Chemically Recyclable Polyethylene-like Sulfur-Containing Plastics from Sustainable Feedstocks

The green revolution in plastics should be accelerated due to growing sustainability concerns. Here, we develop a series of chemically recyclable polymers from the first reported cascade polymerization of H₂ O, COS, and diacrylates. In addition to abundant feedstocks, the method is efficient and air-tolerant, uses common organic bases as catalysts, and yields polymers with high molecular weights under mild conditions. Such polymers, structurally like polyethylene with low-density in-chain polar groups, manifest impressive toughness and ductility comparable to high-density polyethylene. The in-chain ester group acts as a breaking point, enabling these polymers to undergo chemical recycling through two loops. The structures and properties of these polymers also have an immeasurably expanded range owing to the versatility of our method. The readily available raw materials, facile synthesis, and high performance make these polymers promising prospects as sustainable materials in practice.

Polar-Functionalized Polyethylenes Enabled by Palladium-Catalyzed Copolymerization of Ethylene and Butadiene/Bio-Based Alcohol-Derived Monomers

Polar-functionalized polyolefins are high-value materials with improved properties. However, their feedstocks generally come from non-renewable fossil products; thus, it requires the development of renewable bio-based monomers to produce functionalized polyolefins. In this contribution, via the Pd-catalyzed telomerization of 1,3-butadiene and three types of bio-based alcohols (furfuryl alcohol, tetrahydrofurfuryl alcohol, and solketal), 2,7-octadienyl ether monomers including OC8-FUR, OC8-THF, and OC8-SOL were synthesized and characterized, respectively. The copolymerization of these monomers with ethylene catalyzed by phosphine-sulfonate palladium catalysts was further investigated. Microstructures of the resultant copolymers were analyzed by NMR and ATR-IR spectroscopy, revealing linear structures with incorporations of difunctionalized side chains bearing both allyl ether units and polar cyclic groups. Mechanical property studies exhibited better strain-at-break of these copolymers compared to the non-polar polyethylene, among which the copolymer E-FUR with the incorporation of 0.3 mol% displayed the highest strain-at-break and stress-at-break values of 940% and 35.9 MPa, respectively.

Density Functional Theory Analysis of the Copolymerization of Cyclopropenone with Ethylene Using a Palladium Catalyst

Density functional theory has been used to elucidate the mechanism of Pd copolymerization of cyclopropenone with ethylene. The results reveal that introducing ethylene and cyclopropenone to Pd catalyst is thermodynamically feasible and generates the α,β-unsaturated ketone unit (UnitA). Cis-mode insertion and Path A_1a are the most favorable reaction routes for ethylene and cyclopropenone, respectively. Moreover, cyclopropenone decomposition can generate CO in situ without a catalyst or with a Pd catalyst. The Pd-catalyzed decomposition of cyclopropenone exhibits a lower reaction barrier (22.7 kcal/mol) than its direct decomposition. Our study demonstrates that incorporating CO into the Pd catalyst can generate the isolated ketone unit (UnitB). CO is formed first; thereafter, UnitB is generated. Therefore, the total energy barrier of UnitB generation, accounting for the CO barrier, is 22.7 kcal/mol, which is slightly lower than that of UnitA generation (24.0 kcal/mol). Additionally, the possibility of copolymerizing ethylene, cyclopropenone, and allyl acetate (AAc) has been investigated. The free energy and global reactivity index analyses indicate that the cyclopropenone introduction reaction is more favorable than the AAc insertion, which is consistent with the experimental results. Investigating the copolymerization mechanism will help to develop of a functionalization strategy for polyethylene polymers.

Recent Advances in the Copolymerization of Ethylene with Polar Comonomers by Nickel Catalysts

The less-expensive and earth-abundant nickel catalyst is highly promising in the copolymerization of ethylene with polar monomers and has thus attracted increasing attention in both industry and academia. Herein, we have summarized the recent advancements made in the state-of-the-art nickel catalysts with different types of ligands for ethylene copolymerization and how these modifications influence the catalyst performance, as well as new polymerization modulation strategies. With regard to α-diimine, salicylaldimine/ketoiminato, phosphino-phenolate, phosphine-sulfonate, bisphospnine monoxide, N-heterocyclic carbene and other unclassified chelates, the properties of each catalyst and fine modulation of key copolymerization parameters (activity, molecular weight, comonomer incorporation rate, etc.) are revealed in detail. Despite significant achievements, many opportunities and possibilities are yet to be fully addressed, and a brief outlook on the future development and long-standing challenges is provided.

