Coordination−Insertion Copolymerization of Fundamental Polar Monomers

Hydrophilic Catalysts with High Activity and Stability in the Aqueous Polymerization of Ethylene to High‐Molecular‐Weight‐Polyethylene

Water‐soluble synthetic transition metal catalysts have been studied extensively for many reactions, but for olefin polymerization such catalysts have been lacking. We report herein a straightforward synthesis of phosphinephenolato Ni^II catalysts endowed permanently with a hydrophilic sulfonate moiety bound to the chelating ligand. These catalysts’ hydrophilic active sites promote aqueous ethylene polymerization with high activity (TOF up to 6.3×10⁴ mol_Ethylene mol_Ni⁻¹ h⁻¹) to high molecular weight polyethylene (HDPE), with half‐lives on the order of hours also at elevated temperatures. The obtained polyethylene dispersions feature narrow particle size distributions without any aggregates.

Selective branch formation in ethylene polymerization to access precise ethylene-propylene copolymers

Polyolefins with branches produced by ethylene alone via chain walking are highly desired in industry. Selective branch formation from uncontrolled chain walking is a long-standing challenge to generate exclusively branched polyolefins, however. Here we report such desirable microstructures in ethylene polymerization by using sterically constrained α-diimine nickel(II)/palladium(II) catalysts at 30 °C–90 °C that fall into industrial conditions. Branched polyethylenes with exclusive branch pattern of methyl branches (99%) and notably selective branch distribution of 1,4-Me₂ unit (86%) can be generated. The ultrahigh degree of branching (>200 Me/1000 C) enables the well-defined product to mimic ethylene-propylene copolymers. More interestingly, branch distribution is predictable and computable by using a simple statistical model of p(1-p)ⁿ (p: the probability of branch formation). Mechanistic insights into the branch formation including branch pattern and branch distribution by an in-depth density functional theory (DFT) calculation are elucidated.

Selective branch formation from uncontrolled chain walking is a longstanding challenge to generate exclusively branched polyolefins. Here the authors report such desirable microstructures in ethylene polymerization enabled by a nickel catalyst at 30 °C–90 °C that fall into industrial conditions and mimic ethylene-propylene copolymers.

A comprehensive understanding of carbon-carbon bond formation by alkyne migratory insertion into manganacycles

Migratory insertion (MI) is one of the most important processes underpinning the transition metal-catalysed formation of C–C and C–X bonds. In this work, a comprehensive model of MI is presented, based on the direct observation of the states involved in the coupling of alkynes with cyclometallated ligands, augmented with insight from computational chemistry. Time-resolved spectroscopy demonstrates that photolysis of complexes [Mn(C^N)(CO)₄] (C^N = cyclometalated ligand) results in ultra-fast dissociation of a CO ligand. Performing the experiment in a toluene solution of an alkyne results in the initial formation of a solvent complex fac-[Mn(C^N)(toluene)(CO)₃]. Solvent substitution gives an η²-alkyne complex fac-[Mn(C^N)(η²-R¹C₂R²)(CO)₃] which undergoes MI of the unsaturated ligand into the Mn–C bond. These data allowed for the dependence of second order rate constants for solvent substitution and first order rate constants for C–C bond formation to be determined. A systematic investigation into the influence of the alkyne and C^N ligand on this process is reported. The experimental data enabled the development of a computational model for the MI reaction which demonstrated that a synergic interaction between the metal and the nascent C–C bond controls both the rate and regiochemical outcome of the reaction. The time-resolved spectroscopic method enabled the observation of a multi-step reaction occurring over 8 orders of magnitude in time, including the formation of solvent complexes, ligand substitution and two sequential C–C bond formation steps.

Time-resolved spectroscopy and computational chemistry have informed a unified model of alkyne migratory insertion, an important processes underpinning the transition metal-catalysed formation of C–C and C–X bonds.

Photoinduced SET to access olefin-acrylate copolymers

Single-electron transfer (SET)-induced decarboxylative backbone radical generation was exploited to produce statistical olefin-acrylate copolymers. Quenching of the backbone radical with an H atom donor yielded ethylene or propylene repeat units.

Telechelic polyethylene, poly(ethylene-co-vinyl acetate) and triblock copolymers based on ethylene and vinyl acetate by iodine transfer polymerization

Various iodo functionalized chain transfer agents (CTAs) were successfully employed in the iodine transfer polymerization (ITP) of ethylene conducted at 80 bars at 70°C in dimethylcarbonate. Comparative studies performed on...

Anthranilamide-protected vinylboronic acid: rational monomer design for improved polymerization/transformation ability providing access to conventionally inaccessible copolymers

We designed a vinyl-boronic-acid protected by anthranilamide as a “transformable” monomer in radical polymerization to synthesize conventionally inaccessible copolymers, such as poly(vinyl alcohol-co-styrene) and poly(ethylene-co-acrylate).

Copolymerization of ethylene with non-vinyl polar monomers

Introduction of functional groups on polyethylene endows it with a higher surface property and thus various catalysts have been developed for the copolymerization of ethylene with polar vinyl monomers. Aside from vinyl monomers, however, other classes of polar monomers have not found application in the copolymerization with ethylene. Here, in this short review article, our latest studies on catalyst development aiming at the use of non-vinyl polar monomers and the properties of the resulting copolymers are summarized.

