Ethylene/α‐olefin copolymerization with bis(β‐enaminoketonato) titanium complexes activated with modified methylaluminoxane

Copolymerizations of ethylene with α‐olefins (i.e., 1‐hexene, 1‐octene, allylbenzene, and 4‐phenyl‐1‐butene) using the bis(β‐enaminoketonato) titanium complexes [(Ph)NC(R₂)CHC(R₁)O]₂TiCl₂ ( 1a : R₁ = CF₃, R₂ = CH₃; 1b : R₁ = Ph, R₂ = CF₃; and 1c : R₁ = t‐Bu, R₂ = CF₃), activated with modified methylaluminoxane as a cocatalyst, have been investigated. The catalyst activity, comonomer incorporation, and molecular weight, and molecular weight distribution of the polymers produced can be controlled over a wide range by the variation of the catalyst structure, α‐olefin, and reaction parameters such as the comonomer feed concentration. The substituents R₁ and R₂ of the ligands affect considerably both the catalyst activity and comonomer incorporation. Precatalyst 1a exhibits high catalytic activity and produces high‐molecular‐weight copolymers with high α‐olefin insertion. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6323–6330, 2005     

Quasi‐living copolymerization of ethylene with 1‐hexene by heteroligated (salicylaldiminato β‐enaminoketonato) titanium complexes

A series of heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐Bu^t‐2‐OC₆H₃CH = N(C₆F₅)] [PhN = C(R₁)CHC(R₂)O]TiCl₂ [ 3a : R₁ = CF₃, R₂ = ^tBu; 3b : R₁ = Me, R₂ = CF₃; 3c : R₁ = CF₃, R₂ = Ph; 3d : R₁ = CF₃, R₂ = C₆H₄Ph(p ); 3e : R₁ = CF₃, R₂ = C₆H₄Ph(o ); 3f : R = CF₃, R₂ = C₆H₄Cl(p ); 3g : R₁ = CF₃; R₂ = C₆H₃Cl₂(2,5); 3h : R₁ = CF₃, R₂ = C₆H₄Me(p )] were investigated as catalysts for ethylene (co)polymerization. In the presence of modified methylaluminoxane as a cocatalyst, these complexes showed activities about 50%–1000% and 10%–100% higher than their corresponding bis(β‐enaminoketonato) titanium complexes for ethylene homo‐ and ethylene/1‐hexene copolymerization, respectively. They produced high or moderate molecular weight copolymers with 1‐hexene incorporations about 10%–200% higher than their homoligated counterpart pentafluorinated FI‐Ti complex. Among them, complex 3b displayed the highest activity [2.06 × 10⁶ g/mol_Ti?h], affording copolymers with the highest 1‐hexene incorporations of 34.8 mol% under mild conditions. Moreover, catalyst 3h with electron‐donating group not only exhibited much higher 1‐hexene incorporations (9.0 mol% vs. 3.2 mol%) than pentafluorinated FI‐Ti complex but also generated copolymers with similar narrow molecular weight distributions (M _w/M _n = 1.20–1.26). When the 1‐hexene concentration in the feed was about 2.0 mol/L and the hexene incorporation of resultant polymer was about 9.0 mol%, a quasi‐living copolymerization behavior could be achieved. ¹H and ¹³C NMR spectroscopic analysis of their resulting copolymers demonstrated the possible copolymerization mechanism, which was related with the chain initiation, monomer insertion style, chain transfer and termination during the polymerization process. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2787–2797     

Living copolymerization of ethylene with norbornene mediated by heteroligated (Salicylaldiminato)(β‐enaminoketonato)titanium catalysts

