Polyethylene with Reverse Co‐monomer Incorporation: From an Industrial Serendipitous Discovery to Fundamental Understanding

Abstract

A triethylaluminium(TEAl)-modified Phillips ethylene polymerisation Cr/Ti/SiO2 catalyst has been developed with two distinct active regions positioned respectively in the inner core and outer shell of the catalyst particle. DRIFTS, EPR, UV-Vis-NIR DRS, STXM, SEM-EDX and GPC-IR studies revealed that the catalyst produces simultaneously two different polymers, i.e., low molecular weight linear-chain polyethylene in the Ti-abundant catalyst particle shell and high molecular weight short-chain branched polyethylene in the Ti-scarce catalyst particle core. Co-monomers for the short-chain branched polymer were generated in situ within the TEAl-impregnated confined space of the Ti-scarce catalyst particle core in close proximity to the active sites that produced the high molecular weight polymer. These results demonstrate that the catalyst particle architecture directly affects polymer composition, offering the perspective of making high-performance polyethylene from a single reactor system using this modified Phillips catalyst.

Unraveling the Catalytic Synergy between Ti3+ and Al3+ Sites on a Chlorinated Al2O3: A Tandem Approach to Branched Polyethylene

“…To this aim, two cooperative components are engineered into a single catalyst. One component oligomerizes ethylene to short α‐olefins, which are successively incorporated in the growing polyethylene chains through an “in situ branching” mechanism by a second, different, catalytic center . This co‐monomer‐free process for branched polyethylene synthesis opens an attractive atom‐efficient scenario, reducing the costs of feedstock, loading, purification, storage, and downstream recycling.…”

“…In this investigation, we have specifically devised an original step‐by‐step approach to synthesize and characterize a bifunctional heterogeneous catalyst for the production of branched polyethylene using ethylene as the only feed, without any activator. This approach differs from the typical methods in the olefin polymerization field, in which heterogeneous dual‐site catalysts are usually obtained by a partial modification of the original catalyst through the intervention of an external agent . The catalyst is obtained by treating a transitional alumina with TiCl 4 and a subsequent H 2 reduction (as was similarly proposed in previous patents, but never investigated in details), and benefits from the presence of Ti 3+ sites in close proximity to exposed Al 3+ Lewis acid sites on a highly chlorinated surface, each site performing a specific catalytic function.…”

Real‐time Analysis of a Working Triethylaluminium‐Modified Cr/Ti/SiO2 Ethylene Polymerization Catalyst with In Situ Infrared Spectroscopy

“…Therefore, the Cr sites in the Ti‐rich shell are producing shorter, more linear PE in comparison to Ti‐scarce TEAl‐modified Cr sites. The “reverse” co‐monomer incorporation was established, as a higher concentration of co‐monomer was produced in situ by Ti‐scarce TEAl‐modified Cr sites, and subsequently incorporated on the polymerization sites produced longer chains …”

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

“…[8,229,230] TheP hillips catalyst is typically prepared by introducing aC rp recursor,u sually CrO 3 or Cr(OAc) 3 ,t os ilica and calcining at temperatures above 500 8 8C. [231,232,235,236] Thes upport has ap rofound effect on the kinetics of the polymerization and the properties of the polymer. Even if the Phillips catalyst does not require ac o-catalyst, AlEt 3 or BEt 3 enhance the activity, shorten the induction period, [231][232][233][234] tend to broaden the molecular weight distribution, and increase the amount of branching in the polymer.…”