Positive Effect of Polar Solvents in Olefin Polymerization Catalysis

Recent Advancements in the Synthesis of Ultra-High Molecular Weight Polyethylene via Late Transition Metal Catalysts

Ultra-high molecular weight polyethylenes (UHMWPEs) are significant engineering plastics for their unique properties, such as high impact resistance, abrasion resistance, weatherability, lubricity, and chemical resistance. Consequently, developing a suitable catalyst is vital in facilitating the preparation of UHMWPE. The late transition metal catalysts have emerged as effective catalysts in producing UHMWPE due to their availability, enhanced tolerance to heteroatom groups, active polymerization characteristics, and good copolymerization ability with polar monomers. In this review, we mainly focus on the late transition metal catalysts, summarizing advancements in their application over the past decade. Four key metals (Ni, Pd, Fe, Co) for generating linear or branched UHMWPE will be primarily explored in this manuscript.

Aqueous Coordination-Insertion Copolymerization for Producing High Molecular Weight Polar Polyolefins

Hydrocarbons, when used as the medium for transition metal catalyzed organic reactions and olefin (co-)polymerization, are ubiquitous. Environmentally friendly water is highly attractive and long-sought, but is greatly challenging as coordination-insertion copolymerization reaction medium of olefin and polar monomers. Unfavorable interactions from both water and polar monomer usually lead to either catalyst deactivation or the formation of low-molecular-weight polymers. Herein, we develop well-behaved neutral phosphinophenolato nickel catalysts, which enable aqueous copolymerization of ethylene and diverse polar monomers to produce significantly high-molecular-weight linear polar polyolefins (219-549 kDa, 0.13-1.29 mol %) in a single-component fashion under mild conditions for the first time. These copolymerization reactions occur better in water than in hydrocarbons such as toluene. The dual characteristics of high molecular weight and the incorporation of a small amount of functional group result in improved surface properties while retain the desirable intrinsic properties of high-density polyethylene (HDPE).

Synthesis of Polar-functionalized Isotactic Polypropylenes Using Commercial Heterogeneous Ziegler-Natta Catalyst

The efficient synthesis of polar-functionalized polypropylenes with high molecular weight and high stereoregularity represents a challenging task. This challenge becomes even more daunting when pursuing an industrially preferred heterogeneous process. This study demonstrated the realization of these goals through the use of commercial heterogeneous Ziegler-Natta catalysts in the copolymerization of propylene with ionic cluster polar monomers. The results revealed high copolymerization activity (∼1.1 × 107 g mol-1 h-1), moderate polar monomer incorporation ratios (∼4.9 mol %), high copolymer molecular weight (Mw > 105 g mol-1), high stereoregularity ([mmmm] ∼ 96%), and high melting temperature range (150-162 °C). The utilization of ionic cluster polar monomers improved the thermal stability as well as stereoselectivity of the catalyst. Moreover, the Ziegler-Natta catalyst can homopolymerize ionic cluster polar monomers with high activities (>104 g mol-1 h-1). The resulting polar-functionalized isotactic polypropylenes (iPP) exhibited superior tensile strength, impact strength, creep resistance, transparency, and crystallinity compared with nonpolar iPP. This enhancement was attributable to the dual roles of the ionic cluster polar monomer unit, serving as both a transparent nucleating agent and a dynamic cross-linking functionality. Furthermore, the polar-functionalized iPP exhibited improved compatibility with polar materials, offering benefits for applications in composites, recycling of mixed plastic wastes, 3D printing, and other fields. This study offered a comprehensive solution for the future industrial production of polar-functionalized iPP via copolymerization, bridging the gap between an efficient and practical copolymerization process from a synthetic chemistry perspective and enhanced material properties from an application perspective.

Amine-Imine Nickel Catalysts with Pendant O-Donor Groups for Ethylene (Co)Polymerization

The introduction of a secondary interaction is an efficient strategy to modulate transition-metal-catalyzed ethylene (co)polymerization. In this contribution, O-donor groups were suspended on amine-imine ligands to synthesize a series of nickel complexes. By adjusting the interaction between the nickel metal center and the O-donor group on the ligands, these nickel complexes exhibited high activities for ethylene polymerization (up to 3.48 × 10⁶ g_PE·mol_Ni^-1·h^-1) with high molecular weight up to 5.59 × 10⁵ g·mol^-1 and produced good polyethylene elastomers (strain recovery (SR) = 69-81%). In addition, these nickel complexes can catalyze the copolymerization of ethylene with vinyl acetic acid, 6-chloro-1-hexene, 10-undecylenic, 10-undecenoic acid, and 10-undecylenic alcohol to prepare the functionalized polyolefins.