Particle formation and growth in ab initio emulsifier-free emulsion polymerisation under monomer-starved conditions

Particle formation and growth in the monomer-starved emulsifier-free emulsion polymerisation of monomers with different water solubility including methyl acrylate (MA), methyl methacrylate (MMA), and vinyl acetate (VA) were studied. The rate of formation of precursor particles, via homogenous nucleation, is proportional to the monomer concentration in the water phase. One may think that the maximum number of particles will be obtained when the water phase is saturated with the monomer. The number of PMA particles showed a maximum when the water phase was starved with the monomer. The number of PVA particles did not show any sensitivity to the monomer concentration in the water phase. More unexpectedly the final number of PMMA particles showed a minimum when the water phase was just saturated with the monomer. The minimum in the final number of PMMA particles was correlated with the enhanced rate of particle growth due to the gel effect. Under monomer-starved conditions, the number of particles produced was in the order of water solubility of the monomers: MA > VA > MMA. A reverse order was produced under monomer-saturated conditions as particle coagulation became progressively more important for some of the monomers. (C) 2008 Elsevier Ltd. All rights reserved.