Effects of Solvent and Monomer on the Kinetics of Radical Generation in Atom Transfer Radical Polymerization

Unlike classical radical polymerization, the kinetics of atom transfer radical polymerization show significant solvent dependence, possibly arising from solvent effects on the activation step. A kinetic study on the activation of the initiator ethyl α-bromoisobutyrate by [CuITPMA]+ (TPMA=tris(2-pyridylmethyl)amine), an initiator/catalyst combination frequently used in ATRP, was carried out in DMSO, DMF, MeCN, anisole, ethyl acetate, and their 50 vol % mixtures with styrene (STY) and methyl methacrylate (MMA). kact values varying about 3 orders of magnitude from 3.14×105 mol−1 dm3 s−1 in DMSO to 9.41×102 mol−1 dm3 s−1 in ethyl acetate were found. These values showed excellent correlation with the solvent polarity/polarizability parameter π*. The effect of MMA or STY depended on polarity compatibility between the monomer and the solvent: After monomer addition, kact decreased considerably in polar solvents, whereas it was almost unaffected in nonpolar solvents.