Electron-Rich Metal Cations Enable Synthesis of High Molecular Weight, Linear Functional Polyethylenes

Abstract

Group 10 metal catalysts have shown much promise for the copolymerization of nonpolar with polar alkenes to directly generate functional materials, but access to high copolymer molecular weights nevertheless remains a key challenge toward practical applications in this field. In the context of identifying new strategies for molecular weight control, we report a series of highly polarized P(V)-P(III) chelating ligands that manifest unique space filling and electrostatic effects within the coordination sphere of single component Pd polymerization catalysts and exert important influences on (co)polymer molecular weights. Single component, cationic phosphonic diamide-phosphine (PDAP) Pd catalysts are competent to generate linear, functional polyethylenes with M up to ca. 2 × 10 g mol, significantly higher than prototypical catalysts in this field, and with polar content up to ca. 9 mol %. Functional groups are positioned by these catalysts almost exclusively along the main chain, not at chain ends or ends of branches, which mimics the microstructures of commercial linear low-density polyethylenes. Spectroscopic, X-ray crystallographic, and computational data indicate PDAP coordination to Pd manifests cationic yet electron-rich active species, which may correlate to their complementary catalytic properties versus privileged catalysts such as electrophilic α-diimine (Brookhart-type) or neutral phosphine-sulfonato (Drent-type) complexes. Though steric blocking within the catalyst coordination sphere has long been a reliable strategy for catalyst molecular weight control, data from this study suggest electronic control should be considered as a complementary concept less prone to suppression of comonomer enchainment that can occur with highly sterically congested catalysts.

Ethylene (co)Oligomerization by Phosphine‐Pyridine Based Palladium and Nickel Catalysts

“…These cooligomerization parameters are much worse than those of phosphine‐sulfonate palladium catalysts. However, this does represent one of the few catalyst systems that can enable ethylene copolymerizations/cooligomerizations with a series of industrially relevant polar comonomers . The ethylene oligomer generated by Pd‐CH 2 at 20 °C is highly linear based on 13 C NMR analysis (Figure S48, B=3 per 1000 carbon atoms).…”

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

“…[91] Some phosphine-sulfonate palladium complexes with as even-membered chelate ring were designed and synthesized. [93] After ligand modifications, high-performance polymerization catalysts were obtained. Combined with the studies on the X and XI systems,itwas proposed that the smaller metal chelate ring can increase ligand rigidity and lead to catalysts with improved properties.…”

Polar‐Functionalized, Crosslinkable, Self‐Healing, and Photoresponsive Polyolefins

“…Recently, several palladium‐ and nickel‐based catalysts have been reported with these capabilities . For example, phosphine sulfonate and related palladium catalysts have been extensively studied and can copolymerize ethylene with various polar comonomers …”

“…[10][11][12][13][14][15][16] For example,phosphine sulfonate and related palladium catalysts have been extensively studied and can copolymerize ethylene with various polar comonomers. [17][18][19][20][21][22][23] In contrast to the numerous studies focused on catalyst development, fewer studies concerning the material proper-ties of polar-functionalized polyolefins,s uch as density, viscosity,s urface properties,d yeing properties,a nd mechanical properties,have been reported. [24][25][26][27][28][29] Moreover,the polar polyolefins in these studies were limited to thermoplastic-type materials.I n2 014, Mecking and co-workers reported the synthesis of polyolefins bearing siloxanes/glycidyl/anhydride groups via phosphine-sulfonate palladium-catalyzed copolymerizations.…”