Metal-Containing Initiator Systems. 30. Vinyl Polymerization Initiated with Bis(ethyl acetoacetato)copper(II) and Maleimide

Some electron-accepting compounds such as maleimide (MIm), maleic anhydride (MAn), and tetracyanoquinodimethane were found to show pronounced accelerating effects on vinyl polymerization initiated with metal chelates. The polymerization of methyl methacrylate (MMA) initiated with bis(ethyl acetoacetato)-copper(II) (Cu(eacac)₂) and MIm was studied kinetically in benzene. The overall activation energy of the polymerization was calculated to be 11.5 kcal/mol. This value was much lower than that (17.6 kcal/mol) for the polymerization of MMA with Cu(eacac)₂ alone. The polymerization rate (R_p) was expressed as R_p =kMIm]^1/2 Cu(eacac)₂]^1/2 MMA] The first-order dependence of R_p on the monomer concentration indicated that the monomer had no participation in the initiation step, in contrast with polymerization in the absence of MIm (where a monomer concentration dependence of 1.4th order was observed). Electronic spectroscopic study revealed that a complex between MIm and Cu(eacac)₂ had been formed. The ligand radical, an acetylcarboethoxymethyl radical, was trapped by 2-methyl-2-nitrosopropane in the reactions of Cu(eacac)₂ with MIm and with MAn in benzene. From these results the mechanism of the initiation of polymerization is discussed.