SYNTHESIS, STRUCTURE AND PROPERTIES OF HYDROPHOBICALLY ASSOCIATING POLYMERS

Hydrophobically modified water-soluble polymers have recently become t he subject of extensive research because of their use as aqueous visco sity modifiers in oil recovery and latex paint systems. In this study, poly(acrylamide) samples modified with small amounts of a hydrophobic monomer (ethylphenylacrylamide) have been prepared by free radical co polymerization using an aqueous micellar process in which the use of a surfactant ensures the solubilization of the hydrophobe. The copolyme rs exhibit improved thickening properties with respect to homopoly(acr ylamide) analogs due to intermolecular hydrophobic associations. The a queous solution-copolymer properties strongly depend on the amount of surfactant used in the synthesis. The differences observed between the samples are directly related to the copolymer microstructure, that is to a more or less block distribution of the hydrophobic units. The in teractions in aqueous solution of a surfactant (sodium dodecylsulfate (SDS)) with these copolymers have been examined. A strong increase in viscosity is observed upon the addition of SDS below its critical mice lle concentration, owing to the formation of mixed micelles of SDS and hydrophobic monomers. The complex rheological behavior observed is ex plained in terms of the balance between inter and intrachain liaisons. The effects of hydrolysis on the hydrophobic interactions are also di scussed.