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     

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     

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     

Direct synthesis of linear low‐density polyethylene of ethylene/1‐hexene from ethylene with a tandem catalytic system in a single reactor

Tandem catalysis offers a promising synthetic route to the production of linear low‐density polyethylene. This article reports the use of homogeneous tandem catalytic systems for the synthesis of ethylene/1‐hexene copolymers from ethylene stock as the sole monomer. The reported catalytic systems employ the tandem action between an ethylene trimerization catalyst, (η⁵‐C₅H₄CMe₂C₆H₅)TiCl₃ ( 1 )/modified methylaluminoxane (MMAO), and a copolymerization metallocene catalyst, [(η⁵‐C₅Me₄)SiMe₂(^tBuN)]TiCl₂ ( 2 )/MMAO or rac‐Me₂Si(2‐MeBenz[e]Ind)₂ZrCl₂ ( 3 )/MMAO. During the reaction, 1 /MMAO in situ generates 1‐hexene with high activity and high selectivity, and simultaneously 2 /MMAO or 3 /MMAO copolymerizes ethylene with the produced 1‐hexene to generate butyl‐branched polyethylene. We have demonstrated that, by the simple manipulation of the catalyst molar ratio and polymerization conditions, a series of branched polyethylenes with melting temperatures of 60–128 °C, crystallinities of 5.4–53%, and hexene percentages of 0.3–14.2 can be efficiently produced. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4327–4336, 2004     

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     

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     

Homo‐ and copolymerization of ethylene and norbornene with bis(β‐diketiminato) titanium complexes activated with methylaluminoxane

Homo‐ and copolymerization of ethylene and norbornene were investigated with bis(β‐diketiminato) titanium complexes [ArNC(CR₃)CHC(CR₃)NAr]₂TiCl₂ (R = F, Ar = 2,6‐diisopropylphenyl 2a; R = F, Ar = 2,6‐dimethylphenyl 2b ; R = H, Ar = 2,6‐diisopropylphenyl 2c ; R = H, Ar = 2,6‐dimethylphenyl 2d) in the presence of methylaluminoxane (MAO). The influence of steric and electric effects of complexes on catalytic activity was evaluated. With MAO as cocatalyst, complexes 2a–d are moderately active catalysts for ethylene polymerization producing high‐molecular weight polyethylenes bearing linear structures, but low active catalysts for norbornene polymerization. Moreover, 2a – d are also active ethylene–norbornene (E–N) copolymerization catalysts. The incorporation of norbornene in the E–N copolymer could be controlled by varying the charged norbornene. ¹³C NMR analyses showed the microstructures of the E–N copolymers were predominantly alternated and isolated norbornene units in copolymer, dyad, and triad sequences of norbornene were detected in the E–N copolymers with high incorporated content of norbornene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 93–101, 2008     

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     

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     

Highly active ethylene polymerization and copolymerization with norbornene using bis(imino‐indolide) titanium dichloride–MAO system

A catalytic system of new titanium complexes with methylaluminoxane (MAO) was found to effectively polymerize ethylene for high molecular weight polyethylene as well as highly active copolymerization of ethylene and norbornene. The bis (imino‐indolide)titanium dichlorides (L₂TiCl₂, 1 – 5 ), were prepared by the reaction of N‐((3‐chloro‐1H‐indol‐2‐yl)methylene)benzenamines with TiCl₄, and characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. The solid‐state structures of 1 and 4 were determined by X‐ray diffraction analysis to reveal the six‐coordinated distorted octahedral geometry around the titanium atom with a pair of chlorides and ligands in cis‐forms. Upon activation by MAO, the complexes showed high activity for homopolymerization of ethylene and copolymerization of ethylene and norbornene. A positive “comonomer effect” was observed for copolymerization of ethylene and norbornene. Both experimental observations and paired interaction orbital (PIO) calculations indicated that the titanium complexes with electron‐withdrawing groups in ligands performed higher catalytic activities than those possessing electron‐donating groups. Relying on different complexes and reaction conditions, the resultant polyethylenes had the molecular weights M_w in the range of 200–2800 kg/mol. The influences on both catalytic activity and polyethylene molecular weights have been carefully checked with the nature of complexes and reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3415–3430, 2007     

