Emulsion polymerization reactor poly

Continuous Poly(vinyl Acetate) Emulsion Polymerization Reactors... 

Pollock, M. J., MacGregor, J. F., and Hamielec, A. E. (1981) Continuous poly (vinyl acetate) emulsion polymerization reactors dynamic modeling of molecular weight and particle size development and application to optimal multiple reactor system design. Computer Applications in Applied Polymer Science, (ed. T. Provder), ACS, Washington, pp. 209-20. 

Poly(vinyl chloride) prepared by emulsion techniques contains soap residues and, as a result, the heat and colour stabilities and the electrical insulation properties are rather poor compared to those of suspension polymer. Nevertheless, emulsion polymer is manufactured for pastes, which find use in non-critical applications. There is also some direct use of poly(vinyl chloride) latices for coating and impregnating paper and textiles. Emulsion polymerization is carried out in a pressure reactor of the type used for suspension polymerization. A typical basic formulation might be as follows ... 

Chern and Chen [30] studied the effect of the reactive surfactant, sodium dodecyl allyl sulfosuccinate, on the semibatch emulsion polymerization of n-butyl acrylate initiated by sodium persulfate. Sodium dodecyl allyl sulfosuccinate plays a similar role in the particle nucleation and growth stages to the conventional sodium dodecyl sulfate. The final number of latex particles per unit volume of water is proportional to the concentration of sodium dodecyl allyl sulfosuccinate in the initial reactor charge (the most important parameter with regard to particle nucleation) to the 0.72-0.80 power. The saturated particle surface area occupied by one molecule of sodium dodecyl allyl sulfosuccinate is 0.36 nm for the poly (n-butyl acrylate) particles prepared by the... 

O Mealey et al. (2006) studied the effect of microwave irradiation (mnltimode microwave reactor) on the emulsion polymerization of styrene and methyl meth-aciylate. The emnlsion polymerization of methyl methacrylate was faster with microwave irradiation. It was observed that the obtained molecular weights for polystyrene and poly(methyl methacrylate) were higher when the polymerization was performed under microwave irradiation It was ascribed to higher degree of branching, when microwave irradiation was applied. 

FIGURE 5.13 Basic stirred, jacketed batch reactor. For solution polymerizations, solvent, monomer, and intiator are charged. For suspension polymerization, water and a protective colloid such as poly(vinyl alcohol) form one phase, whereas the monomer and initiator form a second phase. In emulsion polymerization, a water-soluble initiator such as potassium persulfate is used together with a surfactant such as sodium stearate. 

The continuous bulk polymerization of methyl methacrylate was used as an example in Section 5.2. A stirred bulk polymerization like that used for styrene (Section 5.4) could be adapted for methyl methacrylate. A suspension process for poly(methyl methacrylate) was described in Section 5.4. The polymerization of ethyl acrylate most often is carried out in emulsion. A process such as that used for vinyl acetate is suitable (Section 16.4). Like vinyl acetate, the monomer is slightly water soluble, so true emulsion polymerization kinetics are not followed. That is, there is initiation of monomer dissolved in water in addition to that dissolved in growing polymer particles. Ethyl acrylate is distinguished by its rapid rate of propagation. Initiation of a 20% monomer emulsion at room temperature by the redox couple persulfate-metabisulflte can result in over 95% conversion in less than a minute. As with vinyl acetate polymerization, a continuous addition of monomer at a rate commensurate with the heat transfer capacity of the reactor is necessary in order to control the temperature. 

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). 

Industrially, polymerizations are carried out to over 99% conversion and thus there is no need to reduce the unreacted monomer unless very low levels are required to meet regulatory. product, or workplace requirements. Most poly(vinyl acetate) emulsions contain less than 0.5 wt % unreacted vinyl acetate. All of the processes are operated in conventional glass-lined or stainless steel kettles or reactors. Control of the process is important to ensure reproducibility of the product. 

The production of styrene-butadiene rubber emulsions is one case where poly-merizabon is deliberately stopped at a low conversion, typically 70-80 %, in order to Hmit the crosslinking reaction from the pendant vinyl groups in the butadiene units. With such large amounts of residual monomer, economics force the recovery and recycling of both butadiene and styrene. After the polymerization stage, residual butadiene is flashed off under vacuum, compressed, cooled and returned to the reactor feed, and styrene is steam stripped in a column stripper, condensed and also returned to the reactor. 

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