N , N -chelated nickel catalysts for highly branched polyolefin elastomers: a survey

Abstract

The physical properties and end applications of polyolefin materials are defined by their chain architectures and topologies. These properties can, in part, be controlled by a judicious choice of the steric and electronic properties of the catalyst and, in particular, the ligand framework. One major achievement in this field is the discovery of thermoplastic polyolefin elastomers that combine the processing and recyclable characteristics of thermoplastics with the flexibility and ductility of elastomers. These polymers are highly sought after as alternative materials to thermoset elastomers. In this perspective, works in the literature related to the development of nickel catalysts as well as their implementations for the synthesis of polyolefin elastomers are summarized in detail. Throughout the perspective, attention has been focused on developing the relationship between catalyst structure and performance, on strategies for the synthesis of polyolefin elastomer using nickel catalysts, on properties of the resultant polyolefin, such as degree of branching and crystallinity, as well as on their effects on mechanical properties. The future perspective regarding the most recent developments in single-step production of polyethylene elastomers will also be presented.

Branched polyethylenes attainable using thermally enhanced bis(imino)acenaphthene-nickel catalysts: Exploring the effects of temperature and pressure

“…In general, the Tm's of the polymers generated in this study using either alkyl-aluminum co-catalyst (MAO or EASC), fall in the range 92.4 -12.3 °C which is in accord with various levels of branching; an observation that is common for nickel polymerization catalysts [27,29] due to their propensity to mediate chain migration/walking [57,58,[76][77][78][79]. The commonly accepted mechanism is shown in Scheme 2, in which the capacity of the active nickel species to mediate chain isomerization through a sequence of β-H elimination/re-insertion steps is key to the observed branched structures; alternative proposals involving γand δ-eliminations have also been proposed [78].…”

Iminopyridine Ni(II) Catalysts Affording Oily Hyperbranched Ethylene Oligomers and/or Crystalline Polyethylenes Depending on the Reaction Conditions: Possible Role of In Situ Catalyst Structure Modifications

“…A related ligand modification introducing a 2,6-dialkylphenyl substituent in the 6-position of pyridine resulted in prevailing ethylene dimerization to 1-butene with minor amounts of C6, C8, and higher oligomers [11]. A large number of complexes with increasing steric bulk Macromol 2021, 1 122 on the arylimino moiety of the ligand, e.g., o-benzhydryl, dibenzhydryl or dibenzocycloheptyl substituents but no substituents on the pyridine moiety, have been synthesized and tested by the group of Sun [12][13][14][15][16][17][18], resulting in thermally stable and highly active catalysts yielding low molecular weight moderately branched polyethylenes (Scheme 1B). Incorporation of very bulky 8-arylnaphtyl substituents on the imino moiety [19], blocking only one of the two coordination sites at the metal center, resulted in catalysts producing moderately branched polyethylenes with increased molecular weight (∼10 4 g mol −1 ) (Scheme 1C).…”

Formation of branched polyethylenes by ethylene homopolymerization using LNiBr2 homo‐ and heterogeneous precatalysts: Interpretation of the polymer structures in comparison with commercial LLDPE

“…Modification of the ligands makes it possible to obtain highly branched PE with different molecular masses–from oligomers 7 to ultrahigh molecular mass polymers 9,10 . The mechanism of branch formation during the ethylene polymerization in the absence of α ‐olefin over late transition metal catalysts is known as the chain walking mechanism 14,17–19 . According to this mechanism, β , γ , δ …‐agostic hydrogen interactions with the metal center are possible during the chain propagation step.…”