Copolymerization of Ethylene and Methyl Acrylate by Dibenzocycloheptyl-Substituted Aryliminopyridyl Ni(II) Catalysts

Abstract

Copolymerization of ethylene with polar vinyl monomers to yield functionalized and possibly easier recyclable polyolefins is challenging and it is currently being pursued mainly using expensive Pd-based catalysts. Herein, the copolymerization of ethylene and methyl acrylate (MA) is achieved by the dibenzocycloheptyl-substituted aryliminopyridyl Ni(II) complexes, affording copolymers with selectively in-chain incorporated MA units as well as both in-chain and end-of-chain inserted MA units depending on the catalyst structure and the reaction conditions

Noncovalent Ni–Phenyl Interactions Promoted α-Diimine Nickel-Catalyzed Copolymerization of Ethylene and Methyl Acrylate

“…Besides, “sandwich” dibenzobarrelene-derived nickel catalysts are also highly tolerant toward the polar MA comonomer. In previously reported nickel systems, a large amount of aluminum cocatalyst (or high Al/MA) is required to successfully realize the copolymerization of ethylene and MA. ,, However, the amount of cocatalyst AlEt 2 Cl is far lower than that of the polar MA monomer (Al/MA = 6/25–6/100) in our systems, indicating high tolerance toward the MA comonomer of “sandwich” catalysts. Increasing the MA concentration from 0.5 to 2 mol/L leads to higher MA incorporation but a lower molecular weight of EMA.…”

“…It is reported that E/MA copolymerizations using α-diimine palladium catalysts commonly produce a highly branched EMA copolymers containing terminal ester groups because of chain walking. , Herein, EMA copolymers produced by α-diimine nickel catalysts were analyzed to clearly identify the location of ester groups on the copolymer chain. As shown in Figure A, multiple resonances are observed at ∼3.6 ppm, indicating the presence of ester groups at different locations. , An approximate ratio of in-chain, pendant, and terminal MA units is 1:1:1 (entry 1 in Table ) based on the integral ratio. In 13 C NMR spectrum (Figure B), three characteristic resonances of carbonyl (C = O) are clearly observed at 176.9, 174.5, and 171.5 ppm, which are respectively, assigned to in-chain ( n = 0), terminal ( n ≥ 2), and pendant ( n = 1) MA units (Table S2) according to previous assignments. , Overall, lightly branched EMA copolymers ( T m = 72–118 °C and BD = 19–58/1000C) have moderate molecular weights (6.2–32.2 kg/mol) with normal distributions ( Đ = 1.57–2.19) and contain both in-chain, pendant, and terminal MA units on the copolymer chain.…”

“…As shown in Figure 5A, multiple resonances are observed at ∼3.6 ppm, indicating the presence of ester groups at different locations. 26,27 An approximate ratio of in-chain, pendant, and terminal MA units is 1:1:1 (entry 1 in Table 2) based on the integral ratio. In 13 C NMR spectrum (Figure 5B), three characteristic resonances of carbonyl (C = O) are clearly observed at 176.9, 174.5, and 171.5 ppm, which are respectively, assigned to in-chain (n = 0), terminal (n ≥ 2), and pendant (n = 1) MA units (Table S2) according to previous assignments.…”

“…8,9 However, early transition metal catalysts have to suffer low activity or inactivity due to their high oxophilicity. 10,11 Since Brookhart's initial work on α-diimine palladium catalysts (Figure 1A), 12 intensive efforts have been devoted to the development of late transition metal (Ni/Pd) catalysts, including phosphine-sulfonato palladium (Figure 1B), 13−15 imidazo [1,5-a] quinolinolate-1-ylidene (IzQO) palladium (Figure 1C), 16,17 bisphosphine monoxide (BPMO) palladium and nickel (Figure 1D), 18−21 biphosphazane monoxide (PNPO) palladium and nickel (Figure 1E), 22,23 phosphinophenolato nickel (Figure 1F), 24,25 and pyridine-imine nickel (Figure 1G), 26,27 for E/MA copolymerization over the past two decades. 28−30 As a kind of the most representative catalyst, α-diimine Ni/ Pd catalysts attracted considerable interest for E/MA copolymerization.…”

Advance on nickel‐ and palladium‐catalyzed insertion copolymerization of ethylene and acrylate monomers

“…Sun reasoned that increase the steric bulk to the arylimino group can enhance EMA copolymers with higher molecular weight and lower branching. The copolymerizations of ethylene and MA catalyzed by the nickel catalysts Ni8 – Ni12 (Figure 2) afford the crystalline copolymers 63 . Ni9 and Ni10 with alkyl substituents display greater catalytic activity, while Ni11 and Ni12 with electron‐withdrawing Cl or F substituents are inactive.…”