Fractionation of Polyolefin Elastomer by a Modified SSA Technique

As an important part of semicrystalline polymer materials, polyolefin elastomers are widely used, and the in-depth analysis of their molecular chain structure information is of great significance to promote their rapid development. We show in this work an effort in characterizing a commercial polyolefin elastomer of ethylene/1-octene copolymer by a modified successive self-nucleation and annealing (SSA)technique. A small amount of linear polyethylene was blended with the ethylene/1-octene copoly...     

~(13)C-NMR STUDY OF ETHYLENE-1-OCTENE COPOLYMERS

A ~(13)C-NMR method is presented for a quantitative determination of the respective monomercomposition and sequence distributions in ethylene-1-octene copolymers prepared with supportedtitanium/magnesium catalyst. On the basis of the sequence distributions, the ethylene-1-octenecopolymerization mechanism was studied. It was found that the observed sequence distributions inethylene-1-octene copolymers are satisfactorily predicted by the two-site model M/M,in whichthe copolymerization proceeds according to first-order Markovian statistics at the two differentsites.     

ESR Study of the Reaction Between Cp2Ti(CO)2 and Cp2TiBr2

Introduction Floriani and Fachinetti have proposed that (Cp_2TiCl)_2 can be prepared by the reaction between Cp_2TiCl_2 and Cp_2Ti(CO)_2. We extended the method to the preparation of (Cp_2TiBr)_2 and characterized an active intermediate by ESR method.     

COPOLYMERIZATION OF ETHYLENE WITH 1-OCTENE USING Et(Ind)2ZrCl2/MAO CATALYST

Copolymerization of ethylene/1-octene was carried out in toluene withvarious concentrations of comonomer in the feed using Et(Ind)_2ZrCl_2/MAO (methyl alu-minoxane) as catalyst. It was found that with the increase of 1-octene concentration in thefeed the content of 1-octene in the copolymer increases, while the density, melting point,crystallinity and intrinsic viscosity of copolymer decrease. A copolymer with very lowdensity, containing 11.5 mol% of 1-octene (VLLDPE) can be produced with this catalystsystem. The effect of temperature and zirconium aluminum mole ratio of the catalyst onthe copolymerization was also investigated. The results of ~(13)C NMR determination of thecopolymer showed that the 1-octene units in the copolymer are principally isolated.     

HOMO- AND COPOLYMERIZATION OF ETHYLENE CATALYZED BY ANSA-METALLOCENES WITH DOUBLY HETERO-BRIDGES

Three ansa-metallocenes(Me_2C)(Me_2Si)Cp_2TiCl_2(1),[(CH_2)_5C](Me_2Si)Cp_2TiCl_2 (2)and (Me_2C)(Me_2Si)Cp_2ZrCl_2 (3)with larger dihedral angles and longer distance from metal to the center of Cp planes were synthesized and used as catalysts for ethylene polymerization in the presence of methylaluminoxane (MAO).In the case of ethylene polymerization,compared the feature structures of unbridged metallocenes, singly bridged metallocenes and doubly bridged metallocenes 1,2,3,there exhibit the relationship ...     

STRUCTURAL INVESTIGATION OF A NEW POLYORGANOSILOXANE CONTAINING NANOTUBULAR CAVITIES USING ORGANIC FLUORESCENT PROBES*

Fluorescent molecules - p-dimethylaminobenzonitrile (DMABN) and trans-stilbene (TSB) -were used as probes to investigate the inner structure of the nanotubular cavities contained in a newpolyorganosiloxane (POS) which was prepared by the hydrosilylation coupling reaction of cis-isotacticladderlike polyvinylsilsesquioxane (Vi-T) with 1, 1,3,3-tetramethyldisiloxane (H-MM) as coupling agent inthe presence of catalyst dicyclopentadienyldichloroplatin (Cp_2PtCl_2). The results from FTIR spectra andfluorescence spectra in combination with molecular simulation revcal that the cross-section of thenanotubular cavity is nearly rectangular in shape, and is about 0.62 nm in width and about 0.38 nm in height.This work gains in-depth knowledge into the inner structure of the nanotubular cavities of POS andfurthermore provides a guide to the selection of proper guest molecules in constructing functionalsupramolecular clathrate based upon POS.     

