Introduction of reactive functionality by the incorporation of divinylbiphenyl in ethylene copolymerization with styrene or 1‐hexene using aryloxo‐modified half‐titanocenes and MAO catalysts

An efficient introduction of vinyl group into poly (ethylene‐co‐styrene) or poly(ethylene‐co?1‐hexene) has been achieved by the incorporation of 3,3′‐divinylbiphenyl (DVBP) in terpolymerization of ethylene, styrene, or 1‐hexene with DVBP using aryloxo‐modified half‐titanocenes, Cp′TiCl₂(O?2,6‐ⁱPr₂C₆H₃) [Cp′ = Cp*, ^tBuC₅H₄, 1,2,4‐Me₃C₅H₂], in the presence of MAO cocatalyst, affording high‐molecular‐weight polymers with unimodal distributions. Efficient comonomer incorporations have been achieved by these catalysts, and the content of each comonomer could be varied by its initial concentration charged. The postpolymerization of styrene was initiated from the vinyl group remained in the side chain by treatment with n‐BuLi. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2581–2587     

Efficient terpolymerization of ethylene and styrene with α‐olefins by aryloxo‐modified half‐titanocene‐based catalysts and cocatalyst systems

Aryloxo‐modified half‐titanocenes, Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) [Cp′ = Cp* ( 1 ), ^tBuC₅H₄ ( 2 )], catalyze terpolymerization of ethylene and styrene with α‐olefin (1‐hexene and 1‐decene) efficiently in the presence of cocatalyst, affording high‐molecular‐weight polymers with unimodal distributions (compositions). Efficient comonomer incorporations have been achieved by these catalysts. The content of each comonomer (α‐olefin, styrene, etc.) could be controlled by varying the comonomer concentration charged, and resonances ascribed to styrene and α‐olefin repeated insertion were negligible. The terpolymerization with p‐methylstyrene (p‐MS) in place of styrene also proceeded in the presence of [PhN(H)Me₂][B(C₆F₅)₄] and AlⁱBu₃ cocatalyst, and p‐MS was incorporated in an efficient matter, affording high‐molecular‐weight polymers with uniform molecular weight distributions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2565–2574     

Efficient introduction of aromatic vinyl group by incorporation of divinylbiphenyl,p‐divinylbenzene in syndiospecific styrene polymerization using aryloxo‐modified half‐titanocene catalysts

An efficient introduction of aromatic vinyl group into syndiotactic polystyrene has been achieved by incorporation of 3,3′‐divinylbiphenyl, p‐divinylbenzene (DVB) in syndiospecific styrene polymerization using aryloxo‐modified half‐titanocenes, Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) (Cp′ = ^tBuC₅H₄, 1,2,4‐Me₃C₅H₂), in the presence of MAO. The resultant polymers possessed high molecular weights with uniform molecular weight distributions, and the DVB contents could be varied by the initial feed molar ratios (6–23 mol %) without decrease in the M_n values. The syndiotactic stereo‐regularity and presence of the vinyl groups were confirmed by NMR spectra. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1902–1907     

Factors affecting product distributions in ethylene/styrene copolymerization by (aryloxo)(cyclopentadienyl)titanium complexes‐MAO catalyst systems

