Polymer latex applications

E. Daniels, E. D. Sudol, and M. S. El-Aasser, eds.. Polymer Latexes Preparation, Characterisation and Applications, ACS Symposium Series, Vol. 492, American Chemical Society, Washington, D.C., 1992. 

Carbon black may serve as a low-cost additive for controlling the gas migration in cement slurries [303]. It is intended as a suitable substitute for polymer latex and silica fume and has been tested in field applications [304,1256]. The concentration of carbon black varies from 2 to 20 parts, based on the weight of the dry cement [1220]. The particle size varies from 10 to 200 nm. A surfactant is necessary for dispersion, for example, formaldehyde-condensed naphthalene sulfonate or sulfonated cumarone or indene resins. 

Of the several types of the polymer-modified mortars and concretes used for various construction applications, latex-modified mortar and concrete are by far the most widely used materials. Latex-modified mortar and concrete are prepared by mixing a latex, either in a dispersed liquid or as a redispersible powder form with fresh cement mortar and concrete mixtures. The polymers are usually added to the mixing water just as other chemical admixtures, at a dosage of 5-20% by weight of cement. Polymer latexes are stable dispersions of very small (0.05-5 pm in diameter) polymer particles in water and are produced by emulsion polymerization. Natural rubber latex and epoxy latex are exceptions in that the former is tapped from rubber trees and the latter is produced by emulsifying an epoxy resin in water by the use of surfactants [87]. 

WATER SOLUBLE POLYMERS. Water-soluble polymers find application in a wide variety of areas that include polymers as food sources, plasma substitutes, and as diluents in medical prescriptions. Other areas of importance for water-soluble polymers include detergents, cosmetics, sewage treatment, stabilizing agents in the production of commodity plashes, rheology modifiers in the various processes for petroleum, textile, paper, and latex coatings production. The water-soluble polymers discussed in this article have significant commercial impact. 

The work represents an application of core-shell light scattering theory to polymer latex suspensions and addresses the separate identification of light scattering by dust, latex particles and low molecular weight solutes. 

Abstract. An overview of the synthesis and applications of microgels and coreshell particles is provided, with emphasis on work originating from the author s laboratory. Microgels, which are cross-linked polymer latex particles, can be used for selective uptake of ions or polymers, or the controlled release of various compounds. Various methods for the synthesis of core-shell particles are described such as interfacial polymerization, layer-by-layer deposition, colloidosomes , internal phase separation, and silica shells. The release kinetics for controlled (sustained or triggered) release purposes is discussed. 

Epoxy modified polymer latex systems offer improved handling performance and moisture and chemical strength advantages over unmodified formulations. The wide range of latex polymers and the range of waterborne epoxy dispersions offer the formulator a wide latitude in performance characteristics required by specific applications. 

Usually or most widely applied, polymer latexes are made by emulsion polymerization [ 1 ]. Without any doubt, emulsion polymerization has created a wide field of applications, but in the present context one has to be aware that an inconceivable restricted set of polymer reactions can be performed in this way. Emulsion polymerization is good for the radical homopolymerization of a set of barely water-soluble monomers. Already heavily restricted in radical copolymerization, other polymer reactions cannot be performed. The reason for this is the polymerization mechanism where the polymer particles are the product of kinetically controlled growth and are built from the center to the surface, where all the monomer has to be transported by diffusion through the water phase. Because of the dictates of kinetics, even for radical copolymerization, serious disadvantages such as lack of homogeneity and restrictions in the accessible composition range have to be accepted. 

Emulsion polymenzaticm without the use of an emulsifier may be achieved even with a monomer with v ter solubility as low as thet of styrene provided one uses an initiator such as potassium persulfate which introduces ionic end groups into the polymer that can stabilize the polymer latex particles produced electrostatically. Emulsifier free emulsion polymerization is advantageous when the object is to obtain a well-characterized model colloid for use in experiments on colloidal stability, etc. Then it is usually desirable that the surfaces of the colloidal particles be clean. When an emulsifier is used in the iH eparation, its removal (e.g., by dialysis) is generally so incomplete that it is simpler to avoid its use in the first place. However, emulsifier-free latexes are necessarily dilute and consequently of little interest for commercial applications. 

In Table II, common characteristics of a variety of polymer latexes are listed. Throughout the text, the more important requirements for each application were alluded to. Initial work on a specific problem should quickly establish the properties needed in both the polymer and its latex. The table is organiz to permit easy determination of the capability of different classes of latexes to satisfy property requirements. Latex producer s specific product literature should he consulted to determine which of the many products within a polymer class would be must likely to satisfy the desired application. Although this book is devoted to emulsion polymerization, natural rubber latex has been included in this chapter for two... 

In water-based paints, the dominant solvent is water. There may be a small amount of other solvents to carry out certain functions. There are two types of water-based paints—one with latexes (composed of fine polymer particles dispersed in the solvent) and the other with water-soluble polymers. Latex paints are very common in the architectural market with flat, semigloss, and gloss coatings. More and more industrial coating applications are switching to water-based paints for environmental reasons. 

Polymer latexes possess a low viscosity by comparison to a solution of the polymer in an organic solvent. During the polymerization process, this enables high yields per reactor volume. The latex products can be handled readily, e.g. they can be pumped. Also, many applications require a restricted viscosity. Polymer... 

Aqueous dispersions of poly(vinyl acetate) and vinyl acetate-ethylene copolymers, homo- and copolymers of acrylic monomers, and styrene-butadiene copolymers are the most important types of polymer latexes today. Applications include paints, coatings, adhesives, paper manufacturing, leather manufacturing, textiles and other industries. In addition to emulsion polymerization, other aqueous free-radical polymerizations are applied on a large scale. In suspension polymerization a water-irnrniscible olefinic monomer is also polymerized. However, by contrast to emulsion polymerization a monomer-soluble initiator is employed, and usually no surfactant is added. Polymerization occurs in the monomer droplets, with kinetics similar to bulk polymerization. The particles obtained are much larger (>15 pm) than in emulsion polymerization, and they do not form stable latexes but precipitate during polymerization (Scheme 7.2). 

In summary, recent advances in aqueous catalytic polymerizations have afforded a range of new materials, particularly polymer latexes previously inaccessible and new water-soluble polymers. Various attractive topics for fundamental research have in turn emerged, and potential applications can be envisioned. The attractiveness and versa ii lily of fhis field results from fhe overlap and combination of polymer chemistry, organometalhc chemistry, catalysis, and colloid science. 

The application potential of polypeptide copolymers has also not been exhausted. Most studies deal with ordinary micelles for the controlled delivery of drugs or genes. Not much attention has, for whatever reason, been paid to other colloidal systems like for instance emulsions, polymer latexes, and inorganic-organic biohybrid nanoparticles. 

The role of the surfactants is two-fold first, to provide a locus for the monomer to polymerise, and second, to stabilise the polymer particles as they are formed. In addition, surfactants aggregate to form micelles (above the cmc), and these can solubilise the monomers. In most cases a mixture of anionic and nonionic surfactant is used for the optimum preparation of polymer latexes. Cationic surfactants are seldom used, except for specific applications where a positive charge is required on the surface of the polymer particles. 

Problem 6.50 The experimental value of dynamic concentration of styrene in polymer latex particles under the conditions of constant rate in emulsion polymerization has been found to be 5.2 mol/liter. Assuming this value to be applicable, calculate the rate of polymerization per liter of aqueous phase in stage II of the reaction of the emulsion polymerization recipe given in Problem... 

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