The Expansion Characteristics of Carboxylic Emulsion Polymers

Summary

Carboxylic monomers are often used as minor constituents in emulsion polymerization to impart desirable properties to latexes and latex films. Incorporated carboxyl groups can also have a major effect on latex viscosity as a result of particle expansion upon neutralization. Evidence from conductometric titrations suggests that carboxyl groups are often concentrated near the particle surface. The resultant. model of an expanded particle is that of a hydrated acid-rich shell surrounding a compact polymer core. This model is used to develop an equation which can be used to estimate the thickness of the expanded layer as a function of pH, and a sedimentation method is described which permits a detailed study of the factors involved in particle expansion. Of particular concern are the effects of polymer concentration and ionic strength on the rate of particle sedimentation.