Versatile synthesis of siloxane-based graft copolymers with tunable grafting density

Abstract

A versatile synthetic platform is reported that affords high molecular weight graft copolymers containing polydimethylsiloxane (PDMS) backbones and vinyl-based polymer side chains with excellent control over molecular weight and grafting density. The synthetic approach leverages thiol-ene click chemistry to attach an atom-transfer radical polymerization (ATRP) initiator to a variety of commercially available poly(dimethylsiloxane-co-methylvinylsiloxane) backbones (PDMS-co-PVMS), followed by controlled radical polymerization with a wide scope of vinyl monomers. Selective degradation of the siloxane backbone with tetrabutylammonium fluoride confirmed the controlled nature of side-chain growth via ATRP, yielding targeted side-chain lengths for copolymers containing up to 50% grafting density and overall molecular weights in excess of 1 MDa. In addition, by using a mixture of thiols, grafting density and functionality can be further controlled by tuning initiator loading along the backbone. For example, solid-state fluorescence of the graft copolymers was achieved by incorporating a thiol-containing fluorophore along the siloxane backbone during the thiol-ene click reaction. This simple synthetic platform provides facile control over the properties of a wide variety of grafted copolymers containing flexible PDMS backbones and vinyl polymer side chains.