Three heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐Bu^t‐2‐OC₆H₃CH?N(C₆F₅)][(p‐XC₆H₄)N?C(Bu^t)CHC(CF₃)O]TiCl₂ ( 3a : X = F, 3b : X = Cl, 3c : X = Br) were synthesized and investigated as the catalysts for ethylene polymerization and ethylene/norbornene copolymerization. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts exhibited high activities toward ethylene polymerization, similar to their parallel parent catalysts. Furthermore, they also displayed favorable ability to efficiently incorporate norbornene into the polymer chains and produce high molecular weight copolymers under the mild conditions, though the copolymerization of ethylene with norbornene leads to relatively lower activities. The sterically open structure of the β‐enaminoketonato ligand is responsible for the high norbornene incorporation. The norbornene concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resulting copolymer. When the norbornene concentration in the feed is higher than 0.4 mol/L, the heteroligated catalysts mediated the living copolymerization of ethylene with norbornene to form narrow molecular weight distribution copolymers (M_w/M_n < 1.20), which suggested that chain termination or transfer reaction could be efficiently suppressed via the addition of norbornene into the reaction medium. Polymer yields, catalytic activity, molecular weight, and norbornene incorporation can be controlled within a wide range by the variation of the reaction parameters such as comonomer content in the feed, reaction time, and temperature. ©2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6072–6082, 2009     

Novel vanadium(III) complexes with tridentate phenoxy‐phosphine [O,P(O),O] ligands: Synthesis,characterization, and catalytic behavior of ethylene polymerization and copolymerization with 10‐undecen‐1‐ol

A series of novel vanadium(III) complexes bearing tridentate phenoxy‐phosphine [O,P,O] ligands and phosphine oxide‐bridged bisphenolato [O,P?O,O] ligands, which differ in the steric and electronic properties, have been synthesized and characterized. These complexes were characterized by Fourier transform infrared spectroscopy (FTIR) and mass spectra as well as elemental analysis. Single‐crystal X‐ray diffraction revealed that complexes 3c and 4e adopt an octahedral geometry around the vanadium center. In the presence of Et₂AlCl as a cocatalyst, these complexes displayed high catalytic activities up to 22.8 kg PE/mmol_V.h.bar for ethylene polymerization, and produced high‐molecular‐weight polymers. Introducing additional oxygen atom on phosphorus atom of [O,P,O] ligands has resulted in significant changes on the aspect of steric/electronic effect, which has an impact on polymerization performance. 3c and 4c /Et₂AlCl catalytic systems were tolerant to elevated temperature (70 °C) and yielded unimodal polyethylenes, indicating the single‐site behavior of these catalysts. By pretreating with equimolar amounts of alkylaluminums, functional α‐olefin 10‐undecen‐1‐ol can be efficiently incorporated into polyethylene chains. 10‐Undecen‐1‐ol incorporation can easily reach 14.6 mol % under the mild conditions. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature, Al/V (molar ratio), and comonomer concentration, are also examined in detail. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Copolymerization of ethylene and cyclopentene with bis(β‐enaminoketonato) titanium complexes

The copolymerizations of ethylene and cyclopentene with bis(β‐enaminoketonato) titanium complexes {[(Ph)NC(R₂)CHC(R₁)O]₂TiCl₂; R₁ = CF₃ and R₂ = CH₃ for 1a , R₁ = Ph and R₂ = CF₃ for 1b ; and R₁ = t‐Bu and R₂ = CF₃ for 1c } activated with modified methylaluminoxane (MMAO) as a cocatalyst were investigated. High‐molecular‐weight copolymers with cis‐1,2‐cyclopentene units were obtained. The catalyst activity, cyclopentene incorporation, polymer molecular weight, and polydispersity could be controlled over a wide range through the variation of the catalyst structure and reaction parameters, such as the Al/Ti molar ratio, cyclopentene feed concentration, and polymerization reaction temperature. The complex 1b /MMAO catalyst system exhibited the characteristics of a quasi‐living ethylene polymerization and an ethylene–cyclopentene copolymerization and allowed the synthesis of polyethylene‐block‐poly(ethylene‐co‐cyclopentene) diblock copolymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1681–1689, 2005     

New tethered ansa‐bridged zirconium catalysts: Insights into the “self‐immobilization” mechanism

New ω‐alkenyl‐substituted ansa‐bridged bisindenyl zirconium complexes are prepared and tested as self‐immobilized catalysts for ethene polymerization. But, even at very high concentration of the tethered complexes and low pressure of ethene, there is no evidence of their insertion into the polyethene chain. A “cross polymerization” test, performed by copolymerizing the tethered complexes with ethene using rac‐Me₂Si(2‐MeBenzInd)₂ZrCl₂ ( MBI ), does not lead to their incorporation into the polyethene chain. However, the corresponding ligand proves to be a suitable comonomer for ethene, and, through copolymerization promoted by MBI, innovative poly(ethene‐co‐2,2′‐bis[(1H‐inden‐3′‐yl)‐hex‐5‐ene) copolymers are prepared and characterized by ¹³C NMR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Half‐titanocene complexes bearing dianionic 6‐benzimidazolylpyridyl‐2‐carboximidate ligands: Synthesis,characterization, and their ethylene polymerization

