Gas Phase Polymerization of Ethylene with Supported α-Diimine Nickel(II) Catalysts

Abstract

An efficient synthetic strategy for new 2,5-and 2,6-substituted unbridged and 1,4-dithiane bridged ligands is presented. The reaction of the latter compounds with Ni(acac) 2 and trityl tetrakis-(pentafluorophenyl)borate gave the corresponding Ni(II) complexes in high yields. The structure of one of these complexes was determined by X-ray analysis. These complexes were supported on silica without a chemical tether and were used as catalysts for ethylene polymerization reactions in the gas phase. Furthermore, ethylene was polymerized with the unsupported 2,5-complexes in homogeneous solution for comparison. The influence of the ligand structure, hydrogen and temperature on the polymerization performance was investigated. The supported catalysts showed moderate to high activities and produced polyethylenes ranging from HDPE to LLDPE, without further addition of an 1-olefin comonomer. In contrast to 2,6complexes, which generate high molecular weight polyethylene, the 2,5-compounds afford materials of lower molecular weight comprising terminal and internal double bonds. In addition, video microscopy experiments allowed to investigate the growth of single polyethylene particles. Electron microscopy was applied to show that their morphology is a replicate of the starting catalyst grains.Chart 1. r-Diimine Nickel(II) Complexes

Post‐Metallocenes in the Industrial Production of Polyolefins

“…The synthetically elegant cyclophane motif also provides relatively temperature‐stable Ni II catalysts that polymerize ethylene to high‐molecular‐weight, highly branched polymers with relatively narrow molecular‐weight distributions that are as low as M w / M n =1.23 (at 50 °C polymerization temperature) 182. Supported versions of the [Ni(diimine)] catalysts have been reported, employing silica mostly, and studied in slurry as well as gas‐phase polymerization 183–189…”

Recent advances in Ni-mediated ethylene chain growth: Nimine-donor ligand effects on catalytic activity, thermal stability and oligo-/polymer structure

“…3) [52]. These catalysts showed moderate to high activities and produced polyethylene ranging from LLDPE to HDPE; the former PE grade being notably generated without the need for the addition of an α-olefin co-monomer.…”

“…These catalysts showed moderate to high activities and produced polyethylene ranging from LLDPE to HDPE; the former PE grade being notably generated without the need for the addition of an α-olefin co-monomer. On comparison 3a with 3b, 3a affords material of lower molecular weight containing terminal and internal double bonds while 3b gives high molecular weight polyethylene [52].…”

8-(2-Cycloalkylphenylimino)-5,6,7-trihydro-quinolylnickel halides: polymerizing ethylene to highly branched and lower molecular weight polyethylenes

“…It is worth mentioning the possibility of inaccurate data regarding measuring molecular weights of such polyethylene waxes because the measurement range of our equipment is set for 10 K to one million g mol −1 . 16 The polyethylenes with lower molecular weights and high branching are in high demand as additives for lubricants and pour-point depressants in industry. Interpreted according to the literature, 15 the spectrum (Fig.…”