Langmuir 2001, 17, 4519-4524
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Microemulsion Polymerization via Hollow-Fiber Feeding of Monomer X. J. Xu,† K. S. Siow,† M. K. Wong,† and L. M. Gan*,‡ Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, and Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602 Received January 8, 2001. In Final Form: March 29, 2001 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.
Introduction By use of different surfactants or/and cosurfactants, various microlatexes with particle sizes ranging from 20 to 50 nm and molar masses over 1 million can easily be obtained by microemulsion polymerization.1-3 A conventional microemulsion polymerization only produces microlatexes with a relatively low polymer contents (5 wt %) of SDS or alkyltrimethylammonium bromide
Microemulsion Polymerization
Langmuir, Vol. 17, No. 15, 2001 4523
Figure 7. Relationship between np and Dw for the systems as stated in Figure 6.
Figure 6. (a) Change of Nd and (b) the Dw during the CTABmicroemulsion polymerizations of styrene, BMA, and MMA via hollow-fiber feedings up to 10 wt % St or BMA or 15 wt % MMA. Initial microemulsion consisted of 1.0 wt % CTAB, 0.5 wt % St or BMA, or 2.0 wt % MMA, and 4 mM of equimolar APS/TMEDA.
and yet produced a low weight ratio (
