Interparticle Monomer Transport in Miniemulsion Copolymerization

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Narrative: The proposed research project is the continuation of an experimental as well as theoretical attempt to elucidate the fundamental physical relationships in miniemulsion copolymerization. Miniemulsion polymerization is done in a heterogenous system consisting of oily droplets suspended in a larger aqueous phase. The oily phase contains the monomer and final polymer product and is held together by both a surfactant (such as sodium dodecyl sulfate) and a cosurfactant (such as hexadecone or cetyl alcohol). Miniemulsion polymerization falls between two well known heterogeneous polymerization processes: suspension polymerization and emulsion polymerization. In both cases there are two phases present, an aqueous solution phase and an oily phase in which the polymerization occurs, the difference being that in suspension polymerization the initiator is soluble in the oily phase while in emulsion polymerization it is soluble in the aqueous phase. The process is considered miniemulsion polymerizaton if the monomer droplets are very small (0.1 to 10 microns) and both water soluble and oil soluble initiators produce similar results. In miniemulsion copolymerization, the morphology of the droplets can vary from the copolymer composition being uniform throughout the cross section of the particle to the core being rich in one polymer and the shell rich in other. This particle morphology is determined by the comonomer composition and concentration at the site of polymerization as a function of the polymerzation time and the reactivity ratios and water solubilities of the two monomers. This work is aimed at studying the mechanism and the rate of interparticle monomer transport between miniemulsion droplets and its effect on particle morphology. The results could ultimately be used to predict the conditions (additive concentration and droplet size) under which the transport of one monomer or the other to the site of the polymerization becomes limiting and thus develop a novel method for regulating the particle morphology and therefore the microstructure of the final copolymer. The PIs have completed research that showed the role and effect of the cosurfactant on the particle generation mechanism and the comonomer distribution during the miniemulsion copolymerization. During this final phase they plan to determine the role and effect of the cosurfactant on the transport of monomer to the different phases.