A DFT Quantum‐Chemical Study of Ion‐Pair Formation for the Catalyst Cp2ZrMe2 /MAO

A process of ion‐pair formation in the system Cp₂ZrMe₂/methylaluminoxane (MAO) has been studied by means of density functional theory quantum‐chemical calculations for MAOs with different structures and reactive sites. An interaction of Cp₂ZrMe₂ with a MAO of the composition (AlMeO)₆ results in the formation of a stable molecular complex of the type Al₅Me₆O₅Al(Me)O–Zr(Me)Cp₂ with an equilibrium distance r(Zr–O) of 2.15 Å. The interaction of Cp₂ZrMe₂ with “true” MAO of the composition (Al₈Me₁₂O₆) proceeds with a tri‐coordinated aluminum atom in the active site (OAlMe₂) and yields the strongly polarized molecular complex or the μ‐Me‐bridged contact ion pair ( d ) [Cp₂(Me)Zr(μMe)Al≡MAO] with the distances r(Zr–μMe) = 2.38 Å and r(Al–μMe) = 2.28 Å. The following interaction of the μ‐Me contact ion pair ( d ) with AlMe₃ results in a formation of the trimethylaluminum (TMA)‐separated ion pair ( e ) [Cp₂Zr(μMe)₂AlMe₂]⁺–[MeMAO]^– with r[Zr–(MeMAO)] equal to 4.58 Å. The calculated composition and structure of ion pairs ( d ) and ( e ) are consistent with the ¹³C NMR data for the species detected in the Cp₂ZrMe₂/MAO system. An interaction of the TMA‐separated ion pair ( e ) with ethylene results in the substitution of AlMe₃ by C₂H₄ in a cationic part of the ion pair ( e ), and the following ethylene insertion into the Zr–Me bond. This reaction leads to formation of ion pair ( f ) of the composition [Cp₂ZrCH₂CH₂CH₃]⁺–[Me‐MAO]^– named as the propyl‐separated ion pair. Ion pair ( f ) exhibits distance r[Zr–(MeMAO)] = 3.88 Å and strong C_γ‐agostic interaction of the propyl group with the Zr atom. We suppose this propyl‐separated ion pair ( f ) to be an active center for olefin polymerization.     

Preparation of functionalized montmorillonites and their application in supported zirconocene catalysts for ethylene polymerization

Ethylene polymerization was carried out with zirconocene catalysts supported on montmorillonite (or functionalized montmorillonite). The functionalized montmorillonite was from simple ion exchange of [CH₃O₂CCH₂NH₃]⁺ (MeGlyH⁺) ions with interlamellar cations of layered montmorillonites. The functionalized montmorillonites [high‐purity montmorillonite (MMT)‐MeGlyH⁺] had larger interlayer spacing (12.69 Å) than montmorillonites without treatment (9.65 Å). The zirconocene catalyst system [Cp₂ZrCl₂/methylaluminoxane (MAO)/MMT‐MeGlyH⁺] had much higher Zr loading and higher activities than those of other zirconocene catalyst systems (Cp₂ZrCl₂/MMT, Cp₂ZrCl₂/MMT‐MeGlyH⁺, Cp₂ZrCl₂/MAO/MMT, [Cp₂ZrCl]⁺[BF₄]/MMT, [Cp₂ZrCl]⁺[BF₄]^?/MMT‐MeGlyH⁺, [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT‐MeGlyH⁺, and [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT). The polyethylenes with good bulk density were obtained from the catalyst systems, particularly (Cp₂ZrCl₂/MAO/MMT‐MeGlyH⁺). MeGlyH⁺ and MAO seemed to play important roles for preparation of the supported zirconocenes and polymerization of ethylene. The difference in Zr loading and catalytic activity among the supported zirconocene catalysts is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1892–1898, 2002     

Ethylene polymerization catalyzed by metallocene/methylaluminoxane systems: quantum-mechanical study on the role of olefin separated ion pairs (OSIP) in the polymerization mechanism

DFT (density-functional theory) calculations were performed to investigate the thermodynamics of formation of Olefin Separated Ion Pairs (OSIP) Cp₂MtCH₃⁺/C₂H₄/Cl₂Al[O(AlMe₃)AlHMe] (Cp = η₅-C₅H₅, Mt = Ti, Zr, Me = CH₃) from ethylene and Cp₂MtMe · Cl₂Al[O(AlMe₃)AlHMe]₂, a model of adduct produced by metallocence/methylaluminoxane (MAO) systems for olefin polymerization. The results account for the high cocatalytic activity of MAO and show that titanium complexes are potentially more active than zirconium homologues, as confirmed by low temperature polymerization tests.     