Ethylene/styrene copolymerizations using Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) [Cp′ = Cp* (C₅Me₅, 1 ), 1,2,4‐Me₃C₅H₂ ( 2 ), tert‐BuC₅H₄ ( 3 )]‐MAO catalyst systems were explored under various conditions. Complexes 2 and 3 exhibited both high catalytic activities (activity: 504–6810 kg‐polymer/mol‐Ti h) and efficient styrene incorporations at 25, 40°C (ethylene 6 atm), affording relatively high molecular weight poly (ethylene‐co‐styrene)s with unimodal molecular weight distributions as well as with uniform styrene distributions (M_w = 6.12–13.6 × 10⁴, M_w/M_n = 1.50–1.71, styrene 31.7–51.9 mol %). By‐productions of syndiotactic polystyrene (SPS) were observed, when the copolymerizations by 1 – 3 ‐MAO catalyst systems were performed at 55, 70 °C (ethylene 6 atm, SPS 9.0–68.9 wt %); the ratios of the copolymer/SPS were affected by the polymerization temperature, the [styrene]/[ethylene] feed molar ratios in the reaction mixture, and by both the cyclopentadienyl fragment (Cp′) and anionic ancillary donor ligand (L) in Cp′TiCl₂(L) (L = Cl, O‐2,6‐ⁱPr₂C₆H₃ or N=C^tBu₂) employed. Co‐presence of the catalytically‐active species for both the copolymerization and the homopolymerization was thus suggested even in the presence of ethylene; the ratios were influenced by various factors (catalyst precursors, temperature, styrene/ethylene feed molar ratio, etc.). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4162–4174, 2008     

Vinyl homo/copolymerization of norbornene and ethylene using sterically enhanced 1,2‐bis(arylimino)acenaphthene–palladium precatalysts

A family of unsymmetrical 1,2‐bis(imino)acenaphthene‐palladium methyl chloride complexes [1‐[2,6‐{(C₆H₅)₂CH}₂‐ 4‐{C(CH₃)₃}‐C₆H₂N]‐2‐(ArN)C₂C₁₀H₆]PdMeCl (Ar = 2,6‐Me₂Ph Pd1 , 2,6‐Et₂Ph Pd2 , 2,6‐ⁱPr₂Ph Pd3 , 2,4,6‐Me₃Ph Pd4 , 2,6‐Et₂‐4‐MePh Pd5 ) have been prepared and fully characterized by ¹H/¹³C NMR, FTIR spectroscopies, and elemental analysis. X‐ray diffraction analysis of Pd2 complex revealed a square planar geometry. Upon activation with methylaluminoxane, all the palladium complexes displayed high activities for norbornene (NBE) homo‐polymerization producing insoluble polymer. For the copolymerization of NBE with ethylene, Pd4 complex exhibited good activities with high incorporation of ethylene (up to 59.2–77.4%) and the resultant copolymer showed high molecular weights as maximum as 150.5 kg mol⁻¹. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 922–930     

Copolymerization behavior of titanium imidazolin‐2‐iminato complexes

Monocyclopentadienyl titanium imidazolin‐2‐iminato complexes [Cp′Ti(L)X₂] 1a (Cp′ = cyclopentadienyl, L = 1,3‐di‐tert‐butylimidazolin‐2‐imide, X = Cl), 1b (X = CH₃); 2 (Cp′ = cyclopentadienyl, L = 1,3‐diisopropylimidazolin‐2‐imide, X = Cl); 3 (Cp′ = tert‐butylcyclopentadienyl, L = 1,3‐di‐tert‐butylimidazolin‐2‐imide, X = Cl), upon activation with methylaluminoxane (MAO) were active for the polymerization of ethylene and propylene and the copolymerization of ethylene and 1‐hexene. Catalysts derived from imidazolin‐2‐iminato tropidinyl titanium complex 4 = [(Trop)Ti(L)Cl₂] (Trop = tropidinyl, L = 1,3‐di‐tert‐butylimidazolin‐2‐imide) were much less active. Narrow polydispersities were observed for ethylene and propylene polymerization, but the copolymerization of ethylene/hexene led to bimodal molecular weight distributions. The productivity of catalysts derived from the dialkyl complex 1b activated with [Ph₃C][B(C₆F₅)₄] or B(C₆F₅)₃ were less active for ethylene/hexene copolymerization but yielded ethylene/hexene copolymers of narrower molecular weight distributions than those derived from 1a/MAO. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6064–6070, 2008     

Highly active copolymerization of ethylene with 10‐undecen‐1‐ol using phenoxy‐based zirconium/methylaluminoxane catalysts

