Strong influences of cocatalyst on ethylene/propylene copolymerization with a MgCl2/SiO2/TiCl4/diester type Ziegler-Natta catalyst

Using triethylaluminum (TEA), triisobutylaluminum (TIBA) or TEA/TIBA mixtures of molar ratio 75/25, 50/50 and 25/75 as the cocatalyst, five different ethylene-propylene copolymer samples were synthesized by a MgCl₂/SiO₂/TiCl₄/diester type Ziegler-Natta catalyst in a slurry polymerization process. The synthesized copolymers are strongly heterogeneous in chain structure and were fractionated into part of nearly random copolymer and part of segmented copolymer. Both polymerization activity and copolymer structure were found to be markedly changed when the cocatalyst was changed from TEA to TEA/TIBA mixtures or pure TIBA. As the content of TEA in cocatalyst increases, yield of the random part of product increases and the yield of the crystalline segmented copolymer part decreases. There is also a decrease in ethylene content of the whole product with increasing TEA amount. Copolymerization behaviors of the TEA/TIBA mixture activated catalysis systems are not simple superposition of those activated by pure TEA and TIBA. When a 50/50 TEA/TIBA mixture was used as cocatalyst, the copolymerization activity became the highest, and yields of both the random copolymer part and the segmented copolymer part are close to the highest level. On the other hand, both parts of the copolymer produced with a 50/50 TEA/TIBA mixture are relatively more blocky than the products of TEA or TIBA systems, and difference in ethylene content between the random part and the segmented part was the smallest. The segmented copolymer part of three typical samples was further fractionated by temperature-gradient extraction fractionation into fractions of different ethylene content and sequence distribution. Changing TEA content in the cocatalyst exerted strong influences also on the fraction distribution of the segmented part of copolymer.     

Ethylene/1-hexene copolymerization with TiCl4/MgCl2/AlCl3 catalyst in the presence of hydrogen

A TiCl₄/AlCl₃/MgCl₂ (Cat-B) catalyst containing 5.2 wt.% Al was prepared by the reaction of TiCl₄ with ethanol adduct of AlCl₃/MgCl₂ mixture. A TiCl₄/MgCl₂ catalyst (Cat-A) without doped AlCl₃ was also prepared by the same method. Ethylene-1-hexene copolymerization catalyzed by Cat-B in the presence of hydrogen showed slightly higher efficiency and higher 1-hexene incorporation than Cat-A. Comonomer incorporation was markedly increased when the cocatalyst AlEt₃ was replaced by Al(i-Bu)₃. Adding Ph₂Si(OMe)₂ as external donor in the catalyst system caused decrease in polymerization activity and 1-hexene incorporation. Each copolymer sample was fractionated into three fractions: n-heptane insoluble fraction (fraction A), n-heptane soluble and n-hexane insoluble fraction (fraction B) and n-hexane soluble fraction (fraction C). In most cases the amount of intermediate fraction (fraction B) was smaller than the other fractions and did not increase as the total 1-hexene content increase, indicating the presence of two classes of copolymer fractions with greatly different comonomer content and clear bimodality of the copolymer composition distribution. Doping AlCl₃ in the catalyst, changing cocatalyst and adding external donor mainly changed the weight ratio of fraction A to fraction C, but exerted little influences on their composition. According to the sequence distribution data of the fractions, doping AlCl₃ in the catalyst resulted in slight decrease of product of reactivity ratios (r₁r₂) in both fraction A and fraction C.     

TiCl4/t-BuNH2 as the sole catalyst for a hydroamination-based Fischer indole synthesis

A system comprising TiCl₄ and t-BuNH₂ acts as a catalyst for highly regioselective hydroamination reactions of alkynes using hydrazines and at the same time a Lewis acid in the transformation of the generated hydrazones into indole derivatives, while a 1,3-diyne is converted to pyrroles using the same precatalyst.     

Molecular structure of the azidoalane [Me2N(CH2)3]AltBu(N3). X-ray structural determination and ab initio calculations

A single crystal of the azidoalane [Me₂N(CH₂)₃]AltBu(N₃) (1a), grown in a capillary using a miniature zone melting procedure, was investigated by X-ray analysis. Compound 1a (C₉H₂₁AlN₄) is a monomeric species in the solid state, which crystallizes in the monoclinic space group P2₁ with a=6.8560(14) Å, b=12.251(3) Å, c=7.786(2) Å, β=108.51(3)° and Z=2. The results of the X-ray structural determination are compared with the calculated structure of 1a (HF/6-31G(d) and B3LYP/6-31G(d) level of theory). Whereas the overall agreement between the measured and calculated structure is good, the Al–N donor-bond length differs by 11 and 12 pm at the HF and B3LYP level, respectively. To evaluate the effects of a polar environment on the molecular structure of 1a self-consistent reaction field (SCRF) calculations at the HF and B3LYP level with the 6-31G(d) basis set were performed.     

