Suppressing Coalescence and Improving Uniformity of Polymer Beads in Suspension Polymerization Using a Two-Stage Stirring Protocol

In a typical suspension polymerization, both emulsification and polymerization occur simultaneously in a single-stirred vessel reactor using a constant stirring speed and stabilizer concentration. This work introduces a novel two-stage stirring protocol for improving the uniformity of polymer beads produced in suspension polymerization reactors. In the two-stage stirring protocol proposed, the polymerization stage was carried out at a reduced stirring speed. This policy, verified by mathematical modeling, led to the drops coalescence being suppressed, and as a result, the drops average size and size distribution being maintained in the course of polymerization. The particle size distribution narrowing was more significant if the emulsification stage was carried out at room temperature, the stabilizer concentration was low, and the difference between the stirring speeds used in the two stages was large. The two-stage stirring protocol was extended to include a two-stage stabilizer-addition protocol, which further improved the quality of the beads.