Studies of the dispersion polymerisation of methyl methacrylate in nonaqueous media

The dispersion polymerisation process has been known for many years but has received comparatively little attention relative to conventional emulsion polymerisation. The dispersion polymerisation technique can be considered as a modified precipitation polymerisation that is carried out in the presence of an amphipathic polymeric stabiliser. This polymeric surfactant imparts colloidal stability to the precipitate that is formed during the reaction, thus allowing further growth into well‐defined, sterically stabilised latex particles. In this paper we discuss the effect that experimental variables such as stabiliser concentration, solvency of the disperson medium, initiator concentration and temperature have on the size of the particles that are formed. This is followed by a review of the polymerisation kinetics. It is concluded that when the dispersion medium is a non‐solvent for the polymer being formed then the locus of polymerisation is largely within the growing paticle and the system follows bulk polymerisation kinetics. The particles that are formed are usually submicron in size. As the solvency of the dispersion medium for the growing polymer particles is increased, then polymerisation of polymer in solution also occurs. The polymeric radicals that are formed in solution are then captured by growing particles. Consequently the locus of the particle polymerisation process changes and there is a concomitant change in the kinetics of polymerisation. Particles of up to 15 μm diameter have been formed in such systems. The reasons for these large variations in particle size are discussed in terms of the coalescence of primary particles that takes place during the polymerisation reaction.