CONTROL OF SURFACTANT LEVEL IN STARVE-FED EMULSION POLYMERIZATION .1.SULFATE-CONTAINING OLIGOMERS - PREPARATION AND APPLICATION AS SURFACTANT IN EMULSION POLYMERIZATION

It is well known that the amount of surfactant must be carefully contr olled during starve-fed emulsion polymerization processes. Too little surfactant leads to emulsion instability and coagulation, while too mu ch surfactant leads to secondary particle formation. Although these re lationships are qualitatively understood in the art, there is little q uantitative basis to guide the synthetic chemist, especially in multis tep starve-fed emulsion polymerization processes to make larger superm icron particles. We have developed a method, which will be described i n a companion article, to control the surfactant level by monitoring t he surface tension during polymerization. In order to quantitatively p redict how much surfactant to add at any given time, one needs to know in advance the adsorption characteristics of the soap. Further compli cating the matter is the formation of ''in situ'' or oligomeric surfac tant during polymerization with aqueous initiators such as ammonium pe rsulfate. This work demonstrates how to prepare surface-active oligome rs and how to make latex particles using them as surfactant. First, we established the mass balance for the initiator-derived sulfate groups in seed latexes by conductometric, potentiometric, and iodometric tit rations. Based on the characterization of seed latexes, a method for d etermining the effective sulfate concentration has been developed. Whe n surface-active oligomers were used as the only surfactant, we obtain ed a series of monodisperse, supermicron copolymer latex particles wit h diameters up to 3.22 mu m. This is a similar result to that obtained with a commercially made anionic surfactant. (C) 1995 John Wiley and Sons, Inc.