Suspension polymerization vinyl chloride

Hydroxyhydroquinone and pyrogaHol can be used for lining reactors for vinyl chloride suspension polymerization to prevent formation of polymer deposits on the reactor walls (98). Hydroxyhydroquinone and certain of its derivatives are useful as auxiUary developers for silver haUde emulsions in photographic material their action is based on the dye diffusion-transfer process. The transferred picture has good contrast and stain-free highlights (99). 5-Acylhydroxyhydroquinones are useful as stabilizer components for poly(alkylene oxide)s (100). 

Note that suspension polymerization is only superficially related to emulsion polymerization, which was outlined in Chapter 8. In suspension processes the coagulation of the dispersion is controlled by agitation plus the action of a water-soluble polymer and/or a fine particle size inorganic powder. The role of water is to act primarily as a heat transfer medium. In vinyl chloride suspension polymerization the specific heat of the monomer and polymer are about equal and are one-quarter that of water, on an equal weight basis. Thus, at the typical 1.5/1 water/vinyl chloride mass ratio the heat capacity of the aqueous phase is about six times that of the organic phase. Another use of water is, of course, to keep the viscosity of the reaction medium at a useful level. Water/monomer ratios of 1.5/1 to 1.75/1 provide a good compromise between suspension concentration and viscosity. 

Commercial grade PVC is produced primarily by free-radical-initiated suspension and emulsion polymerization of vinyl chloride. Suspension polymerization accoimts for over 80% of PVC produced. Solution and bulk polymerization are also employed to some extent. However, there are difficulties with bulk polymerization because PVC is insoluble in its monomer and therefore precipitates. In suspension polymerization, vinyl chloride droplets are suspended in water by means of protective colloids such as poly(viEyl alcohol), gelatin, or methyl cellulose in pressure vessels equipped with agitators and heat... 

Suspension polymerization (60-63) is of special meaning for the production of technically important polymers, as for instance, expanded polystyrene and poly(vinyl chloride). Suspension polymerization refers to the carrying out of a polymerization in micron-sized droplets with oil-soluble initiators. Emulsification and polymerization take place in the same vessel and at the same time. A polymeric stabilizer or protective colloid is... 

De Roo, T., Wieme, J., Heynderickx, G.J., Matin, G.B., 2005. Estimation of intrinsic rate coefficients in vinyl chloride suspension polymerization. Polymer 45, 8340-8354. 

Faria J. R. Machado F, Lima EL, Pinto JC. Monitoring of vinyl chloride suspension polymerization using NIRS. 1. Prediction of morphological properties. Comput-Aided Chem Eng 2009 27 327-332. 

Vinyl chloride is polymerized in bulk or aqueous suspension to yield a dry-blend resin of porous particle surface. In aqueous emulsion it... 

Vinyl chloride is polymerized primarily by peroxide-initiated polymerization in aqueous suspension,... 

Each year, hundres of thousands of tons of vinyl chloride are polymerized in the world. Commensurate attention is thus paid to studies of its polymerization. Vinyl chloride is one of those monomers that are transformed to polymer by a complicated mechanism. Poly(vinyl chloride) is soluble neither in its own monomer nor in the common solvents. Its formation is therefore connected with the appearance of a solid phase the process has the character of precipitation polymerization. This greatly complicates the kinetics of solution and bulk (suspension) polymerization. 

Uses Initiator for suspension polymerization of vinyl chlorides, solution polymerization of various monomers... 

Vinyl chloride is polymerized in bulk, suspension, emulsion, or in the gas phase. The bulk polymerization is a precipitation polymerization. To prevent excessive heat buildup because of the heat of polymerization, it is carried out in two stages. In the gaseous phase polymerization, prepolymerized PVC is loaded with vinyl chloride below the saturated vapour pressure and then further polymerized continuously in a fluidized bed or cascade process. Emulsion polymerizates always contains foreign material, and so, are only used as pastes. 

A total of 70-75% of all vinyl chloride is polymerized in suspension or emulsion, where yields of practically 100% are obtained with suspensions and 50% with emulsions. To prevent degradation or coagulation of the product, the reaction vessel is made of stainless steel or is glass-lined. Very pure water must be used in suspension polymerizations the poly-merizate is centrifuged and subsequently dried in dry tumblers. The emulsion polymerizates are worked up by either coagulation or spray-drying. In the latter case, the product still contains about 5% solid impurity and therefore limited to use as pastes. 

Polymers. Foam is often a particular problem in the production of polymers. There are numerous situations where foam can reduce the production capacities of vats and vessels and cause problems in pumps, meters, and other equipment, particularly distillation and evaporation equipment. Foam is frequently a problem when stripping off a monomer from a polymer. Examples are in the production of styrene-butadiene [9003-55-8] and acrylonitrile-butadiene [9003-18-3] rubber latices. These latices are stabilized by surfactants that greatly contribute to foaming difficulties. Another problem foam area is in the stripping of imreacted monomer from poly(vinyl chloride) suspensions. In this process, vinyl chloride [75-01-4], a gas at room temperature, is liquefied by pressure, emulsified in water with surfactants and catalysts, and heated to bring about polymerization. The recovery of unpolymerized monomer by distillation from this mixture produces a severe foaming problem. 

Poly(vinyl chloride) (PVC) is one of the most widely produced polymeric materials in use today. It is commercially produced by four major processes suspension, bulk, emulsion and solution. An industrially important method of production of PVC is emulsion polymerization. There are a lot of data regarding the kinetics and mechanism of emulsion polymerization of vinyl monomers. However, relatively little work has been done on the kinetics of vinyl chloride emulsion polymerization and much less on the emulsion copolymerization. Concerning the preparation of copolymer latexes of vinyl chloride monomer, there are only patents [1-3]. 

