Mechanism of alkali‐thickening of acid‐containing emulsion polymers. II. Examination of latexes with the light microscope

The mechanism of alkali thickening of acid‐containing emulsion polymers has been confirmed by visual examination of the swelling and disappearance of latex particles with the light microscope. Specially prepared large particle‐sized latexes were used in this study. Each latex was examined from 0%–200% neutralization with base. The particle swelling and dissolution behavior correlated with viscosity measurements, high viscosity being present for swollen particle systems and low viscosity for true solutions. The neutralized state of all acid‐containing latexes can be pictured in a cube with the important variables being per cent acid, hydrophilicity of the comonomers, and Tg. At the bottom will be latexes only slightly affected by neutralization, above this will be a swollen particle zone, and the largest area will be a true solution zone. The true solution zone will be enlarged by lowering the molecular weight of the latex polymer.