Efficient Suppression of Chain Transfer and Branching via C_s‐Type Shielding in a Neutral Nickel(II) Catalyst

Abstract

An effective shielding of both apical positions of a neutral NiII active site is achieved by dibenzosuberyl groups, both attached via the same donors’ N‐aryl group in a Cs‐type arrangement. The key aniline building block is accessible in a single step from commercially available dibenzosuberol. This shielding approach suppresses chain transfer and branch formation to such an extent that ultrahigh molecular weight polyethylenes (5×106 g mol−1) are accessible, with a strictly linear microstructure (<0.1 branches/1000C). Key features of this highly active (4.3×105 turnovers h−1) catalyst are an exceptionally facile preparation, thermal robustness (up to 90 °C polymerization temperature), ability for living polymerization and compatibility with THF as a polar reaction medium.

Star Ultrahigh-Molecular-Weight Polyethylene

“…The control sample of linear UHMWPE using the nickel(II) catalyst bearing the same ligand reported by us previously was synthesized for a comparison. 35 Based on the close molecular weight and the virtually same branching density, three-arm and four-arm star UHMWPEs exhibited high stress-at-break values (39.5 and 39.2 MPa), but which were lower than that of linear UHMWPE (46.8 MPa) (Figure 3C). As expected, these star UHMWPEs possessed better strain-at-break values (393 and 412%) relative to that of linear UHMWPE (330%).…”

“…Although the mononuclear nickel(II) catalyst could bear a wide temperature range of 25−90 °C, a low temperature of 25 °C was selected because of the very narrow molecular weight distribution at this condition. 35 With Ni(COD) 2 as the scavenger to remove the strongly coordinated PMe 3 molecules, ethylene polymerizations were performed at 25 °C and 8 bar using the neutral multinuclear nickel(II) catalysts Ni 3 and Ni 4 (Table 1). Ni 3 directly enabled the formation of a three-arm star UHMWPE (M w = 1580 kDa) in a high catalytic activity of 4.38 × 10 6 g mol −1 h −1 .…”

Highly Active and Thermally Robust Nickel Enolate Catalysts for the Synthesis of Ethylene‐Acrylate Copolymers

“…Compared to Ni0 , bulkier catalysts produce polymers with significantly higher Mw. Specifically, polyethylene produced by Ph PO Ph ‐Ni , which has a sandwich‐like geometry, features Mw nearly 10 times higher than that by Ni0 , indicating significant inhibition of β‐H elimination and demonstrating the importance of axial steric hindrance [7b, 16c] . Previously, Ni−Na multimetallic catalysts supported by phosphine‐enolate‐sulfonate ligands generate high Mw polyethylene with high dispersity (PDI 11–25), though the ligands design elements promoting this performance are unclear [14b] .…”

“…While sandwich‐like α‐diimine or salicylaldiminato Pd or Ni catalysts have been studied extensively, [15b, 16c, 20] analogous P,O type catalysts have not been reported. To evaluate this ligand design strategy, we first screened the catalysts via ethylene polymerization at 90 °C in high throughput parallel reactors (Table 1).…”