ETHYLENE POLYMERIZATION AND COPOLYMERIZATION WITH POLAR MONOMERS BY A NEUTRAL NICKEL CATALYST COMBINED WITH CO-CATALYST OF Ni(COD)_2 OR AL(i-Bu)_3

A neutral nickel(Ⅱ)catalyst D,{[O-(3-cyclohexyl)(5-Cl)C_6H_2-ortho-C(H)=N-2,6-C_6H_3(i-Pr)_2]Ni(Ph_3P)(Ph)}hasbeen synthesized and characterized by IH-NMR,FTIR and elemental analysis.The results indicate that Al(i-Bu)_3 is aneffective cocatalyst for the neutral nickel catalyst.With bis(1,5-cyclooctadiene)nickel(0)[Ni(COD)_2]or Al(i-Bu)_3 as a co-catalyst,the neutral nickel catalyst D is active for ethylene polymerisation and copolymerisation with polar monomers(tert-butyl 10-undecenoate(BU),methyl 10-undecenoate(MU),allyl alcohol(AA)and 4-penten-1-ol(PO))under mild conditions.The resulting polymers were characterized by (?)H-NMR,FTIR,DSC,and GPC.From the comparative studies,Ni(COD)_2 ismore active than Al(i-Bu)_3 for ethylene homopolymerization,while Al(i-Bu)_3 is more effective than Ni(COD)_2 for ethylenecopolymerisation with polar monomers.The polymerization parameters which affect both the catalytic activity and propertiesof the resulting polyethylene were investigated in detail.Under the conditions of 20 μmol catalyst D and Ni(COD)_2/D=3(molar ratio) in 30 mL toluene solution at 45℃,12×105 Pa ethylene for 20 min,the polymerization activity reaches ashigh as 7.29×105 gPE.(mol.Ni.h)^(-1) and M_η,is 7.16×104 g.mol^(-1).For ethylene copolymerization with polar monomers,theeffect of comonomer concentrations was examined.As high as 0.97 mol% of MU,1.06 mol% of BU,1.04 mol% of AA and1.37 mol% of PO were incorporated into the polymer,respectively,catalyzed by D/Al(i-Bu)_3 system.

Phosphine/Benzocyclone-based Neutral Nickel Catalysts for Ethylene Polymerization and Copolymerization with Polar Monomers

The efficient copolymerization of olefin with polar monomers using nickel-based catalysts presents a longstanding challenge. In this contribution, three phosphine-benzocyclone ligands and corresponding neutral nickel catalysts(Ni1: Ar = Ph;Ni2: Ar = 2-(C_(6)H_(5))C_(6)H_(4);Ni3: Ar = 2-[2',6'-(Me O)_(2)-C_(6)H3]C_(6)H_(4)) were prepared and applied for the ethylene polymerization and copolymerization with polar monomers without any cocatalyst. The bulky substituent groups in complexes Ni2 and Ni3 contributed to high catalytic activities(up to 7.24×10^(6) and 9.04×10^(6)g·mol Ni^(-1)·h^(-1), respectively), and produced high-molecular-weight polyethylene(Mw up to 545.7 k Da). Complex Ni3 exhibited high activities for ethylene polymerization at the level of 10^(6) g·mol Ni^(-1)·h^(-1) across a wide range from 30 ℃ to 120 ℃, exhibiting excellent high temperature tolerance. These nickel complexes were also effectively employed in the copolymerization of ethylene with methyl acrylate, ethyl acrylate, butyl acrylate and lauryl acrylate, producing copolymers with high molecular weights(Mw up to 80.5 k Da) and high polar monomer incorporation(up to 8.2 mol%). Microstructure analyses revealed that the introduction of large sterically hindered substituents facilitated the incorporation of polar functional units into the polymer backbone. This study demonstrates the potential of these nickel-based catalysts for efficient copolymerization of olefin with polar monomers.

