Direct evidence of the second‐order dependence of propagation rate on propene concentration in living polymerization with the [t‐BuNSiMe2Flu]TiMe2/B(C6F5)3 catalyst

Propene polymerization was conducted with the [t‐BuNSiMe₂Flu]TiMe₂/B(C₆F₅)₃ catalyst at –50°C at various concentrations of propene. The polymerization proceeds in a living manner regardless of the propene concentration employed. Molecular weight of polymer obtained in a certain polymerization time with low monomer conversion increases with increasing concentration of propene. The logarithmic plot of molecular weight against propene concentration gives a straight line with a slope of 1.8, which indicates that the propagation rate is almost of second order with respect to propene concentration.     

Polymerization of propene with the XTiCl3/MgCl2–Al(i-Bu)3 catalyst system (X = cyclopentadienyl,pentamethylcyclopentadienyl, indenyl,and heptamethylindenyl) in the absence and presence of a lewis base

Several kinds of MgCl₂-supported half titanocene (XTiCl₃; X = cyclopentadienyl, pentamethylcyclopentadienyl, indenyl, and heptamethylindenyl) catalysts were prepared and applied to propene polymerization using Al(i-Bu)₃a as cocatalyst. It was confirmed from the catalyst analysis that the ligand (X) is attached to titanium even after the reaction with Al(i-Bu)₃. When polymerization was conducted without any external donor, those catalysts predominantly gave atactic PP. However, addition of a suitable monofunctional Lewis base like ethylbenzoate caused to change the stereospecificity of polymer from aspecific into highly isospecific. On the other hand, the use of a bifunctional donor like di-n-butylphthalate killed the activity almost completely. The isotactic PP was found to have a microstructure similar to that obtained with metallocene catalysts. © 1997 John Wiley & Sons, Inc.     

Copolymerization of propene with high-1-olefin using a MgCl2/TiCl4 catalyst

Copolymerization of propene and 1-olefins including 1-octene, 1-decene, 1-dodecene, 1-tetradecene, and 1-hexadecene were studied with the catalyst system MgCl₂/TiCl₄-Al(i-Bu)₃. It was found that the polymerization productivity and the consumption rate of propene are improved significantly in the presence of the comonomer. The total productivity of propene/1-olefin copolymerizations decreases as follows: 1-octene> 1-decene>1-dodecene>1-hexadecene>1-tetradecene. The reactivity ratios were estimated from the copolymerization results. ¹³C NMR was used to characterize the microstructures of propene/1-octene copolymer. Finally, the oxygen enrichment behavior of propene/1-octene copolymer was investigated.     

Reactions of Me2Si(2‐Me‐4,5‐BenzInd)Zr(Cl)(NEt2) and Me2Si(2‐Me‐4,5‐BenzInd)ZrCl2 (BenzInd = benzindenyl) with trimethylaluminum and methylaluminumoxane: Correlation of spectroscopy and propene polymerizations

The activity of metallocene/methylaluminumoxane (MAO) catalysts in olefin polymerization is highly dependent on both the alkylation and activation of the complexes. The leaving ligands have an important role in the complex activation, influencing the activity of the system. The aim of this work was to study the reactions of complexes Me₂Si(2‐Me‐4,5‐BenzInd)₂ZrCl₂ ( A ; BenzInd = benzindenyl) and Me₂Si(2‐Me‐4,5‐BenzInd)₂Zr(Cl)(NEt₂) ( B ) with trimethylaluminum (TMA) and MAO. The reaction kinetics and products were studied by both ultraviolet–visible and NMR spectroscopy. In addition, the polymerization behavior of the different species was investigated in propene polymerizations. Complex B was more easily monomethylated by TMA than complex A and resulted in L₂Zr(Me)(NR₂)‐type species. Monomethylation of the complexes before polymerization enhanced the polymerization activity of both complexes. When complexes A and B reacted with MAO, similar cationic species were formed, giving equal polymerization activities. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6455–6464, 2005     

Synergetic effect between NiO and Ni3V2O8 in propane oxidative dehydrogenation

The oxidative dehydrogenation (ODH) of propane was investigated on Ni-V-O catalysts in a wide range of vanadium contents (5-40%). The addition of a small amount of vanadium significantly increased the catalytic activity of NiO for oxidative dehydrogenation of propane to propene. The formation of propene has a good correlation with the coexistence of NiO and Ni₃V₂O₈. This result strongly suggests that a synergetic effect exists between them in Ni_XV_1-XO_Y (X = 0.95 to 0.6). The best results were obtained with a high Ni/V ratio (e.g. X = 0.95 to 0.85). The active sites and selective oxygen species are discussed. The influence of the catalyst preparation technique and the redox properties of the catalyst were also examined.     

