Mechanism of alkali thickening of acid-containing emulsion polymers. I. Examination of latexes by means of viscosity

TLDR: In this paper, the authors measured the viscosity-versus-pH relationship for a large number of methacrylic acid-containing emulsion polymers and derived the postulated mechanism involved in the transition from an unneutralized latex particle to the neutralized species in terms of varying degrees of particle swelling.

Abstract: Viscosity-versus-pH relationships for a large number of methacrylic acid-containing emulsion polymers have been measured. The monomers chosen for this study were so selected because they represent synthesized latexes of high and low Tg and comparative hydrophilicity. These were styrene, methyl methacrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. The postulated mechanism involved in the transition from an unneutralized latex particle to the neutralized species is accounted for in terms of varying degrees of particle swelling. In the limiting case, particle swelling is followed by complete solution of the polymer. The most important variables are the per cent methacrylic acid and the polymer Tg and hydrophilicity as determined by the comonomers present. The degree of particle swelling ranges from none for high styrene-containing latexes to high degrees of swelling followed by polymer solubilization for high ethyl acrylate-containing latexes.