Theoretical Study on Molecular Structures of Methylaluminoxane Nanotubes

Density functional theory was used to optimize structures of different methylaluminoxane nanotubes with general formula [（AIOMe）2]n, [（AlOMe）3]n and [（A1OMe）4]n cycle unit, where n ranges from 1 to 10. To explore the stability of nanotubes, the binding energies and total energies are calculated. The results indicate that [（A1OMe）3]n and [（A1OMe）4]n have the stable structure of nanotubes. When n is 3, they have the most stable structure in all systems. Moreover, [（A1505）]n and [（A17OT）]n are also considered, but their dimers have irregular and distorted structures. So [（A1505）]n and [（A17OT）]n nanotubes are impossible to exist.

Synthesis of Syndiotactic Polystyrene with Novel Titanocene Catalysts Activated by Modified Methylaluminoxane

Novel highly active eta(5)-pentamethylcyclopentadienyltribenzyloxy titanium catalyst activated by modified methylaluminoxane (m-MAO) was prepared for styrene syndiospecific polymerization. The influences of the contents of trimethylaluminum (TMA) in m-MAO and external addition of tri-isobutylaluminum (TIBA) on the distribution of the oxidation states of titanium were investigated in detail. The Ti (III) is in favour of styrene syndiospecific polymerization in higher catalytic activity.

Polymerization of methyl methacrylate catalyzed by mono-/bis-salicylaldiminato nickel(Ⅱ) complexes and methylaluminoxane

Two types of salicylaldiminato-based nickel complexes,mono-ligated Ni(II)complexes([O-C_(6)H_(4)-o-C(H)=N-Ar]Ni(PPh_(3))(Ph)(5),[O-(3,5-Br_(2))C_(6)H_(2)-o-C(H)=N-Ar]Ni(PPh_(3))(Ph)(6),[O-(3-t-Bu)C_(6)H_(3)-o-C(H)=N-Ar]Ni(PPh_(3))(Ph)(7))and bis-ligated Ni(II)complexes([O-(3,5-Br_(2))C_(6)H_(2)-o-C(H)=N-Ar]_(2)Ni(8),[O-(3,5-Br_(2))C_(6)H_(2)-o-C(H)=N-2-C_(6)H_(4)(PhO)]_(2)Ni(9),Ar=2,6-C_(6)H_(3)(i-Pr)_(2))were synthesized and characterized by Fourier transform infrared spectroscopy(FT-IR),nuclear magnetic resonance(NMR),mass spectrography(MS)and elemental analysis(EA).In the presence of methylaluminoxane(MAO)as cocatalyst,all the nickel complexes exhibited high activities for the polymerization of methyl methacrylate(MMA)and syndiotactic-rich poly(methyl methacrylate)(PMMA)was obtained.The complexes with less bulky substituents on salicylaldiminato framework possessed higher activities,while with the same salicylaldiminato,the mono-ligated nickel complexes showed higher catalytic activity than bis-ligated ones.

Stereochemical control in propylene polymerization with asymmetrically substituted titanocene/methylaluminoxane catalyst

A new mono-substituted titanocene,(η~5-cyclopentadienyl)[η~5-(1-(4-methoxyphenyl)cyclohexyl) cyclopentadienyl]dichlorotitanium(I),has been prepared via a novel modified synthesis,and its X-ray crystal structure has been determined.It crystallizes in the orthorhombic space group P2_12_12_1 with cell constants a=0.9680(5)nm,b=1.2846(5)nm,c=1.6944(6)nm,Z=4,R=0.066.The I/methylaluminoxane(MAO)catalyst system produces at different polymerization temperatures either an isotactic or a syndiotactic polypropylene, both of which have the combined influence of enantiomorphic-site control and chain-end control,or an atactic polypropylene controlled by Bernoallian propagation mechanism.

The effect of polymerization conditions on crystalline of polybutene-1 catalyzed by metallocene catalyst

Polybutene-1 was synthesized stereoselectively with the precursor η(5)-(pentamethyl-cyclopentadienyl) tribenzyloxide titanium (Cp*Ti(OBz)3) and methylaluminoxane (MAO). The effects of polymerization conditions, trimethyl alumina (TMA) content in MAO and temperature on the crystalline and molecular weight of the products, and catalytic activity were investigated. The structural properties of the polybutene-1 were characterized with (13)C NMR and WAXD.

COPOLYMERIZATION OF ETHYLENE AND PROPYLENE WITH (CpCH_2CH_2CH=CH_2)_2MCl_2(M=Zr,Hf)AND Cp_2ZrCl_2 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.

COPOLYMERIZATION OF ETHYLENE WITH 1-OCTENE USING Et(Ind)_2ZrCl_2/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.

Tandem Catalysis of One Metallocene Catalyst Combined with Two Different Cocatalysts for Preparing Branched Polyethylene

Tandem catalytic systems, consisting of ethylene bis（indenyl） zirconium dichloride with two different cocatalysts, alkylaluminum（diethylaluminium chloride or trialkylaluminum） and methylaluminoxane, were employed in preparing branched polyethylene from ethylene as sole monomer. The catalytic system rac-Et（Ind）2Zr Cl2/Al Et2Cl/MAO exhibited high incorporation（29.0/1000C）. The oligomerization and copolymerization reaction conditions in the tandem catalytic system, as well as the different cocatalysts, have effects on the catalytic activity and the properties of the obtained polymer, such as melting temperature, crystallinity, molecular weight and molecular weight distribution. Moreover, the oligomerization reaction condition is the main factor in altering the properties and structures of polyethylene.