Copolymers obtained by grafting polyacrylarnide (PAA) onto polydextran (DEX) have been synthesised by ceric-ion-reduccd redox initiation method. These copolymers have been characterized by light scattering. self-exclusion chromatography and viscometry in aqueous solutions. The short range molecular structure has been studied by small-angle X-ray scattering. From these results it is suggested that close to the anchoring point the grafted chains are extended while they take oil a random conformation far from this point. A few investigations have been carried out in water/DMF (dimethyl formamide) mixtures. It is observed that the molecular weight depends strongly on the dimethyl formamide fraction. These results are discussed by contemplating the existence of PAA/DMF complexes. (c) 2006 Elsevier Ltd. All rights reserved.