Study of the chain transfer reaction by hydrogen in the initial stage of propene polymerization

The chain transfer reaction by hydrogen in the initial stage of propene polymerization with MgCl₂-supported Ziegler catalyst was studied by means of the stopped-flow polymerization. The yield and molecular weight of polypropene produced in the initial stage were not affected by hydrogen. Thus, the method was successfully applied to find the region in which hydrogen does not act as a chain transfer reagent. On the other hand, a chain transfer reaction proceeded in the initial stage of polymerization by using Zn(C₂H₅)₂. Furthermore, when the catalyst was treated with Al(C₂H₅)₃ before polymerization, the molecular weight of the produced polymer was decreased by using hydrogen, indicating that it acted as a chain transfer agent for the catalyst modified by pre-treatment.     

Donor- and acceptor-modified metallocene-based homogeneous Ziegler-Natta catalysts

The polymerization kinetics of propene polymerization using metallocene/methylaluminoxane (MAO) homogeneous catalysts have been investigated to explore the role of donor/acceptor interactions and to enhance the catalyst productivities. In the case of the non-stereospecific Cp₂ZrCl₂/MAO model system it has been demonstrated that, in addition to the well known irreversible deactivation, reversible deactivations, which are second order relative to the zirconium active site concentration, account for the decay of the polymerization rate. While MAO injection during polymerization enhances the polymerization rate, zirconocene addition deactivates the catalyst which can be reactivated by injecting additional MAO. A sequence of dynamic equilibria involving the formation of active cationic metallocene intermediates as well as inactive zirconocene species, e.g., zirconocene dimers, is proposed. Lewis base and Lewis acid additives have been added as probes to examine the role of such equilibria in the case of metallocene-based catalyst systems such as MAO-activated Cp₂ZrCl₂, racemic ethylenebisindenyl zirconium dichloride (EBIZrCl₂), and racemic ethylenebis (4,5,6,7-tetrahydroindenyl) zirconium dichloride (EBTHIZrCl₂). While the conventional donors such as 2,6-ditert.butyl-4-methylphenol (BHT) and 2,2,6,6-tetramethylpiperidine (TMP) reduce catalyst productivities, even at very low donor/Al molar ratios, increasing propene concentration and addition of trimethylboroxine (TMB) substantially enhance catalyst productivities and affect molecular weights of the polypropylene produced with metallocene/MAO catalysts.     

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.     

In situ CP MAS NMR spectroscopy under continuous-flow conditions to monitor real time dynamics during propene polymerization over a supported Ziegler catalyst

In situ propene polymerization was observed using CP MAS (cross polarization with magic angle spinning) ¹³C NMR spectroscopy under the conditions of continuously flowing propene through a supported Ziegler catalyst treated with triethylaluminium. The signals at 44, 26, and 22 ppm attributed to the CH₂, CH, and CH₃ groups of polypropene, respectively, were found to appear upon exposure to the propene flow (0.1 L/min). An increase in intensities of these lines was observed for 30 min, then they remained approximately constant. The cross-polarization parameters of nascent polypropene, measured using standard techniques, were close to those of typical crystalline polypropene. The technique has a great potential as an effective tool for the investigation of the polypropene formation on the Ziegler catalyst.     

Influence of Metallocene Type on the Order of Ethylene Polymerization and Catalyst Deactivation Rate in a Solution Reactor

The solution polymerization of ethylene using rac-Et(Ind)₂ZrCl₂/MAO and (Dimethylsilyl(tert-butylamido)(tetramethyl- cyclopentadienyl)titanium Dichloride)(CGC-Ti)/MAO was studied in a semi-batch reactor at 120 °C under different monomer pressures and catalyst concentrations. The kinetics of ethylene polymerization with rac-Et(Ind)₂ZrCl₂/MAO can be described with first order reactions for polymerization and catalyst deactivation. When (CGC-Ti)/MAO is used, however, second order kinetics are observed for catalyst decay and the order of polymerization changes from 2 to 1 with increasing ethylene pressure.     

Stopped‐flow polymerizations of ethene and propene in the presence of the catalyst system rac‐Me2Si(2‐methyl‐4‐phenyl‐1‐indenyl)2ZrCl2/methylaluminoxane

The kinetics of ethene and propene polymerization at 20–60°C in the presence of the homogeneous catalyst system rac‐Me₂Si(2‐methyl‐4‐phenyl‐1‐indenyl)₂ZrCl₂/methylaluminoxane was investigated by means of stopped‐flow techniques. The specific rate of chain propagation, measured at the very short reaction times typical of this method, turned out to be ≈10² times higher for ethene than for propene; this suggests that diffusion limitations through the poly(ethylene) precipitating at longer reaction times may be responsible for the fact that the two monomers polymerize instead at comparable rates under “standard” conditions. It was also found that the concentration of active sites is significantly lower than the analytical Zr concentration.     

