Polymerization in emulsion

Early efforts to produce synthetic mbber coupled bulk polymerization with subsequent emulsification (9). Problems controlling the heat generated during bulk polymerization led to the first attempts at emulsion polymerization. In emulsion polymerization hydrophobic monomers are added to water, emulsified by a surfactant into small particles, and polymerized using a water-soluble initiator. The result is a coUoidal suspension of fine particles,... 

Suspension polymerization produces beads of plastic for styrene, methyl methacrviaie. viny l chloride, and vinyl acetate production. The monomer, in which the catalyst must be soluble, is maintained in droplet fonn suspended in water by agitation in the presence of a stabilizer such as gelatin each droplet of monomer undergoes bulk polymerization. In emulsion polymerization, ihe monomer is dispersed in water by means of a surfactant to form tiny particles held in suspension I micellcsK The monomer enters the hydrocarbon part of the micelles for polymerization by a... 

Butadiene could be polymerized using free radical initiators or ionic or coordination catalysts. When butadiene is polymerized in emulsion using a free radical initiator such as cumene hydroperoxide, a random polymer is obtained with three isomeric configurations, the 1,4-addition configuration dominating ... 

Much has been written on RAFT polymerization under emulsion and miniemulsion conditions. Most work has focused on S polymerization,409-520 521 although polymerizations of BA,461 522 methacrylates382-409 and VAc471-472 have also been reported. The first communication on RAFT polymerization briefly mentioned the successful semi-batch emulsion polymerization of BMA with cumyl dithiobenzoate (175) to provide a polymer with a narrow molecular weight distribution.382 Additional examples and discussion of some of the important factors for successful use of RAFT polymerization in emulsion and miniemulsion were provided in a subsequent paper.409 Much research has shown that the success in RAFT emulsion polymerization depends strongly on the choice of RAFT agent and polymerization conditions.214-409-520027... 

The spectra may first be evaluated qualitatively.The polyisoprene prepared in solution shows a pronounced band at 888 cm which indicates a high proportion of 3,4-link-ages. For the product of bulk polymerization this band is much reduced in favor of absorptions at 1127 and 1315 cm indicating predominantly c/s-1,4-linkage of the monomeric units in this case.The polymer made by radical polymerization in emulsion (see Example 3-12) shows the presence of all possible structural units,although the proportion of c/s-1,4-linkages is low. 

It can be shown that the degree of polymerization in emulsion polymerization can be derived from general polymerization kinetics [Eq. (3.79)] by neglecting chain transfer ... 

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... 

This scries of robbers includes monomer ratios up to about 50% styrene. The addition of more than 50% styrene makes the materials more like plastic than robber. The most commonly used SBR rubbers contain about 25% styrene, which is polymerized in emulsion systems at 5-l0°C. Most SBR goes into tires, but the type for the tread differs from that of the sidewall or carcass. SBRs for adhesives, shoe soles, and other products also differ. The formulation permits vast varieties of end products. Among the processing variables that can be manipulated tu provide different end characteristics are temperature, viscusily. use of different emulsifiers and solvents, use of different antioxidants for stabilization, different oils, carbon blacks, and coagulation techniques. 

Polymerization in emulsion under normal pressure and in the temperature range from —20 C to 60°C uses a fine emulsion of oil-soluble monomers in water and initiates the reaction with a system of water-soluble catalysts. This method is probably the most important of all, because it is used in very large scale in die copolyiuerization of butadiene and styrene and in the polymerization of many other monomers, such as chloroprene and vinyl chloride, to produce latices of the various synthetic rubbers. 

Using a similar procedure as is used for cold rubber , various mixtures of 3-6 with styrene and butadiene (ratio by weight 1 3, whereby various amounts of styrene were substituted by the azo compound) have been polymerized in emulsion at 5 °C using a redox initiating system. 

Cooper, W., and M. Fielden Graft polymerization in emulsion using visible and ultraviolet light. J. Polymer Sci. 28, 442 (1958). 

In emulsion polymerization the compartmentalization of reaction loci and the location of monomer in polymer particles favor the growth and slow down termination events. The contribution of solution polymerization in the continuous phase is strongly restricted due to the location of monomer in the monomer droplets and/or polymer particles. This gives rise to greatly different characteristics of polymer formation in latex particles from those in bulk or solution polymerization. In emulsion polymerization, where polymer and monomer are mutually soluble, the polymerization locus is the whole particle. If the monomer and polymer are partly mutually soluble, the particle/water interfacial region is the polymerization locus. 