C-NMR study of Ti(IV) species formed by Cp*TiMe3 and Cp*TiCl3 activation with methylaluminoxane (MAO)

Using ¹³C- and ¹H-NMR spectroscopy, titanium(IV) species formed in the catalytic systems Cp*TiMe₃/MAO and Cp*TiCl₃/MAO (Cp*=C₅(CH₃)₅) in toluene and chlorobenzene were studied within the temperature range 253-293 K and at Al/Ti ratios 30-300. It was shown that upon activation of Cp*TiMe₃ with methylaluminoxane (MAO) mainly the ‘cation-like’ intermediate Cp*Me₂Ti⁺←Me⁻Al(MAO) (2) is formed. Three types of titanium(IV) complexes were identified in Cp*TiCl₃/MAO catalytic system. They are methylated complexes Cp*TiMeCl₂ and Cp*TiMe₂Cl, and the ‘cation-like’ intermediate 2. Complex 2 dominates in Cp*TiCl₃/MAO system in conditions approaching to those of practical polymerization (Al/Ti ratios more than 200). According to the EPR measurements, the portion of EPR active Ti(III) species in the Cp*TiCl₃/MAO system is smaller than 1% at Al/Ti=35, and is about 10% at Al/Ti=700.     

COPOLYMERIZATION OF ETHYLENE AND PROPYLENE WITH CpCH2CH2CH=CH2)2MCl2(M=Zr,Hf)AND Cp2ZrCl2 CATALYSTS

(CpCH_2CH_2CH = CH_2)_2MCl_2(M=Zr, Hf)/MAO and Cp_2ZrCl_2/MAO (Cp=cyclopentadienyl; MAO=methylaluminoxane) catalyst systems have been compared for ethylene copolymerization to investigate the influence of theligand and transition metal on the polymerization activity and copolymer properties. For both CH_2CH_2CH=CH_2 substitutedcatalysts the catalytic activity decreased with increasing propene concentration in the feed. The activity of the hafnocenecatalyst was 6～8 times lower than that of the analogous zirconocene catalyst, ~(13)C NMR analysis showed that the copolymerobtained using the unsubstituted catalyst Cp_2ZrCl_2 has greater incorporatien of propene than those produced byCH_2CH_2CH=CH_2 substituted Zr and Hf catalysts. The melting point, crystallinity and the viscosity-average molecularweight of the copolymer decreased with an increase of propenc concentration in the feed. Both CH_2CH_2CH= CH_2 substitutedZr and Hf catalysts exhibit little or no difference in the melting point and crystallinity of the produced copolymers. However,there are significant differences between the two zirconocene catalysts. The copolymer produced by Cp_2ZrCl_2 catalyst havemuch lower T_m and X_c than those obtained with the (CpCH_2CH_2CH=CH_2)_2ZrCl_2 catalyst. The density and molecular weightof the copolymer decreased in the order: (CpCH_2CH_2CH=CH_2)_2HfCl_2>(CpCH_2CH_2CH=CH_2)_2ZrCl_2>Cp_2ZrCl_2. The kineticbehavior of copolymerizaton with Hf catalyst was found to be different from that with Zr catalyst.     

