Monomer substituent effects in catalytic chain transfer polymerization: Tert-butyl methacrylate and dimethyl itaconate

Kinetic and mechanistic studies have been performed on the cobaloxime-mediated catalytic chain transfer polymerization (CCTP) of tert-butyl methacrylate (t-BMA) and dimethyl itaconate (DMI) in order to further elucidate the role of monomer substituents in the hydrogen-abstraction reaction. The studies on t-BMA, which include a pulsed-laser polymerization study for the determination of the propagation rate coefficient, are inconclusive insofar that they cannot unambiguously distinguish between possible monomer viscosity effects and direct steric interactions between the substituents at the radical center and the cobalt catalyst in the hydrogen-abstraction reaction. Studies on the CCTP of DMI included ¹H, ¹³C, COSY, NOESY, HMQC, and HMBC NMR studies of a mixture of DMI oligomers, which showed that the hydrogen abstraction occurs preferentially from the α substituent of the radical center rather than from the backbone yielding predominantly E isomers. The low chain transfer rate coefficient for DMI is conceivably caused by steric hindrances as a result of the large substituents.