![]() Emulsion polymerization is a rather complex process because nucleation, growth and stabilization of polymer particles are controlled by the free radical polymerization mechanisms in combination with various colloidal phenomena. These emulsion polymers find a wide range of applications such as synthetic rubbers, thermoplastics, coatings, adhesives, binders, rheological modifiers, plastic pigments. Typical polymerization monomers involve vinyl monomers of the structure (CH 2=CH-). 2,2-azobisisobutyronitrile (AIBN)) in the presence of stabilizer which may be ionic, nonionic or protective colloid to disperse hydrophobic monomer through aqueous solution. potassium persulfate (K 2S 2O 8) or an oil-soluble initiator (e.g. He also serves as a consultant for the Prospector materials search engine, advising on issues related to optimization and organization materials within the database.Emulsion polymerization is a unique process involves emulsification of hydrophobic monomers by oil-in water emulsifier, then reaction initiation with either a water soluble initiator (e.g. Ron Lewarchik, Author of article & President of Chemical DynamicsĪs a contributing writer, Ron pens articles on topics relevant to formulators in the coatings industry. To read the rest of the article, written by Ron Lewarchik, please click here to head over to UL Prospector. ![]() In the continuous process, the reaction system is continuously fed to, and removed from, a suitable reactor at rates such that the total volume of the system undergoing reaction at any instant is constant. It is also common to start the polymerization using a seed latex. In this method, the monomer concentration is low, also called under-starved monomer conditions, to facilitate temperature control. In the semi-continuous batch process, monomers and initiators are added in proportions and at a controlled rate so that rapid polymerization occurs. Commercial latex polymers are made using a semi-continuous or continuous process rather than a simple batch process because the heat evolved in a simple emulsion batch process would be uncontrollable in a large reaction vessel. monomer in the aqueous phase.Ī less commonly used emulsion technique called the inverse emulsion-polymerization process involves dispersing an aqueous solution of monomer in the nonaqueous phase.Įmulsion polymerization can occur using a batch process, semi-continuous process or continuous process. The resultant emulsion particle is an oil in water emulsion. Chain transfer agents are added to control the molecular weight. Unlike solution polymers, the viscosity of latexes are governed by the viscosity of the medium the particles are dispersed in (continuous medium). Since only one free radical is present in the micelle prior to termination, very high molecular weights are possible., on the order of 1,000,000 or higher. As the polymerization proceeds, more monomers migrate into the micelle to enable the polymerization to continue. Initiator radicals are generated in the aqueous phase and migrate into the soap micelles that are swollen with monomer molecules. In emulsion polymerization, monomers are first dispersed in the aqueous phase. Waterborne coatings that primarily use emulsion polymers are the largest type of coating technology used on a global basis and are expected to continue to grow as a percent of the total coatings market. The emulsion-polymerization process results in a latex particle, which is a dispersion of polymer in water. Emulsion polymerization was developed by The Goodyear Tire & Rubber Company in the 1920s. This article will detail the fundamentals of emulsion polymerization.
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