Free-radical dispersion polymerization

Presented in this paper is a specific example of a semi-batch, free radical, dispersion polymerization. In this example, SimuSolv is used to quantify a Icinetic model derived from free radical polymerization principles and then used to define a new finishing process to reduce residual monomer to an acceptable level. Finally, experimental results are compared with those predicted by the computer simulation. 

The peroxide-initiated, free radical, dispersion polymerization of the single monomer is assumed to progress according to the simultaneous reactions of initiator decomposition, initiation, propagation and termination with appropriate reaction orders described elsewhere.(2-6)... 

Shim, S.E. Oh, S. Chang, Y.H. Jin, M.J. Choe, S. Solvent effect on TEMPO-mediated living free radical dispersion polymerization of styrene. Polymer 2004, 45 (14), 4731-4739. 

Living radical dispersion polymerization techniques have been explored to provide polymer dispersions with controlled morphology in contrary to the traditional free radical dispersion polymerization. Although living radical dispersion polymerization gives both the controlled molar mass and particle morphology, only a few studies have been reported with broad... 

Figure 9. Poly(methyl methacrylate) particles formed in free-radical dispersion polymerization in supercritical carbon dioxide using comb-like stabilizers. [Adapted from ref. 27].

Table 1. Thermal (A) and microwave-induced (MW) non-aqueous free-radical dispersion polymerization of MMA in the presence of SEP dispersing agent. Reprinted from (1996) Acta Polym 47 74 [37] with permission...

The most commonly used combination of chemicals to produce a polyacrylamide gel is acrylamide, bis acrylamide, buffer, ammonium persulfate, and tetramethylenediarnine (TEMED). TEMED and ammonium persulfate are catalysts to the polymerization reaction. The TEMED causes the persulfate to produce free radicals, causing polymerization. Because this is a free-radical driven reaction, the mixture of reagents must be degassed before it is used. The mixture polymerizes quickly after TEMED addition, so it should be poured into the gel-casting apparatus as quickly as possible. Once the gel is poured into a prepared form, a comb can be appHed to the top portion of the gel before polymerization occurs. This comb sets small indentations permanently into the top portion of the gel which can be used to load samples. If the comb is used, samples are then typically mixed with a heavier solution, such as glycerol, before the sample is appHed to the gel, to prevent the sample from dispersing into the reservoir buffer. 

The controlled free-radical miniemulsion polymerization of styrene was performed by Lansalot et al. and Butte et al. in aqueous dispersions using a degenerative transfer process with iodine exchange [91, 92]. An efficiency of 100% was reached. It has also been demonstrated that the synthesis of block copolymers consisting of polystyrene and poly(butyl acrylate) can be easily performed [93]. This allows the synthesis of well-defined polymers with predictable molar mass, narrow molar mass distribution, and complex architecture. 

Transition metal catalyzed, ring opening polymerization Dispersion, cationic polymerization Homogeneous/precipitation, cationic polymerization Homogeneous, free radical/cationic polymerization Precipitation, free radical polymerization Dispersion, free radical polymerization Norbornene polymer, polycarbonate Isobutylene polymer Vinyl ether polymer Amorphous fluoropolymers Vinyl polymer, semicrystalline fluoropolymers Polyvinyl acetate and ethylene vinyl acetate copol5Tner... 

The synthesis of stable latexes requires suitable nucleation of primary particles and subsequent stabilization. In classical free-radical emulsion polymerization water-soluble initiators are used. Chain growth initially affords water-soluble oligomeric radicals, which can nucleate particles by collapsing upon themselves or by entering a surfactant micelle (cf. Section 7.1). Similar considerations appear reasonable for the aforementioned catalytic polymerization to stable latexes by the water-soluble complex 6a (Scheme 7.7) [65, 71]. As a different strategy, a very fine initial dispersion of a hydrophobic catalyst precursor can be achieved as a solution in a large number of toluene/hexadecane miniemulsion droplets (0 ca. 100 nm), dispersed in the continuous aqueous phase [77, 82]. 

The upsurge of interest in this type of colloidal system followed the development in the 1950s of the technique known as dispersion polymerization [3.54]. This process provides a means of preparing nonaqueous polymer dispersions in a controlled manner. A wide range of such dispersions have been made, mainly by free-radical addition polymerization. 

Vinyl acetate is polymerized in dispersion form using various initiators. Exanples of ionic initiators commonly used for free-radical emulsion polymerizations are ammonium, sodium or potassium persulfate. Topical nonionic hydrophobic initiators include 2,2 -azobis(isobutyronitrile) (AIBN) and benzoyl peroxide. Water-soluble nonionic initiators such as tertiary-butyl hydroperoxide are also employed. The initiator 4,4 -azobis(4-cyanovaleric acid) in its acid state is oil soluble, while neutralization causes it to become water soluble providing for further diversity in initiators. 

The second means of transforming a liquid adhesive entirely into a solid without the loss of a solvent or dispersion medium is to produce solidification by a chemical change rather than a physical one. Such reactive adhesives may be single-part materials that generally require heating or exposure to electron beam or UV or visible radiation (see Radiation-cured adhesives) to perform the reaction, and which may be solids (that must be melted before application), liquids or pastes. The alternative two-part systems require the reactants to be stored separately and mixed only shortly before application. The former class is exemplified by the fusible, but ultimately reactive, epoxide film adhesives and the latter by the two-pack Epoxide adhesives and Polyurethane adhesives and by the Toughened acrylic adhesives that cure by a free-radical Chain polymerization mechanism. 

Surfactant-acrylamide Polymers. Copolymers of acrylamide and alkylarylpoly(ethoxy)-acrylate were prepared using standard free radical solution polymerization techniques. The alkylarylpoly(ethoxy)-acrylate monomers referred to as Surf" monomers were water dispersible and thus additional surfactants were not needed to effect random copolymerization. These so called "PAM-SURF" polymers were prepared with a variety of Surf monomers containing different amounts of ethylene oxide and different alkylaryl functionality. 

On the other hand, by free radical suspension polymerization of MMA in n-heptane solution in the presence of poly(styrene)-Wocfc-poly(ethene-aZt-propene) (SEP) as a dispersing agent, PMMA samples were prepared with similar molecular weights and polydispersity under both conventional and microwave conditions [37]. The reactions were run for 1 h at 70 °C with different monomer (9.0-28.3vol.%), SEP (21.7-5.4 wt%), and AIBN (1.0-0.27 wt%) concentrations (Table 1). In a typical experiment, 30 ml of the reaction mixture was fed into a 50-... 

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