35b/MAO

For catalyst 35b/MAO, a kinetic isotope effect experiment was devised using the monomers do-propylene and 2-<7i-propylene for polymerization. 2- /i-Propylene was chosen for this experiment since P-hydride elimination is a component of the mechanism for chain epimerization. Polymerizations were carried out at 25 °C in toluene solution with 1 atm of propylene (0.8 M) (Figure4.17). The deuterated polymer was examined by NMR spectroscopy this technique showed that most of the deuterium was incorporated as -CD(CH3), with 2-3% incorporation as -CH(CH2D). The latter can be attributed to chain epimerization, which appears to be consistent with the 2-3% mm triads observed under similar conditions for propylene polymerization with 35a-c/MAO. 

Based on H NMR analysis of low molecular weight polypropylene formed by 40b/MAO at 25 C with a propylene concentration of 0.5 M (in toluene solution), the predominant chain termination pathway appears to be f)-H elimination (i.e., vinylidene end groups are present). The primary kinetic isotope effect observed for 35b/MAO (vide supra) is also indicative of P-H elimination operating as the predominant chain termination pathway. No fl-CH3 elimination was observed for these catalysts specifically, no vinylic end groups are present in the H NMR spectra. For 35a-c and 40c, chain transfer was found to be primarily unimolecular, derived from f)-H elimination. For 40b, a small bimolecular contribution (chain dansfer to monomer) was also suggested, owing to the less than first order dependence of molecular weight on propylene concentration. 

In polymerization tests, 35b was activated with MAO, 36b was activated with [CPh3]+[B(C6F5)4] , and 36a was activated with [CPh3]+[B(C6F5)4] or BfC Fsls. The authors carried out these experiments to investigate whether fluorinated borane or borate activators would provide comparable stereoselectivity and productivity as compared to MAO as a cocatalyst. All three compounds were found to be active precatalysts for 1-pentene polymerization. Polymerizations were... 

The effect of the substitution at the ortho position of the phenoxide moiety was investigated utilizing complexes 35b,c and 40a,b (Figure 9.5) (Furuyama et al, 2005a). When activated with MAO at 25 °C, each complex produced PE with a narrow molecular-weight distribution = 1.05-1.16, up to 75 000 g/mol), however, reaction times... 

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