CuBr coordinated by the ionic liquid [N4MIM]Cl as a catalyst for biphasic ATRP in 1-allyl-3-methylimidazolium chloride ionic liquid

•The ionic liquid [N4MIM]Cl was obtained to replace of traditional organic ligand to coordinate with CuBr catalyst for ATRP.•[N4MIM]Cl displayed the favorable coordination with CuBr and a fine compatibility to the organic ligand medium.•[N4MIM]Cl/CuBr presented perfect controllability to ATRP in IL medium.•The Cu catalyst was easily separated from the obtained polymer with [N4MIM]Cl as ligands.