Synthesis and characterization of oxazoline-amine zirconium complexes for ethylene homo- and co-polymerization catalysis

Abstract

The development of group IV catalysts for homogeneous olefin polymerizations is crucial for both industrial and academic research. In this study, we present the synthesis and full characterization (1H NMR, 13C NMR, Elem. Anal. and X-ray) of a new class of oxazoline-amine zirconium complexes. When used in combination with Ph3C+−B(C6F5)4 as the cocatalyst in the absence of scavenger, these complexes show high activity (up to 29.5 kg/(mol·min·atm)) in ethylene homopolymerization giving PE with Mw up to 392.4 kg/mol. On average, these complexes generate less than one polymer chain per catalyst, and negligible olefinic end groups were observed by NMR, both suggesting the absence or lack of chain transfer during polymerization. Furthermore, these complexes are also effective in ethylene/1-octene copolymerization, showing activity up to 42.9 kg/(mol·min·atm) and octene enchainment ratio up to 25.2 mol%. Gradually increasing the reaction time from 1 to 15 min leads to an increase in polymer Mw, chains/cat (up to 14.4) and a decrease in activity. Octene incorporation ratio increases from 12.6 to 17.9 mol% over reaction time (1 to 5 min) at 50 °C, likely suggesting mass transfer limitations at long reaction times. Increasing temperature from 50 °C to 90 °C leads to reduced activity and product Mw (> 5 ×), and increased chains/cat (≈5 ×) in the copolymerization. Olefinic end group analysis by 1H NMR suggests β-H elimination/transfer occurs after octene 2,1-insertion (vinylene; predominant), ethylene insertion (vinyl) and octene 1,2-insertion (vinylidene) at high temperatures.