Copper(II)/Tertiary Amine Synergy in Photoinduced Living Radical Polymerization: Accelerated Synthesis of ω-Functional and α,ω-Heterofunctional Poly(acrylates)

Abstract

Photoinduced living radical polymerization of acrylates, in the absence of conventional photoinitiators or dye sensitizers, has been realized in "daylight'"and is enhanced upon irradiation with UV radiation (λ(max) ≈ 360 nm). In the presence of low concentrations of copper(II) bromide and an aliphatic tertiary amine ligand (Me6-Tren; Tren = tris(2-aminoethyl)amine), near-quantitative monomer conversion (>95%) is obtained within 80 min, yielding poly(acrylates) with dispersities as low as 1.05 and excellent end group fidelity (>99%). The versatility of the technique is demonstrated by polymerization of methyl acrylate to a range of chain lengths (DP(n) = 25-800) and a number of (meth)acrylate monomers, including macromonomer poly(ethylene glycol) methyl ether acrylate (PEGA480), tert-butyl acrylate, and methyl methacrylate, as well as styrene. Moreover, hydroxyl- and vic-diol-functional initiators are compatible with the polymerization conditions, forming α,ω-heterofunctional poly(acrylates) with unparalleled efficiency and control. The control retained during polymerization is confirmed by MALDI-ToF-MS and exemplified by in situ chain extension upon sequential monomer addition, furnishing higher molecular weight polymers with an observed reduction in dispersity (Đ = 1.03). Similarly, efficient one-pot diblock copolymerization by sequential addition of ethylene glycol methyl ether acrylate and PEGA480 to a poly(methyl acrylate) macroinitiator without prior workup or purification is also reported. Minimal polymerization in the absence of light confers temporal control and alludes to potential application at one of the frontiers of materials chemistry whereby precise spatiotemporal "on/off" control and resolution is desirable.