Effect of Cu(II) on the kinetics of the homogeneous atom transfer radical polymerization of methyl methacrylate

The kinetics of CuBr-mediated homogeneous atom transfer radical polymn. (ATRP) of Me methacrylate (MMA) using 2-hydroxyethyl-2-bromoisobutyrate (HEBIB) as initiator and N-(n-hexyl)pyridylmethanimine (NHPMI) as ligand was investigated. The exptl. results showed that initially added Cu(II) can have strong effects on the kinetics of the ATRP depending on the [Cu(II)]0/[Cu(I)]0 ratio. When ?10% Cu(II) relative to Cu(I) was added at the beginning of the polymn., the kinetics can be well described by Fischer's equation (ln([M]0/[M]) ~ t2/3). The obtained reaction orders for initiator, Cu(I) and Cu(II), are quite close to or the same as those in Fischer's equation, verifying the applicability of Fischer's equation in ATRP systems. On the other hand, when [Cu(II)]0/[Cu(I)]0 >= 0.1, the kinetics can be well interpreted by Matyjaszewski's equation (ln([M]0/[M]) ~ t). The polymn. rate shows almost first order with respect to the concns. of initiator and Cu(I) and inverse first order with respect to the concn. of Cu(II), suggesting that the \"self-regulation\" and radical termination becomes unimportant for the ATRP process when enough Cu(II) is added at the beginning of the reaction. This result is of great potential importance for better control of ATRP systems. Besides, the equil. const. Keq and termination const. kt of the ATRP system at 90 DegC were detd. to be 7.2 * 10-8 and 8.9 * 107 M-1 s-1, resp. [on SciFinder (R)