Two macromonomers containing ethylene oxide (EO) segments with different degrees of polymerization (DPPEO = 5 and 23), capped by a methoxy and a methacrylate group (PEOMA), were polymerized by atom transfer radical polymerization (ATRP) in organic solvents. In addition to the direct preparation of densely grafted brush copolymers by "grafting through" the macromonomers, the lower molecular weight PEOMA (MWav = 300 g/mol, DPPEO = 5) was also employed in a "grafting from" reaction using a well-defined multifunctional macroinitiator poly(2-(2-bromopropionyloxy)ethyl methacrylate) (PBPEM, M-n,M-app = 82 x 10(3) g/Mol, M-w/M-n = 1.16, degree of polymerization of backbone DPb = 428). This procedure allowed the preparation of densely double-grafted brush copolymers with various degrees of polymerization of the side chains (DPsc = 12-43). Attempts to prepare double-grafted brushes with DPsc > 50 or to use a macromonomer with a longer PEO chain (MWav = 1100 g/mol, DPPEO = 23) in the "grafting from" reaction resulted in formation of a cross-linked gel. Both the cross-linked mono- and double-grafted brush copolymers are examples of a new class of elastomeric materials with soft rubbery properties (G' similar to 10(4) Pa).