Ultrafast Synthesis of Ultrahigh Molar Mass Polymers by Metal-Catalyzed Living Radical Polymerization of Acrylates, Methacrylates, and Vinyl Chloride Mediated by SET at 25 °C

TLDR

Conventional metal‑catalyzed living radical polymerizations in nonpolar solvents, such as ATRP, rely on an inner‑sphere electron‑transfer mechanism and typically employ Cu(I)X species with N‑containing ligands. The reaction uses solvent‑induced disproportionation of Cu(I)X to Cu(0) and Cu(II)X(2), generating radicals via Cu(0) and deactivating them via Cu(II)X(2) through a low‑activation‑energy outer‑sphere single‑electron‑transfer mechanism, with the process driven by catalytic amounts of electron‑donor Cu(0) or Cu(II) chalcogenides rather than Cu(I)X. In polar solvents, Cu(I)X disproportionates instantly to Cu(0) and Cu(II)X(2), enabling ultrafast room‑temperature synthesis of ultrahigh‑molecular‑weight polymers from electron‑withdrawing monomers such as acrylates, methacrylates, and vinyl chloride, initiated by alkyl halides, sulfonyl halides, or N‑halides.

Abstract

Conventional metal-catalyzed organic radical reactions and living radical polymerizations (LRP) performed in nonpolar solvents, including atom-transfer radical polymerization (ATRP), proceed by an inner-sphere electron-transfer mechanism. One catalytic system frequently used in these polymerizations is based on Cu(I)X species and N-containing ligands. Here, it is reported that polar solvents such as H(2)O, alcohols, dipolar aprotic solvents, ethylene and propylene carbonate, and ionic liquids instantaneously disproportionate Cu(I)X into Cu(0) and Cu(II)X(2) species in the presence of a diversity of N-containing ligands. This disproportionation facilitates an ultrafast LRP in which the free radicals are generated by the nascent and extremely reactive Cu(0) atomic species, while their deactivation is mediated by the nascent Cu(II)X(2) species. Both steps proceed by a low activation energy outer-sphere single-electron-transfer (SET) mechanism. The resulting SET-LRP process is activated by a catalytic amount of the electron-donor Cu(0), Cu(2)Se, Cu(2)Te, Cu(2)S, or Cu(2)O species, not by Cu(I)X. This process provides, at room temperature and below, an ultrafast synthesis of ultrahigh molecular weight polymers from functional monomers containing electron-withdrawing groups such as acrylates, methacrylates, and vinyl chloride, initiated with alkyl halides, sulfonyl halides, and N-halides.