Suspension polymerisation in the presence of an inhibitor; prolonged transition stage and suppressed emulsion particle formation

A typical suspension polymerisation accommodates a simultaneous emulsion polymerisation that produces emulsion particles. A consecutive emulsion and suspension polymerisation was carried out, which clearly indicates that these emulsion particles destabilise the suspension by adsorbing the stabiliser and thus enlarge the size of final beads. These emulsion particles can coagulate and reach a size that is similar to those of satellite particles formed by drop rupture mechanisms in the stirred reactors. Methyl methacrylate was considered as a model monomer. Inclusion of a water-soluble inhibitor in the formulation recipe was found to decrease the average bead particle size and sharpen their size distribution. An inhibition effect contributes to drop stability in two ways. First, it does not allow polymerisation to occur in the drops during induction time and thus prolongs the transition period during which the size of drops is reduced. Second, it hinders particle nucleation in the water phase so that the stabiliser remains available for protecting the bead particles against coalescence. The main conclusion is that the inhibitor should not always be removed from monomers prior to suspension polymerisation.