Metallocene/mao polymerization catalysts supported on cyclodextrin

By treating cyclodextrin(CD) with methylaluminoxane (MAO such as PMAO or MMAO) or trimethylaluminium (TMA) followed by Cp₂ZrCl₂, CD/PMAO/Cp₂ZrCl₂, CD/MMAO/Cp₂ZrCl₂ and CD/TMA/Cp₂ZrCl₂ catalysts were prepared. The catalysts were analyzed by ¹³C-CP/MAS NMR spectrometer and ICP to examine the structure of catalyst and content of Zr and Al. Ethylene polymerization was conducted with MAO or TMA as cocatalyst. Styrene polymerization was also carried out with α-CD/MMAO/Cp*TiCl₃ and α-CD/TMA/Cp*TiCl₃ catalysts. While the ordinary trialkylaluminium such as TMA as well as MAO can be used as cocatalyst for ethylene polymerization, only MAO could initiate the styrene polymerization with α-CD supported catalysts.     

Comparison of the catalytic activity of Ziegler-type catalysts based on Cp2ZrCl2 and (Cp2ZrCl)2O

The rates of ethylene polymerization catalyzed by Cp₂ZrCl₂-polymethylalumoxane and (Cp₂ZrCl)₂O-polymethylalumoxane are equal. According to NMR and ESR spectral data, the same precatalyst, presumably Cp₂ZrMe₂, is formed in both systems by the action of AlMe₃. This accounts for the equal catalytic activity of the systems based on Cp₂ZrCl₂ and (Cp₂ZrCl)₂O. A scheme of reactions resulting in cleavage of the Zr-O-Zr bridge is proposed and confirmed by spectroscopic data.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2104–2107, December, 1993.     

Ethylene polymerization by novel 4,4′-bis(methylene)biphenylene bridged homodinuclear titanocene and zirconocene combined with MAO

4,4′-Bis(methylene)biphenylene bridged homodinuclear titanocene (3) and zirconocene (4) have been synthesized by treatment of CpTiCl₃ and CpZrCl₃ · DME with Na₂[C₅H₄CH₂C₆H₄-p-C₆H₄CH₂C₅H₄], respectively, in THF and characterized by ¹H NMR and element analysis. After activation with methyl aluminoxane (MAO), these catalysts were used for the homogeneous polymerization of ethylene. The influences of reaction conditions, such as temperature, time, catalyst concentration and molar ratio of MAO/Cat. on ethylene polymerization were investigated in detail. The catalytic activities of 3 and 4 are more than three times higher than that of the phenyldimethylene bridged homodinuclear metallocene of titanocene (5) and zirconocene (6), respectively, and also twice higher than that of Cp₂TiCl₂/MAO and Cp₂ZrCl₂/MAO, respectively. However, the catalytic activity of 3 is nearly half as high as that of 4, which reached 1.31 × 10⁶ g PE/mol cat h. The molecular weight of polyethylene increases simultaneously with prolongation of polymerization time. GPC spectra show that 3 and 4 produce polyethylene with broad molecular weight distribution (4.28 and 3.18). The high melting points of the products (131-134 °C) indicate that the polyethylene formed is highly linear and highly crystalline.     

Rare‐Earth‐Metal Alkylaluminates Supported by N‐Donor‐Functionalized Cyclopentadienyl Ligands: C?H Bond Activation and Performance in Isoprene Polymerization