Effect of ligand in ethylene/styrene copolymerization by [Me2Si(C5Me4)(NR)]TiCl2 (R = tert-Bu, cyclohexyl) and (1,3-Me2C5H3)TiCl2(O-2,6-Pr2C6H3)-MAO catalyst system

Copolymerization of ethylene with styrene using linked cyclopentadienyl-amide titanium(IV) complexes, [Me₂Si(C₅Me₄)(R)]TiCl₂ [R=tert-Bu (1), cyclohexyl (2)], and non-bridged (1,3-Me₂C₅H₃)TiCl₂(O-2,6-ⁱPr₂C₆H₃) (3)-MAO catalysts have been explored. Although the catalytic activity by 2 was lower than 1, 2 showed more efficient styrene incorporation than 1 under the same conditions. Moreover, the resultant copolymer prepared by 2 possessed completely different microstructure from those by 1, indicating that the nature of amide ligand affects both styrene incorporation and monomer sequence.     

Theoretical study of C24N4 molecule

Both ab initio 6-31G, 3-21G and STO-3G basis sets and semiempirical PM3 and AM1 molecular orbital calculations are carried out on the C₂₄N₄ molecule of the T_d symmetry group. Results on the fully optimized structure which constrained T_d symmetry, molecular orbitals and vibrational frequency were obtained by both ab initio and semiempirical methods. The binding energy and various thermodynamic properties were also calculated via the PM3 and AM1 semiempirical methods. All the evidence of this work proves that the C₂₄N₄ molecule is stable and that its four six-membered rings with a remarkable delocalized C…C bond are similar to the related rings in the C₆₀ buckminsterfullerene structure.     

B12Sc4和B12Ti4团簇的储氢性质

提出了两个稳定的团簇B₁₂Sc₄和B₁₂Ti₄, 基于理论计算, 研究了它们的结构与储氢性质. 结果发现, 在这两个稳定的团簇中, 过渡金属原子不会聚合在一起而影响它们对氢气的吸附. B₁₂Sc₄最多可以吸附12个氢分子, 达到7.25% (质量分数)的储氢量. 它的平均每氢分子吸附能量为10.5 kJ·mol^-1. B₁₂Ti₄最多只能吸附8个氢分子, 储氢量为4.78%. 但平均每氢分子吸附能量可达50.2 kJ·mol^-1. 进一步计算表明, 即使在77 K,也需要很高的氢气压力才能使12个氢分子都吸附到B₁₂Sc₄上. 电子结构分析表明, B₁₂Ti₄-nH₂吸附结构中的Kubas作用要大于相应B₁₂Sc₄-nH₂结构中的Kubas作用.     

CCl2自由基与H2O分子反应动力学研究

用213 nm激光光解CCl4产生CCl2自由基，用LP LIF技术测定了室温下基态CCl2自由基与H2O分子的反应速率常数为(5.45±0.95)×10－14 cm3•molecule－1•s－1.在G2MP2理论水平上计算了CCl2＋H2O反应的最低单重态势能面，揭示了插入与加成 消除两种反应机理，得到了三个可能的产物通道:HCl＋HClCO、HCl＋trans ClCOH以及HCl＋cis ClCOH.并用RRKM TST和传统过渡态理论计算了这三个通道的分支比及其温度效应.结果说明在低温下（273 K），插入机理的产物通道的分支比远大于加成 消除机理的产物通道， HCl＋HClCO是主要产物，分支比为77.4％，其次是HCl＋cis ClCOH，分支比为22.6％.而在高温下（3000 K），加成 消除机理的反应通道大于插入机理， HCl＋trans ClCOH分支比为82.3％.     