Multivariate Linear Regression Models to Predict Monomer Poisoning Effect in Ethylene/Polar Monomer Copolymerization Catalyzed by Late Transition Metals

This study combined density functional theory (DFT) calculations and multivariate linear regression (MLR) to analyze the monomer poisoning effect in ethylene/polar monomer copolymerization catalyzed by the Brookhart-type catalysts. The calculation results showed that the poisoning effect of polar monomers with relatively electron-deficient functional groups is weaker, such as ethers, and halogens. On the contrary, polar monomers with electron-rich functional groups (carbonyl, carboxyl, and acyl groups) exert a stronger poisoning effect. In addition, three descriptors that significantly affect the poisoning effect have been proposed on the basis of the multiple linear regression model, viz., the chemical shift of the vinyl carbon atom and heteroatom of polar monomer as well as the metal-X distance in the σ-coordination structure. It is expected that these models could guide the development of efficient catalytic copolymerization system in this field.

Chromium Complexes Supported by NNO-Tridentate Ligands: An Unprecedent Activity with the Low Requirement of MAO

The development of metal catalysts with high activity and thermal stability but low requirement of MAO as cocatalyst is highly desired for polyolefin industrial application. In this contribution, a series...

Ruthenium-Catalyzed Diazoacetates/Cyclooctene Metathesis Copolymerization

As a powerful synthetic tool, ruthenium-catalyzed ring-opening metathesis polymerization (ROMP) has been widely utilized to prepare diverse polymers. In this contribution, we demonstrated the polymerization of cyclooctene in the presence...

Influences of Ligand Backbone Substituents on Phosphinecarbonylpalladium and -nickel Catalysts for Ethylene Polymerization and Copolymerization with Polar Monomers

A series of phosphinecarbonylpalladium and -nickel catalysts bearing various substituents on the ligand backbone were prepared, characterized, and used in ethylene polymerization and copolymerization with polar monomers. The Pd and Ni catalysts can achieve high activities as well as high polymer molecular weights in both ethylene polymerization and copolymerization with polar monomers. The electron-donating group from the carbonyl side can effectively increase the polymer molecular weights. Utilization of a cyclic backbone structure can increase the catalytic activities at the expense of the polymer molecular weights. Moreover, installation of a pyridyl moiety in the ligand backbone can enable Lewis acid responsiveness and can enhance the polymerization activities. These results suggest the importance of the ligand backbone for the properties of catalysts in ethylene polymerization and copolymerization reactions.

Controlled di-lithiation enabled synthesis of phosphine-sulfonamide ligands and implications in ethylene oligomerization

Catalyst design for ethylene oligomerization has attracted significant interest. Herein, we report the synthesis of phosphine-sulfonamide-derived palladium complexes and examine their performance in ethylene oligomerization. Arresting a dilithiation intermediate of N-(2-bromophenyl)-4-methylbenzenesulfonamide (1) at -84 °C selectively produced N-(2-(bis(2-methoxyphenyl)phosphanyl)phenyl)-4-methylbenzenesulfonamide (L1A). However, the same reaction at -41 °C delivered a different ligand; 2-(bis(2-methoxyphenyl)phosphanyl)-4-methyl-N-phenylbenzenesulfonamide (L2A). The generality of our strategy has been demonstrated by preparing N-(2-(diphenylphosphanyl)phenyl)-4-methylbenzenesulfonamide (L1B) and 2-(diphenylphosphanyl)-4-methyl-N-phenylbenzenesulfonamide (L2B). Subsequently, L1A and L1B were treated with a palladium precursor to yield 5-membered complexes C1 and C2, respectively. In contrast, L2A upon treatment with palladium produced a 6-membered metal complex C3. Thus, a small library of 7 palladium complexes (C1-C7) were synthesized by varying the donor moiety (pyridine, DMSO, and acetonitrile). The identity of palladium complexes was unambiguously ascertained using a combination of spectroscopic and analytical methods, including single-crystal X-ray diffraction. The performance of the complexes C1-C7 was investigated in ethylene oligomerization and almost all of them were found to be active. The resultant ethylene oligomers were characterized using 1H and 13C NMR, MALDI-ToF-MS, and GPC. Detailed screening of reaction parameters revealed 100 °C and 40 bars ethylene to be optimal conditions. Complex C5 outperformed other complexes and produced ethylene oligomers with a molecular weight of 1000-1900 g mol-1.

