Vinyl acetate suspension polymerization

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... 

For the copolymerization of ethene and vinyl acetate, solution polymerization, suspension polymerization, emulsion polymerization and bulk polymerization may be used, but solution polymerization is preferred (1). A method of either continuous type or batch type may be employed. Methanol is generally used as the solvent. 

Suspension Polymerization. The suspension or pearl polymerization process has been used to prepare polymers for adhesive and coaling applications and for conversion to poly(vinyl alcohol). Suspension polymerization are carried out with monomer-soiubie initiators predominantly, with low levels of stabilizers Continuous tubular polymerization of vinyl acetate in suspension yields stable dispersions of beads with narrow particle size distributions at high yields. 

Suspension polymerization is designed to combine the advantages of both the bulk and solution polymerization techniques. It is one of the extensively employed techniques in the mass production of vinyl and related polymers. Suspension polymerization (also referred to as bead or pearl polymerization) is carried out by suspending the monomer as droplets by efficient agitation in a large mass (continuous phase) of nonsolvent, commonly referred to as the dispersion or. suspension medium. Water is invariably used as the suspension medium for all water insoluble monomers because of the many advantages that go with it. Styrene, methyl methacrylate, vinyl chloride, and vinyl acetate are polymerized by the suspension... 

Vinyl acetate is polymerized free radically in bulk, emulsion, or suspension. Bulk polymerization occurs at the boiling temperature of the monomer (72.5 C at 1 bar), and yields highly branched polymer because of chain transfer via the ester groups (see also Section 20.4.3). Commercially, the polymerization is taken to a specific yield and the residual monomer is removed by thin-layer evaporation. Alternatively, continuous polymerization can be carried out in a tower. But this method only produces moderate degrees of polymerization since the tower process requires that the polymer should flow and the flow temperature should lie below the decomposition tempera-... 

The latexes that result from vinyl acetate polymerization have been used for exterior and interior water-based paints. Emulsion polymerization can be carried to high conversion fairly rapidly [24], The rate is controlled by continuous addition of monomer. Rate of addition is limited primarily by rate of heat removal. A final heating to 90°C may be used to react the last bit of monomer. When the latex is to be used as an adhesive, a plasticizer may be added. The popular white glues for paper and wood often are partly hydrolyzed poly(vinyl acetate) suspensions plasticized with liquids such as castor oil. 

Polymerization Processes. Vinyl acetate has been polymerized industrially by bulk, solution, suspension, and emulsion processes (34). Perhaps 90% of the material identified as poly(vinyl acetate) or copolymers that are predominantly vinyl acetate are made by emulsion techniques. Detailed information is in patent and scientific Hterature and in procedures available in the brochures from monomer producing companies (15,34). 

Often a chain-transfer agent is added to vinyl acetate polymerizations, whether emulsion, suspension, solution, or bulk, to control the polymer molecular weight. Aldehydes, thiols, carbon tetrachloride, etc, have been added. Some emulsion procedures call for the recipe to include a quantity of preformed PVAc emulsion and sometimes antifoamers must be added (see Foams). 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

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). 

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. 

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... 

A process for the preparation of porous polyvinyl alcohol gels in three steps is (1) suspension polymerization of vinyl acetate with diethylene glycol dimethacrylate in the presence of a diluent as porogen, (2) saponifying of the resulting porous polyvinyl acetate gel with an alkali, and then (3) subjecting... 

A polyvinyl alcohol is obtained by suspension polymerization of vinyl acetate and the cross-linking agent, triallyl isocyanurate, with a triazine ring followed by alkali hydrolysis. The polyvinyl alcohol gel is used as packing for gel-... 

Lignin, brown coal polymer of methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinyl acetate, methyl vinyl ether, ethyl vinyl ether, N-methylmeth-acrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, or 2-acrylamido-N-methylpropane sulfonic acid free radical polymerization of a water-soluble vinyl monomer in an aqueous suspension of coals [705,1847]... 

Emulsion polymerization is used for 10-15% of global polymer production, including such industrially important polymers as poly(acrylonitrile-butadiene-styrene) (ABS), polystyrene, poly(methyl methacrylate), and poly (vinyl acetate) [196]. These are made from aqueous solutions with high concentrations of suspended solids. The important components have unsaturated carbon-carbon double bonds. Raman spectroscopy is well-suited to address these challenges, though the heterogeneity of the mixture sometimes presents challenges. New sample interfaces, such as WAI and transmission mode, that have shown promise in pharmaceutical suspensions are anticipated to help here also. 

