Emulsion coagulum

The quahty of the water used in emulsion polymerization has long been known to affect the manufacture of ESBR. Water hardness and other ionic content can direcdy affect the chemical and mechanical stabiUty of the polymer emulsion (latex). Poor latex stabiUty results in the formation of coagulum in the polymerization stage as well as other parts of the latex handling system. 

The suspension or emulsion will be coagulated and the coagulum or precipitate will contain the coagulating anion in amount necessary to give the original suspension electric neutrality. 

The colloidal stability of polymer dispersion prepared by the emulsion copolymerization of R-(EO)n-MA was observed to increase with increasing EO number in the macromonomer [42, 96]. Thus C12-(EO)9-MA did not produce stable polymer latexes, i.e., the coagulum was observed during polymerization. This monomer, however, was efficient in the emulsion copolymerization with BzMA (see below). The C12-(EO)20-MA, however, appears to have the most suitable hydrophilic-hydrophobic balance to make stable emulsions. The relative reactivity of macromonomer slightly decreases with increasing EO number in macromonomer. The most hydrophilic macromonomer with co-methyl terminal, Cr(EO)39-MA, could not disperse the monomer so that the styrene droplets coexisted during polymerization. The maximum rate of polymerization was observed at low conversions and decreased with increasing conversion. The decrease in the rate may be attributed to the decrease of monomer content in the particles (Table 2). In the Cr(EO)39-MA/St system the macromonomer is soluble in water and styrene is located in the monomer droplets. Under such conditions the polymerization in St monomer droplets may contribute to the increase in r2 values. 

The formation of coagulum is observed in all types of emulsion polymers (i) synthetic rubber latexes such as butadiene-styrene, acrylonitrile-butadiene, and butadiene-styrene-vinyl pyridine copolymers as well as polybutadiene, polychloroprene, and polyisoprene (ii) coatings latexes such as styrene-butadiene, acrylate ester, vinyl acetate, vinyl chloride, and ethylene copolymers (iii) plastisol resins such as polyvinyl chloride (iv) specialty latexes such as polyethylene, polytetrafluoroethylene, and other fluorinated polymers (v) inverse latexes of polyacrylamide and other water-soluble polymers prepared by inverse emulsion polymerization. There are no major latex classes produced by emulsion polymerization that are completely free of coagulum formation during or after polymerization. 

Despite these generalizations, the reduction or elimination of coagulum is usually best accomplished by a "systems approach", i.e., a consideration of latex properties to be achieved in the emulsion polymerization, the economics of the polymerization process, and the deliberate design of the reactor system for that particular polymerization system. Each polymerization system must be considered as a separate system and treated as such. The most effective approach to reduce or eliminate the formation of coagulum is to determine the mechanism by which it is formed and... 

Vinyl acetate is polymerized in aqueous emulsion and used widely in surface coating and in adhesives. Copolymerized with vinyl esters of branched carboxylic acids and small quantities of acrylic acid, it gives paint latices of excellent performance characteristics. G. C. Vegter found that a coagulum-free latex of very low residual monomer content can be produced from a mixture of an anionic and a nonionic emulsifier according to a specific operating procedure. The freeze/thaw stability of polymeric latices has been investigated by H. Naidus and R. Hanzes. 

Of the various methods of latex preparation known and practiced, a variant of the emulsion-addition method was chosen for further investigation because the reaction temperature is easy to control and coagulum... 

Figure 5. Plot of the amount of coagulum vs. soap concentration in the emulsion polymerization of 1,4-DVB at two different volume ratios monomer/water...

Diblock polyoxyethylene-polyoxypropylene styrenic macromonomers, with the polymerizable group at the end of the hydrophobic part have been prepared and used in styrene emulsion polymerization [34]. Latexes of high stability towards added electrolyte have been obtained. However the HLB was not well-optimized so that a high amount of coagulum was formed (Surfmer XI). 

In conclusion we can say that the inisurfs known today have different chemical structures and consequently different properties. Experimental data are available showing that emulsion polymerization is posssible using inisurfs without any additional emulsifiers, thus reducing the electrolyte content in the latex serum as well as foam formation. From a more technical point of view problems existing today concern the low initiator efficiencies as well as the fact that the solid content of the latexes is restricted to approximately 40% without coagulum formation. 

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