High solids content emulsion polymerisation without intermediate seeds. Part I. Concentrated monomodal latices

In order to produce high solid content latexes in an unseeded process it is necessary to first begin by generating a concentrated latex with a monomodal particle size distribution and high solid contents. A process for the emulsion polymerisation of methyl methacrylate with butyl acrylate at solid contents of over 60% per unit volume is presented. The process relies on the use of an electrically neutral initiation system, combined with a stabilisation system rich in non-ionic surfactant. It was demonstrated that during the critical semi-batch growth stage, it is necessary to add the surfactant at a variable flow rate in order to avoid accumulating it in the water phase, and thereby ensuring that particles created by homogeneous nucleation are not stabilised. It is also shown that correctly adjusting the flow rate leads to a robust, reproducible process. Finally, a ‘stability band’ is clearly identified, and it is clear that the system is ‘self-regulating’ in the sense that an equilibrium between auto-flocculation and stabilisation of new particles leads to a latex with a surface coverage of 80–95% at high solid contents.