Ternary microemulsions of vinylic and acrylic monomers

Ternary systems consisting of sodium dodecyl sulfate (SDS) as surfactant, water and several vinyl and acrylic monomers [vinyl acetate (VAc), acrylonitrile (ACN), ethyl acrylate (EtA), butyl acrylate (BuA), 2-ethylhexyl acrylate (EHA), methyl methacrylate (MMA), butyl methacrylate (MMB) and styrene (St)] were studied. The solubilization of monomer in aqueous solutions of SDS was found to be dependent on its structure and concentration. The molar specific solubility was observed to decrease with hydrophobicity and increase with polarity of monomer, that is, it was lowest for St, EHA and highest for MMA, EtA. The NMR and fluorescence studies indicate that solubilization occurred at a different domain of the interfacial layer. The hydrophobic monomers are solubilized toward the hydrocarbon interior of the micelles whereas the hydrophilic ones, toward the hydrated tail of the surfactant. The penetration of monomers into the oil-in-water interface is limited because the screening of charged ions of emulsifier is not operative. A relationship between the persulfate initiator decomposition rate and the lability of the α-hydrogen linked to the substituted carbon of the double bond was established. The initiator productivity was the highest for MMA (lacking such α-hydrogen) and the lowest for VAc and St, the monomers in which the C–Hα bond is the most reactive.