Studies in polymerization - XXII. Initiation of polymerization by reaction between tetrakis(triphenyl phosphite)nickel(0) and halides: methyl methacrylate

Abstract
Tetrakis(triphenyl phosphite)nickel(0) (NiP4) in solution in methyl methacrylate (MMA) undergoes reversible ligand exchange to form a species NiP3(MMA). Kinetic studies based on absorbance measurements are consistent with the view that a rate-controlling dissociation of NiP4is followed by rapid and almost complete complexing of NiP3with MMA. The enthalpy and entropy of activation for the dissociation have been determined, and also the standard enthalpy and entropy changes for the overall reaction. The initiation of polymerization which occurs in the presence of carbon tetrachloride has been shown to arise from reaction between NiP3(MMA) and CCI4, and the absolute rate constant of this process has been measured at various temperatures. Each NiP3(MMA) yields approximately one free radical, and it is thought that the final product is a NiIIderivative. Part of the oxidation must therefore proceed by a route which does not form radicals. The kinetics of the overall polymerization have been investigated by numerical solution of the appropriate differential equations, using the parameters evaluated, without any stationary state assumptions about the concentration of species involved in initiation. The agreement with experiment is satisfactory over a wide range of conditions.

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