Robust Bulky [P,O] Neutral Nickel Catalysts for Copolymerization of Ethylene with Polar Vinyl Monomers

Abstract

Several nickel complexes bearing sterically bulky phosphino-phenolate ([P,O]) ligands were synthesized and explored as catalysts for olefin (co)polymerization. In the absence of an activator, the complexes showed very high catalytic activities (up to 10 7 g mol Ni −1 h −1 ) for ethylene polymerization even at 90 °C or with the addition of a large amount of a polar additive (such as ethyl alcohol, diethyl ether, acetone, or even water), affording linear polymers with high molecular weights (up to 6.53 × 10 5 ). In contrast, most of the previously reported nickel catalysts suffer from severe activity suppression at elevated temperature. It is rare that a catalyst has so many good performances simultaneously, including high catalytic activity, good tolerance for polar groups, strong thermal stability, and yielding high molecular weight linear polyethylene. Most importantly, these bulky nickel complexes used in this study also effectively copolymerized ethylene with challenging polar vinyl monomers, including commercially available acrylates and an acrylamide. As we expected, introducing a bulky substituent group on the phosphorus atom of the complex was vital for enhanced catalytic activity and the formation of high molecular weight linear copolymers. Microstructure analyses revealed that the polar functional units were mainly incorporated into the polymer main chain and also located at the chain end with insertion percentages of up to 7.4 mol %. The bulky [P,O] neutral nickel complexes reported herein are promising alternatives to the well-established palladium catalysts for direct copolymerization of olefins with commercially available polar vinyl comonomers.

A simple and versatile nickel platform for the generation of branched high molecular weight polyolefins

“…With proper structural modifications, this type of catalyst can produce high molecular weight polyethylene 16 . For example, some nickel complexes bearing o-bis(aryl)-phosphinophenolate ligands (IV) possess advantageous properties for ethylene polymerization and copolymerization with acrylate comonomers 17,18 . Recently, extensive research efforts have been focused on the design and development of nickel catalysts based on phosphine-derived ligands (V-VII) [19][20][21][22] , partially due to their potential for generating polar-functionalized polyolefins through copolymerization.…”

Emerging Palladium and Nickel Catalysts for Copolymerization of Olefins with Polar Monomers

“…Surprisingly, very high catalytic activities (up to 3230 kg mol −1 h −1 ), extremely high copolymer molecular weights ( M n up to 143,000), and moderate comonomer incorporation (0.3–4.5 mol %) were achieved. Subsequently, Li and co‐workers expanded the polar monomer substrate scope to acrylamide, and further improved the properties of this type of nickel catalyst through ligand modifications . Furthermore, Nozaki and co‐workers demonstrated the copolymerization of propylene with some polar monomers using this type of catalyst .…”

Facile synthesis of sterically demanding SHOP‐type nickel catalysts for ethylene polymerization

“…Recently, Li et al . have evaluated the capability of the ethylene polymerization using some bulky phosphino‐phenolate based nickel complexes (Scheme , B ), which exhibited very high activities of up to 10 7 g PE (mol Ni h) − 1 even at 90 °C. More surprisingly, these nickel catalysts are compatible with some polar vinyl monomers .…”

“…have evaluated the capability of the ethylene polymerization using some bulky phosphino‐phenolate based nickel complexes (Scheme , B ), which exhibited very high activities of up to 10 7 g PE (mol Ni h) − 1 even at 90 °C. More surprisingly, these nickel catalysts are compatible with some polar vinyl monomers . In addition, Gibson et al showed that some modified SHOP catalyst through the introduction of the bulky group adjacent to the oxygen atom (Scheme , A ) could dramatic increased the catalytic activities .…”