Bulk polymerization vinyl chloride

There is autoacceleration in the bulk polymerization rate of vinyl chloride. It was suggested by Schindler and Breitenbach that the acceleration is due to trapped radicals present in the precipitated polymer swollen by monomer molecules. This influences the rate of the termination that decreases progressively with the extent of the reaction, while the propagation rate remains constant. The autocatalytic effect in vinyl chloride bulk polymerizations, however, depends on the type of initiator used. Thus, when 2,2 -azobisisobutyronitrile initiates the polymerization, the autocatalytic effect can be observed up to 80% of conversion. Yet, when benzoyl peroxide initiates the reaction it only occurs up to 20-30% of conversion. 

In heterogeneous polymerizations in bulk, the formed polymer is insoluble in its monomer and the polyreaction is performed below the softening point of the polymer. On an industrial scale, this type of process is especially utilized for chain polymerizations, for example, the radical polymerization of liquid vinyl chloride, the polymerization of liquid propylene with Ziegler-Natta or with metallocene catalysts, and the polymerization of molten trioxane. 

Figure 3.21 Schematic diagram of vinyl chloride bulk, continuous polymerization. Reprinted, by permission, from A. Krause, Chem. Eng., 72, p. 72. Copyright 1965 by McGraw-Hill.

The ability of vinyl chloride to polymerize was first observed over 150 years ago. Polyvinyl chloride has been industrially manufactured since approximately 1930. Even though pure PVC is fairly unstable, it is ranked second after PE for bulk plastic production. The manifold applications of PVC are made possible by the discovery of effective stabilizers and other additives for the polymer. 

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

Polyvinyl chloride is produced by the free-radical polymerization of vinyl chloride. Bulk, emulsion, solution, and suspension polymerization processes have been used. 

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. 

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... 

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. 

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]. 

In two other patents reported by Mazzolini et al. [252,254] for bulk polymerization of vinyl chloride, they used the same type of catalytic system as above. Thus, vinyl chloride was polymerized at — 30°C in the presence of a mixture of cumene hydroperoxide or tert-Bu hydroperoxide, a meth-anolic solution of SO2, and a methanolic solution of NaOMe, NaOEt, or KOMe. 

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] ... 

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). 

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... 

PVC can be prepolymerized in bulk to approximately 7-8% conversion. It is then transferred to an autoclave where the particles are polymerized to a solid powder. Most vinyl chloride, however, is polymerized... 

Perhaps the only process where such correlations have been published is the bulk polymerization of vinyl chloride as reported by Ray, Jain and Salovey (14). 

Finally, similar autoacceleration in the polymerization rate was reported by Crosato-Arnaldi, Gasparini and Talamini (18) for the bulk polymerization of vinyl chloride. 

The literature on the modeling and design of precipitation polymerization reactors is limited primarily to reactor for the bulk polymerization of vinyl chloride (31-38), although other systems have been discussed, particularly in the patent literature (39,40,41). 

Vinyl chloride Free radical polymerization in bulk or emulsion rapid in presence of peroxides susceptible to photochemical polymerization —CH2—CH— 75 Largely amorphous, except when highly oriented by stretching. Hard. Soluble in ketones and esters... 

Polymerization of vinyl chloride occurs through a radical chain addition mechanism, which can be achieved through bulk, suspension, or emulsion polymerization processes. Radical initiators used in vinyl chloride polymerization fall into two classes water-soluble or monomer-soluble. The water-soluble initiators, such as hydrogen peroxide and alkali metal persulfates, are used in emulsion polymerization processes where polymerization begins in the aqueous phase. Monomer-soluble initiators include peroxides, such as dilauryl and benzoyl peroxide, and azo species, such as 1,1 -azobisisobutyrate, which are shown in Fig. 22.2. These initiators are used in emulsion and bulk polymerization processes. 

It is clear, however, that a simultaneous increase in polymerization rate and molecular weight could either follow from a reduction in the rate of termination or from an increase in the rate of propagation. This last possibility has seldom been considered, except in some of the very early studies such as in the work of BENGOUGH and NORRISH (2J on the bulk polymerization of vinyl chloride where a "catalytic" action was attributed to the precipitated polymer. 

Monomer and initiator must be soluble in the liquid and the solvent must have the desired chain-transfer characteristics, boiling point (above the temperature necessary to carry out the polymerization and low enough to allow for ready removal if the polymer is recovered by solvent evaporation). The presence of the solvent assists in heat removal and control (as it also does for suspension and emulsion polymerization systems). Polymer yield per reaction volume is lower than for bulk reactions. Also, solvent recovery and removal (from the polymer) is necessary. Many free radical and ionic polymerizations are carried out utilizing solution polymerization including water-soluble polymers prepared in aqueous solution (namely poly(acrylic acid), polyacrylamide, and poly(A-vinylpyrrolidinone). Polystyrene, poly(methyl methacrylate), poly(vinyl chloride), and polybutadiene are prepared from organic solution polymerizations. 

Most poly(vinyl chloride) (PVC) is commercially produced by suspension polymerization [Brydson, 1999 Endo, 2002 Saeki and Emura, 2002 Tomell, 1988]. Bulk and emulsion... 

The production of vinyl chloride monomer is only a part of PVC production. Polymerization of the monomer completes the process. Commercially, it is a batch operation by one of three methods suspension, emulsion, or bulk. In all three methods, the chemical reaction is a free radical-initiated chain reaction. Peroxides or redox systems generally are used to provide the initial free radicals. 

Uses. The azobisnitriles have been used for bulk, solution, emulsion, and suspension polymerization of all of the common vinyl monomers, including ethylene, styrene vinyl chloride, vinyl acetate, acylonitrile, and methyl methacrylate. The polymerizations of unsaturated polyesters and copolymerizations of vinyl compounds also have been initiated by these compounds. 

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