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     

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     

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     

Vanadium(V) complexes containing tetradentate amine trihydroxy ligands as catalysts for copolymerization of cyclic olefins

A series of vanadium(V) complexes bearing tetradentate amine trihydroxy ligands [NOOO], which differ in the steric and electronic properties, have been synthesized and characterized. Single crystal X‐ray analysis showed that these complexes are five or six coordinated around the vanadium center in the solid state. Their coordination geometries are octahedral or trigonal bipyramidal. In the presence of Et₂AlCl, these complexes have been investigated as the efficient catalysts for ethylene polymerization and ethylene/norbornene copolymerization at elevated reaction temperature and produced the polymers with unimodal molecular weight distributions (MWDs), indicating the single site behaviors of these catalysts. Both the steric hindrance and electronic effect of the groups on the tetradentate ligands directly influenced catalytic activity and the molecular weights of the resultant (co)polymers. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature, ethylene pressure, and comonomer concentration, are also examined in detail. Furthermore, high catalytic activities of up to 3.30 kg polymer/mmol_V·h were also observed when these complexes were applied to catalyze the copolymerization of ethylene and 5‐norbornene‐2‐methanol, producing the high‐molecular‐weight copolymers (M_w = 157–400 kg/mol) with unimodal MWDs (M_w/M_n = 2.5–3.0) and high polar comonomer incorporations (up to 12.3 mol %). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1122–1132, 2010     

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     

Copolymerization of ethylene with cycloolefins by titanium complexes containing tridentate [o−NSR] ligands

A family of titanium complexes of the general formula [N‐(3,5‐di‐tert‐butylsalicylidene)‐2‐alkylsulfanylanilinato]Ti(IV)Cl₃ 5a – f was prepared from the reaction of TiCl₄ with the potassium salts of the corresponding ligands. These complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 5b and 5e were further confirmed by single‐crystal X‐ray analyses. Complexes 5a – f (except for 5c ) exhibited good to high catalytic activities in ethylene copolymerization with cycloolefins such as norbornene, cyclopentene, dicyclopentadiene in the presence of modified methylaluminoxane. The reaction conditions and the steric hindrance of the alkyl substituents on sulfur atom in the precatalysts influenced strongly the copolymerization behaviors and the structures of the resultant copolymers. Complex 5c with bulky tert‐butylthio sidearm showed both low catalytic activity and comonomer incorporation ratio. The n‐alkylthio complexes 5a , 5d – f all exhibited good ethylene copolymerization capabilities with cycloolefins, which is superior to the corresponding phenylthio complex 5g . © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 2807–2819, 2008     

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     

Facile,efficient functionalization of polyethylene via regioselective copolymerization of ethylene with cyclic dienes

The copolymerizations of ethylene with cyclic dienes [dicyclopentadiene (DCPD) and 2,5‐norbornadiene (NBD)] using bis(β‐enaminoketonato)titanium complexes [PhN = C(R₂)CHC(R₁)O]₂TiCl₂ ( 1a : R₁ = CF₃, R₂ = CH₃; 1b : R₁ = t‐Bu, R₂ = CF₃; 1c : R₁ = Ph, R₂ = CF₃) have been investigated. In the presence of modified methylaluminoxane, these complexes exhibited high catalytic activities in the copolymerization of ethylene with DCPD or NBD, affording high molecular weight copolymers with unimodal molecular weight distributions. ¹H and ¹³C‐NMR spectra reveal ethylene/DCPD copolymerizations by catalysts 1a – c proceeds through the enchainment of norbornene ring. Catalysts 1a and 1c showed a tendency to afford alternating copolymers. More noticeably, catalysts 1b and 1c bearing bulky substituents on the ligands promote ethylene/NBD copolymerization without crosslinking, affording the copolymer containing intracyclic double bonds. The NBD incorporation as high as 27.2 mol % has been achieved by catalyst 1c . Moreover, the microstructures of the copolymers were further confirmed by the measurement of reactivity ratios and dyad monomer sequences as well as mean sequence lengths. The intracyclic double bonds of ethylene/DCPD or ethylene/NBD copolymers can be fully converted into polar groups such as epoxy, amine, silane, and hydroxyl groups under mild conditions. Convenient synthesis of hydroxylated polyethylene can be provided for the first time through the ring opening reaction of epoxide. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1764–1772, 2010     

