Light as a Catalytic Switch for Block Copolymer Architectures: Metal–Organic Insertion/Light Initiated Radical (MILRad) Polymerization

Abstract

We detail a polymer synthetic methodology that merges the techniques of insertion and radical polymerization methods into a single organometallic catalyst. This metal–organic insertion/light initiated radical (MILRad) polymerization technique proves successful at polymerizing methyl acrylate (MA) and hexene, using light as a critical stimulus to activate the dormant photoresponsive nature of the insertion catalyst. In this study, we describe a novel approach that uses visible light (460 nm) to switch the catalytic activity of a cationic palladium catalyst from an insertion route to a radical process when desired. We discovered that in a mixture of MA and hexene one monomer can be selectively polymerized using light and dark cycles, respectively. As a result, this polymerization process enables the copolymerization of MA and hexene to create homo- and block copolymer architectures facilitated solely by visible light. In this work, we show the synthesis of MA homopolymers in molecular weight ranges (Mn 50–400 kDa) with dispersities of ∼1.7. Synthesis of MA (A) and hexene (B) block copolymers were accomplished with a single catalyst in both a sequential and novel one-pot approach, relying solely upon visible light irradiation. A series of BA block copolymers were prepared with tunable monomer compositions, molecular weight ranges of (Mn 11–36 kDa), and well-controlled polydispersities (∼1.3–1.6) in a robust rapid synthesis. MILRad polymerization circumvents the need for quantitative conversions during block formation afforded by the orthogonal monomer reactivity dependent upon a light stimulus to acquire distinct polymer architectures with variable block compositions. The use of a photocontrollable “switch” affecting a single organometallic catalyst allows access to block polymers from nonpolar and polar olefins in a novel and facile approach.