Homoleptic tetramethylaluminate complexes [Ln(AlMe₄)₃] (Ln=La, Nd, Y) reacted with HCp^NMe2 (Cp^NMe2=1‐[2‐(N,N‐dimethylamino)‐ethyl]‐2,3,4,5‐tetramethyl‐cyclopentadienyl) in pentane at ?35 °C to yield half‐sandwich rare‐earth‐metal complexes, [{C₅Me₄CH₂CH₂NMe₂(AlMe₃)}Ln(AlMe₄)₂]. Removal of the N‐donor‐coordinated trimethylaluminum group through donor displacement by using an equimolar amount of Et₂O at ambient temperature only generated the methylene‐bridged complexes [{C₅Me₄CH₂CH₂NMe(μ‐CH₂)AlMe₃}Ln(AlMe₄)] with the larger rare‐earth‐metal ions lanthanum and neodymium. X‐ray diffraction analysis revealed the formation of isostructural complexes and the C? H bond activation of one aminomethyl group. The formation of Ln(μ‐CH₂)Al moieties was further corroborated by ¹³C and ¹H‐¹³C HSQC NMR spectroscopy. In the case of the largest metal center, lanthanum, this C? H bond activation could be suppressed at ?35 °C, thereby leading to the isolation of [(Cp^NMe2)La(AlMe₄)₂], which contains an intramolecularly coordinated amino group. The protonolysis reaction of [Ln(AlMe₄)₃] (Ln=La, Nd) with the anilinyl‐substituted cyclopentadiene HCp^AMe2 (Cp^AMe2=1‐[1‐(N,N‐dimethylanilinyl)]‐2,3,4,5‐tetramethylcyclopentadienyl) at ?35 °C generated the half‐sandwich complexes [(Cp^AMe2)Ln(AlMe₄)₂]. Heating these complexes at 75 °C resulted in the C? H bond activation of one of the anilinium methyl groups and the formation of [{C₅Me₄C₆H₄NMe(μ‐CH₂)AlMe₃}Ln(AlMe₄)] through the elimination of methane. In contrast, the smaller yttrium metal center already gave the aminomethyl‐activated complex at ?35 °C, which is isostructural to those of lanthanum and neodymium. The performance of complexes [{C₅Me₄CH₂CH₂NMe(μ‐CH₂)AlMe₃}‐ Ln(AlMe₄)], [(Cp^AMe2)Ln(AlMe₄)₂], and [{C₅Me₄C₆H₄NMe(μ‐CH₂)AlMe₃}Ln(AlMe₄)] in the polymerization of isoprene was investigated upon activation with [Ph₃C][B(C₆F₅)₄], [PhNMe₂H][B(C₆F₅)₄], and B(C₆F₅)₃. The highest stereoselectivities were observed with the lanthanum‐based pre‐catalysts, thereby producing polyisoprene with trans‐1,4 contents of up to 95.6 %. Narrow molecular‐weight distributions (M_w/M_n<1.1) and complete consumption of the monomer suggested a living‐polymerization mechanism.     

Role of ion-pair equilibria in homogeneous Ziegler-Natta olefin polymerization catalysis

By means of a multinuclear NMR study of the complexes formed between AlCl₃ and either Cp₂TiCl₂ or Cp₂Ti(CH₂SiMe₃)Cl in methylene chloride solution, isomeric forms of the resulting 1:1 complexes have been detected. The influence of temperature, concentration, ratio of the titanocene chloride to aluminum chloride and nature of the solvent upon the ¹H, ¹³C and ²⁷Al NMR spectra has been investigated. The spectral changes caused by the foregoing factors give compelling evidence for a equilibrium in such Cp₂Ti(R)Cl · AlCl₃ complexes (R = Cl, CH₂SiMe₃) between contact ion pairs, Cp₂TiR · Cl · AlCl₃, and solvent-separated ion pairs, Cp₂TiR⁺ AlCl₄⁻. Upon experimental variations in temperature, concentration, solvent and ratio of R_nAlCl_3−n to the titanium catalyst, the polymerization activity of the catalyst system towards ethylene was markedly altered. Such changes in activity support the conclusion that the most active sites for polymerization in such systems are the solvent-separated ion pairs.     

Key intermediates in metallocene-and post-metallocene-catalyzed polymerization

The structures of intermediates formed upon the activation by methylaluminoxane (MAO) of a wide range of metallocene and post-metallocene catalysts of olefin polymerization were studied by ¹³C, ¹H, and ¹⁹F NMR. For all metallocenes considered (L₂ZrCl₂ and L₂TiCl₂), under conditions similar to real polymerization conditions (Al/Zr > 200), two types of intermediates were identified in the reaction solution, namely, heterodinuclear ion pairs [L₂ M(μ-Me)₂AlMe₂]⁺[Me-MAO]^? (III) and zwitterionic intermediates L₂ MMe⁺←Me-Al^?≡MAO (IV (M = Zr, Ti). The relative concentration of III increases with an increase in the Al/Zr ratio. In the post-metallocene/MAO catalytic systems, the reaction solution can be dominated either by heterodinuclear pairs of type III (bis(imino)pyridyl iron complexes) or by zwitterionic intermediates of type IV (half-titanocenes, complexes with restricted geometry). Both species III and species IV catalyze olefin polymerization. Both the species initiating polymerization, [L ₂ ^′ TiMe(S)]⁺[Me-MAO]^?, and the species responsible for chain growth, [L [L ₂ ^′ TiP]⁺[Me-MAO]^? (P is the polymer chain, and S is a solvent molecule), were characterized in the bis(phenoxyimine) titanium complex/MAO system.     

