Kinetics and Mechanisms of Emulsion Polymerization

Besides being an interesting method fw industrial processes, seeded polymerization of VC has provided valuable insight into kinetics and mechanisms of emulsion polymerization. 

Emulsion polymerization involves the emulsification of monomers in an aqueous phase, and stabilization of the droplets by a surfactant. Usually, a water-soluble initiator is used to start the free-radical polymerization. The final product is a dispersion of submicrometer polymer particles, which is called latex. The locus of polymerization is the micelle. Typical applications are paints, coatings, adhesives, paper coatings and carpet backings. The latex particles can have different structures (see Fig. 2). Excellent text books on the applications and structure-property relationships exist [11-15]. Besides a full description of the kinetics and mechanism of emulsion polymerization [16], a textbook adapted for use as material for people entering the field is also available [17]. 

Some Peculiarities of the Kinetics and Mechanism of Emulsion Polymerization [24-36]... 

Ugelstad, J. and Hansen, F.K. (1976) Kinetics and mechanism of emulsion polymerization. Rubber Chem. Technol, 49, 536. 

SOME PECULIARITIES OF THE KINETICS AND MECHANISM OF EMULSION POLYMERIZATION... 

Our account of the aforesaid factors influencing the kinetics and mechanism of emulsion polymerization (in both presence and absence of an emulsifier) has enabled the inflnence of comonomers on the processes of formation of polymeric dispersions based on (meth)acrylates to be explained. Changes of some conditions of reaction have tnmed ont to affect the character of influence of other ones. For example, increasing the concentration of MAA at its copolymerization with MA at a relatively low initiation rate leads to a decrease in the rate and particle nnmber and to an increase in the coagnlnm amonnt. Bnt at high initiation rates, the nnmber of particles in the dispersion in the presence of MAA rises and their stability improves. The same effects were revealed for emnlsifier-free polymerization of bntylacrylate as well, when at high temperatnres its partial replacement by MAA results in better stabilization of the dispersion, an increase in the reaction rate and the nnmber of particles (whereas their decrease was observed in the presence of an emulsifier). 

Emulsion polymerizations vary greatly, and no single reaction mechanism accounts for the behavior of all the important systems. The kinetics and mechanism of emulsion polymerizations are reviewed in detail in Ref. [4]. It is important to note that the nature of the products made by emulsion reactions are highly dependent... 

Poly(vinyl chloride) (PVC) is one of the most widely produced polymeric materials in use today. It is commercially produced by four major processes suspension, bulk, emulsion and solution. An industrially important method of production of PVC is emulsion polymerization. There are a lot of data regarding the kinetics and mechanism of emulsion polymerization of vinyl monomers. However, relatively little work has been done on the kinetics of vinyl chloride emulsion polymerization and much less on the emulsion copolymerization. Concerning the preparation of copolymer latexes of vinyl chloride monomer, there are only patents [1-3]. 

Bovey, F. A., I. M. Kolthoff, A. I. Medallia and E. J. Meehan, Emulsion Polymerization , Interscience, New York, 1955. A study of the kinetics and mechanism of emulsion polymerization, of tests for structure, properties and quality of the rubber formed. The standard GR-S recipe is used High Polym., vol. 9). 

Ugelstad, J., and F. K. Hansen, Kinetics and Mechanism of Emulsion Polymerization, Rubber Chem. Technol., 49, 536-609, 1976. 

Emulsion copolymerization of acryhc monomers and imconjugated dienes was studied with the aim to explore the possibihty to synthesize dispersions whose particles would contain reactive polymeric molectrles with free multiple C=C bonds. The usage of such latexes to Dnish fabrics and some other materials promotes getting strong indelible coatings. The kinetics and mechanism of emulsion copolymerization of EA and BA with allylacrylate (AlA) (with ammonimn persulfate (APS) or the APS—sodium thiosirlfate system as initiators) were studied. The foimd constants of copolymerization of AlA with EA (r",y = 1.05 = 0.8) and ALA with BA (r ... 

The kinetic mechanism of emulsion polymerization was developed by Smith and Ewart [10]. The quantitative treatment of this mechanism was made by using Har-kin s Micellar Theory [18,19]. By means of quantitative treatment, the researchers obtained an expression in which the particle number was expressed as a function of emulsifier concentration, initiation, and polymerization rates. This expression was derived for the systems including the monomers with low water solubility and partly solubilized within the micelles formed by emulsifiers having low critical micelle concentration (CMC) values [10]. 

In order to delve deeper into the similarities and differences between the kinetic behaviors of emulsion polymerization initiated by oil-soluble initiators or water-soluble initiators, Nomura et al. [199-202] carried out extensive investigations into the kinetics and mechanisms of the unseeded and seeded emulsion polymerizations of St at 50 °C using sodium lauryl sulfate (NaLS) as the emulsifier and AIBN as the initiator, and obtained the following conclusions ... 

The kinetics and mechanisms of particle growth and polymer structure development are comparatively well understood compared to those of particle nucleation. Therefore, the rate of polymerization and the properties of the polymer produced can be (roughly) estimated as long as the number of polymer particles produced is known (for example, in seeded emulsion polymerization). However, the prediction of the number of polymer particles produced is still far from being an estabUshed technique. Therefore, further efforts are needed to qualitatively and quantitatively clarify the effects of numerous factors that affect the process of particle formation in order to gain a more quantitative understanding of emulsion polymerization. 

Kinetics and Mechanism of the Emulsion Polymerization of Vinyl Acetate... 

The study of Nomura et al. [143] is perhaps one of the most detailed investigations on the kinetics and mechanism of the emulsion polymerization of vinyl acetate published. The work presents a detailed evaluation of the interactions of monomer, surfactant, and initiator concentration in the course of the... 

The second large group of chapters spedfically describes the synthetic aspects of ROP/ROMP. In this section, the architecture of polymers prepared by ROMP, functionalization of poly (ethylene oxide), chain extension by ROP, nonlinear polyethers, as wdl as ROP in heterogeneous media are discussed. It also describes methods of polymerization that provide regular and mostly spherical partides, and gives for the first time a review of the kinetics and mechanism of this particular system that resembles emulsion vinyl polymerization. The chapter on polymerization in confined space (encompassing matrix polymerization) summarizes results that may open the way to the replica polymerization, a process that is typical for the matrix synthesis of biomacromolecules in nature. 

Kinetics and Mechanisms. Early researchers misunderstood the fast reaction rates and high molecular weights of emulsion polymerization (11). In 1945 the first recognized quaHtative theory of emulsion polymerization was presented (12). This mechanism for classic emulsion preparation was quantified (13) and the polymerization separated into three stages. 

Continuous emulsion polymerization systems are studied to elucidate reaction mechanisms and to generate the knowledge necessary for the development of commercial continuous processes. Problems encountered with the development of continuous reactor systems and some of the ways of dealing with these problems will be discussed in this paper. Those interested in more detailed information on chemical mechanisms and theoretical models should consult the review papers by Ugelstad and Hansen (1), (kinetics and mechanisms) and by Poehlein and Dougherty (2, (continuous emulsion polymerization). 

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