Propene polymerization using homogeneous MAO-activated metallocene catalysts: Me2Si(Benz[e]Indenyl)2ZrCl2/MAO vs. Me2Si(2-Me-Benz[e]Indenyl)2ZrCl2/MAO

Propene was polymerized at 40°C and 2-bar propene in toluene using methylalumoxane (MAO) activated rac-Me₂Si(Benz[e]Indenyl)₂ZrCl₂ ( BI ) and rac-Me₂Si(2-Me-Benz[e]Indenyl)₂ZrCl₂ ( MBI ). Catalyst BI /MAO polymerizes propene with high activity to afford low molecular weight polypropylene, whereas MBI /MAO is less active and produces high molecular weight polypropylene. Variation of reaction conditions such as propene concentration, temperature, concentration of catalyst components, and addition of hydrogen reveals that the lower molecular weight polypropylene produced with BI /MAO results from chain transfer to propene monomer following a 2,1-insertion. A large fraction of both metallocene catalyst systems is deactivated upon 2,1-insertion. Such dormant sites can be reactivated by H₂-addition, which affords active metallocene hydrides. This effect of H₂-addition is reflected by a decreasing content of head-to-head enchainment and the formation of polypropylene with n-butyl end groups. Both catalysts show a strong dependence of activity on propene concentration that indicates a formal reaction order of 1.7 with respect to propene. MBI /MAO shows a much higher dependence of the activity on temperature than BI /MAO. At elevated temperatures, MBI /MAO polymerizes propene faster than BI /MAO. © 1995 John Wiley & Sons, Inc.     

Copolymerization of 2‐butene and ethylene with catalysts based on titanium and zirconium complexes

The polymerization of 2‐butene and its copolymerization with ethylene have been investigated using four kinds of dichlorobis(β‐diketonato)titanium complexes, [ArN(CH₂)₃NAr]TiCl₂ (Ar = 2,6‐ⁱPr₂C₆H₃) and typical metallocene catalysts. The obtained copolymers display lower melting points than those produced of homopolyethylene under the same polymerization conditions. ¹³C NMR analysis indicates that 9.3 mol‐% of 2‐butene units were incorporated into the polymer chains with Ti(BFA)₂Cl₂‐MAO as the catalyst system. With the trans‐2‐butene a higher copolymerization rate was observed than with cis‐2‐butene. A highly regioselective catalyst system for propene polymerization, [ArN(CH₂)₃NAr]TiCl₂ complex using a mixture of triisobutylaluminium and Ph₃CB(C₆F₅)₄ as cocatalyst, was found to copolymerize a mixture of 1‐butene and trans‐2‐butene with ethylene up to 3.1 mol‐%. Monomer isomerization‐polymerization proceeds with typical metallocene catalysts to produce copolymers consisting of ethylene and 1‐butene.     

Copolymerization of vinylcyclohexane with ethene and propene using zirconocene catalysts

Vinylcyclohexane (VCH) was copolymerized with ethene and propene using methylaluminoxane‐activated metallocene catalysts. The catalyst precursor for the ethene copolymerization was rac‐ethylenebis(indenyl)ZrCl₂ ( 1 ). Propene copolymerizations were further studied with C_s‐symmetric isopropylidene(cyclopentadienyl)(fluorenyl)ZrCl₂ ( 2 ), C₁‐symmetric ethylene(1‐indenyl‐2‐phenyl‐2‐fluorenyl)ZrCl₂ ( 3 ), and “meso”‐dimethylsilyl[3‐benzylindenyl)(2‐methylbenz[e]indenyl)]ZrCl₂ ( 4 ). Catalyst 1 produced a random ethene–VCH copolymer with very high activity and moderate VCH incorporation. The highest comonomer content in the copolymer was 3.5 mol %. Catalysts 1 and 4 produced poly(propene‐co‐vinylcyclohexane) with moderate to good activities [up to 4900 and 15,400 kg of polymer/(mol of catalyst × h) for 1 and 4 , respectively] under similar reaction conditions but with fairly low comonomer contents (up to 1.0 and 2.0% for 1 and 4 , respectively). Catalysts 2 and 3 , both bearing a fluorenyl moiety, gave propene–VCH copolymers with only negligible amounts of the comonomer. The homopolymerization of VCH was performed with 1 as a reference, and low‐molar‐mass isotactic polyvinylcyclohexane with a low activity was obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6569–6574, 2006     