Vinyl chloride by itself or mixed with C2H4, propylene, or isobutylene is polymerized [198] in the presence of EtsB, BU3B or iso-BusB, and mono-tert-En permaleate at — 30 C to +80°C. Thus, 500 g of vinyl chloride was polymerized at 20°C for 10 hr with 1200 cm of double-distilled H2O, and 1.5 g of HzO-soluble suspension stabUizer was introduced. BU3B (3.14 g) was introduced with the exclusion of oxygen and 4.0 g of mono-ferr-Bu permaleate was added 75.6% polymer conversion was achieved. Much lower yields of polymer were obtained when a peracetate or perbenzoate was used instead of the permaleate. 

The formation of primary radicals governs the rate of initiation and particle population. Because radical generation occurs in the aqueous phase, whereas radical termination occurs in the polymer particles, the polymerization rate and molecular weight can be increased at the same time. In vinyl chloride emulsion polymerization, the emulsifier greatly affects the polymerization kinetics and the physicochemical and colloidal properties of the polymer. The average polymer particle size is of the order 0.1-0.3 p,m, which is the size of primary particle nuclei in bulk and suspension polymerizations. The following is a summary of the typical kinetic features of batch vinyl chloride emulsion polymerization [61] ... 

Uses Emulsifier, surfactant in emulsion polymerization of vinyl chloride and vinyl acetate, suspension polymerization of vinyl chloride dispersant for resins, pigments, polymers, and dyes in org. systems pigment dispersant in printing inks mst preventive food-pi, adhesives, paper/paperboard emulsifier in mfg. of food-contact artides... 

Most vinyl chloride is polymerized by a batchwise suspension process. Jacketed, stirred reactors like the one in Figure 5.13 vary in size from 2,000 to 10,000 gal (8 0 m ). 

Wheieas the BPO—DMA ledox system works well for curing of unsaturated polyester blends, it is not a very effective system for initiating vinyl monomer polymerizations, and therefore it generally is not used in such appHcations (34). However, combinations of amines (eg, DMA) and acyl sulfonyl peroxides (eg, ACSP) are very effective initiator systems at 0°C for high conversion suspension polymerizations of vinyl chloride (35). BPO has also been used in combination with ferrous ammonium sulfate to initiate emulsion polymerizations of vinyl monomers via a redox reaction (36). 

In the suspension polymerization of PVC, droplets of monomer 30—150 p.m in diameter are dispersed in water by agitation. A thin membrane is formed at the water—monomer interface by dispersants such as poly(vinyl alcohol) or methyl cellulose. This membrane, isolated by dissolving the PVC in tetrahydrofuran and measured at 0.01—0.02-p.m thick, has been found to be a graft copolymer of polyvinyl chloride and poly(vinyl alcohol) (4,5). Early in the polymerization, particles of PVC deposit onto the membrane from both the monomer and the water sides, forming a skin 0.5—5-p.m thick that can be observed on grains sectioned after polymerization (4,6). Primary particles, 1 p.m in diameter, deposit onto the membrane from the monomer side (Pig. 1), whereas water-phase polymer, 0.1 p.m in diameter, deposits onto the skin from the water side of the membrane (Pig. 2) (4). These domain-sized water-phase particles may be one source of the observed domain stmcture (7). 

Solution Polymerization. In solution polymerization, a solvent for the monomer is often used to obtain very uniform copolymers. Polymerization rates ate normally slower than those for suspension or emulsion PVC. Eor example, vinyl chloride, vinyl acetate, and sometimes maleic acid are polymerized in a solvent where the resulting polymer is insoluble in the solvent. This makes a uniform copolymer, free of suspending agents, that is used in solution coatings (99). 

Poly(vinyl chloride). Poly(vinyl chloride) (PVC) [9002-86-2] is a thermoplastic for building products. It is prepared by either the bulk or the suspension polymerization process. In each process residual monomer is removed because it is carcinogenic. Oxygen must be avoided throughout the process (see Vinyl polymers). 

Random copolymers of vinyl chloride and other monomers are important commercially. Most of these materials are produced by suspension or emulsion polymerization using free-radical initiators. Important producers for vinyl chloride—vinyUdene chloride copolymers include Borden, Inc. and Dow. These copolymers are used in specialized coatings appHcations because of their enhanced solubiUty and as extender resins in plastisols where rapid fusion is required (72). Another important class of materials are the vinyl chloride—vinyl acetate copolymers. Principal producers include Borden Chemicals Plastics, B. F. Goodrich Chemical, and Union Carbide. The copolymerization of vinyl chloride with vinyl acetate yields a material with improved processabihty compared with vinyl chloride homopolymer. However, the physical and chemical properties of the copolymers are different from those of the homopolymer PVC. Generally, as the vinyl acetate content increases, the resin solubiUty in ketone and ester solvents and its susceptibiUty to chemical attack increase, the resin viscosity and heat distortion temperature decrease, and the tensile strength and flexibiUty increase slightly. 

Emulsions Emulsions have particles of 0.05 to 5.0 [Lm diameter. The product is a stable latex, rather than a filterable suspension. Some latexes are usable directly, as in paints, or they may be coagulated by various means to produce massive polymers. Figures 23-23d and 23-23 show bead and emulsion processes for vinyl chloride. Continuous emulsion polymerization of outadiene-styrene rubber is done in a CSTR battery with a residence time of 8 to 12 h. Batch treating of emulsions also is widely used. 

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... 

Figure 12-4. The European Vinyls Corp. process for producing polyvinyl chloride using suspension polymerization (1) reactor, (2) blow-down vessels (to separate unreacted monomer), (3) stripping column, (4) reacted monomer recovery, (5) slurry centrifuge, (6) slurry drier.

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