Emulsion persulfate catalyst

They have made contributions on fluoropolymers especially on high-temperature and low-temperature adhesives and elastomers. One interesting copolymer is ethylene and tetrafluoroethylene (1 1), which is emulsion polymerized in the presence of a persulfate catalyst. This copolymer, unlike PTPE, is radiation-resistant. Another fluoropolymer project is the copolymerization between tetrafluoroethylene and hexafluoropropene. One high-... 

Hydrogen peroxide-initiated radical polymerization of myrcene in n-butanol solution at 100°C yields OH-terminated polymyrcenes (besides a considerable fraction of side products and dimerized species) with in the range of 2-4 kg/ mol and fairly low polydispersity index (PDI) = 1.3-1.4. The polymyrcenes coti-sist of predominantly 1,4 structural units (77-85% 1,4 and 15-23% 3,4) (Fig. 2), comparable to polyisoprenes, which is further supported by the low glass transition temperature (Tg) of below —50°C [33]. The polymerization of myrcene with potassium persulfate catalyst in emulsion has also been described, yielding a polymyrcene with predominantly 1,4 structure and relatively low molecular weight (MW inherent viscosity 1.3) [34]. Fractions of cis- and trans-l,A units have not been determined, neither in these nor in the following examples. 

Polymerization takes place, in the following manner in the presence of suitable peroxide catalyst these compounds polymerize with themselves (homopolymerizatiOn) in aqueous emulsion. When the reaction is complete, the emulsified polymer may be used directly or the emulsion coagulated to yield the solid polymer (312). A typical polymerization mixture is total monomer (2-vinylthiazole), 100 sodium stearate, 5 potassium persulfate, 0.3 laurylmercaptan, 0.4 to 0.7 and water, 200 parts. 

Emulsion Polymerization. In this method, polymerization is initiated by a water-soluble catalyst, eg, a persulfate or a redox system, within the micelles formed by an emulsifying agent (11). The choice of the emulsifier is important because acrylates are readily hydrolyzed under basic conditions (11). As a consequence, the commonly used salts of fatty acids (soaps) are preferably substituted by salts of long-chain sulfonic acids, since they operate well under neutral and acid conditions (12). After polymerization is complete the excess monomer is steam-stripped, and the polymer is coagulated with a salt solution the cmmbs are washed, dried, and finally baled. 

Latex or emulsion polymers are prepared by emulsification of monomers in water by adding a surfactant. A water-soluble initiator is added, e.g., persulfate or hydrogen peroxide (with a metallic ion as catalyst), that polymerises the monomer yielding polymer particles, which have diameters of about 0.1 pm. The higher the concentration of surfactant added, the smaller the polymer particles. 

Emulsions may be polymerized by use of a water-soluble catalyst (initiator), such as potassium persulfate, or a monomer-soluble catalyst, such as benzoyl peroxide, lauroyl peroxide or azobisisobutyronitrilc. Suspension and solution polymerizations employ the monomer soluble catalysts only. In addition to the above-mentioned initiators, diisopropyl pcroxydi-carbonatc may also be employed, where lower-temperature polymerization may be desired, e.g., to reduce branching and minimize degradation. 

Copolymerization in aqueous emulsion at pH 9-11 with ammonium persulfate as catalyst gave only a low melting wax (mp., 86°C) with a chlorine content of 22.5. ... 

Grafting by chain transfer initiation has been carried out not only in homogenous medium but also by emulsion polymerization techniques, where the monomer and the catalyst are added to a latex containing the original backbone polymer (99). The efficiency of grafting increases with an increase of temperature of polymerization and with an increase of initiator concentration (generally potassium persulfate) these results indicate not only that the chain transfer reaction has a higher activation... 

The emulsion polymerization process involves the polymerization of liquid monomers that are dispersed in an aqueous surfactant micelle-containing solution. The monomers are solubilized in the surfactant micelles. A water-soluble initiator catalyst, such as sodium persulfate, is added to the aqueous phase. The free radicals generated cause the dispersed monomers to react to produce polymer molecules within the micellar environment. The surfactant plays an additional role in stabilizing dispersion of the produced polymer particles. Thus, the surfactants used both provide micelles to house the monomers and macroradicals, and also stabilize the produced polymer particles [193,790], Anionic surfactants, such as dodecylbenzene sulfonates, are commonly used to provide electrostatic stabilization [193], These tend to cause production of polymer particles having diameters of about 0.1-0.3 pm, whereas when steric stabilization is provided by, for example, graft copolymers, then diameters of about 0.1-10 pm tend to be produced [790,791]. 

