Emulsifier during polymerization

The restricted adsorption of anion-active emulsifier during polymerization of polar monomers (vinyl acetate) has also been reported in other work. Breitenbadi eX ul. (1970) established that in the case of polymerization initiated hy a,forming interface. The polymerization rate was found to depend on emulsifier concentration to the power of 0.1. 

The ultrasonification process is connected with the rapidly increased oil-water interfacial area as well as the significant re-organization of the droplet clusters or droplet surface layer. This may lead to the formation of additional water-oil interface (inverse micelles) and, thereby, decrease the amount of free emulsifier in the reaction medium. This is supposed to be more pronounced in the systems with non-ionic emulsifier. Furthermore, the high-oil solubility of non-ionic emulsifier and the continuous release of non-micellar emulsifier during polymerization influence the particle nucleation and polymerization kinetics by a complex way. For example, the hairy particles stabilized by non-ionic emulsifier (electrosteric or steric stabilization) enhance the barrier for entering radicals and differ from the polymer particles stabilized by ionic emulsifier. The hydro-phobic non-ionic emulsifier (at high temperature) can act as hydrophobe. 

Thermal stabilities were assessed by thermogravimetric analysis (TGA). Samples were held at constant temperature (290°C) for 1 h in air in a Perkin-Elmer TGA. Much of the weight loss, particularly for Kel-F 6060, is suspected to be emulsifier used during polymerization. 

Example 5-23) and of ABS-polymers (made from acrylonitrile, butadiene, and styrene), whereby grafting occurs in situ at the beginning of the polymerization process. The formed graft copolymers act in two ways As emulsifiers during the polymerization process and, secondly, in the solid end product as compatibilizer between the thermoplastic hard phase and the rubber-elastic dipersed phase (already in concentrations below 3%). 

Emulsifier is not a necessary component for emulsion polymerization if ihe following conditions are satisfied The particles are formed by homogeneous nucleation mechanism, and the particles are stabilized by factor(s) olher than emulsifier. As to the latter, the sulfate end group that is the residue of persulfate initiator serves for stabilization of dispersion via interparticle electrorepulsive force (20). When the stabilization mechanism works well, a small number of particles grow during polymerization without aggregation, keeping the size distribution narrow. Finally stable, monodisperse, anionic particles are obtained. 

In the foregoing examples the synthesis of block copolymers was based on the solubility differences between two monomers, of which one is water soluble while the other is emulsified. Another polymerization technique is based on the kinetics of the emulsion polymerization. When a water emulsion of a monomer, such as styrene, is irradiated during a short time, the reaction, continues at a nearly steady rate until practically all the monomer is used up. If a second monomer is then added, it will polymerize, being initiated by the radicals occluded in the polymer particles. Although in this case also the yields of block copolymers are low, nevertheless the physical properties of the final product are markedly different from those of statistical copolymers (4, 5, 151, 176). 

The square-root dependence of the rate of polymerization on the initiator concentration and the first-order dependence on the macromonomer concentration strongly deviate from the micellar model. The linear dependence of Rp on the macromonomer concentration was attributed to the linear dependence of the number of micelles on the macromonomer concentration. The deviation results from the fact that the macromonomer acts as monomer and emulsifier and/or surface active component is formed during polymerization, i.e., it takes part in the growth and nucleation events. The increase in the reaction order above 0.4 was also discussed in terms of the variation of the surface activity of graft copolymer with its molecular weight. 

This study illustrates a particular use of FT-Raman spectroscopy (Section 2.4.2) to monitor an emulsion polymerization of an acrylic/methacrylic copolymer. There are four reaction components to an emulsion polymerization water-immiscible monomer, water, initiator, and emulsifier. During the reaction process, the monomers become solubilized by the emulsifier. Polymerization reactions were carried using three monomers BA (butyl acrylate), MMA (methyl methacrylate), and AMA (allyl methacrylate). Figure 7-1 shows the FT-Raman spectra of the pure monomers, with the strong vC=C bands highlighted at 1,650 and 1,630 cm-1. The reaction was made at 74°C. As the polymerization proceeded, the disappearance of the C=C vibration could be followed, as illustrated in Fig. 7-2, which shows a plot of the concentration of the vC=C bonds in the emulsion with reaction time. After two hours of the monomer feed, 5% of the unreacted double bonds remained. As the... 

In the seeded emulsion polymerization of some monomers —e.g., styrene—it is possible to obtain final latexes with uniform, large particles by adjusting, during polymerization, the quantity of added emulsifier the formation of new particles is prevented by the limited amount of emulsifier. For vinyl chloride, limited emulsifier is not sufficient to prevent the formation of new particles in fact, to obtain a monodispersed latex, the surface of the particles seeded in a given water volume must be controlled. It is assumed that the growth of new nuclei is related either to the rate of formation of primary useful radicals or to the rate that these are taken by the surface of sized particles. 