6‐Benzimidazolylpyridyl‐2‐carboximidic half‐titanocene complexes, Cp′TiLCl (Cp′ = C₅H₅, MeC₅H₄, C₅Me₅, L = 6‐benzimidazolylpyridine‐2‐carboxylimidic, C1–C13 ), were synthesized and characterized along with single‐crystal X‐ray diffraction. The half‐titanocene chlorides containing substituted cyclopentadienyl groups, especially pentamethylcyclopentadienyl groups were more stable, while those without substituents on the cyclopentadienyl groups were easily transformed into their dimeric oxo‐bridged complexes, (CpTiL)₂O ( C14 and C15 ). In the presence of excessive amounts of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all half‐titanocene complexes showed high catalytic activities for ethylene polymerization. The substituents on the Cp groups affected the catalytic behaviors of the complexes significantly, with less substituents favoring increased activities and higher molecular weights of the resultant polyethylenes. Effects of reaction conditions on catalytic behaviors were systematically investigated with catalytic systems of mononuclear C1 and dimeric C14 . With C1 /MAO, large MAO amount significantly increases the catalytic activity, while the temperature only has a slight effect on the productivity. In the case of C14 /MAO catalytic system, temperature above 60 °C and Al/Ti value higher than 5000 were necessary to observe good catalytic activities. In both systems, higher reaction temperature and low cocatalyst amount gave the polyethylenes with higher molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3396–3410, 2008     

Ethylene–propylene copolymerization with bis(β‐enaminoketonato) titanium complexes activated with modified methylaluminoxane

Ethylene–propylene copolymerization, using [(Ph)NC(R₂)CHC(R₁)O]₂TiCl₂ (R₁ = CF₃, Ph, or t‐Bu; R₂ = CH₃ or CF₃) titanium complexes activated with modified methylaluminoxane as a cocatalyst, was investigated. High‐molecular‐weight ethylene–propylene copolymers with relatively narrow molecular weight distributions and a broad range of chemical compositions were obtained. Substituents R₁ and R₂ influenced the copolymerization behavior, including the copolymerization activity, methylene sequence distribution, molecular weight, and polydispersity. With small steric hindrance at R₁ and R₂, one complex (R₁ = CF₃; R₂ = CH₃) displayed high catalytic activity and produced copolymers with high propylene incorporation but low molecular weight. The microstructures of the copolymers were analyzed with ¹³C NMR to determine the methylene sequence distribution and number‐average sequence lengths of uninterrupted methylene carbons. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5846–5854, 2006     

Comparison of the C1‐symmetric diastereoisomers of a zirconocene‐based catalyst in ethylene polymerization: A benzyl substituent as a regulator in branch formation

C₁‐symmetric diastereoisomers of a zirconocene dichloride, SiMe₂(3‐benzylindenyl)(indenyl)ZrCl₂, known as catalyst precursors used to produce polypropylenes with similar molecular weights and tacticities, have been investigated in ethylene polymerization. Activated by methylaluminoxane, they produce microstructurally different polymers: high‐density polyethylene and linear low‐density polyethylene, the latter characterized by the presence of ethyl branches. The formation of branches is relevant in the complex having a sterically more crowded (inward) site. A comparison with the complex without substituents, meso‐SiMe₂(indenyl)₂ZrCl₂, shows that the presence of a benzyl group on only one of the two indenyl moieties can regulate the number of branches and the molecular weight of the macromolecule. Actually, the unsubstituted complex is able to give double the number of branches and lower molecular weights, whereas the C₁‐symmetric disubstituted complexes previously reported generally give linear polyethylene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3551–3555, 2006     

Ethylene polymerization and ethylene/hexene copolymerization with vanadium(III) catalysts bearing heteroatom‐containing salicylaldiminato ligands

