Nickel‐ and palladium‐catalyzed olefin polymerization under high pressures

Abstract

The polymerization of 1-hexene under high pressures (100 -750 MPa) was investigated with nickel-␣-diimine complex/methylaluminoxane and palladium-␣-diimine complex/methylaluminoxane as catalyst systems. The catalytic activity of both the nickel and palladium complexes monotonously increased as pressure rose and became two to four times higher than that observed at atmospheric pressure. Palladium catalysts gave poly(1-hexene)s with higher molecular weights under high pressure, whereas nickel-catalyzed high-pressure polymerizations gave polymers with higher molecular weights only at rather low monomer concentrations. The living-like character in the palladium-catalyzed polymerizations was somewhat enhanced under higher pressures, whereas the nickel-catalyzed polymerizations under high pressures were not living. More branches were found in the polymers produced by nickel catalysts at higher pressures. The chain-transfer reaction seemed to be accelerated by the high pressure in the nickel-catalyzed reactions, although this was not apparent in the palladium-catalyzed reactions. Dimers formed and were accompanied by high molecular weight polymers when nickel catalysts were used under high pressures and at high monomer concentrations. The possibility that very congested five-coordinated species act as key intermediates for the dimerization is discussed.

Preparation of ultra high molecular weight amorphous poly(1-hexene) by a Ziegler-Natta catalyst

“…1). [9,12,21] Effect of polymerization temperature Figure 2 indicates that the polymerization activity is increased by raising the polymerization temperature from À10 to 25°C which can be attributed to the exponential increase of the propagation rate coefficient or to increasing the rate of formation of active species with polymerization temperature, the temperature higher than 25°C decreases the productivities that can be a result of the increase in the catalyst deactivation rate constant that overcome the positive effect of increasing propagation rate constant. [11,12] However, decreasing the M v of the polymer with increasing polymerization temperature which is consistent with similar results previously reported may be a result of chain transfer to aluminum, monomer or β-H elimination reactions.…”

“…[1,2,18,21] The polymerization activity increased with increasing monomer concentration. It may be a result of higher access of active catalyst centers to the monomers that leads to increase of propagation rate compared with the chain transfer and deactivation reactions.…”

“…This behavior can be attributed to the faster deactivation of active centers responsible for the formation of shorter chains in the Ziegler-Natta catalysts that makes the average molecular weight to ascend in the course of polymerization. [1,9,21,32] Characterization of poly(1-hexene)…”

Effect of fluorinated acrylate on the surface properties of cationic fluorinated polyurethane‐acrylate hybrid dispersions

“…In 1995, Brookhart and coworkers reported the synthesis of late transition metal catalysts (nickel and palladium‐α‐diimine) for olefin polymerization. These catalyst systems in combination with MAO produce high molecular weight polymer with a unique microstructure which is different from Ziegler (or) metallocene based poly(α‐olefin)s. The rate of transfer (or) termination reactions are presumed to be suppressed by an increase in the axial steric bulk of these catalysts resulting in higher molecular weight poly(α‐olefin)s 12–16. More recently, Sivaram and coworkers reported the synthesis and detailed characterization of the microstructure of poly(α‐olefin)s prepared using nickel(α‐diimine)/MAO catalyst,17 and the consequences of “chain‐walking” mechanism on the crystallization and thermal properties of poly(α‐olefin)s 18…”

Turning a Cr-based heterogeneous ethylene polymerisation catalyst into a selective ethylene trimerisation catalyst

“…Ni-based diimine catalyst can produce polyethylene with shortchain branches through a chain-walking mechanism [5,[19][20][21][22][23][24]. In 1997, Sumitomo Chemical Company has patented a process of ethylene trimerisation that uses this class of ligands.…”