Polymerization emulsion, suspension

Aqueous media, such as emulsion, suspension, and dispersion polymerization, are by far the most widely used in the acryUc fiber industry. Water acts as a convenient heat-transfer and cooling medium and the polymer is easily recovered by filtration or centrifugation. Fiber producers that use aqueous solutions of thiocyanate or zinc chloride as the solvent for the polymer have an additional benefit. In such cases the reaction medium can be converted directiy to dope to save the costs of polymer recovery. Aqueous emulsions are less common. This type of process is used primarily for modacryUc compositions, such as Dynel. Even in such processes the emulsifier is used at very low levels, giving a polymerization medium with characteristics of both a suspension and a tme emulsion. 

Emulsion—Suspension Polymerized Pigment Ink. Polymerization of a polar prepolymer as the internal phase in an oil-based external phase (24) gives a fluorescent ink base in which spherical fluorescent particles are dispersed. This base is suitable for Htho and letterpress inks (qv). An... 

Emulsion Polymerization. Emulsion and suspension reactions are doubly heterogeneous the polymer is insoluble in the monomer and both are insoluble in water. Suspension reactions are similar in behavior to slurry reactors. Oil-soluble initiators are used, so the monomer—polymer droplet is like a small mass reaction. Emulsion polymerizations are more complex. Because the monomer is insoluble in the polymer particle, the simple Smith-Ewart theory does not apply (34). 

Processes that are essentially modifications of laboratory methods and that allow operation on a larger scale are used for commercial preparation of vinyhdene chloride polymers. The intended use dictates the polymer characteristics and, to some extent, the method of manufacture. Emulsion polymerization and suspension polymerization are the preferred industrial processes. Either process is carried out in a closed, stirred reactor, which should be glass-lined and jacketed for heating and cooling. The reactor must be purged of oxygen, and the water and monomer must be free of metallic impurities to prevent an adverse effect on the thermal stabiUty of the polymer. 

Often a chain-transfer agent is added to vinyl acetate polymerizations, whether emulsion, suspension, solution, or bulk, to control the polymer molecular weight. Aldehydes, thiols, carbon tetrachloride, etc, have been added. Some emulsion procedures call for the recipe to include a quantity of preformed PVAc emulsion and sometimes antifoamers must be added (see Foams). 

ABS (acrylonitrile—butadiene-styrene) resins are two-phase blends. These are prepared by emulsion polymerization or suspension grafting polymerization. Products from the former process contain 20—22% butadiene those from the latter, 12—16%. 

The main purpose of pesticide formulation is to manufacture a product that has optimum biological efficiency, is convenient to use, and minimizes environmental impacts. The active ingredients are mixed with solvents, adjuvants (boosters), and fillers as necessary to achieve the desired formulation. The types of formulations include wettable powders, soluble concentrates, emulsion concentrates, oil-in-water emulsions, suspension concentrates, suspoemulsions, water-dispersible granules, dry granules, and controlled release, in which the active ingredient is released into the environment from a polymeric carrier, binder, absorbent, or encapsulant at a slow and effective rate. The formulation steps may generate air emissions, liquid effluents, and solid wastes. 

Blending vegetable oils Blending gasoline Clay dispersion Fermentation (pharmaceutical) Suspension polymerization Emulsion polymerization Solution polymerization... 

Many polymers can be produced via interfacial polymerization. These multiphase reactions occur in emulsions, suspensions, slurries, or at the interface between a gas and a solid. 

We can readily polymerize styrene by a variety of methods including solution, emulsion, suspension, and bulk processes. Historically, bulk polymerization was the first commercial process, but it has now largely been superseded by solution and suspension polymerization. 

Why are some initiators water soluble and others monomer soluble Which type is used for suspension polymerization Emulsion polymerization ... 

Manufacturing Processes. The three manufacturing processes already mentioned (continuous mass polymerization, batch suspension and emulsion polymerization) continued to compete with each other after 1945. Whereas the third one gradually decreased in importance, the other two were given preference in... 

Heterogeneous polymerization is used extensively to control the thermal and viscosity problems. There are three types of heterogeneous polymerization precipitation, suspension, and emulsion. Emulsion polymerization is discussed in Chap. 4. Precipitation polymerizations begin... 

The initiator is present in the water phase, and this is where the initiating radicals are produced. The rate of radical production if, is typically of the order of 1013 radicals L-1 s-1. (The symbol p is often used instead of Rj in emulsion polymerization terminology.) The locus of polymerization is now of prime concern. The site of polymerization is not the monomer droplets since the initiators employed are insoluble in the organic monomer. Such initiators are referred to as oil-insoluble initiators. This situation distinguishes emulsion polymerization from suspension polymerization. Oil-soluble initiators are used in suspension polymerization and reaction occurs in the monomer droplets. The absence of polymerization in the monomer droplets in emulsion polymerization has been experimentally verified. If one halts an emulsion polymerization at an appropriate point before complete conversion is achieved, the monomer droplets can be separated and analyzed. An insignificant amount (approximately <0.1%) of polymer is found in the monomer droplets in such experiments. Polymerization takes place almost exclusively in the micelles. Monomer droplets do not compete effectively with micelles in capturing radicals produced in solution because of the much smaller total surface area of the droplets. 