A series of novel vanadium(III) complexes bearing heteroatom‐containing group‐substituted salicylaldiminato ligands [RN?CH(ArO)]VCl₂(THF)₂ (Ar = C₆H₄, R = C₃H₂NS, 2a ; C₇H₄NS, 2c ; C₇H₅N₂, 2d ; Ar = C₆H₂tBu₂ (2,4), R = C₃H₂NS, 2b ) have been synthesized and characterized. Structure of complex 2c was further confirmed by X‐ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et₂AlCl. Complexes 2a–d exhibited high catalytic activities (up to 22.8 kg polyethylene/mmol_V h bar), and affording polymer with unimodal molecular weight distributions at 25–70 °C in the first 5‐min polymerization, whereas produced bimodal molecular weight distribution polymers at 70 °C when polymerization time prolonged to 30 min. The catalyst structure plays an important role in controlling the molecular weight and molecular weight distribution of the resultant polymers produced in 30 min polymerization. In addition, ethylene/hexene copolymerizations with catalysts 2a–d were also explored in the presence of Et₂AlCl, which leads to the high molecular weight and unimodal distributions copolymers with high comonomer incorporation. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled over a wide range by the variation of catalyst structure and the reaction parameters, such as comonomer feed concentration, polymerization time, and polymerization reaction temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3573–3582, 2009     

Living regioselective copolymerization of ethylene with nonconjugated bicyclic dienes using (salicylaldiminato)(β‐enaminoketonato) titanium catalysts

A series of heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐^tBu‐2‐OC₆H₃CH?N(C₆F₅)] [PhN?C(CF₃)CHCRO]TiCl₂ [ 3a : R = Ph, 3b : R = C₆H₄Cl(p), 3c : R = C₆H₄OMe(p), 3d : R = C₆H₄Me(p), 3e : R = C₆H₄Me(o)] were synthesized and characterized. Molecular structures of 3b and 3c were further confirmed by X‐ray crystallographic analyses. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts displayed favorable ability to incorporate 5‐vinyl‐2‐norbornene (VNB) and 5‐ethylidene‐2‐norbornene (ENB) into the polymer chains, affording high‐molecular weight copolymers with high‐comonomer incorporations and alternating sequence under the mild conditions. The comonomer concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resultant copolymer. At initial comonomer concentration of higher than 0.4 mol/L, the titanium complexes with electron‐donating groups in the β‐enaminoketonato moiety mediated room‐temperature living ethylene/VNB or ENB copolymerizations. Polymerization results coupled with density functional theory calculations suggested that the highly controlled living copolymerization is probably a consequence of the difficulty in chain transfer of VNB (or ENB)‐last‐inserted species and some characteristics of living ethylene polymerization under limited conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Titanium tetrachloride supported on atom transfer radical polymerized poly(methyl acrylate‐co‐1‐octene) as catalyst for ethylene polymerization

Ethylene polymerizations were performed using catalyst based on titanium tetrachloride (TiCl₄) supported on synthesized poly(methyl acrylate‐co‐1‐octene) (PMO). Three catalysts were synthesized by varying TiCl₄/PMO weight ratio in chlorobenzene resulting in incorporation of titanium in different percentage as determined by UV‐vis spectroscopy. The coordination of titanium with the copolymer matrix was confirmed by FTIR studies. The catalysts morphology as observed by SEM was found to be round shaped with even distributions of titanium and chlorine on the surface of catalyst. Their performance was evaluated for atmospheric polymerization of ethylene in n‐hexane using triethylaluminum as cocatalyst. Catalyst with titanium incorporation corresponding to 2.8 wt % showed maximum activity. Polyethylenes obtained were characterized for melting temperature, molecular weight, morphology and microstructure. The polymeric support utilized for TiCl₄ was synthesized using activators regenerated by electron transfer (ARGET) Atom Transfer Radical Polymerization (ATRP) of methyl acrylate (MA) and 1‐octene (Oct) with Cu(0)/CuBr₂/tris(2‐(dimethylamino)ethyl)amine (Me₆TREN) as catalyst and ethyl 2‐bromoisobutyrate (EBriB) as initiator at 80 °C. The copolymer poly(methyl acrylate‐1‐octene; PMO) obtained showed monomodal curve in Gel Permeation Chromatography (GPC) with polydispersity of 1.37 and copolymer composition (¹H NMR; F_MA) of 0.75. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7299–7309, 2008     

