Densely grafting copolymers of ethyl cellulose with polystyrene and poly (methyl methacrylate) were synthesized through atom transfer radical polymerization (ATRP). First, the residual hydroxyl groups on the ethyl cellulose reacted with 2-bromoisobutyrylbromide to yield 2-bromoisobutyryloxy groups, known to be an efficient initiator for ATRR Subsequently, the functional ethyl cellulose was used as a macroinitiator in the ATRP of methyl methacrylate and styrene in toluene in conjunction with CuBr/N,N,N',N '',N ''-pentamethyldiethylenetriamine as a catalyst system. The molecular weight of the graft copolymers increased without any trace of the macroinitiator, and the polydispersity was narrow. The molecular weight of the side chains increased with the monomer conversion. A kinetic study indicated that the polymerization was first-order. The morphology of the densely grafted copolymer in solution was characterized through laser light scattering. The individual densely grafted copolymer molecules were observed through atomic force microscopy, which confirmed the synthesis of the densely grafted copolymer. (c) 2005 Wiley Periodicals, Inc.