The role of dormant sites in propene polymerization using methylalumoxane activated metallocene catalysts

Propene polymerization of methylalumoxane (MAO) activated rac-Me₂Si(Benz[e]Indenyl)₂ZrCl₂ ( BI ) and rac-Me₂Si(2-Me-Benz[e]Indenyl)₂ZrCl₂ ( MBI ) was studied to investigate the influence of the ligand substitution pattern and the role of dormant sites. Poly(propene) end group composition as well as regio- and stereoirregularities were examined by means of ¹H- and ¹³C-NMR spectroscopy. Dormant sites, resulting from 2, 1-propene insertion, were reactivated either by β-hydrogen transfer to propene, yielding 2-butenyl end groups, or by 1, 2-insertion of propene, yielding regioirregularities. Propene polymerization in the presence of hydrogen gave n-butyl end groups and less regioirregularities as expected for hydrogenolysis of such dormant sites. Methyl substitution in 2-position of the benz[e]indenyl ligand suppressed β-hydrogen transfer to propene, and increased molecular weight with increasing propene concentration. Also, activation energy increased from 30 kJ/mol ( BI /MAO) to 59 kJ/mol ( MBI /MAO). For both catalysts activity depended on propene concentration. The order of reaction relative to propene was 1.7.     

New architecture of supported metallocene catalysts for alkene polymerization

We report the synthesis of a supported metallocene catalyst that exhibits the same activity as a homogeneous catalyst for ethylene polymerization reactions. The key to this new catalytic system is a hybrid organic–inorganic polymer obtained by the cocondensation of an organotrialkoxysilane (OTAS; 40 mol %) with tetraethoxysilane (TEOS; 60 mol %). The particular organic group of OTAS enabled us to avoid gelation when the hydrolytic condensation was performed with a thermal cycle attaining 150 °C. The resulting product [soluble functionalized silica (SFS)] was a glass at room temperature that was soluble in several organic solvents such as tetrahydrofuran and toluene. The ²⁹Si NMR spectrum of SFS showed that the OTAS units were fully condensed (T₃ species), whereas the TEOS units were mainly present as tricondensed (Q₃) and tetracondensed (Q₄) units. SFS was grafted onto activated silica through a reaction of silanol groups. The metallocene [(nBuCp)₂ZrCl₂] was covalently bonded to the SFS‐modified support. The polymerization of ethylene was carried out in toluene in the presence of methylaluminoxane. The activity of the supported catalyst was similar to that of the metallocene catalyst in solution. The simplest explanation accounting for this fact is that most of the metallocene was grafted to SFS species issuing from the surface of the support through a reaction with their silanol groups. This improved the accessibility of the monomer to the reaction sites. Specific interactions of the metallocene species with neighboring organic branches of SFS might also affect the catalytic activity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5480–5486, 2007     

Alkyne-functionalized metallocene complexes: Synthesis, structure, and catalytic ethylene polymerization

Reactions of phenylethynyl lithium with substituted cyclopentenones gave the corresponding pendant phenylethynyl substituted cyclopentadienes. Subsequent deprotonation and transmetallation with TiCl₄·2THF, ZrCl₄, and Cp^∗ZrCl₃ yielded the alkyne-functionalized metallocene complexes [C₅Me₄(CCPh)]₂MCl₂ [M = Ti (1), Zr (2)], Cp^∗[C₅Me₄(CCPh)]ZrCl₂ (3), and Cp^∗[C₅H₂R′₂(CCPh)]ZrCl₂ [R′ = Me (4), Ph (5)]. These complexes were fully characterized by ¹H NMR, ¹³C NMR, MS spectra, and elemental analysis. The molecular structure of 2 was determined by single crystal X-ray diffraction analysis. Ethylene polymerization was studied with these complexes in the presence of methylaluminoxane (MAO).     

