Brush copolymers synthesized by controlled radical polymerizations were crosslinked either covalently or physically, resulting in elastomers with an unusually low equilibrium shear modulus G(e), of order I kPa. Examples are given for both crosslink motifs, along with the dynamic viscoclastic properties of these materials. The results are discussed in terms of the effect of the side chains on the brush polymers, which behave in some respect as a low molecular weight diluent that cannot be leached from the sample. (c) 2006 Elsevier Ltd. All rights reserved.