Semibatch emulsion polymerization of butyl acrylate. II. Effects of emulsifier distribution

The effects of emulsifier distribution ratio between the initial charge and the feed on particle formation and kinetics of butyl acrylate emulsion pol ymerization, using sodium lauryl sulfate as emulsifier and potassium persul fate as initiator, were investigated. The number of particles increased wit h initial emulsifier concentration in the reactor charge. It was shown that traditional ranking, in terms of number of particles produced, of semibatc h emulsion polymerization with monomer emulsion feed is not always justifie d and a semibatch emulsion polymerization can produce far more particles th an a conventional batch emulsion polymerization. The number of polymer part icles was found to be practically independent of the emulsifier distributio n ratio between the charge and the feed for a high overall emulsifier conce ntration, while for a low overall emulsifier concentration, the number of p articles increased with initial loading of the emulsifier. The polydispersi ty index (PDI) of the final latexes showed a minimum with emulsifier distri bution. A bimodal particle size distribution, and a latex with a large PDI, was obtained when there was no emulsifier in the charge. As the initial em ulsifier charge increased, a unimodal PSD with a smaller PDI was obtained. With higher proportions of emulsifier in the initial charge, the PDI rose a gain due to particle nucleation at monomer-starved conditions, and a skewed unimodal PSD was obtained. (C) 2000 John Wiley & Sons. Inc.