Kinetic and mechanism of alkene polymerization

Triphenylmethyl salts of the very weakly-coordinating borate anions [CN{B(C₆F₅)₃}₂]⁻ (1), [H₂N{(C₆F₅)₃}₂]⁻ and [M{CNB(C₆F₅)₃}₄]²⁻ (M = Ni, Pd) have been prepared in simple one-pot reactions. Mixtures of (SBI)ZrMe₂/1/AlBu ₃ ⁱ (SBI = rac-Me₂Si(Ind)₂) are 30–40 times more active in ethylene polymerizations at 60–100°C than (SBI)ZrCl₂/MAO. The quantification of anion effects on propene polymerization activity at 20°C gives the order [CN{B(C₆F₅)₃}₂]⁻ > [H₂N{(C₆F₅)₃}₂]⁻ ≈ B(C₆F₅) ₄ ⁻ ≫ [MeB(C₆F₅)₃]⁻. The highest productivities were of the order of ca. 3.0 × 10⁸ g PP (mol Zr)⁻¹ h⁻¹ [C₃H₆]⁻¹, about 1.3–1.5 times higher than with B(C₆F₅) ₄ ⁻ as the counter anion. The titanium system CGCTiMe₂/1/AlBu ₃ ⁱ gave activities that were very similar to the zirconocene catalyst. The concentration of active species [C*] as determined by quenched-flow kinetic techniques indicates typical values of around 10%, independent of the counter anion, for both the borate and MAO systems. Pulsed field-gradient spin echo and nuclear Overhauser effect NMR experiments on systems designed to be more realistic models for active species with longer polymeryl chains, (SBI)M(CH₂SiMe₃)(μ-Me)B(C₆F₅)₃ and [(SBI)MCH₂SiMe ₃ ⁺ ...B(C₆F₅) ₄ ⁻ ] (M = Zr, Hf), demonstrated the influence of bulky alkyl chains on the ion pair solution structures: while the MeB(C₆F₅)₃ compound exists as a simple inner-sphere ion-pair, the B(C₆F₅) ₄ ⁻ compound is an outer-sphere ion pair (OSIP), a consequence of the relegation of the anion into the second coordination sphere by the γ-agostic interaction with the alkyl ligand. The OSIP aggregates to ion hextuples (10 mM) or quadruples (2 mM). Implications for the polymerization mechanism are discussed; the process follows an associative interchange (I _a) pathway. The text was submitted by the authors in English.     

Tuning the ligand structure in metallocene polymerization catalysts

Meso-[Me₂Si(2-Me-4,6-ⁱPr₂Ind)₂ZrCl₂ was synthesized in a pure form and used as catalyst for the copolymerization of ethene and α-olefins. The results are compared with polymers obtained by C₁-symmetric metallocenes and constrained geometry catalysts. The activity of the meso form is remarkable high and reaches more than 100000 kg polymer/mol Zr · h. The ligand structure has large influence on the incorporation of 1-octene forming thermoplastics (LLDPE) and thermoplastic elastomers (POE).     

Stereospecific living Ziegler-Natta polymerization via rapid and reversible chloride degenerative transfer between active and dormant sites

The successful realization of a stereospecific chloride degenerative transfer living Ziegler-Natta polymerization process that provides isotactic polyolefins of narrow polydispersity (Mw/Mn 相似文献   

Classical and metallocene catalytic systems: Comparison between the stereochemical mechanisms of α-olefin polymerization

Classical Ziegler-Natta and Kaminsky-Ewen catalysts promoting polymerization of hydrocarbon monomers are compared considering the reactivity and the stereochemical mechanisms of polymerization. It is suggested that also the “active sites” of heterogeneous catalysts could be cationic.     

Mechanistic aspects of the olefin polymerization with metallocene catalysts

With C₁-, C₂- or C_s-symmetric metallocenes, different intermediates and types of copolymers can be obtained from randomly distributed to alternating structures. Substitution of the Cp-ring in [Me₂C-(tert-Bu Cp)(Flu)]ZrCl₂ yields ethene/norbornene copolymers with an alternating structure, because the rigid norbornene can only be inserted from the open side of the metallocene. By variation of the polymerization parameters, copolymers with glass transition temperatures above 180°C and molecular weights > 100 000 are synthesized. By supporting different metallocenes on a silica/methylaluminoxane (MAO) carrier the deactivation reaction under electron and hydrogen transfer can be suppressed. This is proved for different Al/Zr ratios when trimethylaluminum (TMA) is used as cocatalyst by the lack of methane evolution by metallocenes and by near independence of the polymerization activity on the prereaction time, after reaching maximum activity. Aluminumalkyls and MAO leach Cp₂ZrCl₂ from the carrier, the leached metallocene is only active in polymerization by adding MAO.     

Kinetic heterogeneity of the active sites of titanium-containing catalytic systems in the stereospecific polymerization of isoprene

The kinetic heterogeneity of the active sites of titanium-containing catalytic systems in the stereospecific polymerization of isoprene was studied based on solving inverse problems for the molecular-weight distribution of polyisoprene with the use of the Tikhonov regularization method. It was found that from two to four types of active sites can occur depending on the nature of the organoaluminum compound used in the catalytic system. The rate constants of elementary steps of the polymerization process for particular types of active sites were obtained for the first time by solving inverse kinetic problems.     

