The preparation of sterically stabilized polymer dispersions

The emulsion polymerizations of styrene (St) and butyl acrylate (BA) stabilized by nonionic polyoxyethylene type emulsifiers did not show the long stationary rate interval. This was discussed in terms of two opposing effects: 1) the decreased monomer concentration at the reaction loci due to the depletion of monomer droplets or depressed monomer droplet degradation and 2) the increased number of polymer particles with increasing conversion. The continuous particle nucleation is attributed to the continuous release of emulsifier from the emulsifier saturated monomer droplets and/or the presence of monomer swollen micelles (microdroplets). The limited particle flocculation operative at lower emulsifier concentrations increases the nonstationary-state polymerization. The particle agglomeration is accompanied by the increased reaction order x (N_p vs. E]^x) above 0.6. The increased uniformity of monomer emulsion stabilized by Tween 20 by homogenization of monomer emulsion increased the final conversion and the polymerization rate as well. The polymerization rate vs. conversion curve of the homogenized emulsion characterized with broader stationary rate interval reminds the four rate intervals system typical for miniemulsion. The accumulation of polymer and nonionic emulsifier within the monomer phase preserves the monomer droplets up to high conversion. The decreased monomer droplet degradation rises the monomer-starved condition or the depressed transport of both monomer and emulsifier to the reaction loci.