A“Catalyst+Support”Strategy for Salicylaldimine Nickel Catalyzed Ethylene Polymerization and Copolymerization with Polar Monomers

Polyolefins,as one of the most productive synthetic polymer materials,have been widely used in industry and daily life[1-2].However,due to their"non-polar"nature,polyolefins have poor compatibility and adhesion to polar materials,limiting their application in many fields[3-5].

Enhancement on Hemilabile Phosphine-Amide Palladium and Nickel Catalysts for Ethylene(Co)Polymerization with Polar Monomers Using a Cyclizing Strategy

To address the issue of hemilabile catalyst in olefin polymerization catalysis, a cyclizing strategy was used to construct novel N-bridged phosphine-carbonyl palladium and nickel catalysts, resulting in improvements on ethylene(co)polymerizations. The N-bridged phosphinecarbonyl Pd catalysts(Pd1-Pd5) and Ni catalysts(Ni1-Ni5) bearing five-to eight-membered-ring structures were designed and synthesized.Catalytic performance for ethylene(co)polymerization became better as the size of N-containing bridge increased. The seven-membered-ring bridged catalysts Pd4 and Ni4 exhibited the best performance in terms of catalytic activity, polymer molecular weight and incorporation of acrylates and acrylic acid. The better performance of these catalysts bearing larger-size bridges was tentatively attributed to the methyleneinduced higher electron density around nitrogen, which strenghtens the coordination of carbonyl group to metal center, and also to the steric effect offered by this cyclization. This work provides a new strategy to enhance hemilabile polymerization catalysts.

Efficient Copolymerization of Ethylene with Polar Divinyl Monomer by Phosphino-Phenolate Nickel Catalyst

Direct copolymerization of olefin with polar monomers via a coordination-insertion mechanism appears as the most efficient and at-tractive method to prepare functionalized polyolefins.Herein,we carried out direct copolymerization of ethylene and allyl acrylate by a bulky phosphino-phenolate nickel catalyst,in which high-molecular-weight copolymers bearing polar five-membered and six-membered ring structures were afforded.Comprehensive NMR and FT-I R analyses revealed multiplex structure of the obtained copolymers,in which both the noncyclic structural units bearing pendant allyl moiety(A)as well as acrylate moiety(B)and the cyclic structural units,y-butyrolactones(C)andδ-valerolactone(D)were found.Exhilaratingly,the content of different structural units of the produced copolymer could be tuned by adjusting the concentration of the comonomer.Moreover,we also proved that the nick-el-based catalyst could produce related copolymers with significantly enhanced copolymer molecular weights in the copolymeriza-tion of allyl acrylate and ethylene compared with the palladium-based catalyst under the same conditions.

Research on poly(styrene-acrylic acid)-supported neodymium complex in catalytic copolymerization of styrene and 4-vinylpyridine

The catalytic activity of poly（styrene-acrylic acid） （PSAA） supported neodymium chloride （NdCl3） complex for the copolymerization of styrene and 4-Vinylpyridine was studied. The influence of various factors, such as Al/Nd molar ratio, reaction time, macromolecular carder （PSAA）, and ratio of styrene to 4-vinypyridine （g/g）, on the copolymerization yield of styrene and 4-Vinylpyridine was investigated. The results showed that the copolymerization of polar monomers with olefins occurred efficiently and the catalytic activity of polymer-supported catalyst was higher than that of the similar small molecular catalysts. The activity of PSAA.Nd complex increased with in- creasing Al/Nd molar ratios and decreased with increasing polymerization time. The highest activity of PSAA＇Nd was observed at 120 min, and the highest yield was found at the ratio of styrene to 4-vinylpyridine of 4：2. DSC analysis presented that the resulted polymer had only one glass transition temperature, and showed very good thermal stability.

