Gas-Phase Ethylene Polymerization by Single-Site Cr Centers in a Metal–Organic Framework

Abstract

We report a systematic study on the gas-phase polymerization of ethylene by a metal–organic framework (MOF) catalyst. Cr3+-exchanged MFU-4l (Cr­(III)-MFU-4l, MFU-4l = Zn5Cl4(BTDD)3, H2BTDD = bis­(1H-1,2,3,-triazolo­[4,5-b],[4′,5′-i])­dibenzo­[1,4]­dioxin)) serves as an exemplary system to demonstrate prereaction treatment with alkylaluminum species as a simple method to isolate an active MOF catalyst for liquid-free polymerization of ethylene. AlMe3-treated Cr­(III)-MFU-4l subjected to 40 bar of ethylene exhibits a polymerization activity of 52 000 molEthylene·molCr –1·h–1, an order of magnitude higher than that observed in a slurry-phase reaction with Cr­(III)-MFU-4l and excess alkylaluminum species. Furthermore, product polyethylene exhibits a low polydispersity index of 1.36 and a free-flowing granular morphology favorable for industrial processing, highlighting the advantages conferred by the single-site MOF catalysts in gas-phase ethylene polymerization.

Recent Advances in the Application of Metal–Organic Frameworks for Polymerization and Oligomerization Reactions

“…But knowledge in the structure of the active catalysts and understanding of reaction mechanism is still lacking. Therefore, Dincă and co-workers [65] synthesized a MOF catalyst, through the exchange of inorganic nodes of MFU-4l with Cr(III) salt to obtain Cr(III)-MFU-4l (Figure 3F). No co-catalyst or solvent is needed in the catalytic process.…”

Influence of Pore Structure and Metal‐Node Geometry on the Polymerization of Ethylene over Cr‐Based Metal–Organic Frameworks

“…[27][28][29] Until now,t hey have been used as such in numerous reactions, for example, others alkene oligomerization reactions [30][31][32][33][34][35][36][37][38][39] as well as polymerization reactions. [30,37,[40][41][42][43][44][45][46][47][48] Dincǎ,R oman-Leshkova nd co-workers investigatedt he ethylene polymerizationp roperties of MFU-41 (MFU = metal-organic framework Ulm-University) MOFs. [41,45] The gas-phase eth-ylene polymerization properties of Cr 3 + ion-exchanged MFU-4l MOF material were investigated, revealing ap olymerization MOF that produced PE with ad ispersity index ()o fa bout 1.4, the being defined as the M w /M n ,w ith the M w representing the weight averagedm olecular weighto ft he polymer and the M n representingt he number averaged molecular weight of the polymer.T his indicates that active sites are similar in nature, and is an excellent example of aC r-based MOF acting as ah eterogenized single-site ethylene polymerization catalyst.…”

“…[30,37,[40][41][42][43][44][45][46][47][48] Dincǎ,R oman-Leshkova nd co-workers investigatedt he ethylene polymerizationp roperties of MFU-41 (MFU = metal-organic framework Ulm-University) MOFs. [41,45] The gas-phase eth-ylene polymerization properties of Cr 3 + ion-exchanged MFU-4l MOF material were investigated, revealing ap olymerization MOF that produced PE with ad ispersity index ()o fa bout 1.4, the being defined as the M w /M n ,w ith the M w representing the weight averagedm olecular weighto ft he polymer and the M n representingt he number averaged molecular weight of the polymer.T his indicates that active sites are similar in nature, and is an excellent example of aC r-based MOF acting as ah eterogenized single-site ethylene polymerization catalyst. However,i nt he case of MOFs, forming true single-site catalysts depends strongly on the materials tructure and its evolution upon reaction with co-catalyst species; and it merits detailed studies on ap er case basis.…”

“…The ability to change the pore structure, metal‐node and electronic structure with relative ease, make MOFs increasingly prominent candidates for heterogenized single‐site catalysis [27–29] . Until now, they have been used as such in numerous reactions, for example, others alkene oligomerization reactions [30–39] as well as polymerization reactions [30, 37, 40–48] …”

“…Dincǎ, Roman‐Leshkov and co‐workers investigated the ethylene polymerization properties of MFU‐41 (MFU=metal–organic framework Ulm‐University) MOFs [41, 45] . The gas‐phase ethylene polymerization properties of Cr 3+ ion‐exchanged MFU‐4l MOF material were investigated, revealing a polymerization MOF that produced PE with a dispersity index ( Ð ) of about 1.4, the Ð being defined as the M w /M n , with the M w representing the weight averaged molecular weight of the polymer and the M n representing the number averaged molecular weight of the polymer.…”