Polar additive triggered chain walking copolymerization of ethylene and fundamental polar monomers

The use of a polar additive efficiently triggers chain walking copolymerization of ethylene with a broad scope of fundamental polar monomers, which is long-sought in an α-diimine Pd(ii) system.

Design and synthesis of binuclear vanadium catalysts for copolymerization of ethylene and polar monomers

Binuclear vanadium complexes exhibited higher activity than monometallic complexes in ethylene polymerization and afforded UHMWPE. The binuclear catalysts also showed moderate activity in copolymerization with 10-undecen-1-ol and methyl 10-undecenoate.

Crystalline sulfur-functionalized poly(α-olefin) synthesized by scandium-catalyzed coordination polymerization

Combined with organoborate, the scandium complex catalyzed monomers to produce a series of syndiotactic sulfur-functionalized poly(α-olefin)s (rrrr of up to 0.95) which formed crystalline materials with a Tm of up to 91 °C.

Isospecific (co)Polymerization of Unmasked Polar Styrenes by Neutral Rare-earth Metal Catalysts

Syndioselective polymerization of unprotected polar styrenes has achieved great success via specially designed catalysts and establishment of "self-assisted" theory. On contrary, isospecific polymerization of polar styrenes has remained less explored, which needs to break the dilemma of high selectivity and activity of the involved catalysts. Herein, we present new racemic ansa-bis(benz[e]indenyl) rare-earth metal complexes and their high activity and perfect isoselectivity ( mmmm > 99 %) for the polymerization of unmasked polar styrenes without any activators. Moreover, the copolymerizations of para / meta -methoxystyrenes with styrene give gradient and random copolymers, respectively. The insertion rate of polar monomers could be readily tuned in the range of 0-100 mol % by changing their loading ratios. The resultant isotactic polar polystyrenes are quantitatively transformed into hydroxyl or methylsulfonyl polystyrenes with high T g s. DFT calculations reveal the isospecific mechanim.

Living Aqueous Microemulsion Polymerization of Ethylene with Robust Ni(II) Phosphinophenolato Catalysts

Due to chain transfer events being competitive with chain growth, ethylene polymerization by P,O-chelated Ni(II) complexes usually affords low molecular weight polymers or oligomers. We now show that appropriately bulky substituted phosphinophenolato Ni(II) can polymerize in a living fashion, virtually devoid of chain transfer. Aqueous polymerizations with microemulsions of [κ²-P,O-2-(2-(2',6'-(MeO)₂C₆H₃)C₆H₄)(Ph)P-6-(3',5'-(CF₃)₂C₆H₃)C₆H₃O-NiMe(pyridine)] (3) at 30 °C yield polyethylenes with narrow molecular weight distributions (M_w/M_n 1.02 to 1.34) and ultrahigh molecular weights (up to 2 × 10⁶) in the form of aqueous nanoparticle dispersions. Catalyst stability and activity are maintained up to 70 °C in water.

Terpolymerization of Ethylene and Two Different Methoxyaryl-Substituted Propylenes by Scandium Catalyst Makes Tough and Fast Self-Healing Elastomers

The terpolymerization of a non-polar olefin (such as ethylene) and two different polar functional olefins in a controlled fashion is of great interest and importance but has hardly been explored to date. We report for the first time the terpolymerization of ethylene (E) and two different methoxyaryl-substituted propylenes (A^R1 P=hexylanisyl propylene; A^R2 P=methoxynaphthyl propylene or methoxypyrenyl propylene) by a half-sandwich scandium catalyst. The terpolymerization took place in a sequence-controlled fashion, affording unique multi-block copolymers composed of two different ethylene-alt-methoxyarylpropylene sequences E-alt-A^R1 P (soft segments) and E-alt-A^R2 P (hard segments) and relatively short ethylene-ethylene (EE) blocks (crystalline segments). The terpolymers exhibited excellent elasticity and unprecedented self-healing as a result of microphase separation of nanodomains of the crystalline EE segments and the hard amorphous E-alt-A^R2 P segments from a very flexible E-alt-A^R1 P matrix, demonstrating unique synergy of the three different components.

One-Pot Synthesis of Polyethylene-Based Block Copolymers via a Dual Polymerization Pathway

Polyethylene-poly(methyl acrylate) multiblock copolymers were obtained using a catalyst system consisting of a pentamethylcyclopentadienyl cobalt complex (Co^III(η⁵-C₅H₅)P(OMe)₃I₂) and iso-butyl modified methylaluminoxane (MMAO). As the chain-growth mechanism, the self-switching between organometallic-mediated radical polymerization (OMRP) and coordination-insertion polymerization (CIP) is suggested. As a possible polymerization mechanism, we propose that (1) the methyl and iso-butyl groups transfer from Al to Co and the single methyl acrylate (MA) unit insertion into the Me-Co and H-Co allows for the in situ formation of Co-C(COOMe) bonds as an initiator for OMRP of MA, (2) the migratory insertion of ethylene into Co-C(COOMe) bonds leads to the formation of an alkyl-Co species as active species for CIP of ethylene, and (3) MA insertion to the alkyl-Co to regenerate a Co-C(COOMe) bond. The architectures of copolymers were confirmed by various nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), and size-exclusion chromatography (SEC) analyses.