Research on Poly(Styrene-Crylicacid)-Suported Neodymium Complex Catalytic Copolymerization of Styrene and 4-Vinylpyridine

The catalytic activity of poly（styrene-cryli- caeid） （PSAA） supported neodymium chloride （NdCl3） complex for the copolymerization of styrene and 4-vinylpyridine was studied. The influence of various factors, such as Al/Nd molar ratio, reaction time, and ratio of styrene to 4-vinypyridine （g· g^-1 ）, on copolymerization of styrene and 4-Vinylpridine was investigated. The results show that the copolymerization of polar monomers with olefins occurs efficiently. The catalytic activity of polymer-supported catalyst is higher than that of the similar small molecule catalysts. The activity of PSAA· Nd complex increases with increasing Al/Nd ratios and decreases with increasing polymerization time, the highest activity of PSAA· Nd is observed at 120 min. High yield is found at the ratio of styrene to 4-vinylpyridine is 4：2. The resulted polymer shows very good thermal stability.

Lewis pairs polymerization of polar vinyl monomers

The globally increasing demands for polymer materials stimulate the significantly intense attention focused on the Lewis pair polymerization(LPP) of various polar vinyl monomers catalyzed by Lewis pairs(LPs) composed of Lewis acid(LA) and Lewis base(LB). According to the degree of interaction between LA and LB, LPs could be divided into classical Lewis adduct(CLA), interacting Lewis pair(ILP) and frustrated Lewis pair(FLP). Regulation of the Lewis basicity, Lewis acidity, and steric effects of these LPs has a significant impact on the polymer chain initiation, propagation and termination as well as chain transfer reaction during polymerization. Compared with other polymerization strategies, LPP has shown several unique advantages towards the polymerization of polar vinyl monomers such as high activity, control or livingness, mild conditions, and complete chemo-or regioselectivity. We will comprehensively review the recent advances achieved in the LPP of polar vinyl monomers according to the classification of the employed LPs based on different LAs, by highlighting the key polymerization results, polymerization mechanisms as well as the currently unmet challenges and the future research directions of LPP chemistry.

Synthesis of Ultra-High-Molecular-Weight Polyethylene by Transition-Metal-Catalyzed Precipitation Polymerization

Ultra-high-molecular-weight polyethylene(UHMWPE)plays an important role in many important fields as engineering plastics.In this contribution,a precipitation polymerization strategy is developed by combination of highly active phosphino-phenolate nickel catalysts with polymer-insoluble solvent(heptane)to access UHMWPE(Mn up to 8.3×10^(6)g mol^(-1))with good product morphology,free-flowing characteristics,and great mechanical properties.Compared with the academically commonly used aromatic solvent(toluene),the utilization of heptane offers simultaneous enhancement in important parameters including activity,polymer molecular weight,and catalyst thermal stability.This system can also generate polar functionalized UHMWPE with molecular weight of up to 1.6×10^(6)g mol^(-1)in the copolymerization of ethylene with polar comonomers.More importantly,this precipitation polymerization strategy is generally applicable to several representative transition metal catalyst systems,leading to UHMWPE synthesis with good product morphology control.

Dual roles of trifluoroborate in nickel-catalyzed ethylene polymerization:Electronic perturbation and anchoring for heterogenization

Brookhart-typeα-diimine nickel and palladium catalysts have been extensively studied over the past several decades;however,the heterogenization of these metal complexes has received much less attention.In this contribution,we installed a trifluoroborate potassium substituent on anα-diimine framework.The ionic nature of trifluoroborate potassium endowed theα-diimine nickel complex with a strong affinity for the SiO_(2)support,while its electron-donating nature enhanced the catalyst stability and polyethylene molecular weight.In the presence of only 100 equiv.of Et2AlCl cocatalyst,the SiO_(2)-supported catalyst demonstrated significantly better performance than its homogeneous analog during ethylene polymerization,with extremely high activity(1.42–6.53×10^(7)g mol^(−1)h^(−1))and high thermal stability.The heterogeneous system led to the formation of high-molecular-weight polyethylenes(Mn 142,500–732,800 g/mol),narrow polydispersities(2.18–3.00),tunable branching densities(21–64 per 1000 carbon atoms),and great mechanical properties.Moreover,the efficient copolymerization of ethylene with comonomers such as methyl 10-undecenoate,6-chloro-1-hexene or 5-hexenylacetate was achieved.These superior properties enabled by the trifluoroborate potassium moiety may inspire its applications in other polymerization catalyst systems.

