Partition of carboxylic acids in an emulsion copolymerization system

Abstract

Reaction in the aqueous phase is often significant in emulsion polymerization systems that contain one or more water-soluble monomers. Accurate prediction of the partition of monomers between the aqueous, particle, and droplet phases is necessary for determining reaction rates, copolymer compositions, and surface properties of the latex particles. A model for predicting the partition of monomers between the various phases has been developed for an emulsion copolymer system.-A method for experimentally obtaining thermodynamic interaction parameters that are often not available in the literature has also been developed. This method was applied to two carboxylic acid/styrene systems. The model predictions of the monomer partitioning for these systems were in good agreement with experimental results measured from batch emulsion copolymerization samples. IntroductionThe rate of reaction in an emulsion copolymerization system containing water-soluble monomer(s) depends on the rates in the particle and aqueous phases. The rates of reaction in each phase depend on the local concentrations of monomer. Therefore, it is very important to understand how each monomer is partitioned between the aqueous phase, particles, and droplets.Preliminary experiments involving mixtures of acid monomer (either acrylic acid, AA, or methacrylic acid, MAA, both 100% soluble in water), water, and styrene were conducted to observe the effect of monomer (acid + styrene)/water ratio on the partition of the acid between the aqueous and organic phases. The partition coefficients were measured by mixing specified amounts of the three components, separating the two phases, measuring the aqueous-phase concentration of acid, and then using a mass balance to determine the concentration of acid in the organic phase. No polymer particles were present, and it was assumed that the concentration of styrene in the aqueous phase was negligible. Figure 1 shows that increasing the monomerfwater ratio resulted in a significant increase in the fraction of MAA in the organic phase but produced almost no effect on the fraction of AA distributed in the organic phase. The different partition behavior between the two monomers may be related to differences in hydrophobicity. Due to the extra methyl group, MAA is more hydrophobic than is AA. If the amount of acid is increased relative to the amount of water present, MAA is more likely to associate with the organic phase to a greater extent than does AA due to its more hydrophobic nature or, conversely, the water is more likely to solvate the more hydrophilic AA monomer units than the less hydrophilic MAA monomer units.A more fundamental study of MAA/styrene/water and AA/styrene/water mixtures using the approach of Prausnitz et al. (1986) with a wider range of monomer concentrations led to a better understanding of the partition of acid between styrene and water. These systems are comprised of a solute (acid) that is distributed between two immiscible liquid solvents (styrene, water). Liquid/ liquid equilibrium may be de...

Emulsion copolymerization of styrene andn-butyl acrylate in presence of acrylic and methacrylic acids: Effect of pH on kinetics and carboxyl group distribution

“…Because MAA is the more hydrophobic of the two, it polymerizes inside the particles whereas the more hydrophilic AA Table I. tween the aqueous and particulate phases depends on the pH of the reaction environment. 6,34 A previous study showed that the partitioning of…”

“…34 The negative charge on the dissociated (anionic) form of MAA renders it more polar than these graphs. Given that the individual rate curves for MAA are similar at pH 2.2 and 4, it is the nondissociated form, and thus increases its relative attraction for other polar molecules such probably safe to say that at a pH lower than the pK a (pK a of MAA Å 4.36), 6 the rate of consump-as water and decreases its attraction for nonpolar species such as St or BA. Increasing the pH leads tion of MAA is independent of the pH.…”

Influence of unsaturated acid monomer on the morphology of latex particles in the preparation of hollow latex via the alkali post‐treatment

“…As early as 1970s, Ceska have studied the carboxyl distribution in styrene (St)–butadiene copolymer latexes prepared in the presence of unsaturated acid monomers by neutron activation analysis and turbidimetric titration 18, 19. Subsequently, Shoaf and Poehlein investigated the partitioning of unsaturated acid monomers between St phase and aqueous phase and the kinetic behavior of emulsion copolymerization of St with unsaturated acid monomers 20–22. Okubo et al revealed the relationship between secondary nucleation and methacrylic acid (MAA) content in the emulsion copolymerization system of St and MAA 23.…”

Influences of MAA on the porous morphology of P(St–MAA) latex particles produced by batch soap-free emulsion polymerization followed by stepwise alkali/acid post-treatment

“…As early as 1970s, Ceska studied the effect of carboxyl monomers on the particle formation and stabilization in soap-free emulsion polymerization [12,13]. Subsequently, Shoaf and Poehlein investigated the partitioning of carboxyl monomers between styrene and aqueous phase and the kinetic behavior of emulsion copolymerization with carboxyl monomers [14][15][16]. Moreover, the influences of carboxyl content and its distribution on particle morphology were also studied [9,17,18].…”