Propene polymerization with the MgCl2-supported dichlorobis(β-diketonato)titanium catalysts activated by ordinary alkylaluminums

Several kinds of dichlorobis(β-diketonato)titanium complexes, i.e., Ti(ace-tylacetonato)₂Cl₂, Ti(1-benzoylacetonato)₂Cl₂, Ti(2,2,6,6-tetramethyl-3,5-heptanedionato)₂Cl₂ and Ti(4,4,4-trifluoro-1-phenyl-1,3-butanedionato)₂Cl₂, were synthesized and the corresponding MgCl₂-supported catalysts were prepared by impregnation method. The test of them for propene polymerization revealed that those MgCl₂-supported catalysts could be activated not only by methylaluminoxane (MAO) but also by ordinary alkylaluminums as well. The effect of typical Lewis bases on the catalyst performance was investigated in some detail, which indicated that organic silanes are most effective for the improvement of isospecificity of those catalysts. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 129–135, 1998     

Ethylene polymerization with porous polystyrene spheres supported Cp2ZrCl2 catalyst

A catalyst with porous polystyrene beads supported Cp₂ZrCl₂ was prepared and tested for ethylene polymerization with methylaluminoxane as a cocatalyst. By comparison, the porous supported catalyst maintained higher activity and produced polyethylene with better morphology than its corresponding solid supported catalyst. The differences between activities of the catalysts and morphologies of the products were reasonably explained by the fragmentation processes of support as frequently observed with the inorganic supported Ziegler–Natta catalysts. Investigation into the distribution of polystyrene in the polyethylene revealed the fact that the porous polystyrene supported catalyst had undergone fragmentation during polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3313–3319, 2003     

Catalyseurs Zieger-Natta supportés sur MgCl2 pour la polymérisation stéréorégulée du propène. II. Système catalytique simple: Solide binaire MgCl2-TiCl4 et solution cocatalytique triéthylaluminium,benzoate d'ethyle

The kinetics of propene polymerization in heptane slurry at 1–4 bars was studied with a catalytic system that consisted of a solid catalyst prepared by adsorption of TiCI₄ on pure porous MgCl₂ (by dehydrating MgCl₂, 6 H₂O with thionyl chloride) and a cocatalytic, heptanic solution of ethylbenzoate (BE) and triethylaluminium (TEA). At a temperature approaching 60°C/polymerization began immediately after the introduction of the monomer. The polymerization rate decreased continuously during the reaction. The loss in activity, however, was not due to a diffusional effect (e.g., blocking of the catalyst by the growing polymer). Studies of the ageing of the catalytic system showed a deactivation of the catalytic system itself as a function of the time of contact between the catalyst and the cocatalyst. The product of the thermal decomposition of the complex 1:2 formed by the reaction of BE with TEA was not associated with the deactivation process or stereospecific control, which depend on the BE/AI ratio and the presence of the complex.     

Syntheses and characterizations of polypropene,polystyrene and their block copolymers with titanocene catalysts

Pentamethylcyclopentadienyltitanium tribenzyloxide, Cp^*Ti(OBz)₃, was used as the catalyst precursor for polymerizations of propene and styrene. The titanocene catalyst affords atactic polypropene and syndiotactic polystyrene with high activities in the presence of methylalumimoxane (MAO). Block copolymerization of propene and styrene was carried out in the presence of Cp^*Ti(OBz)₃/MAO catalyst system by the means of external addition of triisobutylaluminum (TIBA) and sequential monomer feed. The copolymerization product is mainly a mixture of atactic polypropene(aPP) and syndiotactic polystyrene(sPS) homopolymers and aPP-b-sPS block copolymers, which can be separated into fractions with successive extraction with boiling methylethyl ketone(MEK), heptane, tetrahydrofuran(THF), and chloroform. Studies on thermal properties showed that rubbery phases and crystalline regions both appear in the block copolymer at the room temperature and that aPP-b-sPS block copolymer has better toughness than sPS.     

Amalgamation of ziegler-natta and metallocene catalysts

The MgCl₂ supported half titanocenes and Ti(4, 4, 4-trifluoro-1-phenyl-1, 3-butanedionato)₂Cl₂ catalysts were synthesized and applied to propene polymerization. Without supporting on MgCl₂, those complexes displayed almost no activity even using methylaluminoxane (MAO) as cocatalyst. When supported on MgCl₂, on the other hand, the resulting catalysts could be activated by ordinary alkylaluminums to yield polypropene in fairly high yields. The catalyst isospecificity was markedly improved by the addition of a suitable Lewis base.