Boosting the Thermal Stability of α-Diimine Palladium Complexes in Norbornene Polymerization from Construction of Intraligand Hydrogen Bonding and Simultaneous Increasing Axial/Equatorial Bulkiness

Increasing the thermostability of α-diimine late-transition-metal complexes and therefore rendering them more active at higher temperatures is of great importance, yet challenging for the olefin polymerization field. In the present research, a new family of α-diimine palladium complexes that can promote norbornene polymerization at high temperatures (up to 140 °C) is disclosed. Because of the conformational restriction caused by increasing the axial and equatorial bulkiness as well as the presence of intraligand H···F hydrogen bonds, N-aryl rotations can be efficiently restricted, therefore circumventing the deactivation of the active species at high temperatures. At 80-140 °C, these complexes can efficiently catalyze norbornene homopolymerizations, giving high catalytic activities up to 5.65 × 10⁷ g of PNB per mole Ni per hour and polymers with high molecular weights up to 37.2 × 10⁴ g/mol, which are highly superior to catalytic systems mediated by CF₃-free complexes. Moreover, these complexes could also afford medium catalytic activities in the presence of polar 5-norbornene-2-carboxylic acid methyl ester (NB-COOCH₃).

Propylene homopolymerization and copolymerization with ethylene by acenaphthene-based α-diimine nickel complexes to access EPR-like elastomers

A series of acenaphthene-based α-diimine nickel complexes were synthesized and subsequently used for accessing branched EPR-like elastomers with different compositions and chain structures.

Influence of intramolecular π–π and H-bonding interactions on pyrazolylimine nickel-catalyzed ethylene polymerization and co-polymerization

Pyrazolylimine-based nickel catalysts bearing intramolecular π–π and H-bonding interactions show high activity, thermal stability, and Mn of polyethylene.

Custom-made polar monomers utilized in nickel and palladium promoted olefin copolymerization

In this review, the functions of custom-made polar monomers are insightfully emphasized in the preparation of functional polyolefins.

Ortho-Functionalized Dibenzhydryl Substituents in α-Diimine Pd Catalyzed Ethylene Polymerization and Copolymerization

Sterically bulky diarylmethyl-based ligands have received increasing attention in the field of late-transition-metal catalyzed olefin polymerization. Ortho-substituents may have a significant impact on the performance of diarylmethyl-based α-diimine Pd catalysts. In this contribution, a series of α-diimine Pd catalysts bearing ortho-methoxyl/hydroxyl functionalized dibenzhydryl units were prepared, characterized, and investigated in ethylene polymerization and copolymerization with methyl acrylate (MA). The catalytic performances were improved by introducing more ortho-substituents. The catalysts exhibited good thermal stabilities at high temperatures, producing branched polyethylenes. The catalysts bearing hydroxyl groups possessing intramolecular H-bonding, resulted in slightly higher incorporation ratios of MA unit when compared with the catalysts bearing methoxyl groups.

Living Chain-Walking (Co)Polymerization of Propylene and 1-Decene by Nickel α-Diimine Catalysts

Homo- and copolymers of propylene and 1-decene were synthesized by controlled chain-walking (co)polymerization using phenyl substituted α-diimine nickel complexes activated with modified methylaluminoxane (MMAO). This catalytic system was found to polymerize propylene in a living fashion to furnish high molecular weight ethylene-propylene (EP) copolymers. The copolymerizations proceeded to give high molecular weight P/1-decene copolymers with narrow molecular weight distribution (Mw/Mn ≈ 1.2), which indicated a living nature of copolymerization at room temperature. The random copolymerization results indicated the possibility of precise branched structure control, depending on the polymerization temperature and time.