Abstract
The effects of agitation in emulsion copolymerization have been studied using a semibatch emulsion copolymerization recipe that gave a latex with ca. 44 wt% solids. The two‐stage polymerization process consisted of an in situ seed‐formation step followed by copolymerization of the continuously added n‐butyl methacrylate and N‐methylol acrylamide monomers under monomer‐starved conditions. A 2‐dm3 glass reactor and Rushton turbine agitators of different diameters (4, 6 and 8 cm) were used in the study. Agitation influenced the particle number at the end of the seed stage. This influenced properties like latex viscosity, the amount of water‐soluble polymer, and the particle size in the final latex. Analysis of the water‐soluble polymer using NMR spectroscopy showed that it was mostly a homopolymer of N‐methylol acrylamide. With the 4 cm diameter agitator, the mixing of the pseudoplastic latex was poor during the feed stage. Formation of a zone of poor mixing could be observed on top of the fluid in the reactor, when the monodisperse particles in the latex formed an iridescent structure. Poor emulsification of the added n‐butyl methacrylate monomer resulted in a greater amount of water‐soluble polymer.
Acknowledgments
The help of Mr. William Anderson in acquiring and interpreting the 1H‐NMR spectra and the financial support from the Emulsion Polymers Liaison Program are greatly appreciated.