Synthesis of Hydroxy-functionalized Ultrahigh Molecular Weight Polyethylene Using Fluorenylamidotitanium Complex

Copolymerizations of ethylene and 1-dodecene were conducted with a series of ansa-fluorenylamidodimethyltitanium complexes, [t-BuNSiMe2Flu]TiMe2（1a）, [t-BuNSiMe2（2,7-^tBu2Flu）]TiMe2（1 b）, and [（1-adamantyl）NSiMe2（2,7-^tBu2Flu）]TiMe2（1c） activated by modified methylaluminoxane. The activity increased by the introduction of the alkyl groups on the fluorenyl and amido ligands, and 1c produced the highest molecular weight copolymers. Complex 1c also promoted copolymerization of ethylene and ^iBu3 Al protected 10-undecen-1-ol with high activity（～2000 kg·mol^-1·h^-1）, affording hydroxy-functionalized ultrahigh molecular weight polyethylene. The hydroxy content of the copolymers obtained was controllable by changing comonomer feed ratio. The introduction of a small amount of hydroxy group can alter the surface properties of polyethylene.

Photoresponsive α-Diimine Nickel Modulated Ethylene (Co)Polymerization

Beyond the single ligand electronic and/or steric modifications, external stimuli are a useful tool for modulating catalytic polymerization reactions. Light stands out from external stimuli, but the corresponding photoresponsive transition metal catalysts are significantly rare for olefin polymerization due to the difficult synthesis. In this contribution, in consideration of the key role of steric shielding on the axial sites, we installed four concerted azobenzene moieties into symmetrically terphenyl-based α-diimine Ni(II) complexes to prepare photoresponsive catalysts, which were applied to ethylene polymerization and copolymerization with polar monomer. Via the trans-cis isomerization of azobenzene-functionalized Ni(II) catalysts in dark or under UV light, catalytic activity, polymer molecular weight, branching density, incorporation of co-monomer, and even the ratio of branching pattern were significantly modulated in ethylene (co)polymerizations. This photo-controlled strategy behaved an opposite influence between ethylene polymerization and copolymerization, in terms of catalytic activity and polymer molecular weight. As a result, slightly branched ultrahigh molecular weight polyethylenes and high molecular weight functionalized polyethylenes were produced at ambient conditions.

Benzosuberyl Substituents as a"Sandwich-like"Function in Olefin Polymerization Catalysis

For the rational design of metal catalyst in olefin polymerization catalysis,various strategies were applied to suppress the chain transfer by bulking up the axial positions of the metal center,among which the"sandwich"type turned out to be an eficient category in achieving high molecular weight polyolefin.In the a-dimine system,the"sandwich"type catalysts were built using the typical 8-aryl-naphthyI framework.In this contribution,by introducing the rotationally restrained benzosuberyl substituent into the ortho-position of N-aryl rings,a new class of "sandwich-like"a-diimine nickel catalysts was constructed and fully identified.The rotationally restrained benzosuberyl substituents played a"sandwich-like"function by capping the nickel center from two axial sites.Compared to the nickel catalyst Ni1 bearing freely rotated benzhydryl substituent,Ni2 featuring benzosubery|substituent enabled the increase(8 times)of polymer molecular weights from 8 kDa to 65 kDa in the polymerization of ethylene.By further increasing the steric bulk of another ortho-site of the N-aryl ring,the polymer molecular weight even reached an ultrahigh level of 833 kDa(Mw=1857 kDa)using the optimized Ni3.Notably,these nickel catalysts could also mediate the copolymerization of ethylene with methyl 10-undecenoate,with Ni3 giving the highest copolymer molecular weight(88 kDa)and the highest incorporation of comonmer(2.0 mol1%),along with high activity of up to 10^(5)g·mol^(-1)·h^(-1).