Surface chemistry of selected supported metallocene catalysts studied by DR‐FTIR,CPMAS NMR,and XPS techniques

Two supported metallocene catalysts (CS 1: PQ 3030/MAO/Cp₂ZrCl₂ and CS 2: PQ 3030‐BuGeCl₃/MAO/Cp₂ ZrCl₂) were prepared by sequentially loading MAO and Cp₂ZrCl₂ on partially dehydroxylated silica PQ 3030. In catalyst CS 2, ⁿBuGeCl₃ was used to functionalize the silica. These catalysts were characterized by DR‐FTIR spectroscopy, CPMAS NMR spectroscopy, and XPS. Their catalytic performance was evaluated by polymerizing ethylene using the MAO cocatalyst and characterizing the resulting polymers by GPC. Both catalysts produced two metallocenium cations (Cation 1: [Cp₂ZrCl]⁺ and Cation 2: [Cp₂ZrMe]⁺) with comparable equilibrium concentrations and showed varying solid‐state electronic environments. The modified supports (PQ 3030/MAO and PQ 3030‐BuGeCl₃/MAO) acted as weakly coordinating polyanions and stabilized the above cations. BuGeCl₃ did not affect the solid‐state electronic environment. However, it increased the surface cocatalyst to catalyst molar ratio (Al:Zr), acted as a spacer, increased catalyst activity, and enhanced chain‐transfer reactions. The separately fed MAO cocatalyst shifted the equilibrium between Cation 1 and Cation 2 toward the right. Consequently, more Cation 2 was generated, which acted as the effective and active single‐site catalytic species producing monomodal PDI. Copyright © 2006 John Wiley & Sons, Ltd.     

Ethylene Polymerization in the Presence of Iron(II) 2,6-Bis(imine)pyridine Complex: Structures of Key Intermediates

The structures of intermediates generated by the activation of 2,6-bis[1-(2,6-dimethylphenylimino)ethyl]pyridineiron(II) chloride (1) with various cocatalysts, methylalumoxane (MAO), trimethylaluminum (TMA), and TMA in combination with B(C₆F₅)₃and Ph₃CB(C₆F₅)₄, is studied by ¹H and ²HNMR spectroscopy. The 1/AlMe₃system exhibits a higher catalytic activity in ethylene polymerization than the 1/MAO system. The activity of the latter decreases sharply with a decrease in the amount of AlMe₃in MAO. Neutral Fe(II) complexes rather than cationic intermediates are suggested to be active components in both catalytic systems.     

Effect of trimethylaluminum on the formation of active sites of the catalytic system bis[N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinato]titanium(IV) dichloride—MAO and catalytic isomerization of hex-1-ene

The transformations of bis[N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinato]-titanium(iv) dichloride (L₂TiCl₂) occurring in toluene under the action of methylalumoxane (MAO) were studied by ¹H NMR spectroscopy. The commercially available MAO containing trimethylaluminum (AlMe₃) and MAO free of AlMe₃ (the so called “dry” MAO) were used. The catalytic transformations of hex-1-ene involving the systems L₂TiCl₂-MAO were studied. We proposed the structures of the cationic titanium complexes formed in the absence and in the presence of hex-1-ene under the action of MAO. In the absence of olefin, neutral and cationic titanium complexes are decomposed under the action of AlMe₃ according to the exchange reaction of the complex ligand with the methyl groups of AlMe₃ to form LAlMe₂. The neutral complexes react considerably faster than the cationic ones. In the presence of olefin, decomposition of complexes under the action of AlMe₃ is suppressed. The titanium complex activated by “dry” MAO isomerizes hex-1-ene to hex-2-ene. In the presence of large amounts of TMA (commercial MAO), this reaction does not take place.     