In the derivation of the kinetic relations it was assumed that free radicals enter the particles one by one the initiation process just described satisfies this condition. This is not the case when radicals are formed by thermal decomposition of an oil-soluble initiator. Such decomposition produces pairs of radicals in the hydrocarbon phase. One would expect a pair of radicals, confined to the extremely small volume of a latex particle, to recombine rapidly. The kinetics of this type of polymerization have been described above. It is recalled here that the subdivision factor, z, and hence rate and degree of polymerization are smaller than 1 and decrease with a. These predictions from kinetic theory are in contradiction to experimental observations. Although some oil-soluble initiators, which are good catalysts in solution systems, are poor initiators in emulsion polymerizations—e.g., benzoyl peroxide—other thermally decomposing peroxides and azo compounds produce polymer in emulsion at rates comparable to those observed in polymerization initiated by water-soluble catalysts, where the radicals enter the particles one by one. Such is the case for cumene hydroperoxide, which at low concentrations yields a rate of polymerization per particle equal to that of a persulfate-initiated reaction. It must therefore be concluded that, although oil-soluble initiators may decompose into radical pairs within the particles, polymer radicals are formed one by one. The following mechanisms are consistent with formation of polymer radicals singly. 

PTFE is produced by free-radical polymerization mechanism in an aqueous media via addition polymerization of tetrafluoroethylene in a batch process. The initiator for the polymerization is usually a water-soluble peroxide, such as ammonium persulfate or disuccinic peroxide. A redox catalyst is used for low temperature polymerization. PTFE is produced by suspension (or slurry) polymerization without a surfactant to obtain granular resins or with a perfluori-nated surfactant emulsion polymerization) to produce fine powder and dispersion products. Polymerization temperature and pressure usually range from 0 to 100°C and 0.7 to 3.5 MPa. 

Catalyst for bulk and suspension, 0.5 per cent benzoyl peroxide for emulsion, 0.5 per cent potassium persulfate. 

The kinetics of aqueous dispersion polymerization differ very little from acrylonitrile bulk or emulsion polymerization. Redox initiation is normally used in commercial production of polymers for acrylic fibers. This type of initiator can generate free radicals in an aqueous medium efficiently at relatively low temperatures. The most common redox system consists of ammonium or potassium persulfate (oxidizer), sodium bisulfite (reducing agent), and ferric or ferrous iron (catalyst). This system gives the added benefit of supplying dye sites for the fiber. 

The basic monomer unit is a totally fluorinated ethylene molecule (—CF —CF —). It is well known under its common trade name Teflon. It was discovered in 1938 by Roy J. Plunkett a DuPont scientists. Industrially, polytetrafluoroethylene is obtained from several consecutive of steps. First, chloroform reacts with hydrofluoric acid to yield chlorodifluoromethane. The chlorodifluoromethane is then pyrolized at 800-1000 C to yield the monomer, i.e., tetra-fluoroethylene (CF2=CF2, TFE) which is purified and polymerized in aqueous emulsion or suspension using organic peroxides, persulfates or hydrogen peroxide as catalysts. The simple polymerization reaction is as follows. 

Poljmerization was initiated by addition of an aqueous potassium persulfate solution to the reactor. The emulsion temperature was maintained near 40°C by control of a combination of three variables (f) reactor jacket temperature, (2) agitator speed, and (3) catalyst addition rate. The progress of polymerization (86) was... 

One of the ways that aqueous emulsion polymerization processes can be classified is on the basis of the types of the initiators also referred to as catalysts. In one type of polymerization system, an organic peroxide, preferably water-soluble, is used. The organic peroxides include cumene hydroperoxide, diisopropyl benzene hydroperoxide, triisopropyl benzene hydroperoxide, and tertiary butyl hydroperoxide. A second type of emulsion polymerization employs an inorganic peroxide. Suitable compounds include perborates, persulfates, perphosphates, percarbonates, barium peroxide, zinc peroxide, and hydrogen peroxide. Specific examples of inorganic peroxides are ammonium persulfate and sodium perphosphate. 

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