Minimizing star–star coupling in Cu(0)-mediated controlled radical polymerizations

Conditions for the synthesis of star-shaped polymers via controlled radical polymerization (CRP) with minimized star-star coupling are presented. By systematically grafting a variety of polyacrylates (methyl acrylate, tert-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate) from cores carrying 4-8 initiating sites, it was found that traditional factors increasing star-star coupling, (i) the number of arms, (ii) the length of the arms, and (iii) the steric bulk of the monomer side-chain, could be controlled. This allows high monomer conversion (>95%) and low-dispersity polymers (D < 1.08) to be obtained for molecular weights up to similar to 300 000 g mol(-1). In addition to the suppression of coupling events, these improved reaction conditions maximize chain-end fidelity and permit the synthesis of well-defined (multi)block copolymer stars through in situ chain extension reactions. These advantages significantly broaden the synthetic scope and structural integrity for CRP-derived star polymers