Polymerization, free-radical addition suspension

The reaction engineering aspects of these polymerizations are similar. Good heat transfer to a comparatively inviscid phase makes them suitable for vinyl addition polymerizations. Free-radical catalysis is mostly used, but cationic catalysis is used for nonaqueous dispersion polymerization (e.g., of isobutene). High conversions are generally possible, and the resulting polymer, either as a latex or as beads is directly suitable for some applications (e.g., paints, gel permeation chromatography beads, expanded polystyrene). Suspension polymerizations are run in the batch model. Continuous emulsion polymerization is common. 

Poly(vinyl acetate) (PVA) and ethylene-vinyl acetate (EVA) copolymer adhesives have much in common, yet represent extremes in the degree of sophistication of their production processes. Both products are stable suspensions in water of a film-forming polymer, the particles of which are generally spherical. They are made by emulsion polymerization, which uses a free-radical addition mechanism to polymerize the monomer in the presence of water and stabilizers. Vinyl acetate is the sole or major monomeric raw material. 

Commercially, suspension polymerization has been hmited to the free-radical addition of water-insoluble liquid monomers. With a volatile monomer such as vinyl chloride, moderate pressures are required to maintain it in the hquid state. It is possible, however, to perform inverse suspension polymerizations with a hydrophilic monomer or an aqueous solution of a water-soluble monomer suspended in a hydrophobic continuous phase. 

As with suspension polymerization, commerdal emulsion polymerization has pretty much been restricted to the free-radical addition of water-insoluble, liquid monomers (with volatile monomers such as butadiene and vinyl chloride, moderate pressures are required to keep them in the liquid phase). Inverse emulsion polymerizations, with a hydrophylic monomer phase dispersed in a continuous hydrophobic phase, are possible, however. 

A polymeric composition for reducing fluid loss in drilling muds and well cement compositions is obtained by the free radical-initiated polymerization of a water-soluble vinyl monomer in an aqueous suspension of lignin, modified lignins, lignite, brown coal, and modified brown coal [705,1847]. The vinyl monomers can be methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinylacetate, methyl vinyl ether, ethyl vinyl ether, N-methylmethacrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, and additional AMPS. In this process a grafting process to the coals by chain transfer may occur. 

All four polymerization processes can be used to make PS. The reaction is an addition polymerization using a free radical initiator (benzoyl peroxide or di-tertiary butyl peroxide). Mostly, the suspension or bulk processes are... 

Aqueous suspension polymerization requires the usual additives, such as free radical initiators, colloidal dispersants (not always), and chain transfer agents to control molecular weight. After the process is completed, the suspension contains spherical particles approximately 100 pm in diameter. Suspension polymers are available as free-flowing powder or in pellet form for extrusion or injection molding.58... 

In addition to blending with SPMI copolymers, PMI can be incorporated into ABS using mass, emulsion [46-50] or suspension [42] free radical polymerization techniques. The high heat ABS resin can be completely produced by mass polymerization, or mass polymerized PMI-SAN can be blended with (emulsion polymerized) SAN-grafted rubber concentrates and/or conventional mass ABS. Sumitomo Naugatuck determined an empirical relation for the compatibility of SAN/SAN-PMI blends based on the polar monomers in each component [51]. Figure 15.4 shows that the miscibility window with SANs becomes wider with increasing PMI level in the terpolymer [52]. 

Polymaleimide is prepared by free-radical polymerization of maleimide in the presence of divinylbenzene (.5%) or N,N -methylenebisacrylamide (5-10%) as cross-linking agents. PNCS is obtained by addition of chlorine in carbon tetrachloride to a suspension of the polymer in aqueous sodium hydroxide solution,... 

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. 

Aqueous dispersions of poly(vinyl acetate) and vinyl acetate-ethylene copolymers, homo- and copolymers of acrylic monomers, and styrene-butadiene copolymers are the most important types of polymer latexes today. Applications include paints, coatings, adhesives, paper manufacturing, leather manufacturing, textiles and other industries. In addition to emulsion polymerization, other aqueous free-radical polymerizations are applied on a large scale. In suspension polymerization a water-irnrniscible olefinic monomer is also polymerized. However, by contrast to emulsion polymerization a monomer-soluble initiator is employed, and usually no surfactant is added. Polymerization occurs in the monomer droplets, with kinetics similar to bulk polymerization. The particles obtained are much larger (>15 pm) than in emulsion polymerization, and they do not form stable latexes but precipitate during polymerization (Scheme 7.2). 

