Investigations on the Ethylene Polymerization with Bisarylimine Pyridine Iron (BIP) Catalysts

Abstract

The kinetics and terminations of ethylene polymerization, mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts, and activated by large amounts of methyl aluminoxane (MAO) was studied. Narrow distributed paraffins from initially formed aluminum polymeryls and broader distributed 1-polyolefins and (bimodal) mixtures, thereof, were obtained after acidic workup. The main pathway of olefin formation is beta-hydrogen transfer to ethylene. The rate of polymerization in the initial phase is inversely proportional to the co-catalyst concentration for all pre-catalysts; a first-order dependence was found on ethylene and catalyst concentrations. The inhibition by aluminum alkyls is released to some extent in a second phase, which arises after the original methyl groups are transformed into n-alkyl entities and the aluminum polymeryls partly precipitate in the toluene medium. The catalysis is interpretable in a mechanism, wherein, the relative rate of chain shuttling, beta-hydrogen transfer and insertion of ethylene are determining the outcome. Beta-hydrogen transfer enables catalyst mobility, which leads to a (degenerate) chain growth of already precipitated aluminum alkyls. Stronger Lewis acidic centers of the single site catalysts, and those with smaller ligands, are more prone to yield 1-olefins and to undergo a faster reversible alkyl exchange between aluminum and iron.

HDPE@UHMWPE Powders for Power Bed Fusion Based Additive Manufacturing

“…Complex 1 leads to a catalyst that yields HDPE in a range of 10–100 kDa. [ 53,54 ] This was initially considered a suitable component to form a processable blend with UHMWPE. [ 33 ]…”

“…Latter compound reacts with complex 1 and its products after MAO treatment to make it virtually inactive for polyethylene formation, either through coordination to the active site or by formation of soluble paraffins and alkenes by chain transfer processes. [ 54 ] Thus, any catalyst derived from 1 dissociating from the silica tends to become inactive for HDPE formation in solution. It is thus found that most of the HDPE was homogeneously formed on the immobilized silica@UHMWPE.…”

“…Complex 1 leads to a catalyst that yields HDPE in a range of 10-100 kDa. [53,54] This was initially considered a suitable component to form a processable blend with UHMWPE. [33] Formation of the shell from ethylene was reached by addition of the silica@UHMWPE particles coated with the activated catalyst to a reactor containing toluene saturated with ethylene.…”

Disentangled UHMWPE@silica powders for potential use in power bed fusion based additive manufacturing

“…This low temperature was chosen for the lower swelling of the polymeric product. Typical BIP FeCl 2 complexes like those based on ligands prepared from ortho alkyl substituted anilines become active ethylene polymerization catalysts in combination with MAO at such temperatures [57]. The expected color change from blue to orange did also not occur.…”

Toward the Direct Synthesis of HDPE Powders for Powder Bed Fusion Based Additive Manufacturing

“…This indicates that the molecular weight is in the lower range for the action of catalyst 1. [61] A molecular weight determination by size exclusion chromatography was hampered by the presence of the silica particles. The elongation at break decreased from 33.2 ± 9.6 % at 0 wt% silica to as low as 15 ± 0.8% at 7.5 wt% silica.…”