A study of the kinetics of the emulsion polymerization of butyl methacrylate

Abstract

The kinetics of the emulsion polymerization of butyl methacrylate at 50 °C have been studied dilatometrically. Thermal initiation, γ-radiolysis initiation and initiation by K₂S₂O₈ were employed, the last over a wide concentration range. Rates were obtained for the steady state, for the approach to steady state and (for γ-radiolysis initiation) for the decay from steady state on removal from the radiolysis source. These data yield unambiguous and accurate values for the rate coefficients for free-radical propagation, exit (desorption), entry (as a function of initiator concentration) and bimolecular termination. It is found that aqueous-phase kinetics are characterized by re-entry of desorbed free radicals into the particles and by a capture efficiency of primary free radicals that is significantly less than 100%. Exit is found to be a transfer-diffusion-dominated process. The system has a comparatively high average number of free radicals per latex particle (e.g. ca. 0.7 for [S₂O^2–₈]= 10^–3 mol dm^–3). The methodology presented here should be applicable to other emulsion-polymerization systems.