Influence of Backbone and Axial Substituent of Catalyst onα-Imino-ketone Nickel Mediated Ethylene(Co)Polymerization

Theα-imino-ketone nickel catalyst is an emerging versatile platform that is easy to prepare and allows for the production of branched high molecular weight functionalized polyethylenes.However,study on this catalyst system is rare thus far.In this contribution,by introducing different backbones,flexible and rigid axial substituents into theα-imino-ketone framework,a family of cationic nickel catalysts were synthesized and fully characterized.Without the addition of any activator,systematic studies on ethylene polymerization and copolymerization with polar monomers were performed to explore the influence of both backbone and axial substituent on catalytic activity,polymer molecular weight,branching density and incorporation.In particular,owing to the unique semi-opening feature of theα-imino-ketone framework,the preferred nickel catalyst exhibited high activity of 175 kg·mol^(-1)·h^(-1)to produce functionalized polyethylene with molecular weight of 13.4 kg·mol^(-1)and comonomer incorporation of 2.9 mol%.

Synthesis of Block Copolymers of 2-Ethylhexyl Methacrylate, n-Hexyl Methacrylate and Methyl Methacrylate via Anionic Polymerization at Ambient Temperature

It still remains a concern to break through the bottlenecks of anionic polymerization of polar monomers, such as side reactions, low conver- sion and low temperature （-78 ℃）. In this work, potassium tert-butoxide （t-BuOK） was chosen to initiate the anionic polymerization of 2-ethylhexyl methacrylate （EHMA） in tetrahydrofuran. The conversions were above 99% at 0 or 30 ℃, and above 95% at 60 ℃ without side reaction inhibitors. The high conversions implied t-BuOK could suppress the side reactions. A series of block copolymers of EHMA, n-hexyl methacrylate （HMA） and methyl methacrylate （MMA） were further synthesized at 0 ℃, and the conversions were all above 99%. The GPC and IH NMR results confirmed the successful synthesis of the block copolymers. The molecular size of monomer and the state of t-BuOK （free ion pairs or aggregates） remarkably affected the polymerization rates and the molecular structures of the products. The DMA results indicated that the glass transition temperatures of PEHMA or PHMA block and PMMA block were 20 ℃ and 60 ℃, respectively, which deviated from -2 ℃ and 105 ℃ of homopolymer, respectively, due to the partial com- patibility of the blocks. This work explored a route of the anionic polymerization of polar monomers at room temperature.

Direct Synthesis of Ultrahigh Molecular Weight Functionalized Isotactic Polypropylene

Ultrahigh molecular weight functionalized isotactic polypropylene(f-UHMW-iPP)through the direct copolymerization of propylene with polar monomers is highly desirable but has not been accessed thus far because it involves challenging regio-and stereochemistry along with usually reduced molecular weight.Herein,in contrast to the unsuccessful catalyst strategy,a polar monomer-assisted strategy is used to access the above material.The introduction of O-or S-functionalized long-chain polar olefins into the hafnium-catalyzed copolymerization of propylene(and bulkierα-olefins)significantly increases the copolymer molecular weight with a maximum observed increase of+488%.f-UHMW-iPP and functionalized isotactic poly(α-olefin)s(M_(w)>2000 kDa,[mmmm]:99%)are thus prepared at ambient conditions.The incorporation of 1 mol%of polar monomer improves the surface property and significantly increases the long-sought toughness(860%)of brittle iPP,without reducing the tensile strength(42 MPa)due to the key achievement of ultrahigh molecular weight.A discussion of the mechanism involved in the beneficial effects of incorporating the polar monomer is herein presented by an in-depth density functional theory calculation.