The properties of aqueous solutions of some short chain cosurfactants used for radical polymerization of vinyl acetate

Abstract

The refractive index and excess molar volume, of the following short hydrocarbon chain cosurfactants were studied: ethylene glycol, ethylene glycol monomethyl ether, ethanol, n-, i-propanol, acrylic acid, ethyl monomethylmaleate and acrylamide. The refractive indexes of the aqueous solutions of these compounds vary nonlinearly with composition. The maximum variation of refractive indexes occurs up to a cosurfactant/water molar ratio equal to 1/5. The fluorescence probe method was successfully used to evidence the structure modifications of the alcohol-water mixtures. The intensity ratio of pyrene fluorescence vibrational bands varies nonlinearly with the composition of the systems; in case of 1-propanol, the sudden decrease of the ratio is similar to that of micellar solutions, so that a critical concentration of association can be determined at a 0.88 water mole fraction. It was shown, in good agreement with data in literature, that the compounds mentioned penetrate into the cluster structure of water and associate. At concentrations higher than critical, restructuring of aqueous solutions continues and structures of bicontinuous or w/o type may arise. The excess volume of the first six compounds is negative owing to the restructuring just mentioned. Vinyl acetate may penetrate in the structures of binary systems to form homogeneous systems. The number of homogeneous systems decreases in the sequence: ethanol, i-propanol, acrylic acid, n-propanol, the monomethylether of ethyleneglycol, methyl monomaleate. The vinyl acetate over cosurfactant molar ratio of limiting homogeneous systems varies in inverse sequence at the same monomer/water ratio. After radical polymerization of VAc in homogeneous samples transparent systems were obtained only when the polymer was solubilized in cosurfactant water mixtures.