Some colloid-chemical features of emulsion polymerisation

Abstract

Emulsion polymerisation is of great technical and economical importance as well as a process with a lot of colloid chemical features. Two of these colloid features, namely particle nucleation and swelling of polymer particles with monomer, are considered in more detail. It is shown that the particle nucleation can be described with a model based on the classical nucleation theory. This consideration is able to predict the chain length of the nucleating oligomers which is mainly influenced by the water solubility of the oligomers. With increasing water solubility the chain length of the nucleating oligomers becomes longer in good accordance with experiemntal findings. The activation energy of nucleation turned out to be a crucial parameter for further theoretical developments on particle nucleation in emulsion polymerisation. In this sense the development of a set-up for experimental investigations of the nucleation process is of importance. With a new developed experimental set-up based on a combination of on-line tansmission and conductivity measurement with offline particle size analytic it is possible to investigate the nucleation period. The results obtained so far indicate a strong influence of the emulsifier concentration on the particle concentration time curves in the very early stages of an emulsion polymerisation. Swelling experiments have been performed with toluene and latexes carrying chemically different stabilising groups. The latexes have been cleaned very carefully by ultrafiltration before they have been used. The results prove the enormous influence of the nature of the particle water interface on the swelling cpabilityof the particles. It is to conclude that the Morton-Kaizerman-Altier equation cannot be applied for a complete be applied for a complete description of latex particle swelling.