The Making of a Polymer Colloid

Emulsion Polymers Institute and Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015 

The industrial production of polymer colloids or latexes comprises several different polymer families, each with its own appli- 

The preparation of polymer colloids is both a science and an art. It is a science in which the kinetic principles of free radical-initiated vinyl addition polymerization are superimposed on the heterogeneous polymer latex system. It is an art in that the preparer uses a recipe which comprises monomer, water, emulsifier, initiator, and other ingredients, and the quality of the latex obtained depends upon small variations in the polymerization parameters as well as the skill of the preparer. The purpose of this paper is to review the different types of polymer latexes and the mechanisms proposed for their preparation, and to give examples of the preparation of different types. 

Conventional emulsion polymerization comprises emulsification of a water-immiscible monomer in a continuous water medium using an oil-in-water emulsifier and polymerization using a water-soluble or oil-soluble initiator to give a colloidal dispersion of polymer particles in water. The average particle size of conventional latexes is usually 0.1-0.3ym in contrast to the original emulsion droplet size of 1-lOym. Thus the mechanism of polymerization is not a simple one of polymerization of the monomer droplets, and any mechanism proposed for the process must explain the order-of-magnitude reduction in particle size observed upon converting monomer to polymer. 

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