Activated with methylaluminoxane (MAO), phenoxy‐based zirconium complexes bis[(3‐^tBu‐C₆H₃‐2‐O)‐CH?NC₆H₅]ZrCl₂, bis[(3,5‐di‐^tBu‐C₆H₂‐2‐O)‐PhC?NC₆H₅] ZrCl₂, and bis[(3,5‐di‐^tBu‐C₆H₂‐2‐O)‐PhC?N(2‐F‐C₆H₄)]ZrCl₂ for the first time have been used for the copolymerization of ethylene with 10‐undecen‐1‐ol. In comparison with the conventional metallocene, the phenoxy‐based zirconium complexes exhibit much higher catalytic activities [>10⁷ g of polymer (mol of catalyst)^?1 h^?1]. The incorporation of 10‐undecen‐1‐ol into the copolymers and the properties of the copolymers are strongly affected by the catalyst structure. Among the three catalysts, complex c is the most favorable for preparing higher molecular weight functionalized polyethylene containing a higher content of hydroxyl groups. Studies on the polymerization conditions indicate that the incorporated commoner content in the copolymers mainly depends on the comonomer concentration in the feed. The catalytic activity is slightly affected by the Al_(MAO)/Zr molar ratio but decreases greatly with an increase in the polymerization temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5944–5952, 2005     

Imino‐indolate half‐titanocene chlorides: Synthesis and their ethylene (co‐)polymerization

A series of imino‐indolate half‐titanocene chlorides, Cp′Ti(L)Cl₂ ( C1 – C7 : Cp′ = C₅H₅, MeC₅H₄, C₅Me₅, L = imino‐indolate ligand), were synthesized by the reaction of Cp′TiCl₃ with sodium imino‐indolates. All complexes were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. Moreover, the molecular structures of two representative complexes C4 and C6 were confirmed by single crystal X‐ray diffraction analysis. On activation with methylaluminoxane (MAO), these complexes showed good catalytic activities for ethylene polymerization (up to 7.68 × 10⁶ g/mol(Ti)·h) and ethylene/1‐hexene copolymerization (up to 8.32 × 10⁶ g/mol(Ti)·h), producing polyolefins with high molecular weights (for polyethylene up to 1808 kg/mol, and for poly(ethylen‐co‐1‐hexene) up to 3290 kg/mol). Half‐titanocenes containing ligands with alkyl substituents showed higher catalytic activities, whereas the half‐titanocenes bearing methyl substituents on the cyclopentadienyl groups showed lower productivities, but produced polymers with higher molecular weights. Moreover, the copolymerization of ethylene and methyl 10‐undecenoate was demonstrated using the C1 /MAO catalytic system. The functionalized polyolefins obtained contained about 1 mol % of methyl 10‐undecenoate units and were fully characterized by several techniques such as FT‐IR, ¹H NMR, ¹³C NMR, DSC, TGA and GPC analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 357–372, 2009     

Olefin polymerization and copolymerization with soluble transition‐metal complex catalysts

Olefin polymerizations catalyzed by Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 1 – 5 ; Cp′ = cyclopentadienyl group), RuCl₂(ethylene)(pybox) { 7 ; pybox = 2,6‐bis[(4S)‐4‐isopropyl‐2‐oxazolin‐2‐yl]pyridine}, and FeCl₂(pybox) ( 8 ) were investigated in the presence of a cocatalyst. The Cp*TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 5 )–methylaluminoxane (MAO) catalyst exhibited remarkable catalytic activity for both ethylene and 1‐hexene polymerizations, and the effect of the substituents on the cyclopentadienyl group was an important factor for the catalytic activity. A high level of 1‐hexene incorporation and a lower r_E · r_H value with 5 than with [Me₂Si(C₅Me₄)(N^tBu)]TiCl₂ ( 6 ) were obtained, despite the rather wide bond angle of Cp Ti O (120.5°) of 5 compared with the bond angle of Cp Ti N of 6 (107.6°). The 7 –MAO catalyst exhibited moderate catalytic activity for ethylene homopolymerization and ethylene/1‐hexene copolymerization, and the resultant copolymer incorporated 1‐hexene. The 8 –MAO catalyst also exhibited activity for ethylene polymerization, and an attempted ethylene/1‐hexene copolymerization gave linear polyethylene. The efficient polymerization of a norbornene macromonomer bearing a ring‐opened poly(norbornene) substituent was accomplished by ringopening metathesis polymerization with the well‐defined Mo(CHCMe₂Ph)(N‐2,6‐ⁱPr₂C₆H₃)[OCMe(CF₃)₂]₂ ( 10 ). The key step for the macromonomer synthesis was the exclusive end‐capping of the ring‐opened poly(norbornene) with p‐Me₃SiOC₆H₄CHO, and the use of 10 was effective for this polymerization proceeding with complete conversion. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4613–4626, 2000     

