate maximum from the Morgan model predicted rate maximum in terms of non-linear monomer partitioning, biradical termination, and diffusion limitations to propagation.…”