Water-soluble amphiphilic dendrigrafts constituted of a hydrophobic polystyrene core and a hydrophilic poly(ethylene oxide) shell have been prepared via a 'grafting onto' procedure from polystyrene dendrigraft precursors. The introduction of the surrounding hydrophilic shell was achieved through cyclic trans-acetalization between omega-acetal functionalized branches of the polystyrene precursor and PEO grafts bearing a alpha-bis(hydroxymethyl) chain end (A(2)-PEO). Yields of grafting are strongly affected by the increase of the degree of polymerization of the reactive PEO grafts (respectively, 100, 87, and 38% with A(2)-PEO20, A(2)-PEO100 and A(2)-PEO150). However, paradoxically, only the use of A(2)-PEO100 or A(2)-PEO150 as reactive grafts affords water-soluble dendrigrafts due to higher PEO weight content (respectively, 41 and 36%). The dimensions and the shape of the PScore-PEOshell Polymers were investigated in solution (THF and water) by dynamic light scattering and in the dry state by TEM and AFM. (c) 2005 Elsevier Ltd. All rights reserved.