Low polydispersity star polymers via cross-linking macromonomers by ATRP.

A new method for the synthesis of star polymers with high molecular weight and narrow molecular weight distribution (MWD) is presented. The star copolymers were prepared by atom transfer radical (co)polymerization (ATRP) of linear macromonomers with divinyl cross-linkers using low molar mass initiator. In contrast to prior "arm-first" procedures with macroinitiators, by using lower ratio of concentration of initiator to MM, the star polymers contained less initiating sites in the core, which decreased the extent of star-star coupling reactions and resulted in formation of star polymers with narrower MWD. Addition of more cross-linker and initiator during the reaction increased the star molecular weight and star yield while retaining the narrow MWD of the star polymer. For example, we synthesized a star polymer with molecular weight Mn = 466 000 g/mol and Mw/Mn < 1.2 in >98% yield.