The polymerization rate in the presence of alkyd was slower than that without alkyd. Doubling the initiator and emulsifier concentration increased the reaction rate, but not to the level achieved with the miniemulsion polymerization without alkyd. This retardation (as reported also by Nabuurs) increased with increasing alkyd level. The latexes obtained from the miniemulsion polymerization of the alkyd-acrylate mixtures were uniform emulsions, and no coagulation occurred during polymerization. Macroemulsion polymerization with alkyd resulted in colloidal instabihty, probably due the inabihty of the alkyd to reach the locus of polymerization. 

Comparison of published tota on vinylacetate polymerization kinetics, for which a steady-state period is typical (13), to the kinetics of variation of the number of particles which decreases during the process up to a factor of 40 (14), permits us to conclude that there is no correlatlonbetween the rate and the number of particles. This conclusion was supported by Medvedev et al. ( ) in the case of emulsion polymerization of methylm hacrylate. We deduce from the above data that the emulsifier concentration itself does not determine either the total surface of the disperse phase or the mmber of particles during polymerization of polar monomers. 

Similar results were obtained by Yeliseyeva ei al. (1973, 1975) when studying the sodium alkylsulfonate emulsifier adsorption kinetics during polymerization of butyl acrylate and its copolymerization with such water-soluble monomers (3 o) as methacrylic acid, JV-melhacrylamide, and JV-methylolmethacrylamide, In all cases the introduction of water-soluble comonomers resulted in a decrease of the effective rate and in the value of the emulsifier adsorption. The authors attributed this to the hydrq>hili-zation and increase of polarity of latex particle surfaces. 

Fig. 10, Variation of the number of partides during polymerization of ethyl acrylate in the presence of emulsifiers (i) sodium alkylsulfonate (2) oxyethylated (30) cclyl alcohol and (3) AAOES. Recipe m.p. ethyl acrylate, lOO emulsifier, AO ammonium persuUate. 0.5 water.

In order to ensure necessary stability of ibe latex during polymerization of BMA tbe initial emulsifier concentration in aqueous phase was tahen equal to 3.3%. 

In semibatch emulsion polymerizations the polymer particles are kept monomer-starved to obtain higher rates of polymerization and to permit easier control of the rate and particle size distribution. There are two aspects to the control of PSD. The controlled addition of emulsifier during particle growth stabilizes the particles without further particle nucleation. The second aspect is related to the particle sticky stage which often occurs... 

Monomer emulsions prepared by the methods described above have been applied to the preparation of polymer dispersions. The crucial point in such applications is to establish conditions that ensure that the initiation takes place in the monomer droplets. In practice, this requires that the concentration of emulsifier in the aqueous phase during polymerization be as low as possible and certainly below the CMC (Hansen and Ugelstad, 1979). 

One of the most important problems of emulsion polymerization is the locus in which the elementary processes (initiation propagation, etc.) take place during polymerization, i.e. monomer droplets, monomer-water interface, monomer-saturated emulsifier micelles, or the monomer aqueous solution. Depending on the existing conditions (emulsifier, monomer and initiator) the polymerization reaction will preponderantly develop in one of the possibilities. 

Typical enulsifiers used in emulsion polymerization of VC are anirmic emulsifiers like sodium alkyl sulfonates, sodium diaUcyl sulfosucdnates, fatty acid soaps and sodium ethoxy sulfates. Neutral emulsifiers like alltyl phenol ethoxylates and fatty acid ethoxylates are often added during after polymerization in Oder b> increase latex stability. The emulsifiers are not only chosen for control of the particle formation and latex stability during polymerization, but for a number of other reasons like mechanical stability, reactor wall build-up, plastisol formation, heat and colour stability and water resistance of the final product [1]. 

It is the simplest approach, where suitable monomer (precursor of CP/ ICP) has been polymerized (Figure 1.45) in the presence of dispersed filled inclusion (another CP metallic, dielectric, or magnetic NPs QCNs any suitable combination of them). Depending upon the nature of reaction medium (i.e., presence of solvent, dispersant, or emulsifier), the polymerization may proceed via bulk, solution, suspension, or emulsion route [14,375,502]. During the process, monomer(s) tends to adsorb over filler and polymerize over the same, thereby enwrapping it and causing its dispersion within the formed polymer matrix. 

The latices that result from the emulsion polymerization find immediate application as adhesives, paints, coatings, or in the processing of leather. For this, control over the distribution of the latex particles is desired. If emulsifier and water are added at the beginning of the polymerization and monomer and initiator are added continually during the course of the polymerization, then only those latex particles initially formed will continue to grow. The latex particles are relatively small and show a narrow distribution of size. If, on the other hand, just one part of the initial sample is polymerized and the rest is added as an emulsion during polymerization, then new latex particles will be produced. Since the particles formed first are very large and those formed last remain relatively small, the distribution of sizes becomes very wide. 

The surface tension of the continuous phase of a polymer emulsion during emulsion polymerization may be used as a measure of the free emulsifier concentration. The term free emulsifier is used here to denote surfactant which is dissolved in the aqueous phase rather than being adsorbed onto polymer particles or monomer droplets, or aggregated into micelles. The free-emulsifier concentration is widely considered to be a critical variable in particle nucleation, steady-state oscillation in a CSTR, and in preventing coagulation during polymerization. 

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