Syntheses of Some New Group 4 non-Cp Complexes Bearing Schiff-base, Thiophene Diamide Ligands Respectively and Their Catalytic Activities for a-Olefin Polymerization

Totally sixteen new titanium and zirconium non-Cp complexes supported by Schiff-base, or thiophene diamide ligands have been synthesized. The complexes are obtained by the reaction of M(OPr-i)4(M=Ti,Zr) with the corresponding Schiff-base ligand in 1:1 molar ratio in good yield. The thiophene diamide titanium complex has been prepared from trimethylsilyl amine [N,S,N] ligand and TiCl4 in toluene at 120℃. All complexes are well charac-terized by ^1H NMR, IR, MS and elemental analysis. When activated by excess methylaluminoxane (MAO), complexes show moderate catalytic activity for ethylene polymerization, and complex If (R^1=CH3,R^2=Br) exhibits the highest activity for ethylene and styrene polymerization. When the complexes were preactivated by triethylaluminum (TEA), both polymerization activities and syndiotacticity of the polymers were greatly improved.     

Bis(2‐(6‐methylpyridin‐2‐yl)‐benzimidazolyl)titanium dichloride and titanium bis(6‐benzimidazolylpyridine‐2‐carboxylimidate): Synthesis,characterization, and their catalytic behaviors for ethylene polymerization

A series of 6‐(benzimidazol‐2‐yl)‐N‐organylpyridine‐2‐carboxamide were synthesized and transformed into 6‐benzimidazolylpyridine‐2‐carboxylimidate as dianionic tridentate ligands. Bis(2‐(6‐methylpyridin‐2‐yl)‐benzimidazolyl)titanium dichloride ( C1 ) and titanium bis(6‐benzimidazolylpyridine‐2‐carboxylimidate) ( C2 – C8 ) were synthesized in acceptable yields. These complexes were systematically characterized by elemental and NMR analyses. Crystallographic analysis revealed the distorted octahedral geometry around titanium in both complexes C1 and C4 . Using MAO as cocatalyst, all complexes exhibited from good to high catalytic activities for ethylene polymerization. The neutral bis(6‐benzimidazolylpyridine‐2‐carboxylimidate)titanium ( C2 – C8 ) showed high catalytic activities and good stability for prolonged reaction time and elevated reaction temperature; however, C1 showed a short lifetime in catalysis as being observed at very low activity after 5 min. The elevated reaction temperature enhanced the productivity of polyethylenes with low molecular weights, whereas the reaction with higher ethylene pressure resulted in better catalytic activity and resultant polyethylenes with higher molecular weights. At higher ratio of MAO to titanium precursor, the catalytic system generated better activity with producing polyethylenes with lower molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3411–3423, 2008     

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     

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     

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     

Dichlorovanadium (IV) complexes with salen‐type ligands for ethylene polymerization

Vanadium complexes with tetradentate salen‐type ligands were first time explored in ethylene polymerizations. The effects of the vanadium complex structure, the alkyl aluminum cocatalysts type (EtAlCl₂, Et₂AlCl, Et₃Al, and MAO), and the polymerization conditions (Al/V molar ratio, temperature) on polyethylene yield were explored. It was found that EtAlCl₂ in conjunction with investigated vanadium complexes produced the most efficient catalytic systems. It was shown, moreover, that the structural changes of the tetradentate salen ligand (type of bridge which bond donor nitrogen atoms and type of substituent on aryl rings) affected activity of the catalytic system. The complexes containing ligands with cyclohexylene bridges were more active than those with ethylene bridges. Furthermore, the presence of electron‐withdrawing groups at the para position and electron‐donating substituents at the ortho position on the aryl rings of the ligands resulted in improved activity in relation to the systems with no substituents (with the exception of bulky t‐Bu group). The results presented also revealed that all vanadium complexes activated by common organoaluminum compounds gave linear polyethylenes with high melting points (134.8–137.6 °C), high molecular weights, and broad molecular weight distribution. The polymer produced in the presence of MAO possesses clearly lower melting point (131.4 °C) and some side groups (around 9/1000 C). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6940–6949, 2008     

