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 polymerizat ion (ATRP) of methyl methacrylate (MMA) using 2-hydroxyethyl-2-bromoisobuty rate (HEBIB) as initiator and N-(hexyl)pyridylmethanimine (NHPMI) as ligand was investigated. The experimental results showed that initially added Cu( II) can have strong effects on the kinetics of the ATRP depending on the [C u(II)](0)/[Cu(I)](0) ratio. When less than or equal to 10% Cu(II) relative to Cu(I) was added at the beginning of the polymerization, the kinetics can be well described by Fischer's equation (In([M](0)/[M]) proportional to t( 2/3)).(9) 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 a pplicability of Fischer's equation in ATRP systems. On the other hand, when [Cu(II)](0)/[Cu(I)](0) greater than or equal to 0.1, the kinetics can be w ell interpreted by Matyjaszewski's equation (In([M](0)/[M]) proportional to t).(8) The polymerization rate shows almost first order with respect to th e concentrations of initiator and Cu(I) and inverse first order with respec t to the concentration of Cu(II), suggesting that the "self-regulation" and radical termination becomes unimportant for the ATRP process when enough C u(II) is added at the beginning of the reaction. This result is of great po tential importance for better control of ATRP systems. Besides, the equilib rium constant K-eq and termination constant kt of the ATRP system at 90 deg reesC were determined to be 7.2 x 10(-8) and 8.9 x 10(7) M-1 s(-1), respect ively.