HNCO热解为CO2和HNCNH的反应机理理论研究

利用从头算ＲＨＦ／３－２１Ｇ方法研究了ＨＮＣＯ二聚后生成ＨＮＣＮＨ和ＣＯ２的反应机理。计算表明,该反应是分步反应,由反应物经第一过渡态生成四元环中间体,再经过第二过渡态分解为产物,与实验得到的结论一致。反应的第一步是速度控制步骤,计算得到的活化位垒为１７２．５５ｋＪ·ｍｏｌ＾－１,与实验上测得的１７６．４０±１６．３０ｋＪ·ｍｏｌ＾－１相吻合。反应的第二位垒为８３．６８ｋＪ·ｍｏｌ＾－１,在实验条     

A qualitative model for polymerisation of propylene with a MgCl2-supported TiCl4 Ziegler-Natta catalyst

A qualitative model for polymerisation of propylene with a MgCl₂-supported TiCl₄ Ziegler-Natta catalyst is developed. A series of polymerisation with increasing external electron donor/Ti ratio is performed and the polymers are analysed with GPC, ¹³C NMR and DSC. The model explains the trends in isotacticity and isotactic sequence length based on an equilibrium reaction of the electron donor, which is either coordinated next to an active site or extracted to the solution by the cocatalyst AlR₃. Different rates for propagation and termination reactions when the donor is present or absent are used to explain the trends in activity and molar mass. The possibilities for a quantitative model and parameter estimation are discussed.     

CH2+O2反应的反应机理

The mechanisms of the CH2＋ O2→ H2O＋ CO and CH2＋ O2→ H2＋ CO2 reactions have been studied by performing ab initio CAS(8,8)/6-31G(d,p) calculations, and five intermediates(IMn) and eight transitions(TSn) have been located along the reaction paths. The predicted path for the CH2＋ O2→ H2O＋ CO is: CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS5→ H2O＋ CO. For the CH2＋ O2→ H2＋ CO2 reaction, there are two paths: (i) CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS6→ H2＋ CO2 and (ii) CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS7→ IM4b→ TS8→ H2＋ CO2, with the latter path more favorable energetically.     

Theoretical investigation on the model active site for isotactic polypropylene in heterogeneous Ziegler-Natta catalyst: A density functional study

The stereoselectivity of the model active site formed by the adsorption of Ti₂Cl₇ on the (1 0 0) surface of MgCl₂ was investigated by density functional calculations. The analysis of energetics for successive propylene insertions into the model active site reveals that the insertion of propylene into the model active site is energetically more favorable when a growing chain and one chlorine atom (that makes the active site chiral) are on the opposite side rather than on the same side. From this result, it is realized that the model active site is highly stereoselective. It is also observed that the Cl atoms near the growing chain significantly affect the activation energy barrier through the interaction with the growing chain.     

原子团簇离子TinP+m的几何结构与电子性质研究

用量子化学ab initio方法研究激光等离子体反应生成的Ti     

CH3NO2和CH3自由基吸氢反应途径和变分速率常数计算

采用MP2(full)/6-311G(d, p)从头算方法,优化了硝基甲烷和甲基自由基吸氢反应的过渡态结构,经QCISD(T)方法进行能量校正,得出该反应的正逆向反应的活化位垒分别是58.21 kJ•mol－1和67.17 kJ•mol－1.沿IRC分析指出该反应是氢转移协同反应,而且在反应途径上存在一个引导反应进行的振动模式,这一反应模式引导反应进行的区间在反应坐标S的-0.9～1.0(amu)1/2bohr之间;在温度为800～2600 K范围内,运用改进的变分过渡态理论(ICVT),计算了该反应的速率常数,并与实验类比所得的速率常数随温度的变化趋势进行了比较.     

Effect of methylaluminoxane/transition-metal ratio on the physical properties and chemical composition distributions of ethylene-hexene copolymers produced by a rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst

A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for the impregnation of TiCl₄ and rac-Et(Ind)₂ZrCl₂. The prepared rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO(methylaluminoxane)/SMB catalyst was applied to the ethylene-hexene copolymerization under the conditions of variable Al(MAO)/Zr ratio and fixed Al(TEA, triethylaluminum)/Ti ratio. The effect of Al(MAO)/Zr ratio on the physical properties and chemical composition distributions of ethylene-hexene copolymers produced by a rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB catalyst was investigated. The catalytic activity of rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB was steadily increased with increasing Al(MAO)/Zr ratio from 200 to 500. The ethylene-hexene copolymer produced with Al(MAO)/Zr = 300, 400, and 500 showed two melting points at around 110 °C and 130 °C, while that produced with Al(MAO)/Zr = 200 showed one melting point at 136 °C. The number of chemical composition distribution (CCD) peaks was increased from 4 to 7 and the short chain branches of ethylene-hexene copolymer were distributed over lower temperature region with increasing Al(MAO)/Zr ratio. The lamellas in the copolymer were distributed over lower temperature region and the small lamellas in the copolymer were increased with increasing Al(MAO)/Zr ratio. The rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB catalyst preferably produced a ethylene-hexene copolymer with non-blocky sequence ([EHE]) with increasing Al(MAO)/Zr ratio.     