Ethylene polymerization with FI complexes having novel phenoxy‐imine ligands: Effect of metal type and complex immobilization

A series of bis(phenoxy‐imine) vanadium and zirconium complexes with different types of R³ substituents at the nitrogen atom, where R³ = phenyl, naphthyl, or anthryl, was synthesized and investigated in ethylene polymerization. Moreover, the catalytic performance was verified for three supported catalysts, which had been obtained by immobilization of bis[N‐(salicylidene)‐1‐naphthylaminato]M(IV) dichloride complexes (M = V, Zr, or Ti) on the magnesium carrier MgCl₂(THF)₂/Et₂AlCl. Catalytic performance of both supported and homogeneous catalysts was verified in conjunction with methylaluminoxane (MAO) or with alkylaluminium compounds (Et_nAlCl_3?n, n = 1–3). The activity of FI vanadium and zirconium complexes was observed to decline for the growing size of R³, whereas the average molecular weight (MW) of the polymers was growing for larger substituent. Moreover, vanadium complexes exhibited the highest activity with EtAlCl₂, whereas zirconium ones showed the best activity with MAO. All immobilized systems were most active in conjunction with MAO, and their activities were higher than those for their homogeneous counterparts, and they gave polymers with higher average MWs. That effect was in particular evident for the titanium catalyst. The vanadium complex 3 was also a good precursor for ethylene/1‐octene copolymerization; however, its immobilization reduced its potential for incorporation of a comonomer into a polyethylene chain. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Novel titanium complexes bearing two chelating phenoxy‐imine ligands and their catalytic performance for ethylene polymerization

Three substituted salicylaldimine ligands ( 1a, 2a, 3a ) and their titanium complexes bis[N‐(5‐nitrosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 1 ), bis[N‐(5‐chlorosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 2 ) and bis[N‐(5‐bromosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 3 ) were synthesized and characterized by mass spectra, ¹H NMR and elemental analyses, as well as complex 1 by X‐ray structure analysis. In the presence of methylaluminoxane (MAO), 1, 2 and 3 are efficient catalysts for ethylene polymerization in toluene. Under the conditions of T = 60 °C, p = 0.2 MPa, and n(MAO)/n(cat) = 1500, the activities of 1–3 reached 4.55–8.80 × 10⁶ g of PE (mol of Ti h bar)^?1, which is much higher than that of the unsubstituted complex bis[N‐(salicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 4 ). The viscosity‐average molecular weight of polyethylene ranged from 24.8 × 10⁴ to 44.9 × 10⁴ g/mol for 1–3 and the molecular weight distribution M_w/M_n from 1.85 to 2.34. The effects of reaction conditions on the polymerization were examined in detail. The increase in ethylene pressure and rise in polymerization temperature are favorable for 1–3 /MAO to rise the catalytic activity and the molecular weight of polyethylene. Copyright © 2007 John Wiley & Sons, Ltd.     

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     

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     

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     

Bis-ligated Ti and Zr complexes of chelating N-heterocyclic carbenes

In this communication we report the synthesis of novel titanium and zirconium complexes ligated by bidentate “salicylaldimine-like” N-heterocyclic carbenes (NHC). Double addition of the NHC chelate to either TiCl₄(thf)₂ or ZrCl₄ forms bis-ligated organometallic fragments with a distorted octahedral geometry. These complexes are rare examples of group IV transition-metal NHC adducts. Preliminary catalytic tests demonstrate that in the presence of methylaluminoxane (MAO) these complexes are useful initiators for the polymerization of ethylene and the copolymerization of ethylene with norbornene and 1-octene.