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

Abstract

In the catalytic chain transfer polymerization of methyl methacrylate, butyl methacrylate and 2‐ethylhexyl methacrylate in toluene, it was found that the chain transfer constants (CT) were independent of solvent concentration and therefore of solution viscosity, and did not differ from the bulk polymerization values. For a diffusion controlled system, theoretical calculations predict an increase in CT when the solution viscosity is lowered. This points at a non‐diffusion controlled catalytic chain transfer step. These results were obtained when the solvent was thoroughly purified using a Grubbs‐type set‐up, whereas a large reduction in CT was found in unpurified solvent. Similar results were obtained for butyl acetate. Therefore it is concluded that the decrease of CT in non‐purified solvents is not related to the solvent itself, but to solvent impurities. Further we found that methyl methacrylate ended radicals do not covalently bind to the cobalt complex, in contrast to styrene and acrylate ended radicals.Chain transfer constant for the CCT polymerization of 2‐ethylhexyl methacrylate in toluene, and predictions for diffusion controlled systems.magnified imageChain transfer constant for the CCT polymerization of 2‐ethylhexyl methacrylate in toluene, and predictions for diffusion controlled systems.

High‐conversion catalytic chain transfer polymerization of methyl methacrylate

“…This results in C T = 40.8 × 10 3 for the bulk polymerization and C T = 46.1 × 10 3 for the solution polymerization. Considering that both are determined from a single point the results are in quite good agreement and compare well with results obtained from low conversion polymerizations 29…”

“…However, Heuts et al18 tested this hypothesis by determining the chain transfer coefficients from experiments at constant catalyst concentrations and varying monomer concentrations and did not obtain any evidence in support of this hypothesis. Results on solvent effects, in which C T proved to be independent of toluene concentration, as discussed in a previous article29 point in the same direction. So the explanation that changes in the ratio of monomer concentration and solvent concentration affect C T can be discarded.…”

“…It is unlikely that this increase can be attributed to scatter only. If the chain transfer coefficient would be calculated from the fourth point in stead of the second, this would give a value around 59 × 10 3 , which is in agreement with the results for low conversion polymerizations at high toluene concentrations as shown in a previous article,29 although conversions were in between 2.4 and 3.6% in the latter case. The origin of the increase in C T at high concentrations of toluene, however, remains unclear.…”

Catalytic Chain Transfer Copolymerization of Methyl Methacrylate and Butyl Acrylate

“…The parameters used for the calculation of Φ MMA are presented in Table 1. Recently, we reported k tr,MMA = 3.3 × 10 7 L · mol −1 · s −1 37 and k tr,BA = 2.2 × 10 7 L · mol −1 · s −1 38. The order of magnitude of the estimates for K cd [P•] is based on a value of 2.4 × 10 9 L · mol −1 for a similar equilibrium between PMA• and tetramesitylporphyrinatocobalt(II) at 50 °C27 and a radical concentration range of 10 −7 to 10 −9 mol · L −1 .…”

“…The parameters used for the calculation of F MMA are presented in Table 1. Recently, we reported k tr,MMA ¼ 3.3 Â 10 7 LÁ mol À1 Á s À1 [37] and k tr,BA ¼ 2.2 Â 10 7 L Á mol À1 Á s À1 . [38] The order of magnitude of the estimates for K cd [P.] is based on a value of 2.4 Â 10 9 L Á mol À1 for a similar equilibrium between PMA.…”