Synthesis,structural characterization,and olefin polymerization behavior of vanadium(III) complexes bearing bidentate phenoxy‐phosphine ligands

Vanadium(III) complexes bearing phenoxy‐phosphine ligands ( 2a–g ) (2‐R₁‐4‐R₂‐6‐PPh₂‐C₆H₂O)VCl₂(THF)₂ ( 2a : R₁ = R₂ = H; 2b : R₁ = F, R₂ = H; 2c : R₁ = Ph, R₂ = H; 2d : R₁ = tBu, R₂ = H; 2e : R₁ = R₂ = Me; 2f : R₁ = R₂ = tBu; 2g : R₁ = R₂ = CMe₂Ph) were prepared from VCl₃(THF)₃ by treating with 1.0 equiv of the ligand in tetrahydrofuran (THF) in the presence of excess triethylamine (TEA). The reaction of VCl₃(THF)₃ with 2.0 equiv of the ligand in THF in the presence of excess TEA afforded vanadium(III) complexes bearing two phenoxy‐phosphine ligands ( 3c–f ). These complexes were characterized by FTIR and mass spectrum as well as elemental analyses. Structures of 2f and 3c were further confirmed by X‐ray crystallographic analyses. Complexes 2a–g and 3c–f were employed as the catalysts for ethylene polymerization under various reaction conditions. On activation with Et₂AlCl, these complexes exhibited high catalytic activities (up to 41.3 kg PE/mmol_V·h·bar) even at high temperature (70°C), and produced high molecular weight polymer with unimodal molecular weight distributions, indicating the polymerization took place in a single‐site nature. Complexes 3c–f displayed better thermal stability than the corresponding complexes 2a–g under similar conditions. In addition, copolymerizations of ethylene and 1‐hexene with precatalysts 2a–g were also explored in the presence of Et₂AlCl. Catalytic activity, comonomer incorporation, and properties of the resultant polymers can be controlled over a wide range by tuning catalyst structures and reaction parameters.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ethylene polymerization and ethylene/hexene copolymerization by vanadium(III) complexes bearing bidentate phenoxy‐phosphine oxide ligands

A series of novel vanadium(III) complexes bearing bidentate phenoxy‐phosphine oxide [O,P=O] ligands, (2‐R₁‐4‐R₂‐6‐Ph₂P=O‐C₆H₂O)VCl₂(THF)₂ ( 2a : R₁ = R₂ = H; 2b : R₁ = F, R₂ = H; 2c : R₁ = tBu, R₂ = H; 2d : R₁ = Ph, R₂ = H; 2e : R₁ = R₂ = Me; 2f : R₁ = R₂ = tBu; 2g : R₁ = R₂ = CMe₂Ph) have been synthesized by adding 1 equiv of the ligand to VCl₃(THF)₃ dropwise in the presence of excess triethylamine. Under the same conditions, the adding of VCl₃(THF)₃ to 2.0 equiv of the ligand afforded vanadium(III) complexes bearing two [O,P=O] ligands ( 3c , 3f ). All the complexes were characterized by FTIR and mass spectra as well as elemental analysis. Structures of complexes 2c and 3c were further confirmed by X‐ray crystallographic analysis. On activation with Et₂AlCl and ethyl trichloroacetate, these complexes displayed high catalytic activities for ethylene polymerization (up to 26.4 kg PE/mmol_V·h·bar) even at high reaction temperature (70 °C) indicative of high thermal stability, and produced high molecular weight polymers with unimodal molecular weight distributions. Additionally, the complexes with optimized structure exhibited high catalytic activities for ethylene/1‐hexene copolymerization. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled in a wide range via the variation of catalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and reaction temperature. The monomer reactivity ratios r_E and r_H were determined according to ¹³C NMR spectra, which indicated these complexes preferred ethylene to 1‐hexene in the copolymerization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5298–5306     

Polypropylene and poly(ethylene‐co‐1‐octene) effective synthesis with diamine‐bis(phenolate) complexes: Effect of complex structure on catalyst activity and product microstructure