Direct dynamics studies on the hydrogen abstraction reactions CF3O+CH4(CD4)→CF3OH(CF3OD)+CH3(CD3)

The dynamics properties of the hydrogen abstraction reaction CF₃O+CH₄→CF₃OH+CH₃ are studied by dual-level direct dynamics method. Optimization calculations are preformed by B3LYP and MP2 with the 6-311G(d,p) basis set, and the single-point calculations are done at the multi-coefficient correction method based on quadratic configuration interaction with single and double excitations (MC-QCISD) method. The rate constants are evaluated by canonical variational transition-state theory with a small-curvature tunneling correction over a wide range of temperature 200–2000 K. The agreement between theoretical and experimental rate constants is good in the measured temperature range. The calculated results show that the variational effect is small and almost neglected over the whole temperature range, whereas, the tunneling correction plays a role in the lower temperature range. The kinetic isotope effect for the reaction is ‘normal’. The value of k_H/k_D is 2.38 at room temperature and it decreases with the temperature increasing.     

Role of titanium oxidation states in polymerization activity of Ziegler-Natta catalyst: A density functional study

The role of titanium oxidation states in olefin polymerization activity for Ziegler-Natta (ZN) catalyst has been investigated using density functional calculations at B3LYP/LANL2DZ as well as extended LANL2DZ basis that includes diffuse and polarization functions for C, H and Cl. Using the simple [TiCl₂CH₃]ⁿ (n = +1, 0, −1) model catalyst systems, we could rationalize some of the well-known experimental facts with varying Ti oxidation states (+4, +3, +2) in the real ZN systems. Firstly, irrespective of Ti oxidation states, the activation barriers (E_act) for ethylene and syn propylene insertion in Ti-CH₃ bond are comparable in accordance with experimental and modeling studies. Secondly, it was observed that Ti(IV) catalyst has the lowest E_act which progressively increase in the order Ti(IV) < Ti(III) < Ti(II) high spin < Ti(II) low spin catalysts in line with experimental and several modeling results. The effect of solvation on olefin insertion barriers are seen more prominent in case of Ti(IV) systems compared to other oxidation states.     

TiCl4溶胶凝胶法制备TiO2纳米粉体

利用TiCl4的乙醇溶液作为前驱体 ,运用溶胶凝胶法制备了TiO2 纳米粉体 .研究结果表明 ,在TiCl4与乙醇混合成溶液的过程中 ,TiCl4即与乙醇及乙醇中的微量水发生醇解和部分水解脱氯反应形成钛酸酯 .在随后的成胶化过程中 ,则主要是钛酸酯吸收气氛中的水气 ,脱去乙醇基形成Ti-OH键并发生缩脱水聚合形成无机聚合物溶胶 .增加成胶化时间 ,可以促进乙醇基的脱去和无机聚合物的形成 ,促进锐钛矿TiO2 纳米颗粒的形成     

An efficient procedure for the synthesis of coumarin derivatives using TiCl4 as catalyst under solvent-free conditions

The ability of titanium(IV) chloride as a catalyst to promote the Pechmann condensation reaction with a range of phenols and β-keto esters is described.The reaction was carried out by addition of TiCl₄ to a mixture of the phenol and the β-keto ester with thorough stirring in the absence of a solvent and represents an improvement on the classical Pechmann conditions. The yields of coumarins obtained via this novel protocol were significantly higher than those using the conventional method and the reaction duration was reduced to a few minutes or even a few seconds.     

Formation of the lithium alkylaluminium secondary amide [Me2Al{(PhCH2)2N}2Li·THF] by a methane elimination/amide insertion process

Synthesised by refluxing the amine adduct [Me₃Al·(PhCH₂)₂NLi·HN(CH₂Ph)₂] in toluene/THF, the title compound has been structurally characterised by X-ray diffraction, and the methane elimination/amide insertion processes involved in its formation have been modelled theoretically through a series of ab initio MO calculations.