N‐(2‐benzimidazolylquinolin‐8‐yl)benzamidate half‐titanocene chlorides: Synthesis,characterization and their catalytic behavior toward ethylene polymerization

A series of N‐(2‐benzimidazolyquinolin‐8‐yl)benzamidate half‐titanocene chlorides, Cp′TiLCl ( C1 – C8 : Cp′ = C₅H₅, MeC₅H₄, or C₅Me₅; L = N‐(benzimidazolyquinolin‐8‐yl)benzamides)), was synthesized by the KCl elimination reaction of half‐titanocene trichlorides with the correspondent potassium N‐(2‐benzimidazolyquinolin‐8‐yl)benzamide. These half‐titanocene complexes were fully characterized by elemental and NMR analyses, and the molecular structures of complexes C2 and C8 were determined by the single‐crystal X‐ray diffraction. The high stability of the pentamethylcyclopentadienyl complex ( C8 ) was evident by no decomposing nature of its solution in air for one week. The oxo‐bridged dimeric complex ( C9 ) was isolated from the solution of the corresponding cyclopentadienyl complex ( C3 ) solution in air. Complexes C1 – C8 exhibited good to high catalytic activities toward ethylene polymerization and ethylene/α‐olefin copolymerization in the presence of methylaluminoxane (MAO) cocatalyst. In the typical catalytic system of C1/ MAO, the polymerization productivities were enhanced with either elevating reaction temperature or increasing the ratio of MAO to titanium precursor. In general, it was observed that higher the catalytic activity of the catalytic system lower the molecular weight of polyethylene. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3154–3169, 2009     

Synthesis of ultra‐high‐molecular‐weight ethylene‐propylene copolymer via quasi‐living copolymerization with N‐heterocyclic carbene ligated vanadium complexes

The quasi‐living copolymerization of ethylene with propylene was achieved by using N‐heterocyclic carbene (NHC) ligated vanadium complex ( V3 , VOCl₃[1,3‐(2,6‐ⁱPr₂C₆H₃)₂(NCH?)₂C:]) due to the stabilization of active center by the introduction of bulky and electron rich NHC ligand with bulky isopropyl substituents at the ortho positions of the phenyl rings. The weight‐average molecular weight (M_w) of the resulting copolymer increases linearly with its weight in 20 min. The ultra‐high‐molecular‐weight (UHMW) ethylene‐propylene copolymer (M_w = 1612 kg mol^?1) can be synthesized with V3 /Et₃Al₂Cl₃ catalytic system. The novel complex V4′ (VCl₃[1,3‐(2,4,6‐Me₃C₆H₂)₂(NCH?)₂C:]·2THF) was constructed by the introduction of two coordinated tetrahydrofuran molecules and decrease in steric hindrance at the ortho positions of phenyl rings. The UHMW ethylene‐propylene copolymer (M_w = 1167 kg mol^?1) can also be synthesized by using V4′ /Et₃Al₂Cl₃ catalytic system. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 553–561     

Copolymerization of norbornene and 5‐norbornene‐2‐yl acetate using novel bis(β‐ketonaphthylamino)Ni(II)/B(C6F5)3/AlEt3 catalytic system

