An Advanced Approach on the Study of Emulsion Polymerization: Effect of the Initial Dispersion State of the System on the Reaction Mechanism, Polymerization Rate, and Size Distribution of Polymer-Monomer Particles

Abstract

According to these ideas, in the presence of surfactants, the initial emulsion consists of two kinds of particles of different sizes: the monomer droplets with diameters of 5-20 microns and colloidal degree of dispersion and monomer-swollen surfactant micelles (5-10 nm).The mechanism of Harkins-Yurzhenko lied in the base of Smith and Ewart quantitative theory [5][6][7], with further refinements in the works of other authors . The main aspect of this theory is that radicals formed in the aqueous phase are trapped by the monomer swollen surfactant micelles and turn to PMP. It is assumed that only one out of every 100-1000 micelles captures a radical and becomes PMP, and the rest of the micelles are spent to stabilize the growing PMPs. Polymer-monomer particles formation ends with the disappearance of micelles of the emulsifier in the aqueous phase, after which the number of particles remains constant.Initial system contains monomer droplets with a diameter of 5-15 microns, their concentration being 10 12 -10 14 droplets/l, the monomer-swollen micelles with diameters of 5-10 nm and the number of micelles 10 18 -10 21 l -1 , and a water-soluble initiator (usually potassium persulfate) at a concentration of 1% per monomer [8]. Only a small fraction of the molecules of the monomer is located in the interior of the micelles (1-2%) and is dissolved in the aqueous phase (0.03% for styrene). In the aqueous phase, 10 14 -10 16 PMP / l are formed with a diameter in the range of 20-200 nm. Monomer droplets due to their relatively small surface area hardly compete with micelles in capturing radicals.In the polymerization process PMPs increase their size due to the diffusion of the monomer from droplets and monomer-swollen micelles which contains no radicals [1-3, 5, 9-15].Three limiting cases were considered:1. The number of free radicals in the particles is small compared with the total number of radicals, thus the average number of radicals per particle is much less that unity. 2. The average number of radicals per particle is equal to 0.5. This case is realized under following conditions: the activity of the radical in the particle persists as long as the second radical enter the particle, and the time of chain-breaking is small as compared with the average time interval of successive absorption of radicals by the particle. The authors believe that case 2 corresponds to the emulsion polymerization of styrene in the presence of potassium persulfate [5]. The rate of formation of primary radicals is equal to 10 13 radicals• ml -1 s -1 . The average number of polymer particles is of the order of 10 14 -10 16 in 1 ml of the system. If all the radicals formed by the decay of the initiator enter the polymer particles, the average frequency at which a radical enters a particle is once per 10 -100 sec. At any time, the particle contains either one radical or does not contain radicals at all, since it is assumed that chain termination occurs immediately in contact with the second radical in the particle. The particle is inactive unt...

An overview of the science and art of encapsulated pigments: Preparation, performance and application

“…The propositions of particle formation during emulsion assumed that polymer monomeric particles are formed from micelles of emulsifiers, followed by the development of macromolecules of the polymer droplet in water (the mechanism of homogeneous nucleation). This process occurs by formation of nucleation aggregates, which combines elements of different modes of particle formation, including microdroplets of monomer 69 …”

“…This process occurs by formation of nucleation aggregates, which combines elements of different modes of particle formation, including microdroplets of monomer. 69 In a typical pigment dispersion via emulsion polymerisation (Figure 6), as described by Viala et al, 70 the process begins with the pouring of deionised water into a reactor The creation of piezoresistive materials via in situ polymerisation…”

Grafting Starch with Acrylic Acid and Fenton’s Initiator: The Selectivity Challenge

“…Kislenko 32 reports that in the graft polymerization of methyl acrylate onto cellulose, emulsions are formed, where interface effects have large impact on the grafting results. The scheme of Figure 8A shows some superficial resemblence to emulsion polymerization but even more to suspension polymerization, well known methods for the polymerization of single monomers 11 , 33 . In both cases, monomer is present in droplets as a separate phase.…”

Grafting Starch with Acrylic Acid and Fenton’s Initiator: The Selectivity Challenge

“…Kislenko [ 32 ] reports that in the graft polymerization of methyl acrylate onto cellulose, emulsions are formed, where interface effects have large impact on the grafting results. The scheme of Figure 8 A shows some superficial resemblance to emulsion polymerization, but even more to suspension polymerization [ 12 , 33 ]. In both cases, monomer is present in droplets as a separate phase.…”