Polymerization of Vinyl Acetate in Suspension (Bead Polymerization)... 

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. 

Polymerization in suspension (bead or pearl polymerization) under normal pressure in the range from 60 to 80°C operates with a suspension of globules of an oil-soluble monomer in water and uses a monomer soluble catalyst. Substantial quantities of polystyrene and poly vinyl acetate are made by this method. 

Vinyl acetate has been polymerized by bulk, suspension, solution, and emulsion methods. It copolymerizes readily with some monomers but not with others,... 

Azad and Fitch (5) investigated the effect of low molecular weight hydrocarbon additives on the formation of colloidafr particles in suspension polymerization of methyl methacrylate and vinyl acetate. It was found that the additives n-octane, n-dodecane, n-octadecane, n-tetracosane and mineral oil exerted a thermodynamic affect depending upon water-solubility and molecular weight. Since these effects on emulsion polymerization have not been considered by the earlier investigators, we have chosen n-pentane and ethyl benzene as additives with limited water-solubility and n-octadecane, and n-tetracosane as water-insoluble ones. Seeded emulsion polymerization was chosen so that the number of particles could be kept constant throughout the experiments and only the effect of the other parameters on the rate could be determined. 

To survey as completely as possible the grafting behavior of EVA copolymers toward various vinyl compounds, our investigations covered the grafting of vinyl acetate, vinylidene chloride, and acrylic and meth-acrylic esters. As polymerization processes, at first we preferred suspension polymerization to exclude the influence of solvents by terminating or transfer reactions during polymerization. Grafting by emulsion polymerization, in which the EVA copolymer was dissolved in the monomer before polymerization, was difficult because coagulate was formed as polymerization proceeded. 

Reichert, K. H. and Moritz, H. V., Continuous Polymerization of Vinyl Acetate in Suspension, J. Applied Polymer Science, Applied Polymer Symposium 36,151-164 (1981). 

As mentioned earlier, polymerization techniques can also be used in the presence of nanotubes for preparation of polymer/CNT nanocomposite materials. In these, in-situ radical polymerization techniques of polymerization in the presence of CNT filler under or without applied ultrasound. Both new factors (presence of CNT and ultrasound) can affect reaction kinetics, stability of suspension or the size of prepared particles. For example, ultrasound waves can open C=C bond of monomer, which starts polymerization initiation. Thus vinyl monomers (styrene, methyl methacrylate or vinyl acetate) can be polymerized without addition of initiator, only by application of ultrasound. This is called sonochemical polymerization method (15,33,34). 

The mechanism of particle formation at submicellar surfactant concentrations was established several years ago. New insight was gained into how the structure of surfactants influences the outcome of the reaction. The gap between suspension and emulsion polymerization was bridged. The mode of popularly used redox catalysts was clarified, and completely novel catalyst systems were developed. For non-styrene-like monomers, such as vinyl chloride and vinyl acetate, the kinetic picture was elucidated. Advances were made in determining the mechanism of copolymerization, in particular the effects of water-soluble monomers and of difunctional monomers. The reaction mechanism in flow-through reactors became as well understood as in batch reactors. Computer techniques clarified complex mechanisms. The study of emulsion polymerization in nonaqueous media opened new vistas. 

Goodall, A. R., Greenhill-Hopper, M. J., Characterization of partially hydrolyzed poly(vinyl acetates) for use as stabilizers in suspension polymerization, Macromol. Chem., Macromol. Symp. 35-36 (1990) 499. 

Commercially, suspension polymerizations have been limited to the free radical polymerization of water-insoluble liquid monomers to prepare a number of granular polymers, including polystyrene, poly(vinyl acetate), poly(methyl methacrylate), polytetrafluoroethylene, extrusion and injection-molding grades of poly(vinyl chloride), poly(styrene-co-acrylonitrile) (SAN), and extrusion-grade poly(vinylidene chloride-covinyl chloride). It is possible, however, to perform inverse suspension polymerizations, where water-soluble monomer (e.g., acrylamide) is dispersed in a continuous hydrophobic organic solvent. 

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