Synthesis and characterization of ethylene‐propylene‐1‐pentene terpolymers

Ethylene (E), propylene (P), and 1‐pentene (A) terpolymers differing in monomer composition ratio were produced, using the metallocenes rac‐ethylene bis(indenyl) zirconium dichloride/methylaluminoxane (rac‐Et(Ind)₂ZrCl₂/MAO), isopropyl bis(cyclopentadienyl)fluorenyl zirconium dichloride/methylaluminoxane (Me₂C(Cp)(Flu)ZrCl₂/MAO, and bis(cyclopentadienyl)zirconium dichloride, supported on silica impregnated with MAO (Cp₂ZrCl₂/MAO/SiO₂/MAO) as catalytic systems. The catalytic activities at 25 °C and normal pressure were compared. The best result was obtained with the first catalyst. A detailed study of ¹³C NMR chemical shifts, triad sequences distributions, monomer‐average sequence lengths, and reactivity ratios for the terpolymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 947–957, 2008     

Synthesis,crystal structure and catalytic performance of bis (imino)pyridyl nickel complexes

Two new Ni(II) complexes of 2,6-bis[1-(2,6-diethylphenylimino)ethyl]pyridine (L¹), 2,6-bis[1-(4-methylphenylimino)ethyl]pyridine (L² ) have been synthesized and structurally characterized. Complex Ni(L¹)Cl₂?·?CH₃CN (1), exhibits a distorted trigonal bipyramidal geometry, whereas complex Ni(L¹)(CH₃CN)Cl₂ (2), is six-coordinate with a geometry that can best be described as distorted octahedral. The catalytic activities of complexes 1, 2, Ni{2,6-bis[1-(2,6-diisopropyl-phenylimino)ethyl]pyridine} Cl₂?·?CH₃CN (3), and Ni{2,6-bis[1-(2,6-dimethylphenylimino) ethyl]pyridine}Cl₂?·?CH₃CN (4), for ethylene polymerization were studied under activation with MAO.     

On study of chemoselectivity of reaction of trialkylalanes with alkenes, catalyzed with Zr π-complexes

The influence of the organoaluminium compound nature, Zr π-ligand environment, solvent type and reagent ratio on the chemoselectivity of reactions of trialkylalanes (AlMe₃, AlEt₃) with alkenes, catalyzed with L₂ZrCl₂ [L = Cp, Cp′ (Cp′-η⁵-C₅H₄CH₃), Cp^∗ (Cp^∗-η⁵-C₅(CH₃)₅), Ind (indenyl), Flu (fluorenyl)] has been studied. It is shown that in the case of AlMe₃, the hydro- and carboalumination products, and alkene dimers are formed. The catalytic reaction of AlEt₃ with the olefins yields aluminacyclopentanes altogether with the hydro- and carboalumination products, and the dimers. A probable reaction mechanism has been proposed.     

Deuteron magnetic resonance study of the mechanism of methyl group exchange between tetramethyltitanium and trimethylaluminium

The exchange of methyl groups between tetramethyltitanium and trimethylaluminium has been studied by the direct observation of a new resonance line in the ²D NMR spectrum of the reaction mixture containing perdeuterated and undeuterated organometallic compounds.The kinetics and mechanism of the exchange reaction are influenced by the ethyl ether concentration in a hexane solution of the tetramethyltitanium compound. At a molar ratio TiMe₄/Et₂0 > 1 rapid exchange occurs between unsolvated metal alkyls. Tetramethyltitanium etherate reacts with trimethylaluminium in two steps, an initial fast complexation to Me₃Ti [AlMe₄] which accounts for the transfer of a single methyl group from the titanium to the aluminium atom and a subsequent slow reverse process which leads to the transfer of methyl groups from the aluminium to the titanium atom and which results ultimately in a random equilibrium distribution of the labelled methyl groups amongst both metal atoms.Mixing the etherates of both titanium and aluminium methyl compounds led to the appearance of an extra signal downfield (τ 5.6 ppm) which is apparently due to the methyl resonance of the species [TiMe₃]⁺ in the solvent-separated ion-pair form of the complex [TiMe₃]⁺ [AlMe₄]^?.     

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     

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.