Emulsion-type polymerization

These kinetic results have led to a variety of interpretations. Magat and associates have proposed kinetic schemes based on the idea that a steady state does not exist and that only small (primary) radicals can terminate polymer chains (52, 93). Bamford and Jenkins have criticized this concept of emulsion-type polymerization (77). They point out that if the source of initiation were removed no more small radicals would be formed and polymerization should continue indefinitely. They cite a photosensitized reaction at 60° in which the light was shut off at about 15% conversion, whereupon the rate fell to one-half of its original value in 60 seconds. Bamford and Jenkins point also to evidence from the fast reaction that argues against emphasis on termination between polymer radicals and small radicals. 

These same workers described an inverse emulsion-type polymerization process.109 They used a conventional process in which microemulsions of water in hydrocarbon readily form in the presence of Aerosol-OT(AOT). The droplets are essentially swollen cells, where radius is controlled by the water/AOT ratio. As droplets collide, hydrophilic reagents contained in them are exchanged. When pyrrole and (NH4)2S208 dispersions were mixed, eventually a sediment appeared. However, if poly(vinyl pyrrolidone) (PVP) was added at different intervals, stable dispersions of small particles could be prepared. 

Since MVK is completely miscible with water, an emulsion-type polymerization without additional emulsifiers is possible. For the oxodisulfate-silver nitrate initiator, the following mechanism is suggested ... 

H) Emulsion and miniemulsion polymerization Emulsion-type polymerizations for ROMP of norbornene and its derivatives were first reported using hydrates of Ru, Ir, and Os four decades ago. " However, polymerization rates were very low. ROMP using water-soluble ruthenium carbene complexes as catalysts was used to polymerize functionalized 7-oxanorbornenes not only in water and methanol, but also in aqueous emulsions. Gationic water-soluble aliphatic phosphines were used in the synthesis of the ruthenium carbene complexes. The polymer polydispersity was low (1.1-1.3), although few details of the dispersed phase polymerization were reported. 

An unusual method for the preparation of syndiotactic polybutadiene was reported by The Goodyear Tire Rubber Co. (43) a preformed cobalt-type catalyst prepared under anhydrous conditions was found to polymerize 1,3-butadiene in an emulsion-type recipe to give syndiotactic polybutadienes of various melting points (120—190°C). These polymers were characterized by infrared spectroscopy and nuclear magnetic resonance (44—46). Both the Ube Industries catalyst mentioned previously and the Goodyear catalyst were further modified to control the molecular weight and melting point of syndio-polybutadiene by the addition of various modifiers such as alcohols, nitriles, aldehydes, ketones, ethers, and cyano compounds. 

ABS compositions with bimodal particle size distributions of the grafted rubber can be prepared by emulsion graft polymerization techniques. The preparation of ABS types by emulsion polymerization consists in brief of (13) ... 

Polymerization reactions were principally conventional emulsion types, although solution, bulk, or suspension techniques may also be used. 

The first step in the manufacture of fine powder resins is to prepare an aqueous colloidal dispersion by polymerization with initiator and emulsifier present.21 Although the polymerization mechanism is not a typical emulsion type, some of the principles of emulsion polymerization apply here. Both the process and the ingredients have significant effects on the product.22 The solids contents of such disper-... 

Cosmetic suspensions are available in two types. The first comprises pigmented products that are suspended in essentially aqueous vehicles (liquid makeup, eyeliners, mascara, and blusher). These products have a high solids content, high density, impalpable powders, and pigments permanently suspended in a primary oil-in-water emulsion-type base or a complex system of hydrophilic cellulose derivatives, clays, and/or polymeric film formers, in which the gelling and suspending properties of the vehicle often are reinforced by a small amount of a Bingham-type plastic such as carbomer. 

In the biomedical applications outlined by Ward et al. (7 ), more so than in any other separation application of synthetic polymeric membranes, the goal is to mimic natural membranes. Similarly, the development of liquid membranes and biofunctional membranes represent attempts by man to imitate nature. Liquid membranes were first proposed for liquid separation applications by Li (46-48). These liquid membranes were comprised of a thin liquid film stabilized by a surfactant in an emulsion-type mixture. Wtille these membranes never attained widespread commercial success, the concept did lead to immobilized or supported liquid membranes. In... 

Conducting polymers such as PANl- or PPY-intercalated clay-type minerals are another type of ER particle material. Kim et al. synthesized PPY-intercalated montmorillonite nanocomposites through inverted emulsion pathway polymerization, and characterized its ER effect under an electric field [38]. The nanocomposites showed not only a typical ER behavior under electric fields but also the existence of a critical electrical field when the yield stress was plotted as a function of the electric field. 

In emulsion polymerization, monomers are polymerized in the form of emulsions and polymerization in most cases involve free-radical reactions. Like suspension polymerization, the emulsion process uses water as the medium. Polymerization is much easier to control in both these processes than in bulk systems because stirring of the reactor charge is easier due to lower viscosity and removal of the exothermic heat of polymerization is greatly facilitated with water acting as the heat sink. Emulsion polymerization, however, differs from suspension polymerization in the nature and size of particles in which polymerization occurs, in the type of substances used as initiators, and also in mechanism and reaction characteristics. Emulsion polymerization normally produces polymer particles with diameters of 0.1-3//. Polymer nanoparticles of sizes 20-30 nm are produced by microemulsion polymerization (Antonietti et al., 1999 Ytldiz et al., 2003). 

TeepoL [Raffi Swanson] Vinyl type polymeric emulsions fabric finishes. 

The literature of the oxidative polymerization of aniline in an aqueous medium describes both dispersion and emulsion types of polymerizations, each with differing types of stabilizers [15-17], In the case of dispersion polymerization a polymeric stabilizer is used, and rather large polymer (latex) particles are pi-caUy obtiuned, e.g. in the order of 300-400 run diamet. Howev, there is also an example of an emulsim polymerization of aniline using dodecylbenz iesul-fonic add (DBSA) as a surfactant [15,18]. The DBSA also acts as a doping ag t fw die PANI. wMe at the same time it makes the PANI easier to process. 

When a mixture of water, monomer, surfectants, initiator, and property control agents forms microdroplets of monomer in water with dimensions of 1 pm, an emulsion has been formed (8). If polymerization occurs in the 1 pm droplets by migration of an initiator active site from the aqueous phase to the microdroplet to completely react the droplet, the process is emulsion polymerization. A major problem in emulsion polymerization is developing a mixture which remains a stable emulsion throughout the polymerization. Polymerization kinetics is controlled by the number of microdroplets in the reaction mixture and the polymerization rate of the monomer. Polymer can be recovered as fine particles fiom the completed reaction but is most often used as the emulsion of polymerized product. Emulsion polymerization is commonly used to synthesize two polymer types covered in this book, polyvinyl chloride... 

From a mathematical point of view, limiting cases of macroemulsion polymerization are mini- and microemulsion polymerizations. In miniemulsion polymerization, only small monomer droplets are present and these are also the main reaction locus. In microemulsion polymerization, the monomer droplets are also small and, in principle, reaction can take place in the monomer droplets as well as in the micelles and polymer particles. An important feature of a microemulsion is that it is thermodynamically stable, whereas the other emulsion types are only kinetically stable. However, if monomer is added very slowly and a small amount of surfactant is present, polymer particles gradually swell starting from a micelle population only. Thus, the emulsion polymerizations differ with respect to the populations present, but in all cases the latex obtained consists of segregated entities with a size at least one order of magnitude smaller than in suspension polymerization. In the most... 

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