Ultra‐High Molecular Weight 21‐Arm Star‐Shaped Polyacrylates via Cu(0)‐RDRP

ABSTRACT Ultra‐high molecular weight (UHMW) star‐shaped polyacrylates are synthesized via Cu(0) wire‐mediated Reversible Deactivation Radical Polymerization (RDRP) using a β‐cyclodextrin (β‐CD)‐derived multifunctional initiator with 21 initiating sites. By optimizing the amount of solvent (dimethyl sulfoxide, DMSO), 21‐arm star shaped polyacrylates were obtained with M n,SEC ≈ 798,000 g·mol −1 and Ð ≈ 1.10 at 78% monomer conversion, with limited star‐star coupling. By increasing the [Cu(II)Br 2 ] to 0.10 eq. relative to each initiating site, UHMWs of M n,SEC ≈ 1,324,000 g·mol −1 and Ð ≈ 1.10 were obtained for a 21‐arm PMA, whilst the sterically hindered side‐chains of PBzA led to synthesis of a 21‐arm PBzA with M n,SEC ≈ 1,820,000 g·mol −1 and very low dispersity ( Ð ≈ 1.05) with only 0.05 eq. of Cu(II)Br 2 with respect to one initiating site. Apart from homopolymers, very high MW 21‐arm statistical copolymers were synthesized while notably, end‐group fidelity was maintained even at M n,SEC ≈ 798,000 g·mol −1 , thus allowing for in situ extension. Notably, the combination of UHMW arms and the compact β‐CD core provided sufficient mass‐thickness contrast, allowing for TEM imaging without staining and enabling the direct visualization of the structural features of individual star polymers.