Synergistic Effects of the ZnCl2-SiCl4 Modified TiCl4 /MgCl2 /THF Catalytic System on Ethylene/1-Hexene and Ethylene/1-Octene Copolymerizations简

The copolymerizations of ethylene with 1-hexene or 1-octene by using TiCl4 /MgCl2 /THF catalysts modified with different metal halide additives(ZnCl2, SiCl4, and the combined ZnCl2-SiCl4) were investigated based on catalytic activity and copolymer properties. It was found that the catalyst modified with mixed ZnCl2-SiCl4 revealed the highest activities for both ethylene/1-hexene and ethylene/1-octene copolymerization. The increase in activities was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Based on the FTIR measurements, the characteristic C―O―C peaks of the catalysts modified with metal halide additives were slightly shifted to lower wavenumber when compared to the unmodified catalyst. This showed that the modified catalysts could generate more acid sites in the TiCl4 /MgCl2 /THF catalytic system leading to an increase in activities as well as comonomer insertion(as proven by13C-NMR). However, Lewis acidmodifications did not affect the microstructure of the copolymers obtained. By comparison on the properties of copolymers prepared with the unmodified catalyst, it was found that polymers with ZnCl2 and/or SiCl4 modification exhibited a slight decrease in melting temperature, crystallinity and density. It is suggested that these results were obtained based on the different amount of α-olefins insertion, regardless of the types of Lewis acids and comonomer.     

POLYMERIZATION OF 1-OCTENE AND DETERMINATION OF MARKHOUWINK CONSTANTS OF POLY(1-OCTENE)

The polymerization of 1-octene initiated by methylalumoxane(MAO)-activated Ni(Ⅱ)-based-α-diimine complexes[(2,6-i-Pr)_2C_6H_3-DAB(An)]NiBr_2 was investigated.Using this catalyst,poly(1-octene)s with molecular weight between 100×10~3 and 400×10~3 and polydispersity(M_w/M_n) between 1.3 and 1.5 were synthesized successfully by varying reaction time at room temperature.The poly(1-octene)s were amorphous polymers and could be well soluble in tetrahydrofuran(THF).After fractional precipitation,poly(1-octene)s...     

Palladium-Catalyzed Addition of Carbon Monoxide and Carbon Tetrachloride to 1-Octene in Supercritical Carbon Dioxide

The Pd-catalyzed addition of carbon monoxide and carbon tetrachloride to 1-octene gave coadduct [alkyl 2-( 2, 2, 2-trichloroethyl)octanoate] as the major product in supercritical carbon dioxide by using pyridine as the base. It was found that the selectivity and the yield of coadduct were greatly affected by the pressure of carbon dioxide, the reaction temperature and the amounts of alcohol and base used.     

THE HYDROSILATION REACTION OF LADDERLIKE POLYALLYLSILSESQUIOXANE(ALLYL-T)AND POLYHYDROSILSESQUIOXANE(H-T)

The one plus one (1 + 1) mode of hydrosilation reaction of ladderlike cis-isotatic polyallylsilsesquioxane (Allyl-T)and polyhydrosilsesquioxane (H-T) using dicyclopentadienylplatinumdichloride (Cp_2PtCl_2) as the catalyst leads to theformation of a new polyorganosiloxane (POS). The presence of nanoscale tubular structure in the product POS waspreliminarily proved by IR, ~1H-NMR, differential scanning calorimetry (DSC), X-ray diffraction (XRD), gel permeationchromatography (GPC), atomic force microscopy (AFM) and molecular simulation.     

Copolymerization of ethylene and 1-octene with Cp*TiCl3 as catalyst supported on 3-aminopropyltrimethoxysilane treated SiO2

Two kinds of SiO₂-supported Cp^*TiCl₃ (Cp^* = η⁵-1,2,3,4,5-pentamethylcyclopentadienyl) catalysts were prepared, using SiO₂ modified with 3-aminopropyltrimethoxysilane (N SiO₂) and the ordinary SiO₂ as the carrier. The copolymerization of ethylene and 1-octene was conducted over them combined with methylaluminoxane (MAO) as cocatalyst. From a detailed analysis of the produced copolymers, it was found that the N SiO₂ supported Cp^*TiCl₃ catalyst gives poly(ethylene-co-1-octene) with a higher content of 1-octene and a narrower molar mass distribution as well as a narrower chemical composition.     

