The catalytic chain transfer agent [bis[μ-[(2,3-butanedione dioximato)(2−)-O,O‘]] tetrafluorodiborato(2−)-N,N‘,N‘‘,N‘‘‘]cobalt (COBF) was investigated in polymerizations of methyl methacrylate and styrene in bulk and in methyl methacrylate in toluene solution. A wide range of polymer molecular weights were produced by these reactions under identical polymerization conditions, enabling the use of these reactions in the examination of the chain length dependence of the average termination rate coefficient. A strong chain length dependence in accord with theoretical predictions for diffusion-controlled termination was observed. A total of five variations of the use of the Mayo equation and the shape of the number distribution were compared as methods of evaluating the chain transfer activity of COBF. MALDI-TOF mass spectrometry and SEC were evaluated for measuring the number distributions of the polymers and deficiencies were exhibited in the distributions from MALDI-TOF. Both the number distribution and Mayo treatments of the data gave similar results. COBF was shown to have a very high chain transfer activity in all of these polymerizations. Chain transfer activities of ca. 36 000 were found for COBF in bulk MMA, ca. 25 000 for MMA in toluene solution, and ca. 1500 for bulk styrene. A marked solvent effect is shown for toluene in the COBF-mediated polymerization of MMA.

Catalytic chain transfer polymerisation of methyl methacrylate has been investigated by a range of cobalt(I1) complexes. The effect of catalyst structure, reaction temperature and solvent has been examined. At 60°C in the absence of solvent, the chain transfer coefficient, Cs, for MMA and cobaloximes modified by bridging BF2 groups e.g. 3 is found to be 40,900, this is constant over a wide mass range. Cs is lowered when catalysts of larger cross sectional area are used supporting a diffusion controlled process. Co-ordinating solvents suppress Cs by competing for coordination of the Co(I1) effectively reducing the concentration of active species. No conclusions can be drawn regarding the effect of temperature and thus the activation energy of the process. CCTP lowers the observed rate of polymerisation.

No abstract

No abstract