Tying Up Loose Ends: Some Mechanistic Aspects of Catalytic Chain Transfer

摘要

Polymerisation of methyl methacrylate in the presence of two catalytic chain transfer agents has been investigated. Several factors were examined to see how they would affect the chain transfer process. Oxygen and initiator impurities added to the system were found to be detrimental. The transfer process was highly intolerant of initiator impurities, but was able to endure a large excess of oxygen. The temperature dependencies of the chain transfer process were determined for cobaloxime boron fluoride (COBF) and cobalt(meso-Ph_4-porphyrin) (CoP). The results showed that a study of MW, or k_(tr) would be a better gauge of the catalyst activity. Activation energies were determined at two concentrations of initiator and it was discovered that the transfer process has a dependence on the initiator concentration. A mechanism for this dependency is proposed that involves a reduction in the active catalyst concentration. As a result, the measured values for C_(tr) and k_(tr), must be apparent values. An additional consequence of the initiator dependence is that the MW of the polymer products will be directly dependent on the concentration of the initiator.