The Impact of Charge in a Ni(II) Polymerization Catalyst

Abstract

A direct comparison between neutral active sites and their corresponding cationic analogues is enabled by protonation of neutral bis(imino)phenoxy complexes, active for ethylene polymerization. The additional imine motif compared to parent salicylaldiminato catalysts does not influence the microstructure of the products in ethylene polymerization, but allows for the incorporation of a proton right next to the active center in an N•••H + •••O bridge yielding cationic complexes. These show an increased Ni−O bond length and a drastically reduced electron density on the Ni atom. In pressure reactor experiments, two different catalysts that produce linear HDPE or undergo extensive chain walking, respectively, in their neutral version, both produce short chain oligomers when the catalyst is charged cationically. A mechanistic analysis by DFT methods reveals an increased propensity for β-hydride elimination compared to ethylene insertion chain growth for the cationic complexes. This results from a higher relative stability of β-agostic species vs olefin-coordinated species.

Alkane-Soluble Bis[tris(alkylphenyl)carbenium] Diborate Cocatalyst for Olefin Polymerizations

“…Note that single-site homogeneous olefin polymerization catalysis usually produces characteristic narrow molecular weight distributions with Đ ∼ 2.0. In some scenarios, broadened polyolefin Đs and multimodality can positively alter melt processing and polyolefin properties. − …”

A tridentate phenoxy-phosphine (POP) divalent chromium complex and its reactivities in olefin polymerization

“…It is worth mentioning that bimodal PEs usually have the advantage of easier processing and altering tensile strength vs. monomodal HDPE type polymers. [61][62][63][64]…”

Chain Walking in the AlCl3 Catalyzed Cationic Polymerization of α‐Olefins

“…Consequently, CW can also be considered as a specific part of intermolecular chain transfers. However, its interest is due to the fact that it can lead to (hyper)branched/dendritic hydrocarbon polymers [24] that are tuned depending on the nature of the catalyst, [25,26,27,28,29] leading to stereospecific polymers, [28] or/with the complexity that the process involves the formation of radical species, [30] and this is also called radical ethene polymerization [31,32,33] . In addition, changing parameters such as monomer concentration or temperature can then block copolymerization [34,35,36,37,38,39] .…”

“…However, its interest is due to the fact that it can lead to (hyper)branched/dendritic hydrocarbon polymers [24] that are tuned depending on the nature of the catalyst, [25,26,27,28,29] leading to stereospecific polymers, [28] or/with the complexity that the process involves the formation of radical species, [30] and this is also called radical ethene polymerization. [31,32,33] In addition, changing parameters such as monomer concentration or temperature can then block copolymerization. [34,35,36,37,38,39] In the previous research on this topic, some remarkable properties were identified for the PAOs synthesized from the AlCl 3 /solvent system, however the mechanism of chain initiation, propagation and transfer was not clearly determined.…”