Synthesis,characterization, and ethylene (Co)polymerization behavior of trichlorotitanium 2‐(1‐(arylimino)propyl)quinolin‐8‐olates

A series of trichlorotitanium complexes containing 2‐(1‐(arylimino)propyl)quinolin‐8‐olates was synthesized by stoichiometric reaction of titanium tetrachloride with the corresponding potassium 2‐(1‐(arylimino)propyl)quinolin‐8‐olates and was fully characterized by elemental analysis, nuclear magnetic resonance spectroscopy, and by single‐crystal X‐ray diffraction study of representative complexes. All titanium complexes, when activated with methylaluminoxane, exhibited high catalytic activity toward ethylene polymerization [up to 1.15 × 10⁶ g mol^?1(Ti) h^?1] and ethylene/α‐olefin copolymerization [up to 1.54 × 10⁶ g mol^?1 (Ti) h^?1]. The incorporation of comonomer was confirmed to amount up to 2.82 mol % of 1‐hexene or 1.94 mol % of 1‐octene, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Titanium and zirconium complexes containing modified TREN ligands for the polymerization of 1‐alkenes—A comparative study

The titanium and zirconium complexes in C₃ and C_s symmetric forms synthesized from corresponding aminotriols in combination with MAO polymerized 1‐hexene in a controlled manner. When the polymerization temperature was lowered, they gave high molecular weight monodisperse polyhexene with narrow polydispersities indicating quazi‐living systems. The isotactic polyhexene obtained from C₃ titanium catalyst has the molecular weight of around 46,500 with PDI of 1.3 and the hemi‐isotactic polymer from C_s titanium catalyst has the molecular weight of around 617,000 with PDI of 1.3. The analogues zirconium complexes upon activation with MAO polymerize hexene to give polyhexene having molecular weight of 53,000 (C₃) and 626,000 (pseudo‐C_s) with PDI ranging from 1.2 to 1.4. The MIX‐titanium catalyst prepared from the 50:50 mixture of aminotriols was also able to polymerize 1‐hexene and the GPC traces of the polyhexene suggests that even though the catalyst was formed from the mixture of aminotriols, the C₃ and C_s symmetry of the catalysts retain its originality avoiding the formation of aggregates or polymeric forms. When one of the arms of aminotriol was methylated yield C₂ and meso aminodiol ligands and their corresponding titanium and zirconium complexes gave higher molecular weight polyhexenes with lower PDI (C₂‐Zr‐M_n: 260,000; PDI: 1.05–1.10; mesoZr‐M_n: 220,000; PDI: 1.05–1.10) possibly suggesting that these systems are close to living systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5470–5479, 2007     

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     

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     

New chiral [N,N,N]‐ligand containing titanium/zirconium precatalysts for 1‐hexene polymerization

The ring‐opening reaction of (S)‐N‐tosyl‐2‐phenylaziridine by benzylamine in ethanol at 80 °C resulted in the formation of the (S,S)‐bis(N‐tosyl‐2‐amino‐2‐phenylethyl)benzylamine ligand in a 60% yield. The corresponding titanium complex, 1‐TiCl₂, was prepared by the reaction of the dilithiated parent ligand with TiCl₄. This precatalyst, in combination with methylaluminoxane, was capable of polymerizing 1‐hexene with good activities, resulting in the formation of good yields of low‐dispersity, high‐molecular‐weight polymers at low temperatures but higher yields of lower molecular weight polymers at higher temperatures. ¹H and ¹³C NMR spectra of the polymers suggested high isotacticity and predominant chain termination via β‐hydride elimination. The enantiomerically pure catalysts, (R,R)‐1‐TiCl₂ and (S,S)‐1‐TiCl₂, showed nearly identical polymerization results at various polymerization temperatures. However, when the catalyst was prepared from a racemic ligand, the obtained polymers had lower molecular weights with a bimodal distribution. This observation suggested diastereomeric aggregation of the racemic catalyst, which was well supported by the NMR studies, and a modified Arrhenius plot (the natural logarithm of the number‐average molecular weight vs the reciprocal of the temperature) also showed sigmoidal behavior, indicating the existence of two or more active species. Analogous zirconium precatalysts showed similar results in the polymerization of 1‐hexene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4006–4014, 2006     

