Emulsion polymerization method

By contrast to other polymerization methods, emulsion polymerization offers a series of technological advantages. The temperature can easily be maintained constant by the water. The use of redox initiators means that polymerizations at fast rates are possible even at relatively low temperatures. The degrees of polymerization can be made quite high also, the unpolymerized monomer can be removed relatively easily by steam distillation. 

Manufacturing processes have been improved by use of on-line computer control and statistical process control leading to more uniform final products. Production methods now include inverse (water-in-oil) suspension polymerization, inverse emulsion polymerization, and continuous aqueous solution polymerization on moving belts. Conventional azo, peroxy, redox, and gamma-ray initiators are used in batch and continuous processes. Recent patents describe processes for preparing transparent and stable microlatexes by inverse microemulsion polymerization. New methods have also been described for reducing residual acrylamide monomer in finished products. 

PVDE is manufactured using radical initiated batch polymerization processes in aqueous emulsion or suspension operating pressures may range from 1 to 20 MPa (10—200 atm) and temperatures from 10 to 130°C. Polymerization method, temperature, pressure, recipe ingredients, the manner in which they are added to the reactor, the reactor design, and post-reactor processing are variables that influence product characteristics and quaUty. 

The incidence of these defects is best determined by high resolution F nmr (111,112) infrared (113) and laser mass spectrometry (114) are alternative methods. Typical commercial polymers show 3—6 mol % defect content. Polymerization methods have a particularly strong effect on the sequence of these defects. In contrast to suspension polymerized PVDF, emulsion polymerized PVDF forms a higher fraction of head-to-head defects that are not followed by tail-to-tail addition (115,116). Crystallinity and other properties of PVDF or copolymers of VDF are influenced by these defect stmctures (117). 

A new process, from Norway, has filled the size gap between emulsion and suspension polymerization techniques [7,8]. This novel polymerization method, the so-called swollen emulsion polymerization has been developed by Ugelstad for producing uniform polymeric particles in the size range of 2-100 /nm. This process comprises successive swelling steps and repolymerizations for increasing the particle size of seed polymer particles by keeping the monodispersity of the seed latex. 

In this chapter, the polymerization methods used for the production of uniform latex particles in the size range of O.I-lOO /Ltm are described. Emulsion, swollen emulsion, and dispersion polymerization techniques and their modified forms for producing plain, functionalized, or porous uniform latex particles are reviewed. The general mechanisms and the kinetics of the polymerization methods, the developed synthesis procedures, the effect of process variables, and the product properties are discussed. 

Uniform macroporous polymer particles have been prepared in the size range of 5-20 iitm by the multistage emulsion polymerization methods. Several methods are available in the literature describing the synthesis and the properties of macroporous uniform particles. The main steps of these methods may be summarized as follows. 

Polystyrene is unusual among commodity polymers in that we can prepare it in a variety of forms by a diversity of polymerization methods in several types of reaction vessel. j Polystyrene may be atactic, isotactic, or syndiotactic. Polymerization methods include free radical, cationic, anionic, and coordination catalysis. Manufacturing processes include bulk, solution, suspension, and emulsion polymerization. We manufacture random copolymers ... 

Caldero, G., Garcfa-Celma, M.J. and Solans, C. (2011) Formation of polymeric nano-emulsions by a low-energy method and their use for nanoparticle preparation. Journal of Colloid and Interface Science, 353, 406-411. 

A distinction is drawn between bulk, suspension and emulsion PVC on the basis of different polymerization methods. 

Figure 10.4 (Plate 8) Polystyrene spheres prepared by emulsion polymerization methods. Because they may be packed together to form columns or beds, these spheres find applications in separations, ion exchange, and as supports for catalysts. (Photographs by John Olive)...

Polymerization Methods. Acrylonitrile and its comonomers can he polymerized by any of the well-known free-radical methods. Bulk polyntenzaiion is the most fundamental of these, but its commercial use is limned by ns aulocutalyiie nature. Aqueous dispersion polymerization is the itiosi common commercial method, whereas solution polymerization is used in cases where the spinning dope can he prepared directly from the polymerization reaction product. Emulsion polymerization is used primarily for modacrylic compositions where a high level of a water insoluble monomer is used or where the monomer mixture is relatively slow reacting. 

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. 

