High Solid Content Multi-sized Emulsion Copolymerization of Styrene, Butyl Acrylate and Methacrylic Acid

摘要

Latices with the multi-modal particle size distribution (PSD) were prepared by introducing some additional surfactants during the semi-continuous emulsion polymerization of styrene, butyl acrylate and methacrylic acid. The polymerization was investigated by following the variation of the particle size, the size distribution, the number of particle , the Tg of particle and the total conversion at different stages of polymerization. The results show that the bimodal and trimodal PSD polymer latices can be obtained by this method and the secondary generation of particles is affected greatly by the amount of the additional surfactants and the moment when they are introduced. With the increase of the additional surfactants, the diameters of both the small and large particles decrease and the number of these particles increase. Earlier introduction of these surfactants favors the generation and the growth of the small particles, and then causes a reduction of the fraction of the large particles. An introduction of 7% based on the total monomers of the additional surfactants makes 100% of the monomers of the second stage polymerization forme the small particles. This fraction decreases with the decreasing amount of the additional surfactants. These results were further demonstrated by the measurement of Tg's of both the large and small particles of two latices in which the Tg of the copolymer produced in each of the stages were different. High solid content (>65%), low viscosity and coagulum free latices have been obtained through secondary nucleation and a minimum in viscosity was found when the weight fraction of the large particles was around 80%.