Catalytic chain transfer polymerisation (cctp) of methyl methacrylate: Effect of catalyst structure and reaction conditions on chain transfer coefficient

Abstract

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.

Preparation and characterization of oligomeric terpolymers of styrene, methyl methacrylate and 2-hydroxyethyl methacrylate: A comparison of conventional and catalytic chain transfer

“…The styrene radicals are about 20 times more reactive than the methacrylate radicals towards thiols. [3] In contrast, the methacrylate radicals are about 20 times more reactive towards COPhBF [14,22] (assuming that the HEMA and MMA radicals have a similar reactivity in chain transfer reactions). Consequently, significant composition drift, leading to different ratios of the propagating radicals, would result in a large drift in the molecular weight distributions.…”

Solvent Effects, Diffusion Control and Mechanistic Aspects of Catalytic Chain Transfer Polymerization

“…This has been suggested by several authors. [8,13,14] Heuts et al [17][18][19] elaborated on this topic and found evidence that supported the hypothesis that the transfer reaction in catalytic chain transfer of methacrylates is indeed diffusion controlled. These conclusions were based on trends in C T for a series of methacrylates [17,19] and on enhanced catalyst activity when polymerizations are run in supercritical CO 2 .…”

“…The values in solution are generally lower than those in bulk. [12][13][14] In earlier literature this decrease was claimed to be caused by so-called solvent effects: interactions of solvent molecules with the active catalytic center. From studies in emulsion polymerization [15] and studies of the polymerization of methacrylic acid, [16] it is known that CoBF decomposes slowly in the presence of acids.…”

“…For solution polymerizations in 2-butanone, differences in catalyst activity have been reported by Haddleton et al between polymerizations in purified and unpurified solvent. [13] From these examples it is clear that various aspects of the polymerization conditions may affect catalyst activity. Therefore, we will first deal with the influence of reaction conditions such as solvent and impurities on the determination of C T 's in order to obtain a set of requirements that have to be fulfilled in order to obtain reliable results.…”

The role of monomer in the chain transfer reaction in cobaloxime-mediated free-radical polymerization

“…This can, in principle, be accomplished by diluting the monomer solution to varying extents. However, significant solvent effects can occur in the current system, as a solvent molecule may act as the axial ligand for the Co(II) complex and may significantly alter the electronic properties of the catalyst 7) . The latter effect may lead to a different reactivity of the catalyst and hence the experiment may not be suitable for testing our predictions.…”