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 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     

High molar mass ethene/1‐olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

The influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C₁‐symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐cyclopentadienyl)ZrCl₂ ( 1 ), ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐fluorenyl)ZrCl₂ ( 2 ), and ethylene(1‐(9)‐fluorenyl‐(R)1‐phenyl‐2‐(1‐indenyl)ZrCl2 ( 3 ). Polyethenes produced with 1 /MAO had considerable, ca. 10% amount of trans‐vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1‐hexene or 1‐hexadecene using 1 /MAO, molar mass of the copolymers varied from high to moderate (531–116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1‐olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2 /MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3 /MAO produced polyethenes with extremely small amounts of trans‐vinylene end groups and relatively low molar mass 1‐hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1 . These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1‐olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3 /MAO. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 373–382, 2008     

Preparation of linear α‐olefins to high‐molecular weight polyethylenes using cationic α‐diimine nickel(II) complexes containing chloro‐substituted ligands

A series of α‐diimine nickel(II) complexes containing chloro‐substituted ligands, [(Ar)N?C(C₁₀H₆)C?N(Ar)]NiBr₂ ( 4a , Ar = 2,3‐C₆H₃Cl₂; 4b , Ar = 2,4‐C₆H₃Cl₂; 4c , Ar = 2,5‐C₆H₃Cl₂; 4d , Ar = 2,6‐C₆H₃Cl₂; 4e , Ar = 2,4,6‐C₆H₂Cl₃) and [(Ar)N?C(C₁₀H₆)C?N(Ar)]₂NiBr₂ ( 5a , Ar = 2,3‐C₆H₃Cl₂; 5b , Ar = 2,4‐C₆H₃Cl₂; 5c , Ar = 2,5‐C₆H₃Cl₂), have been synthesized and investigated as precatalysts for ethylene polymerization. In the presence of modified methylaluminoxane (MMAO) as a cocatalyst, these complexes are highly effective catalysts for the oligomerization or polymerization of ethylene under mild conditions. The catalyst activity and the properties of the products were strongly affected by the aryl‐substituents of the ligands used. Depending on the catalyst structure, it is possible to obtain the products ranging from linear α‐olefins to high‐molecular weight polyethylenes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1964–1974, 2006     

Copolymerization of ethylene with cyclopentene or 2‐butene with half titanocenes‐based catalysts

Half titanocenes (CpCH₂CH₂O)TiCl₂ (1), (CpCH₂CH₂OCH₃)TiCl₃ (2), and CpTiCl₃ (3), activated by methylaluminoxane (MAO) were tested in copolymerization of ethylene with internal olefins such as cyclopentene. All the catalysts were able to give incorporation of cyclopentene in polyethylene matrix. ¹³C NMR analysis of obtained copolymers showed that the catalytic systems have low regiospecificity. In fact, in ethylene–cyclopentene copolymers, cyclic olefin inserts with both 1,2 and 1,3‐enchainment. X‐ray powder diffraction analysis of these copolymers confirmed that 1,2 inserted cyclopentene units are excluded from crystalline phase, whereas 1,3‐cyclopentene units are included, giving rise to expansion of unit cell of crystalline polyethylene. Titanium‐based catalysts were investigated also in the copolymerization of ethylene with E and Z‐2‐butene. Only complex (1) was able to give copolymers and ¹³C NMR analysis of products showed 2‐3, 1‐3, and 1‐2 insertion of 2‐butene. Differential scanning calorimetry analysis displayed that ethylene–cyclopentene, as well as ethylene‐2‐butene, copolymers are crystalline and their melting point decreases by increasing the comonomer content. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4725–4733, 2008