RESINS (Acrylonitrile-Butadiene-Styrene). Commonly referred to as ABS resins, these materials are thermoplastic resins which are produced by grafting styrene and acrylonitrile onto a diene-rubber backbone. The usually preferred substrate is polybutadiene because of its low glass-transition temperature (approximately —80°C). Where ABS resin is prepared by suspension or mass polymerization methods, stereospedfic diene rubber made by solution polymerization is the preferred diene. Otherwise, the diene used is a high-gel or cross-linked latex made by a hot emulsion process. 

Utilizing the seed latex polymerization method to avoid the occurance of new particle formation, the kinetic treatment of an emulsion polymerization is quite straight forward. Assuming that all the particles are the same size, the rate of polymerization,... 

The preparation of polymers through free radical polymerization can be carried out in several ways, both in laboratory and industrial scales. Among the techniques, bulk, suspension, emulsion and solution polymerization methods are of the most practical importance. 

Nanoparticles of synthetic polymers are usually manufactured by dispersion of preformed polymers. Although many methods can be used, they may be classified as monomer polymerization, nanoprecipitation, emulsion diffusion/solvent evaporation, and salting out. An appropriate method is selected mainly depending on polymer and drug natures. Polymerization of polymer monomers has been developed usually using poly(alkyl cyanoacrylate) [96,97]. Organic solvents are usually used in polymerization. A detailed description of this method is not provided here. 

Single-step preparations of composite polymers have been examined in previous sections. The volume fraction of the continuous phase was, however, relatively small in those cases. In contrast, the present method allows us to prepare composites with larger volume fractions of the continuous phase. Composites with large volume fractions of the continuous phase can also be obtained in a single-step by polymerizing an emulsion or a microemulsion [24]. An emulsion of a hydrophobic (hydrophilic) monomer in another hydrophilic (hydrophobic) monomer can be extremely stable (even thermodynamically stable, and then it is called a microemulsion) if a sufficiently large amount of surfactant is introduced into the system. For an emulsion to be thermodynamically stable, a cosurfactant is in most cases needed besides the surfactant. The latter method was used to prepare composites by employing acrylamide... 

A blend was prepared by dissolving a rubber material in styrene and polymerizing the system. The blend contains not only rubber and polystyrene (PS), but also a graft polymer because of the attachment of short polystyrene side chains to the rubber molecules. The toughness of this material was markedly improved compared to that of the unmodified PS. A technology based on bulk polymerization [26] has been widely used the concentrated emulsion polymerization method employed by us, however, allows one to obtain rubber toughened latexes. 

Encapsulation of Solid Particles by the Concentrated Emulsion Polymerization Method [35]... 

In this section the concentrated emulsion polymerization method is employed to encapsulate submicron inorganic powders. In a first step, a stable colloidal dispersion of the powder in an aqueous solution of a monomer containing an appropriate dispersant and a suitable initiator was prepared. This colloidal dispersion was subsequently employed as the dispersed phase of a concentrated emulsion whose continuous phase, decane, contained a surfactant. 

Very fine solid particles, namely fumed silica, were also encapsulated via the concentrated emulsion polymerization method. The amounts of the components involved are listed under PLS1 in Table 21. The PLS1 capsules range in size from 1.0 to 1.5 pm. 

Cross-linked polystyrene porous particles (with 21 mol% DVB) have been prepared by the concentrated emulsion polymerization method, using either toluene or decane as the porogen and an aqueous solution of SDS as the continuous phase. Since toluene is a good solvent for polystyrene while decane is a nonsolvent , the morphologies obtained in the two cases were different. The particles based on toluene (with a volume fraction of dispersed phase of 78%) have very small pores which could not be detected in the SEM pictures. The pore size distribution, which has sizes between 20 and 50 A and was determined with an adsorption analyzer, almost coincides with that in a previous study [49] in which porous polystyrene beads have been prepared by suspension polymerization. In contrast, the porous particles based on decane have pore sizes as large as 0.1-0.3 pm, which could be detected in the SEM pictures [44a], and also larger surface areas (47 m2 g ) than those based on toluene (25 m2 g ). The main difference between the concentrated emulsion polymerization and the suspension polymerization consists of the much smaller volume fraction of continuous phase used in the former procedure. The gel-like emulsion that constitutes the precursor in the former case contains polyhedral cells separated by thin films of continuous phase. The polymerization of the cells does not... 

Compare and contrast suspension and emulsion polymerization methods. 

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. 

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