Functionalization of strong C(sp)–H bonds in the presence of weak C(sp)–H bonds enables the block-selective modification of thermoplastic elastomers

Abstract

Poly(styrene-b-ethylene-r-butylene-b-styrene) (SEBS) is a thermoplastic elastomer with diverse applications that range from adhesives to medical devices. The post-polymerization modification of SEBS would unlock the synthesis of uniquely functionalized polymers, however previous approaches have either indiscriminately functionalized C(sp3)–H sites of the backbone or exclusively derivatized the phenyl pendant groups of the styrene blocks. Herein, we report the selective, contra-thermodynamic functionalization of the stronger, aliphatic C(sp3)–H bonds in the ethylene–butylene mid-block in the presence of weaker benzylic C(sp3)–H bonds in the end-blocks. Our top-down approach leverages amidyl radical-mediated C(sp3)–H functionalization, enabling access to new materials that would be challenging to synthesize through bottom-up copolymerization. Small molecule studies support the sterically dictated, kinetic site selectivity of the system, which overcomes the deleterious chain scissions commonly observed in the functionalization of these materials. The resulting polymers can be diversified into a variety of polar functionalities, demonstrating the differentiated materials accessible through block-selective, contra-thermodynamic polymer functionalization.