The rate of polymerization in emulsion polymerization is proportional to kg-, where kg is the fhain transfer step on the vinyl group (10). Substituting trideuterovinyl acetate for vinyl acetate raised the rate by a factor of 1.76. When the calculation for the isotope effect on rate is done accurately, taking into account the 3% H on the trideuterovinyl, we find that if the effect is purely on k3, the rate should rise by a factor of 1.69 as compared to 1.76 . 02. This is almost within the experimental error. There may be a very slight secondary isotope effect (23,24) on the propagation and re-ini tation rate constants k2 and k, but it cannot be decided from these data. 

Free-Radical Polymerization in Emulsion. In suspension polymerization, the particle size is fixed by the size of the monomer droplet which contains the initiator. Emulsion polymerization differs from suspension polymerization in that the initiator is dissolved in the aqueous phase and the polymer particle grows during polymerization. Free radicals are generated in the water and diffuse to the monomer-water interface. The length of the polymer chain formed, or equivalently the molecular weight, depends on the rate of free radical arrival and termination. S. Katz,... 

The participation of Diels-Alder type intermediates in polymerization was considered by Hill et ah (26) in 1939 as a result of the elucidation of the structures of the butadiene homopolymer and the butadiene-methyl methacrylate copolymer resulting from thermal polymerization in emulsion. The considerable amount of alternating 1,4 and 1,2 structures in the homopolymer and the predominantly 1,4 structure of the butadiene in the copolymer which contained more than 50% alternating units of butadiene and methyl methacrylate led to the proposal that the reaction proceeded through a Diels-Alder dimer complex or activated complex. Chain initiation involved a thermal reaction in which the activated com-... 

Series I Acrylic Latex Emulsions. A series of four acrylic latex emulsions varying in glass transition temperature (Tg) (3) were applied first. Tg is the temperature at which the resin changes from a relatively flexible to a relatively stiff material. The acrylic latexes are made from water-insoluble monomers such as acrylates and alkyl acrylates polymerized in emulsion form to produce an aqueous dispersion or latex of the polymer. Upon drying, the emulsion is irreversibly broken so that the applied material becomes wash-fast. The application requires no catalyst or high temperature heating. 

Producing a fine porous powder which is easy to blend with compounding ingredients. A smaller amount is polymerized in emulsion and spray-dried for plastisols and organosols. And an even smaller amount is copolymerized with vinyl acetate in organic solution, to produce a uniform copolymer which precipitates at a constant composition and molecular weight. 

It is clear from Eq. 1 that the monomer concentration in a polymer particle is one of the three key factors that control the particle growth rate, and accordingly, the rate of polymerization. In emulsion polymerization, the course of emulsion polymerization is usually divided into three stages, namely. Intervals I, II and III. In Intervals I and II of emulsion homopolymerization, the monomer concentration in the polymer particles is assumed to be approximately constant. In Interval III, it decreases with reaction time. Two methods are now used to predict the monomer concentration in the polymer particles in emulsion homopolymerization empirical and thermodynamic methods. 

Different techniques are available to carry out a free radical polymerization in emulsion. In spite of the fact that their names (macro-, mini- and microemul-... 

The mechanism and kinetics of vinyl chloride polymerization in emulsion have been studied extensively, mainly involving the use of chemical initiators, and has been summarized by Talamini and Peg-gion and by Ugelstad et alia (4). The mechanism shows a gradual change as the number of particles (N) is increased. 

In addition to the kinetic considerations illustrated above, operating a living polymerization in emulsion is still the subject of research efforts by many groups [13]. The multi-phase environment complicates the global kinetics of the process and this is particularly evident in an ab initio emulsion polymeriza-... 

The rate equation with strongly acidic catalysts is also second order in silanol and first order in catalyst (75). The mechanism is proposed to proceed via protonation of silanol, followed by an electrophilic attack of the conjugate acid on nonprotonated silanol. The condensation processes outlined in reactions 16a and 16b for sulfonic acids is also an applicable mechanism for the acid catalysis. The condensation polymerization in emulsion catalyzed by dodecylbenzenesulfonic acid is second order in silanol, but the rate has a complex dependence on sulfonic acid concentration (69). This process was most likely a surface catalysis of the oil-water interface and was complicated by self-associations of the catalyst-surfactant. 

In general, for most investigations, y radiation has been used because of its high degree of penetration and the ccanparative ense of estimating dose-depth characteristics and because radical fluxes comparable to those used with chemical initiation can easily be achieved- There have also been a few, comparatively brief, studies using electron accelerators to initiate emulsion polymerization in emulsion. These have mainly been conducted in Japanese laboratories. 

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