Microemulsion polymerization via hollow-fiber feeding of monomer

Abstract

Microemulsion polymerizations of styrene (St), butyl methacrylate (BMA), and methyl methacrylate (MMA) via hollow fiber feeding of monomers have been studied for the preparation of nanosized microlatexes ranging from 15 to 65 nm. A water-soluble redox initiator was used for all polymerizations at room temperature. The monomer-starved latex particles were first generated in the initial microemulsion containing 0.5 wt % St or BMA or 2.0 wt % MMA stabilized by 1.5 wt % SDS or 1.0 wt % CTAB. The subsequent supply of monomer to the prepolymerized microemulsion proceeded via hollow-fiber feeding from the external monomer reservoir. The polymerization produced nearly uniform (Dw/Dn < 1.15) latex particles having high molar masses (106 g/mol) and high polymer/surfactant weight ratios up to 15. The characteristic for the St or BMA system is that the number of polymer particles per milliliter of latex (Nd) remained rather constant while latex particles grew to larger sizes (Dw) during the polymerization. But this is not the case for the MMA system. The change of the number of polymer chains per latex particle (np) during the polymerization for all three monomers follows the same relationship between np and Dw. The possible polymerization mechanisms for these monomers under the controlled feeding are discussed.