Vinyl‐type copolymerization of norbornene (NBE) and 5‐NBE‐2‐yl‐acetate (NBE‐OCOMe) in toluene were investigated using a novel homogeneous catalyst system based on bis(β‐ketonaphthylamino)Ni(II)/B(C₆F₅)₃/AlEt₃. The copolymerization behavior as well as the copolymerization conditions, such as the levels of B(C₆F₅)₃ and AlEt₃, temperature, and monomer feed ratios, which influence on the copolymerization were examined. Without combination of AlEt₃, the catalytic bis(β‐ketonaphthylamino)Ni(II)/B(C₆F₅)₃ exhibited very high catalyst activity for polymerization of NBE. Combination of AlEt₃ in catalyst system resulted in low conversion for polymerization of NBE. For copolymerization of NBE and NBE‐OCOMe, involvement of AlEt₃ in catalyst is necessary. Slight addition of NBE‐OCOMe in copolymerization of NBE and NBE‐OCOMe gives rise to significant increase of catalyst activity for catalytic system bis(β‐ketonaphthylamino)Ni(II)/B(C₆F₅)₃/AlEt₃. Nevertheless, excess increase of the NBE‐OCOMe content in the comonomer feed ratios results in decrease of conversion as well as activity of catalyst. The achieved copolymers were confirmed to be vinyl‐addition copolymers through the analysis of FTIR, ¹H NMR, and ¹³C NMR spectra. ¹³C NMR studies further revealed the composition of the copolymer and the incorporation rate was 7.6–54.1 mol % ester units at a content of 30–90 mol % of the NBE‐OCOMe in the monomer feeds ratios. TGA analysis results showed that the copolymer exhibited good thermal stability (T_d > 410 °C) and failed to observe the glass transitions temperature over 300 °C. The copolymers are confirmed to be noncrystalline by WAXD analysis results and show good solubility in common organic solvents. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3990–4000, 2009     

Highly efficient ethylene/norbornene copolymerization by o‐Di(phenyl)phosphanylphenolate‐based half‐titanocene complexes

A series of o‐di(phenyl)phosphanylphenolate‐based half‐titanocene complexes CpTiCl₂[O‐2‐R¹‐4‐R²‐6‐(Ph₂P)C₆H₂] (Cp = C₅H₅, 2a : R¹ = R² = H; 2b : R¹ = F, R² = H; 2c : R¹ = Ph, R² = H; 2d : R¹ = SiMe₃, R² = H; 2e : R¹ = ^tBu, R² = H; 2f : R¹ = R² = ^tBu) have been synthesized in high yields (65–87%) by treating CpTiCl₃ with 1.0 equiv of the deprotonated ligands in THF. The ¹H and ³¹P NMR spectra indicated that the phosphorus is not coordinated to titanium in complexes 2a – c , but is coordinated to titanium in complexes 2d – f . Structures for 2c – f were further confirmed by X‐ray crystallography. Complex 2c is essentially a four‐coordinate tetrahedral geometry, whereas complexes 2d ‐ f adopt five‐coordinate distorted square–pyramid geometry around the titanium center. All complexes exhibited low to moderate activities toward homopolymerization of ethylene. Excitingly, they displayed excellent ability to copolymerize ethylene with norbornene, and catalytic activity was more than 100 times larger than that of ethylene homopolymerization in the case of Ph₃CB(C₆F₅)₄/ⁱBu₃Al as cocatalyst, affording the copolymers with high comonomer incorporations. Moreover, DFT calculations study had been performed to shed light on the active species and the fundamental role of NBE in improving the catalytic activity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013     

Stereospecific styrene polymerization and ethylene–styrene copolymerization with titanocenes containing a pendant amine donor

