Compositionally homogeneous modified polyacrylamides were synthesized by micellar copolymerization leading to hydrophobically associating polymers with a large range of viscosifying properties. The strength of the hydrophobic associations depends on the structure of the hydrophobic comonomer and its distribution. Hydrophobic comonomers with a bulky structure lead to particularly strong thickening properties. Contrary to polyacrylamides that present a classical high affinity adsorption isotherm on alumino silicate surface, the adsorption of hydrophobically modified polymers increases with polymer concentration. The effect is observed even if no intermocular associations are evidenced in solution. The bound fraction of water was determined by H-1 NMR, thus giving indirect information on the adsorbed layer structure. Some modified polymers nearly completely replace the bound water, forming a quasi impenetrable adsorbed layer.