High molecular weight atactic polypropylene prepared by zirconium complexes of an amine bis(phenolate) ligand

The polymerization of propylene employing the recently developed amine bis(phenolate) zirconium catalysts is reported for the first time. The polymerizations were conducted in liquid propylene employing two different experimental setups, and two different precatalysts, based on the same amine bis(phenolate) ligand having a dimethylamino donor on a sidearm. The first precatalyst studied was a dibenzyl zirconium complex, which was found to lead to high molecular weight atactic polypropylene. The effects of the cocatalyst, the ratio between the cocatalyst and the precatalyst, and the polymerization temperature on the nature of the resulting polymer and the activity of the catalyst were studied. Reducing the relative amount of the cocatalyst and lowering the polymerization temperature increased the molecular weight of the polymer, and a temperature of 50°C led to the most active catalyst. A dichloro zirconium complex of the same ligand, expected to show a higher hydrolytic and thermal stability was developed, its X-ray structure was solved, and its activity in polymerization of propylene was studied and found to be similar to that of the dibenzyl precatalyst.