The cationic palladium a-diimine complexes are remarkably functional-group tolerant. Ethylene polymerizations can be carried out in the presence of ethers, organic esters, and acids, but nitriles tend to inhibit polymerizations. In addition, polymerizations have been carried out in the presence of air and in the presence of an aqueous phase.Aqueous emulsion and suspension polymerizations using these catalysts have been developed as a route to microspheres of polymer for adhesives as well as for other applications.2 ° 2 Preparation of elastomers is often complicated by difficult solvent removal, so polymerizations in supercritical CO2 have been investigated. It is also possible to combine the activity of the palladium catalysts with other polymerization techniques such as living-free-radical polymerizations. One interesting observation is that the... 

Spectrophotometric titration data imply the formation of stable HPA-polyelec-trolyte complexes. On average, 3—3.5 monomer polycation units correspond to one heteropolyanion. Immobilized HPA maintains specific properties of homogeneous HPA solutions. For instance, thqr are capable of both chemical and photochemical reduction. By addition of a Cr q solution to the polymeric complex suspensions, or by ultraviolet irradiation of this suspension, the complexes acquire a reddish tint which indicates the formation of a reduced species of HPA. The ability of highly-reduced HPA species to evolve H2 is attributed to the presence of multi-valenced cations in HPA e.g. W, Mo, etc.) that promote the double-electron reduction of water to H2 without evolution of free radicals. 

Free radical polymerization (FRP) is a very widespread method of polymerization, which has been used for a long time in industiy for many reasons FRP is easy to carry out, can be performed in bulk, in solution in various solvents, and also in dispersed media (suspension, emulsion, etc.). It can be achieved over a large range of reaction temperatures (—100 to -1-200 °C). Additionally, this polymerization technique can be carried out with a lot of monomers, even functionalized ones. For example, monomers can bear standard functional groups or heteroatoms such as silicon or phosphorus. 

Free-radical polymerization n. A reaction initiated by a free radical derived from a polymerization catalyst. Polymerization proceeds by the chain-reaction addition of monomer molecules to the free-radical ends of growing chain molecules. Major polymerization methods such as bulk, suspension, emulsion, and solution polymerization involve free radicals. The free-radical mechanism is also useful in copolymerization, in which alternating monomeric units are promoted by the presence of free radicals. Lenz RW (1967) Organic chemistry of high polymers. Interscience Publishers, New York. Odian G (2004) Principles of polymerization, 4th edn. Wiley-Interscience, New York. 

Suspension polymerization is a very important method of polymerization, especially used in free radical polymerization. The benefit of suspension polymerization over bulk polymerization includes ease of temperature (and hence reaction) control and the formation of a directly usable product. The particles formed can in many cases be used directly as beads for ion exchange resins or chromatography columns or as bulk polymer pellets like common polystyrene and polystyrene copolymers. In addition, there are considerable environmental benefits of performing industrial polymerizations in aqueous media. 

Type of polymerization polycondensation (step-growth) or chain-growth (addition) free-radical, ionic solution including interfacial, emulsion, suspension, bulk (mass) continuous or batch graft, solid state... 

Generic structures of most of the relevant petroleum-based cosmetic monomers used today are shown in Table 1. All of them are based on some type of carbon-carbon unsaturated (olefinic) double bond. Even the oxyalkylene monomers are simply activated olefinic materials. Understanding the nature of the polymerization reaction is not essential to understanding polymer functionality. However, most cosmetically relevant polymers are produced by some type of addition polymerization reactions, which are carbon-carbon bondforming reactions occurring across the unsaturated double bond of the monomers. These reactions can be initiated by free radicals, anions, or cations and can be mn in bulk, in solution, as suspensions, or even as emulsions. 

Addition polymerizations proceed either by free-radical or by ionic mechanisms and can be carried out either in bulk solution, i.e., on the neat monomer, or in suspension or emulsion. Each method has its own advantages and disadvantages. The choice of method of polymerization also depends to a very great extent both on the nature of the monomer and on the product desired. Polycondensations or step-reactions proceed according to the mechanism demanded by the reactive functional groups. Some common step-reactions are esterification, amidification, and urethane formation, as well as ring-opening or transesterification. 

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