Effect of metal type on the metallocene-catalyzed oligomerization of 1-hexene and 1-octene to produce polyα-olefin-based synthetic lubricants

1-Hexene and 1-octene oligomerization reactions were performed with Cp₂ZrCl₂ and Cp₂HfCl₂ in the presence of methylaluminoxane as cocatalyst at 25 and 80 °C to produce polyα-olefin-type oils. By examining the molecular weight results, obtained from gel permeation chromatography, the oligomeric structure of the products was confirmed. Hafnocene produced oligomers with higher molecular weights in comparison with zirconocene under the same reaction condition. In addition, with increasing temperature, the molecular weight decreased. Differential scanning calorimetry analysis of the poly1-hexene- and poly1-octene-type oligomers confirmed their amorphous nature. ¹H-nuclear magnetic resonance (NMR) analysis was performed to study the mechanism of termination reactions. The results obtained from the ¹H-NMR analysis confirmed the vinylidine form (vd) as the only unsaturated structure in all synthesized oligomers. Therefore, in the 1-hexene and 1-octene oligomerization reactions with these two catalytic systems, the chain termination is totally accomplished by β-hydride elimination at both reaction temperatures.     

Temperature dependence of copolymerization parameters in ethene/1-octene copolymerization using homogeneous rac-Me2Si(2-MeBenz[e]Ind)2ZrCl2/MAO catalyst

Ethene was copolymerized with 1-octene using homogeneous MAO-activated rac-Me₂Si(2-MeBenz[e]Ind)₂ZrCl₂ at constant ethene concentration with temperature varying between 0 and 60°C to determine a temperature dependence of copolymerization parameters. At constant 1-octene and ethene concentration (constant ethene/1-octene feed molar ratio) 1-octene incorporation decreased with increasing temperature. Furthermore, when ethene/1-octene molar ratio was varied by varying the temperature keeping 1-octene concentration and ethene pressure constant, increasing temperature accounted for lower molecular masses without affecting 1-octene incorporation. An explanation for the observed temperature dependence of the copolymerization parameters is presented, considering the solution-enthalpy of the gaseous ethene in the solvent. In all cases amorphous poly(ethene-co-1-octene) with 1-octene content varying between 20 and 40 mol % was obtained. © 1997 John Wiley & Sons, Inc.     

Trifluoromethyl- and difluoromethyl-β-lactams as useful building blocks for the synthesis of fluorinated amino acids, dipeptides, and fluoro-taxoids

Enantiopure 1-acyl-3-hydroxyl-4-CF₂H-azetidin-2-ones and 1-acyl-3-hydroxy-4-CF₃-azetidin-2-ones serve as versatile intermediates for the syntheses of CF₂- and CF₃-containing α-hydroxy-β-amino acids, dipeptides, and taxoid anticancer agents. Both enantiomers of 3-hydroxy-4-CF₂H-β-lactams can be obtained in high yields through the diethylaminosulfur trifluoride (DAST) reaction of the corresponding enantiopure 4-formyl-β-lactam that is prepared through [2+2] cycloaddition of acetoxyketene to a 3-methyl-2-butenaldimine, followed by enzymatic optical resolution and ozonolysis. (+)-3-Hydroxy-4-CF₃-β-lactams and (−)-3-hydroxy-4-CF₃-β-lactams can also be readily obtained in enantiopure form through [2+2] cycloaddition of a CF₃-imine with a ketene, followed by enzymatic optical resolution. Practical processes for the preparations of these enantiopure 3-hydroxy-4-R_f-β-lactams as well as their synthetic applications are described.     

Synthesis of 9-(trifluoromethyl)pyrido[1′,2′:1,2]-imidazo[4,5-b]quinoxalines

9-(Trifluoromethyl)pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines (9-CF₃-PIQs) were obtained from the cyclization of 2-amino-3-chloro-6-(trifluoromethyl)quinoxaline ( 1a ) with some substituted pyridines. 3-[2-(4-Pyridyl)ethenyl]-9-CF₃-PIQ, one of thus obtained 9-CF₃-PIQs, cyclized with another molecule of 1a to produce the dihydro bis-PIQ-ethene derivative.     

Interaction of titanocene generated in the system Cp2TiCl2 + Mg in thf with benzyne and tolane. A novel route to titanaindene and titanacyclopentadiene complexes

Direct synthesis of the titanaindene complex Cp₂Ti[o-C₆H₄C(Ph)C(PH)] through of reaction of tolane with Cp₂Ti and benzyne, generated in the system Cp₂TiCl₂ + Mg + o-fluorobromobenzene in THF is described. Under similar conditions, reaction of Cp₂TiCl₂ with Mg in THF, in the presence of tolane only (ratio Cp₂TiCl₂/Mg/Ph₂C₂ ≈ 1/1/2) yields the titanacyclopentadiene complex Cp₂Tic(Ph)C(Ph)C(PH)C(Ph).     

