An inverse free-radical emulsion polymerization technique was used to prepare copolymers of acrylamide and two different hydrophobic comonomers: N,N-dihexylacrylamide (diC6) or N,N-diphenylacrylamide (diPh). The products of the reaction were high molecular weight hydrophobically modified water-soluble polymers (HMWSPs) encapsulated within water droplets dispersed in an organic medium. A comparison of the copolymer compositions prepared under different experimental conditions showed that the level of incorporation of diPh in the final copolymer depended strongly on its localization in the emulsion (aqueous or oil phase) and on the nature of the redox initiator pair (water-soluble or oil-soluble). The rheological properties of the HMWSPs in aqueous solution were investigated as a function of the comonomer content and the nature of the initiator, using steady-flow experiments. The thickening properties were found to be directly correlated to the conditions of synthesis and were optimal when the initiator and the hydrophobic comonomer were located in two distinct phases. An examination of the viscosity as a function of shear rate showed that these solutions exhibit typical characteristics of hydrophobically associative polymers. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 916-924, 2004.