Degradable Linear and Bottlebrush Thioester-Functional Copolymers through Atom-Transfer Radical Ring-Opening Copolymerization of a Thionolactone
Qamar un Nisa, William Theobald, Kyle S. Hepburn, Ian M. Riddlestone, Nathaniel M. Bingham, Maciej Kopeć, Peter J. Roth
Abstract
Polymers with tailored architectures and degradability were prepared through thiocarbonyl addition ring-opening (TARO) atom-transfer radical polymerization (ATRP) using dibenzo[c,e]oxepin-5(7H)-thione (DOT), Cu(I)Br, and tris[2-(dimethylamino)ethyl]amine (Me6TREN) as the thionolactone, catalyst, and ligand, respectively, in combination with a selection of acrylic comonomers. Although copolymers with selectively degradable backbone thioesters and low dispersities (1.10 ≤ D̵ ≤ 1.26) were achieved using DMSO, acetonitrile, or toluene as the solvent, the Cu(I)-catalyzed dethionation of DOT to its (oxo)lactone analogue limited the achievable copolymer DOT content. Using anhydrous polymerization conditions minimized the side reaction and provided degradable copolymers with a higher (≤32 mol %) thioester content. Water-soluble molecular brushes were prepared by grafting poly(ethylene glycol) methyl ether acrylate–DOT copolymers from a pre-made multi-ATRP initiator. Due to copolymerization kinetics, the thioesters were installed close to the junctions and enabled the fast (<1 min) cleavage of the arms from the core to give water-soluble products using 10 mM oxone.