To modify the surface of chitosan powder, grafting of hyperbranched dendritic polyamidoamine, a new class of topological macromolecules, onto the surface was investigated. It was found that hyperbranched dendritic polyamidoamine was propagated from chitosan powder surface by repeating two processes: (1) Michael addition of methyl acrylate (MA) to surface amino groups and (2) amidation of the resulting esters with ethylenediamine to give polyamidoamine dendrimer-grafted chitosan powder. However, theoretical propagation of polyamidoamine dendrimer from chitosan powder surface was hardly achieved, because (a) Michael addition and amination proceeded in heterogeneous systems and (b) the grafting of dendritic polyamidoamine was blocked by grafted chains due to steric hindrance. It was found that the average particle size of hyperbranched dendritic polyamidoamine-grafted chitosan powder was decreased by grafting of dendritic polyamidoamine. Furthermore, living poly(2-methyl-2-oxazoline) and living poly(isobutyl vinyl ether) with controlled molecular weight and narrow molecular weight distribution readily postgrafted to the hyperbranched dendritic polyamidoamine-grafted chitosan powder by termination of the corresponding living polymer cation with terminal amino groups of the dendritic polyamidoamine-grafted chitosan powder. (C) 2000 Elsevier Science B.V. All rights reserved.