A combination of oxime click reaction and atom transfer radical polymerization is applied to obtain novel dextran-block-poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers. The interpolyelectrolyte complexation of these copolymers with sodium poly(styrenesulfonate) demonstrates, for the first time, the stabilization of an interpolyelectrolyte complex by a polysaccharide corona.