Advances in catalytic chain transfer polymerisation mediated by cobaloximes
Catalytic chain transfer copolymerisation of MMA and HEMA (70:30) has been carried out under semi-continuous emulsion polymerisation conditions, using CoBF as catalyst. It has been shown that macromonomers of low molar mass can be synthesised with an apparent chain transfer constant, CSE, of ca. 1300 down to a threshold value of ca. 20 ppm of CoBF. Below this value an initial 20% shot of monomer/catalyst mixture was necessary to prevent events involved in the catalytic chain transfer process becoming diffusion controlled and to prevent the reaction to proceed under monomer starved conditions. Analysis of the Co(II) species by SQUID has been carried out. CoBF shows a value for its effective magnetic susceptibility of 1.77μB. It was found that a correction for the response of the sample container is essential for reliable data to be achieved. Diffusion ordered 2D-NMR spectroscopy (DOSY) has been used as a method to study the catalyst diffusion dependence for the rate coefficient of chain transfer. However, the apparent values of the found diffusion coefficients are an order of magnitude above the natural limit for center of mass diffusion.