A series of group 4 metal complexes bearing amine‐bis(phenolate) ligands with the amino side‐arm donor: (μ‐O)[Me₂N(CH₂)₂N(CH₂‐2‐O‐3,5‐tBu₂‐C₆H₂)₂ZrCl]₂ ( 1a ), R₂N(CH₂)₂N(CH₂‐2‐O‐3‐R¹‐5‐R²‐C₆H₂)₂TiCl₂ (R = Me, R¹, R² = tBu ( 2a ), R = iPr, R¹, R² = tBu ( 2b ), R = iPr, R¹ = tBu, R² = OMe ( 2c )), and Me₂N(CH₂)₂N(CH₂‐2‐O‐3,5‐tBu₂‐C₆H₂)(CH₂‐2‐O‐C₆H₄)TiCl₂ ( 2d ) are used in ethylene and propylene homopolymerization, and ethylene/1‐octene copolymerization. All complexes, upon their activation with Al(iBu)₃/Ph₃CB(C₆F₅)₄, exhibit reasonable catalytic activity for ethylene homo‐ and copolymerization giving linear polyethylene with high to ultra‐high molecular weight (600·× 10³–3600·× 10³ g/mol). The activity of 1a /Al(iBu)₃/Ph₃CB(C₆F₅)₄ shows a positive comonomer effect, leading to over 400% increase of the polymer yield, while the addition of 1‐octene causes a slight reduction of the activity of the complexes 2a‐2d . The complexes with the NMe₂ donor group ( 2a , 2d , 1a ) display a high ability to incorporate a comonomer (up to 9–22 mol%), and the use of a bulkier donor group, N(iPr)₂ ( 2b , 2c ), results in a lower 1‐octene incorporation. All the produced copolymers reveal a broad chemical composition distribution. In addition, the investigated complexes polymerized propylene with the moderate ( 1a , 2a ) to low ( 2b‐2d ) activity, giving polymers with different microstructures, from purely atactic to isotactically enriched (mmmm = 28%). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2467–2476     

Ethylene polymerizations,and the copolymerizations of ethylene with hexene or norbornene with highly active mono(β‐enaminoketonato) vanadium(III) catalysts

Five novel vanadium(III) complexes [PhN = C(R₂)CHC(R₁)O]VCl₂(THF)₂ ( 4a : R₁ = Ph, R₂ = CF₃; 4b : R₁ = t‐Bu, R₂ = CF₃; 4c : R₁ = CF₃, R₂ = CH₃; 4d : R₁ = Ph, R₂ = CH₃; 4e : R₁ = Ph, R₂ = H) have been synthesized and characterized. On activation with Et₂AlCl, all the complexes, in the presence of ethyl trichloroacetate (ETA) as a promoter, are highly active precatalysts for ethylene polymerization, and produce high molecular weight and linear polymers. Catalyst activities more than 16.8 kg PE/mmol_V h bar and weight‐average molecular weights higher than 173 kg/mol were observed under mild conditions. The copolymerizations of ethylene and norbornene or 1‐hexene with the precatalysts were also explored, which leads to high molecular weight copolymers with high comonomer incorporation. Catalyst activity, comonomer incorporation, and polymer molecular weight as well as polydispersity index can be controlled over a wide range by the variation of precatalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and polymerization temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2038–2048, 2008     

Strong activation of MgCl2‐supported Ziegler‐Natta catalysts by treatments with BCl3: Evidence and application of the “cluster” model of active sites

Heterogeneous Ziegler‐Natta precatalysts (with phthalate as internal donor) were modified by treatments with BCl₃ (2 h in heptane; T = 20–90 °C; B/Ti = 0.1–5) before their use in the polymerization of propylene to modify the active sites distribution. If performed on previously “detitanated” precatalysts, the treatment leads to a strong increase of productivity (up to one order of magnitude) without drastic modifications of polypropylenes properties (tacticity, molecular weight distribution). In addition, these findings are in good agreement with the hypothesis of a “cluster” organization of active sites allowing to rationalize activation by BCl₃ by formation of heteronuclear B‐Ti clusters. The activation method was also applied to unmodified precatalysts and gave a significant gain of productivity. The simple and versatile activation process can also be performed under mild conditions (low T and low [BCl₃]). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5784–5791, 2009     