Allyl complexes of dicyclopentadienyl-niobium(III) and -tantalum(III)

The synthesis and the properties of the complexes Cp₂TaCl₂, Cp₂M(allyl), Cp₂M(1-methylallyl) and Cp₂M(2-methylallyl) with M  Nb, Ta are described. The complex Cp₂TaCl₂ has one unpaired electron per tantalum atom, while the allyl complexes are diamagnetic. The IR and PMR spectra indicate that the allyl group is π-bonded to the metal. The mass spectra of the complexes are discussed; the thermal stability of the Cp₂Nb- and Cp₂Ta-(allyl) complexes was investigated by differential thermal analysis. The properties of the niobium and tantalum complexes are compared with those of the corresponding titanium complexes.     

Insertionsreaktionen von Bis(η-cyclopentadienyl)hydridorhenium mit monosubstituierten Acetylenen

Bis(η-cyclopentadienyl)hydridorhenium Cp₂ReH undergoes stereospecific trans insertion reactions when treated with monosubstituted acetylenes HCCR (R  CO₂Me, CN, CF₃). The cis alkenyl complexes Cp₂Re[η¹-(Z)-CHCHR] thus formed isomerize thermally or under acid catalysis to produce the trans isomers Cp₂Re[η¹-(E)-CHCHR]. When Cp₂ReH adds to HCCCOMe only the trans isomer is observed. The regiospecific β-addition of Cp₂ReH contrasts with the α-addition of Cp₂MoH₂ and Cp₂WH₂. The insertion of acetylenes HCCR′ into the metalcarbon bond of some alkenyl complexes Cp₂Re[η¹-(E)-CHCHR] affords butadienyl complexes Cp₂Re[η¹-{(1E,3E)-CHCHR′CHCHR&}] (R,R′  COMe, CO₂Me). The (E,E)-configuration of these compounds is deduced from ³J(¹³-C¹H) coupling constants.     

Monomer-isomerization polymerization. XX. Monomer-isomerization polymerization of 2-, 3-, and 4-octenes with Ziegler–Natta catalyst

A study of the monomer isomerization polymerization of 2-, 3-, and 4-octenes has been made with TiCl₃–(C₂H₅)₃Al catalyst at 80°C in comparison with the ordinary polymerization of 1-octene. It was found that all these octenes underwent monomer-isomerization polymerization to give high-molecular-weight homopolymer consisting exclusively of the 1-octene unit. The addition of an isomerization catalyst such as nickel acetylacetonate accelerated this polymerization. The rates of polymerization were found to decrease in the following order: 1-octene > 2-octene > 3-octene > 4-octene. These results indicate that the isomerization proceeded by a stepwise double-bond migration. It was also found that the monomer-isomerization copolymerization of 2-octene and 2-butene occurred under similar conditions and produced copolymers of both 1-olefin units.     

Metallocene-catalyzed ethene/styrene co- and terpolymerization with olefinic termonomers

Ethene was co- and terpolymerized with 1-octene and styrene using the methylalumoxane (MAO) activated halfsandwich metallocene Me₂Si(Me₄Cp)(N-t.-butyl)TiCl₂(Cp = cyclopentadienyl, Me = methyl) as catalyst. At temperatures of 40 and 60°C styrene concentration was varied in order to investigate the influence of the comonomers. Despite decreasing the overall activity with respect to ethene/1-octene copolymerization, polymerization activity was found to exibit a relative maximum with increasing styrene concentration. An explanation is given taking two different comonomer effects into account. Low styrene concentration promoted higher 1-octene incorporation compared to ethene/1-octene copolymerization but significantly lowered the molecular weight of the terpolymers. With constant ethene and 1-octene concentration it was possible to produce ethene/1-octene/styrene terpolymers with styrene content varying from 0 to 25 mol % and 1-octene content varying from 8 to 21 mol %. All terpolymers were amorphous. With constant ethene content it was found possible to vary their glass transition temperature with 1-octene/styrene molar ratio incorporated in the terpolymer. ¹³C-NMR spectroscopic microstructure analysis showed that no styrene/1-octene sequences were found in the terpolymer backbone. Furthermore terpolymerizations were conducted successfully incorporating norbornene, 1,5-hexadiene and propene as monomers in terpolymertization with ethene and styrene. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2549–2560, 1997