Triblock polymers comprised of polysaccharide, such as heparin or dextran, and a hydrocarbon chain, have been prepared. The triblock polymer adsorbs strongly on the surface of hydrophobic polymer substrates such as polyethylene, through hydrophobic interaction between the polymer and the hydrophobic hydrocarbon chain of the triblock polymer. The surface adsorbed with triblock polymer is resistant to protein deposition, which renders the surface nonthrombogenic.