Effects of different reactor start-up procedures on the continuous-flow emulsion polymerisation of methylmethacrylate

Abstract

The emulsion polymerisation of methylmethacrylate has been carried out using a continuous-flow back-mixed reactor. Particular attention was given to the effects of start-up procedure on reactor behaviour. At high space-times, changes in start-up procedure affected transitory behaviour of the reactor but not the long-term behaviour. At low space-times and low initiator concentrations, the conversion of monomer and the average size of the polymer particles did not attain steady values but oscillated with time. When the initiator concentration was increased, at low space-times, more than one time-average value for the conversion could be obtained. The choice of start-up procedure determined which of these values was obtained for a particular feed composition. Idealised models, for the prediction of particle number, were not compatible with the experimental results from this study even when the reactor attained a near steady state. Coalescence of polymer particles appeared to affect both the number of particles present in the reactor and the latex stability. The total surface area of the polymer particles was often less than the saturation area for the emulsifier. Large increases in particle size, such as occur in the continuous emulsion polymerisation of styrene, were not observed in the continuous emulsion polymerisation of methylmethacrylate. The average number of radicals per particle was sometimes greater than one but this did not appear to be necessary for oscillations, in conversion of monomer, to occur.