Atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in the presence of organic chloride salts, imidazolium chlorides, using alkyl bromide initiator was carried out in 2,2,2-trifluoroethanol (TFE) at 333 K. The ATRP using a sufficient large amount of chloride salts proceeded in a controlled manner to produce polymers with narrow molecular weight distributions (M-w/M-n < 1.2). The model reaction using an alkyl bromide and the imidazolium chloride indicated that a halogen exchange reaction occurred during the ATRP in TFE to form a chloride-terminated propagating species from the alkyl bromide. ATRP of MMA in TFE using an alkyl chloride initiator and CuCl catalyst, however, gave low initiation efficiency and loss of control over the polymerization. The combination of the alkyl bromide initiator, CuBr, and a sufficient amount of organic chloride salts was very effective to improve the control of ATRP in protic solvents, especially in fluoroalcohols. A methacrylate monomer bearing imidazolium chloride moiety was synthesized and polymerized by ATRP without added chloride salts to produce the polymers with well-controlled molecular weights and narrow polydispersities.