Acrylic Elastomers. Acrylic elastomers possess good oil and heat resistance. They are made by polymerizing monomeric acid esters of ethyl or butyl acrylate and methoxyethyl acrylate or ethoxyethyl acrylate. They can be polymerized in emulsion, suspension, or solution systems (9) (see... 

The section on suspension polymerization indicated the differentiation between suspension and emulsion (or latex) polymerizations. Emulsion polymers usually are formed with the initiator in the aqueous phase, in the presence of surfactants, and with polymer particles of colloidal dimensions, i.e., on the order of 0.1 gm in diameter [17]. Generally, the molecular weights of the polymers produced by an emulsion process are substantially greater than those produced by bulk or suspension polymerizations. The rate of polymer production is also higher. As a large quantity of water is usually present, temperature control is often simple. 

For the copolymerization of ethene and vinyl acetate, solution polymerization, suspension polymerization, emulsion polymerization and bulk polymerization may be used, but solution polymerization is preferred (1). A method of either continuous type or batch type may be employed. Methanol is generally used as the solvent. 

An intermediate polymerization technique between emulsion polymerization and suspension polymerization has been described. Here, the monomers are first dispersed in water containing a small amount of surfactant and a high molecular weight alcohol to form very small droplets of monomer. The polymerization is effected with a water-soluble free radical initiator, such as potassium per-oxydisulfate (4). 

Usually, free-radical initiators such as azo compounds or peroxides are used to initiate the polymerization of acrylic monomers. Photochemical and radiation-initiated polymerizations are also well known. Methods of radical polymerization include bulk, solution, emulsion, suspension, graft copolymerization, radiation-induced, and ionic with emulsion being the most important. 

Commercial Polymerisation Methods. Aqueous media, such as emulsion. suspension, and dispersion polymerization, are by far [he most widely used in the acrylic fiber industry. Water acts as a convenient hcai-iranslcr... 

Step 3—In a separate step, styrene-acrylonitrile (SAN) resin is prepared by emulsion, suspension, or mass polymerization by free-radical techniques. The operation is carried out in stainless-steel reactors operated at about 75°C (167°F) and moderate pressure for about 7 hours. Tlie final chemical operation is the blending of the ABS graft phase with the SAN resin, plus adding various antioxidants, lubricants, stabilizers, and pigments. Final operations involve preparation of a slurry of fine resin particles (via chemical flocculation), filtering, and drying in a standard fluid-bed dryer at 121-132°C (250-270°F) inlet air temperature. 

Of great importance to the polymerization is the smooth resolution of the w/o emulsions at the end of the prepolymerization. The transition of w/o emulsion polymerization to suspension polymerization (type o/w) must be complete and must occur without great effort. It has already been pointed out that the stability of w/o emulsions increased with de-... 

Water or other nonsolvent Polymer or polymer in solution Suspension, dispersion, or emulsion polymerization Emulsion polymerization of a rubber latex. Suspension polymerization of expandable polystyrene... 

For example, the particle size distribution in emulsion, suspension, and precipitation polymerization can be a crucial product specification. One of the greatest difficulties in achieving quality control of the polymer product is that the actual customer specifications may be in terms of non-molecular parameters such as tensile strength, crack resistance, temperature stability, color or clarity, absorption capacity for plasticizer, etc. 

Superficially, emulsion polymerization resembles suspension polymerization, but there are a number of important differences. Water is used as the continuous phase and heat transfer is very good for both suspension and emulsion polymerization. In contrast to suspension polymerization, the polymer particles produced in emulsion polymerization are on the order of 0.1 xm in diameter.33 Another important difference is the presence of an emulsifying agent or soap. At the beginning of polymerization the soap molecules aggregate together in a group of about 50-100 molecules to form what is called a micelle. Some of the... 

Heterogeneous polymerizations proceed in two or more phases. Heterogeneity may be caused by the presence of a solid or of a gaseous phase or else the liquid monomer may be dispersed in another liquid with which it does not dissolve. Very important are the systems (a) with a solid initiator and (b) of two practically immiscible liquids. The former is useful for producing stereospecific polymers which are usually formed by a coordination mechanism. The latter makes possible an elegant and efficient removal of the heat of polymerization and it is applied technically with radical polymerizations in suspension or emulsion. 

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