A series of monocyclopentadienyl titanium complexes containing a pendant amine donor on a Cp group ( A = CpTiCl₃, B = Cp^NTiCl₃, C = Cp^NTiCl₂TEMPO, for Cp = C₅H₅, Cp^N = C₅H₄CH₂CH₂N(CH₃)₂, and TEMPO = 2,2,6,6‐tetramethylpiperidine‐N‐oxyl) are investigated for styrene homopolymerization and ethylene–styrene (ES) copolymerization. When activated by methylaluminoxane at 70 °C, complexes with the amine group ( B and C ) are active for styrene homopolymerization and afford syndiotactic polystyrene (sPS). The copolymerizations of ethylene and styrene with B and C yield high‐molecular weight ES copolymer, whereas complex A yields mixtures of sPS and polyethylene, revealing the critical role that the pendant amine has on the polymerization behavior of the complexes. Fractionation, NMR, and DSC analyses of the ES copolymers generated from B and C suggest that they contain sPS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1579–1585, 2010     

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     

Silyl‐functionalized polyolefins via co‐polymerization of vinylsilanes with ethylene or propylene catalyzed by group IV metallocene complexes

Vinylsilanes CH₂CHSiR₃ (R = Me, NMe₂, OMe, OTMS) copolymerize with ethylene rapidly in the presence of catalytic amounts of [Cp′₂ZrMe][MeB(C₆F₅)₃] (Cp′ = η⁵‐C₅Me₅) ( I ) to give high molecular weight silyl‐functionalized polyethylene. The molecular weight of the polymer can be controlled by varying the comonomer concentration as well as the reaction temperature. Relatively low molecular weight polymer was produced at a higher silyl monomer concentration and a higher polymerization temperature. The incorporation of silyl monomer in the polymer is in the range of 0.1‐ 6.0%. On the other hands, catalysts [Cp₂ZrMe][MeB(C₆F₅)₃] (Cp′ = η⁵‐C₅H₅) ( II ) and [Cp″₂ZrMe][MeB(C₆F₅)₃] (Cp″ = η⁵‐1,2‐C₅Me₂H₃) ( III ) show much lower activity. With the use of more coordinatively unsaturated constrained geometry catalysts (CGC), Me₂Si(η⁵‐C₅Me₄)(N^tBu)MMe][MeB(C₆F₅)₃] ( IV , M = Zr; V , M = Ti), the silyl monomer incorporation in the polymer was increased to 40%. The Ti catalyst is more active and produces polymer with a higher molecular weight with a higher silyl monomer incorporation at 23 °C. The copolymerization of vinyltrimethylsilane with propylene was also investigated with these catalysts, yielding high silyl‐functionalized propylene copolymer/oligmer. The microstructure of the copolymers/oligomers has been thoroughly investigated by 1D and 2D NMR techniques (¹H, ¹³C, NOE, DEPT, HETCOR, and FLOCK). The results show that the backbone of the copolymers/oligomers is essentially random. Several termination pathways have been identified. In particular, two unsaturated silyl terminations, cis and/or trans‐TMS CHCH , were identified with the constrained geometry catalysts. Their formation was rationalized based on transition state models. It was found that occasional 1,2‐insertion of either propylene or vinyltrimethylsilane into the chain propagation process has a high probability serving as the trigger for polymer chain termination via β‐H elimination. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1308–1321     

Producing highly linear polyethylenes by using t‐butyl‐functionalized 2,6‐bis(imino)pyridylchromium(III) chlorides

A new family of t‐butyl substituted chromium(III) chloride complexes ( Cr1 – Cr6 ), bearing 2‐(1‐(2,6‐dibenzhydryl‐4‐t‐butylphenylimino)ethyl)‐6‐(1‐(arylimino)ethyl)pyridine (aryl = 2,6‐Me₂C₆H₃ Cr1 , 2,6‐Et₂C₆H₃ Cr2 , 2,6‐i‐Pr₂C₆H₃ Cr3 , 2,4,6‐Me₃C₆H₂ Cr4 and 2,6‐Et₂‐4‐MeC₆H₂ Cr5 ) or 2,6‐bis(1‐(2,6‐dibenzhydryl‐4‐t‐butylphenylimino)ethyl)pyridine ( Cr6 ), has been synthesized by the reaction of CrCl₃·6H₂O in good yield with the corresponding ligands ( L1 – L6 ), respectively. The molecular structures of Cr2 and Cr6 were characterized by X‐ray diffraction highlighted a distorted octahedral geometry with the coordinated N,N,N ligand and three bonded chlorides around the metal center. On activation with modified methylaluminoxane or triisobutyl aluminum, most of the chromium precatalysts exhibit good activities toward ethylene polymerization and produce linear polyethylenes with high‐molecular weight. In addition, an in‐depth catalytic evaluation of Cr2 was conducted to investigate how cocatalyst type and amount, reaction temperature, and run time affect the catalytic activities and polymer properties. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1049–1058     

