Supressing Coalescence and Improving Uniformity of Polymer Beads in Suspension Polymerisation using a Two-Stage Stirring Protocol

In a typical suspension polymerisation, both emulsification and polymerisation occur simultaneously in a single stirred vessel reactor using a constant stirring speed and stabiliser concentration. This work introduces a novel two-stage stirring protocol for improving the uniformity of polymer beads produced in suspension polymerisation reactions. In the two-stage stirring protocol proposed, the polymerisation stage was carried out at a reduced stirring speed. This policy, confirmed by mathematical modelling, led to the drops coalescence being suppressed and as a result drops average size and size distribution being maintained in the course of polymerisation. The particle size distribution narrowing was more significant if the emulsification stage was carried out at room temperature, the stabiliser 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 stabiliser-addition protocol, which further improved the quality of the beads.