Copolymerization of norbornene with ω‐alkenylaluminum as a precursor comonomer for introduction of carbonyl moieties

Norbornene copolymers functionalized with methyl ester group or carboxy group are facilely synthesized by the copolymerization of norbornene and 7‐octenyldiisobutylaluminum (ODIBA) with ansa‐dimethylsilylene(fluorenyl)(t‐butylamido)dimethyltitanium ( 1 ) activated by Ph₃CB(C₆F₅)₄, and the sequential CO₂/methanolysis reactions or CO₂/hydrolysis reactions, respectively. The methanolysis and the hydrolysis are simply switched by engaging acidic methanol or acidic aqueous acetone as the quenching/washing solution, respectively. Meanwhile, the increase of ODIBA in the copolymerization abruptly decreases the yield and number–average molecular weight (M_n) of the product. However, the addition of triisobutylaluminum (8 mM) and the use of excess Ph₃CB(C₆F₅)₄ (twofold of 0.4 mM of 1 ) significantly increase the yield, accompanying the increase in the M_n and the narrowing of the molecular weight distribution (M_w/M_n), especially in the case of the use of excess Ph₃CB(C₆F₅)₄. The yield (g polymer/g monomers), M_n, and M_w/M_n reach up to 0.82, 341,000, and 1.46, respectively, at a copolymerization condition. The carboxy groups in the norbornene copolymers are controlled in the range of 0–1.8 mol % in high polymer yields with high M_n and narrow M_w/M_n accompanied by the decrease in the contact angle with water from 104° to 89°. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5085–5090     

Homo‐ and copolymerization of norbornene derivatives with ethene by ansa‐fluorenylamidodimethyltitanium activated with methylaluminoxane

(t‐BuNSiMe₂Flu)TiMe₂ ( 1 ) activated with Me₃Al‐free methylaluminoxane (dried MAO) which conducts vinyl addition polymerization of norbornene (N) with very high activity was applied for homopolymerization of N derivatives (i.e., 5‐vinyl‐2‐norbornene (5V2N), 5‐ethylidene‐2‐norbornene (5E2N), dicyclopentadiene (DCPD)) at 40 °C. The activities for the N derivatives were about two orders of magnitude lower than that for N and decreased in the following order: 5E2N ? 5V2N ? DCPD. Copolymerization of ethene (E) and 5E2N under an atmospheric pressure of E was then conducted by 1 ‐dried MAO. The copolymerization proceeded with better activity than the homopolymerization of 5E2N and gave poly(E‐co‐5E2N) with narrow molecular weight distribution. The content of the ethylidene group in poly(E‐co‐5E2N) was controlled by the feed ratio of 5E2N/E. The T_g value of the copolymer changed from 70 °C to 155 °C according to the 5E2N content from 27 mol % to 68 mol %. The addition of N as a third monomer to the E‐5E2N copolymerization improved the activity and raised the T_g values of the terpolymer above 200 °C. The content of 5E2N was controlled by the 5E2N/N ratio with keeping the high T_g values. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4581–4587, 2007     

Olefin polymerization and copolymerization by complexes bearing [ONNO]‐Type salan ligands: Effect of ligand structure and metal type (titanium,zirconium, and vanadium)

A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2′‐(OC₆H₃‐5‐t‐Bu)₂‐NHRNH}Cl₂] (Lig¹TiCl₂: R = C₂H₄; Lig²TiCl₂: R = C₄H₈; Lig³TiCl₂: R = C₆H₁₂) and [Ti{2,2′‐(OC₆H₂‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴TiCl₂) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [ M{2,2′‐(OC₆H₃‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴VCl₂: M = V; Lig⁴ZrCl₂: M = Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1‐octene polymerization after activation by MAO and/or Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄]. The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig¹TiCl₂ << Lig²TiCl₂ < Lig³TiCl₂) and declines after adding additional tert‐Bu group on the aromatic rings (Lig³TiCl₂ < Lig⁴TiCl₂). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et₂AlCl‐activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra‐high molecular weight PE (up to 3588 kg mol^?1) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg mol_v^?1), with high molecular weight (1986 kg mol^?1) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1‐octene copolymers, whereas vanadium catalysts produced product mixtures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2111–2123