Inverse dependencies on the polymerization rate in atom transfer radical polymerization of N-isopropylacrylamide in aqueous medium

The controlled and fast atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAm) initiated by ethyl 2-chloropropionate (ECP) and catalyzed by copper chloride ligated with tris(2-dimethylaminoethyl)amine (CuCl·Me6TREN) is reported in water:DMF (1:1 volume based) for a broad range of polymerization conditions (targeted polymerization degree: 50-188; [NIPAm]0 = 0.5-2 M; T: 10-30 °C). For temperatures below 30 °C, a faster ATRP is obtained with decreasing temperature, which is explained by the exothermic formation of a pre-reactive complex during propagation. For sufficiently high initial deactivator concentrations (⩾20 mol%) a faster ATRP also results, which is proposed to be caused by Lewis acid-base interactions between the Cu(II) species and NIPAm. The kinetic study indicates a limited importance of cyclization reactions implying a limited loss of end-group fidelity. Moreover, for an initial NIPAm concentration of 2 M, catalyst disproportionation can be sufficiently suppressed.