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Langmuir 2002, 18, 5058-5063
Articles Polymerization of Styrene with a Polymerizable Cationic Surfactant in Three-Component Microemulsions Xiao-an Fu and Syed Qutubuddin* Department of Chemical Engineering, Case Western Reserve University, Cleveland, Ohio 44106 Received November 19, 2001. In Final Form: April 19, 2002 The polymerization of oil-in-water ternary microemulsions containing water, styrene, and vinylbenzyldodecyldimethylammonium chloride (VDAC) was investigated. VDAC has a polymerizable vinylbenzyl group in the hydrophilic head. Stable transparent microemulsions were prepared by the solubilization of styrene monomer without addition of any cosurfactant. Polymerization of the microemulsions using an oil-soluble free radical initiator leads to either a transparent latex suspension or a hydrogel, depending on the composition. The transparent hydrogels contain up to 92 wt % water and exhibit a reversible gel-to-sol transition on increasing temperature. The hydrogels can be diluted with water to form a clear solution above the gel-to-sol transition. The polymer structure was analyzed using NMR and Fourier transform infrared spectroscopy. Dynamic light scattering was used to measure nanoparticle size, while dynamic rheological experiments were performed to characterize the structure of the hydrogels.
Introduction Microemulsions are thermodynamically stable mixtures of oil and water stabilized by surfactant molecules at the interface.1 One of the characteristic features of microemulsions is the self-assembly structure of nanometer-sized domains. Polymers prepared by microemulsion polymerization have properties different from those produced by emulsion polymerization.2-4 Fast reaction rate and high molecular weight can be achieved in microemulsions because the initiation and propagation reactions are isolated in the nanoscale domains. However, the drawbacks of microemulsion polymerization, including a low monomer/surfactant weight ratio (
