AbstractGraft copolymerization of polar vinyl monomers onto cellulose in the presence of oxidizing agents, ceric ion, and radiation has been presumed to be solely the result of propagation from radical sites generated on the cellulose. The uncatalyzed polymerization and graft copolymerization of methyl methacrylate in the presence of cellulose and water has been presumed to involve the formation of a cellulose‐water‐monomer complex with the resultant generation of a covalently bonded monomer radical which then propagates in the usual manner. The formation of grafted alternating copolymer from the radiation induced polymerization of styrene‐acrylonitrile and butadiene‐acrylonitrile, the radical catalyzed polymerization of styrene‐methyl methacrylate and styrene‐acrylonitrile‐ZnCl2as well as the uncatalyzed polymerization of butadiene‐methyl methacrylate in the presence of cellulose and water indicates the participation of comonomer charge transfer complexes in the graft copolymerization. It is proposed that cellulose acts as a complexing agent for the activation of acceptor monomers and as a matrix for the alignment of acceptor monomer complexes (A*−A‐cellulose‐water) and donor‐acceptor comonomer complexes (D+−A‐cellulose‐water). Polymerization of the complexes is initiated spontaneously or by radicals generated on the cellulose although the latter do not become incorporated into the polymer chain. Graft copolymerization results from termination of the growing polymer chains on cellulose by i