Stereospecific polymerization of methacrylates by metallocene and related catalysts

Stereospecific—isospecific, syndiospecific, and diastereospecific—polymerizations of methacrylates using group 4 metallocene and related catalysts produce polymethacrylates with controlled stereo‐microstructures. The versatility and stereospecificity of these cat‐ alysts for methyl methacrylate polymerization were demonstrated not only in solution‐phase polymerization, but also in polymerizations on silica surfaces and inside silicate nanogalleries. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3395–3403, 2004     

Reactivity of lactams in anionic polymerization

The rate of anionic lactam polymerization is greatly affected by variation of the permittivity of lactams with ring size and substitution, as well as by changes of permittivity during polymerization. Therefore, an estimation of reactivities under comparable conditions is possible in solution only. The lack of any solvent permitting anionic lactam polymerization at low temperatures was circumvented by using living polymers soluble in aprotic solvents as carriers. Such polymers are able to remain in solution even after the addition of a few monomer units of a lactam, the polymer of which is insoluble. In this way, relative reactivities of a series of four-membered lactams, as well as that of the five-membered one were established.     

Reactivity of methacrylates in insertion polymerization

Polymerization of ethylene by complexes [{(P^O)PdMe(L)}] (P^O = κ(2)-(P,O)-2-(2-MeOC(6)H(4))(2)PC(6)H(4)SO(3))) affords homopolyethylene free of any methyl methacrylate (MMA)-derived units, even in the presence of substantial concentrations of MMA. In stoichiometric studies, reactive {(P^O)Pd(Me)L} fragments generated by halide abstraction from [({(P^O)Pd(Me)Cl}μ-Na)(2)] insert MMA in a 1,2- as well as 2,1-mode. The 1,2-insertion product forms a stable five-membered chelate by coordination of the carbonyl group. Thermodynamic parameters for MMA insertion are ΔH(++) = 69.0(3.1) kJ mol(-1) and ΔS(++) = -103(10) J mol(-1) K(-1) (total average for 1,2- and 2,1-insertion), in comparison to ΔH(++) = 48.5(3.0) kJ mol(-1) and ΔS(++) = -138(7) J mol(-1) K(-1) for methyl acrylate (MA) insertion. These data agree with an observed at least 10(2)-fold preference for MA incorporation vs MMA incorporation (not detected) under polymerization conditions. Copolymerization of ethylene with a bifunctional acrylate-methacrylate monomer yields linear polyethylenes with intact methacrylate substituents. Post-polymerization modification of the latter was exemplified by free-radical thiol addition and by cross-metathesis.     

Reactivity of fluorostyrenes in cationic polymerization

Reactivity ratios relative for cationic copolymerization of three fluorostyrenes and styrene were studied. The values of r₁ and r₂ for various experimental conditions were determined. The influence of the nature of the solvent and of the polymerization temperature were studied in particular. Relative activation entropies and enthalpies were determined, and an isokinetic relationship was found for 2-, 3-, and 4-fluorostyrenes. There is a fairly linear correlation between the C8 chemical shift and the values of 1/r₂. All the experimental reactivities were correlated with the quantum chemistry parameters. From this correlation, interaction with C8 and also with C7 and F, was found to be possible, depending on the nature of the monomer.     

Synthesis and structures of cycloalkylidene-bridged cyclopentadienyl metallocene catalysts: effects of the bridges of ansa-metallocene complexes on the catalytic activity for ethylene polymerization

A series of cycloalkylidene-bridged cyclopentadienyl metallocene complexes, [(CH(2))(n)C(C(5)H(4))(2)MCl(2)] (M = Ti, n = 4 (4), 5 (5), 6 (6); M = Zr, n = 4 (7), 5 (8), 6 (9); M = Hf, n = 4 (10), 5 (11), 6 (12)), have been synthesized and applied to ethylene polymerization after activation with methyl aluminoxane (MAO). The cycloalkylidene-bridged titanocene catalysts exhibit much higher activities than the corresponding zirconocene and hafnocene analogues, and have the highest activities at higher temperatures. In comparison, the silacyclopentylidene-bridged metallocene complexes [(CH(2))(4)Si(C(5)H(4))(2)MCl(2)] (M = Ti (13), Zr (14)) and isopropylene-bridged metallocene complexes [Me(2)C(C(5)H(4))(2)MCl(2)] (M = Ti (15), Zr (16)) have also been synthesized and applied to ethylene polymerization. In both cases, the titanocene complexes show much higher activities than the corresponding zirconocene analogues, especially at a lower temperature. The molecular structures of complexes 4-9 have been determined by X-ray diffraction. The structure-activity relationships, especially the effects of the bridges of ansa-metallocene complexes, are discussed.     