Micron‐granula polyolefin with self‐immobilized nickel and iron diimine catalysts bearing one or two allyl groups

Self‐immobilized nickel and iron diimine catalysts bearing one or two allyl groups of [ArN?C]₂(C₁₀H₆)NiBr₂ [Ar = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₂] ( 1 ), [ArN?C(Me)][Ar′N? C(Me)]C₅H₃NFeCl₂ [Ar = Ar′ = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₃, Ar = 2,6‐(i‐Pr)₂C₆H₃, and Ar′ = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₃] were synthesized and characterized. All three catalysts were investigated for olefin polymerization. As a result, these catalysts not only showed high activities as the catalyst free from the allyl group, such as [ArN?C]₂C₁₀H₆NiBr₂ (Ar = 2,6‐(i‐Pr)₂C₆H₂)], but also greatly improved the morphology of polymer particles to afford micron‐granula polyolefin. The self‐immobilization of catalysts, the formation mechanism of microspherical polymer, and the influence on the size of the particles are discussed. The molecular structure of self‐immobilized nickel catalyst 1 was also characterized by crystallographic analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1018–1024, 2004     

Acyclic diene metathesis polymerization of 2,5‐dialkyl‐1,4‐divinylbenzene with molybdenum or ruthenium catalysts: Factors affecting the precise synthesis of defect‐free,high‐molecular‐weight trans‐poly(p‐phenylene vinylene)s

Factors affecting the syntheses of high‐molecular‐weight poly(2,5‐dialkyl‐1,4‐phenylene vinylene) by the acyclic diene metathesis polymerization of 2,5‐dialkyl‐1,4‐divinylbenzenes [alkyl = n‐octyl ( 2 ) and 2‐ethylhexyl ( 3 )] with a molybdenum or ruthenium catalyst were explored. The polymerizations of 2 by Mo(N‐2,6‐Me₂C₆H₃) (CHMe₂ Ph)[OCMe(CF₃)₂]₂ at 25 °C was completed with both a high initial monomer concentration and reduced pressure, affording poly(p‐phenylene vinylene)s with low polydispersity index values (number‐average molecular weight = 3.3–3.65 × 10³ by gel permeation chromatography vs polystyrene standards, weight‐average molecular weight/number‐average molecular weight = 1.1–1.2), but the polymerization of 3 was not completed under the same conditions. The synthesis of structurally regular (all‐trans), defect‐free, high‐molecular‐weight 2‐ethylhexyl substituted poly(p‐phenylene vinylene)s [poly 3 ; degree of monomer repeating unit (DP_n) = ca. 16–70 by ¹H NMR] with unimodal molecular weight distributions (number‐average molecular weight = 8.30–36.3 × 10³ by gel permeation chromatography, weight‐average molecular weight/number‐average molecular weight = 1.6–2.1) and with defined polymer chain ends (as a vinyl group, ? CH?CH₂) was achieved when Ru(CHPh)(Cl)₂(IMesH₂)(PCy₃) or Ru(CH‐2‐OⁱPr‐C₆H₄)(Cl)₂(IMesH₂) [IMesH₂ = 1,3‐bis(2,4,6‐trimethylphenyl)‐2‐imidazolidinylidene] was employed as a catalyst at 50 °C. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6166–6177, 2005     

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