Abstract: Hydrophobicallymodified watersoluble polymers are essentially hydrophilic polymers which also contain a small proportion(up to a few mole percent) of strongly hydrophobic groups, usually in the form of pendant side chains or terminal groups. In recent years, they are attracting much increasing attention because of their unusual rheological and amphipathic properties in the presence of added salt, and potential industrial applications. One of the applications directly relates to clay, for instance, the adsorption of hydrophobic associative polyacrylamide on clay has been studied. However, the interaction of hydrophobicallymodified watersoluble amphoteric polymer with clay has been so far hardly investigated including the adsorption. 　　In the previous paper, the hydrophobicallymodified watersoluble amphoteric cellulosic graft copolymer (carboxymethylcellulose grafting acrylamide and dimethyloctyl(2methacryloxyethyl) ammonium bromide, abbr. CGAO) has been prepared for the first time. In this paper, the adsorption amount (Γ) of CGAO on clay has been investigated as a function of concentration of CGAO and NaCl, temperature, pH, surfactant and clay content by means of the ultraviolet spectrum. The results indicate that Γ tends to increase with the increasing of CGAO concentration, but no saturation of adsorption is observed as in the case of the general polymer; Γ sharply rises up with the increment of NaCl concentration up to 1 mol•L－1; Γ continuously decreases at temperature from 25 ℃ to 60 ℃ or pH from 3.6 to 10.3; Γ exhibits an interesting concave curve with the concentration enhancement of SDS from 0 to 14 mmol•L－1 or CTAB from 0 to 1.3 mmol•L－1; at approximate cmc(critical micelle concentration) of SDS or CTAB, Γ approaches a minimum; and Γ reduces with the increase of clay content from 1 to 5 g•dL－1. CGAO is only adsorbed onto the surface of clay, but not into the intercrystal layer as is verified by the layer distance (d001) of the crystal obtained by Xray diffraction. Laser particle size analysis of clay reveals that CGAO can effectively encapsulate and bridge clay particles,as is also confirmed by the scanning electron microscope, and the complex particle size of clay/CGAO cuts down in the presence of SDS.

Key words: Hydrophobic modification, Amphoteric, Cellulosic graft copolymer, Clay, 　Adsorption, Hydrophobic association