The　exploitation　of　new　green　polymerization　avenues　for　the　effective　synthesis　of　polymers　by　reversible-deactivation　radical　polymerization　plays　a　critical　role　in　pursuing　the　development　of　polymeric　materials.　In　this　work,　serials　of　deep　eutectic　solvents　(DES)　with　intermolecular-hydrogen-bonding　interaction　were　constructed　as　catalysts　and　medium　for　actuating　reversible　complexation-mediated　polymerization　(RCMP)　for　the　first　time,　yielding　methacrylate　polymers　with　high　monomer　conversion　and　narrow　dispersion　molecular　weight　in　both　water　and　oil　systems.　The　mechanism　and　elementary　reaction　of　RCMP　were　explored　deeply,　revealing　that　the　complexation　of　initiator　with　DES　to　generate　radicals　was　a　ratecontrolling　step　and　intermolecular-hydrogen-bond　was　primary　factor　to　influence　polymerization　rate.　Moreover,　the　insights　of　density　functional　theory　calculations　revealed　that　negative　electrostatic　potential　ensured　nucleophilic　capacity.　This　investigation　demonstrated　the　considerable　potential　of　DES　for　RCMP,　which　is　anticipated　for　other　polymerization　applications　as　a　novel　medium　mode.　(Figure　presented.)　©　Science　China　Press　2024.