Reactivity of a new family of diamido-diamine cyclam-based zirconium complexes in ethylene polymerization

Compounds of general formula [(∗Bn2Cyclam)ZrCl2] (∗Bn = 4-tBuC6H4CH2, (4) and 4-CF3C6H4CH2, (5)) were synthesised using Zr(CH2SiMe3)2Cl2(Et2O)2 and the corresponding ligand precursors 1,8-(4-tbutylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H2(4-tBuBn)2Cyclam), (4a), and 1,8-(4-trifluoromethylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H2(4-CF3Bn)2Cyclam), (5a). Complexes 4 and 5, in addition to other [(∗Bn2Cyclam)ZrCl2] compounds previously described by some of us (∗Bn = PhCH2, (1), 3,5-Me2C6H3CH2, (2) and 3,5-tBu2C6H3CH2, (3)) were tested in the polymerization of ethylene in the presence of MAO. System 4/MAO presents the highest activity (2790 g PE molZr−1 h−1 atm−1). The polymers formed are slight to moderately branched polyethylenes with a percentage of branching ranging between 1.2% and 3.3%. The melting points obtained by differential scanning calorimetry (DSC) ranging from 128 to 140 °C, are consistent with rather high average molecular weight polymers with crystallinity close to 50%.

Graphical abstractCompounds of general formula [(∗Bn2Cyclam)ZrCl2], where ∗Bn represents a series of benzyl substituents, were used as ethylene polymerization catalysts. The effect of temperature and co-catalyst: [Zr] ratio on the activity was studied. The polymers formed are slight to moderately branched polyethylenes with a percentage of ramification ranging between 1.2% and 3.3%.Figure optionsDownload full-size imageDownload as PowerPoint slide