Reactivity of propargylamines in complexation and polymerization reactions

Factors were determined which promote the formation of charge-transfer complexes of propargylamines with organic electron acceptors and a change of the activity of the triple bond in propargylamines under the effect of donor-acceptor interactions. On the basis of data from PMR spectroscopy and quantum-chemical calculations it was shown that the tendency of propargylamines to form charge-transfer complexes depends on the electron-donor properties of the substituents at the nitrogen atom. The values of the effective charges at the atoms and an analysis of the structure of the highest occupied molecular orbitals in the propargylamines and their radical cations indicate that mainly electrons localized on nitrogen atoms participate in the complexation reaction. An increase of the reactivity of the triple bond is related to an increase in its polarity under the effect of complexation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 597–601, September–October, 1989.     

Rare earths/main group metal alkyls catalytic systems for the 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene

A series of lanthanum and neodymium complexes comprising the half‐lanthanidocenes Cp*La(BH₄)₂(THF)₂ (Cp* = C₅Me₅) ( 1 ) and Cp*Nd(BH₄)₂(THF)₂ ( 2 ), the trisborohydrides La(BH₄)₃(THF)₃ ( 3 ) and Nd(BH₄)₃(THF)₃ ( 4 ), the trichlorides LaCl₃(THF)₃ ( 5 ) and NdCl₃(THF)₃ ( 6 ), the triisopropoxides La(OⁱPr)₃ ( 7 ) and Nd(OⁱPr)₃ ( 8 ), and the triaryloxide Nd(OC₆H₃‐^tBu₂‐2,6)₃ ( 9 ) has been assessed for the chain transfer polymerization of isoprene. A transmetalation process is occurring efficiently with the borohydride complexes in the presence of magnesium dialkyl. A gradual decrease of the 1,4‐trans stereoselectivity of the reaction is observed at the benefit of 3,4‐selectivity with increasing quantities of magnesium dialkyl. This can be at least partially attributed to the growth of 3,4 polyisoprene units onto the magnesium atom. By combining dialkylmagnesium and trialkylaluminum, a 1,4‐trans stereospecific reversible coordinative chain transfer polymerization of isoprene is reached using the half‐lanthanocene Cp*La(BH₄)₂(THF)₂. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Homogeneous and heterogeneous metallocene/MAO-catalyzed polymerization of trialkylsilyl-protected alcohols

We investigated the ethylene copolymerization by utilizing Me₂Si(Ind)₂ZrCl₂/MAO and Me₂Si(Ind)₂ZrCl₂/MAO/SiO₂ with 10-undecene-1-oxytrimethylsilane and 10-undecene-1-oxytriisopropylsilane and the ethylene copolymerization by using ⁱPr(CpInd)ZrCl₂/MAO and ⁱPr(CpInd)ZrCl₂/MAO/SiO₂ with 5-norbornene-2-methyleneoxytrimethylsilane and 5-norbornene-2-methyleneoxytriisopropylsilane. The trimethylsilyl (TMS) protecting group could not prevent the catalyst deactivation caused by the addition of the polar comonomer. In contrast to that, good catalyst activities and comonomer contents were obtained with the triisopropylsilyl (TIPS) protected monomer. The homopolymerization of 10-undecene-1-OTIPS was carried out with Me₂Si(Ind)₂ZrCl₂/MAO.     

Progress in the syndiotactic polymerization of styrene with metallocene/mao catalysts

Metallocene/MAO catalysts are useful for the production of syndiotactic polystyrene - a new class of high performance polymers. The melting point of the obtained syndiotactic polystyrene depends on the metallocene used and can reach up to 275 °C. In the past, the most active catalysts in polymerization have been half-sandwich titanocenes such as CpTiCl₃ and Cp*TiCl₃. If the chlorinated compounds are changed into the fluorinated compounds as CpTiF₃ and Cp*TiF₃, the activity increases by a factor of 5 to 100. The fluorinated titanocenes are more stable at higher temperatures and need a lower MAO excess in order to obtain optimal activities. Polymers obtained with the unsubstituted CpTiF₃ show melting points which are 17 °C lower than those synthesized by pentamethylcyclopentadienyltitaniumtrifluoride. Especially Cp*TiF₃ shows a much higher activity and, compared with the chlorinated compound, gives polymers with a higher molecular weight. Substituted cyclopentadienyltitanocenes have even higher activities. Ethene/styrene copolymers can be obtained by catalysis with zirconocene compounds.