By controlling the relative rates of chain growth and termination, controlled radical polymerization can yield block copolymers with precisely tailored compositions, molecular weights, and architectures. When immiscible blocks are used, nanoscale inhomogeneities can be engineered to yield valuable physical properties. Amphiphilic block copolymers can be designed for water absorption, and segments with differing solubility characteristics can be employed for rheology modification or for improving the impact resistance of polymer matrices. Examples will be shown and discussed, employing Arkema's unique controller and macroinitiator technology.