Formation, deactivation and transformation of stereospecific active sites on TiCl4/dibutylphthalate/Mg(OEt)2 catalyst induced by short time reaction with Al-alkyl cocatalyst

Formation, deactivation and transformation of stereospecific active sites on TiCl₄/dibutylphthalate (DBP)/Mg(OEt)₂ Ziegler–Natta catalyst induced by short time reaction with triethylaluminum (TEA) cocatalyst (with TEA pretreatment time from 0 to 600 s) were investigated by stopped-flow propene polymerization combined with temperature rising elution fractionation (TREF) and GPC methods. It was demonstrated that both formation and deactivation of active sites with broad multiplicity in isospecificity on the catalyst are slow reactions with an induction period of ca. 0.2 s. It was most important to find that the formation of active sites with the highest isospecificity strongly depends on the interaction between the catalyst and cocatalyst (up to 60 s of pretreatment) even in the presence of internal donor. This newly observed phenomenon (according to our knowledge) suggested that the transformation of monometallic active sites (aspecific or less isospecific) into bimetallic active sites (highly isospecific) through reversible complexing with TEA cocatalyst (or its reaction product diethylaluminum chloride (DEAC)) in Ziegler–Natta catalysts cannot be overlooked even in the presence of internal electron donor. The existence of –OC₂H₅ ligand in the catalyst most probably gave birth to a new group of active titanium species. The stability of active sites increases with increasing isospecificity in the early stage of pretreatment (up to 60 s of pretreatment). While all the active sites became relatively stable in the later stage of pretreatment (from 60 to 600 s of pretreatment). The extraction of internal donor DBP by TEA from the catalyst within the pretreatment procedure is found to initiate from 60 s of pretreatment resulting in slight transformation of isospecific active sites into aspecific sites.     

Analysis of models for the ziegler-natta stereospecific polymerization on the basis of non-bonded interactions at the catalytic site—II: Edges,steps and reliefs on the surface of layered modifications of TiCl3

The computations performed in a previous paper for hypothetical structures of the site active in the polymerization of olefins at the (110) surfaces of TiCl₃-α are extended to edges, steps and reliefs on (111) surfaces of all the layered modifications of TiCl₃. Our computations suggest that edges, steps and reliefs of all the layered modifications of TiCl₃ should behave similarly in providing active sites; polymerization should occur on these more exposed sites because of the much lower activation energies than for plain surfaces. A unique general model emerges: lower steric repulsions appear to be implied for a coordination of the polymeric chain on the more hindered octahedral position at a titanium atom and this, in turn, causes a chiral orientation of the first carbon-carbon bond of the chain. This orientation may be the main factor in determining the stereospecificity.     

Laterally substituted naphthalene-2,7-diol-based bent-shaped liquid crystals

Novel series of laterally 1-substitued (H, Cl, CH₃, CN, NO₂) naphthalene-2,7-diol based liquid crystals were synthesized and their mesomorphic properties identified using DSC studies, texture observation, X-ray investigations and electro-optical measurements. Depending on the chain length and type of lateral substitution, the compounds exhibit a variety of mesophases. In materials with short alkyl chains, the rectangular columnar B₁ phase was found. Increasing the alkyl chain length for the non-substituted core causes the appearance of the so-called B_N phase. In CH₃- and Cl-substituted compounds, the antiferroelectric B₂ phase (SmC_AP_A) was found. Introduction of the CN and NO₂ substituents led to the formation of the B₇ phase.     

烷基链长及肽链电荷分布对脂肽双亲分子自组装及水凝胶化的影响

为阐明脂肽分子烷基链长及肽链电荷分布对其自组装及水凝胶化的影响, 设计合成了C_nV₃K₂ (n=12, 14, 16) 和C_mKV₃K (m=14, 16)两个系列的脂肽分子. 原子力显微镜(AFM)和透射电镜(TEM)结果表明, 两个系列的脂肽分子都可以自组装成一维纳米带结构. 圆二色(CD)光谱结果表明, C_nV₃K₂系列自组装体的二级结构为β折叠; C_mKV₃K系列自组装体中包括α螺旋和β折叠两种二级结构, 其中C14KV3K的α螺旋结构较多, C16KV3K的β折叠结构占优. 烷基链疏水作用的增强会抑制β折叠结构侧向堆积, 使纳米带随烷基链的变长而变窄; 电荷分布于肽链部分的两端有利于纳米带结构的侧向生长. 流变性测试结果表明, 在浓度10 mmol·L^-1、pH 8.4下, 脂肽分子可以形成自支撑水凝胶, 相比烷基链长度, 肽链部分的电荷分布对水凝胶性能影响更大.     

Cl2/TiCl4体系引发IBVE活性阳离子聚合的研究(Ⅰ)——引发活性中心及其络合竞争

采用UV光谱法证明了IBVE/Cl₂/TiCl₁/甲苯聚合体系中同时存在着两种引发活性中心及络合竞争,研究了Cl₂/TiCl₁和H₂O/TiCl₁络合平衡,求出了20℃时2TiCl₁←Cl₂和TiCl₁←H₂O络合平衡不稳定常数.     

Induction of a nematic columnar phase in a discotic hexagonal ordered phase forming system

The induction of a nematic columnar phase in a discotic hexagonal ordered phase forming system is achieved by mixing hexakispentyloxytriphenylene 1 with a long chain derivative of trinitrofluorenone 3. The difference in chain length has a strong influence on the packing behaviour due to steric effects. The long hydrocarbon chains of the acceptor introduce a strong asymmetry into the electron donor acceptor complex. It could be shown by differential scanning calorimetry, optical microscopy and X-ray measurements that a nematic columnar phase is formed. In this mesophase the triphenylenes form columns but no hexagonal or orthorhombic lattice is built up. Each column behaves like a rod-like nematic mesogen. To prove that the long hexadecane alkyl chains of the acceptor are responsible for this induction, the acceptor 3 was mixed with the non-liquid-crystalline triphenylene derivative 2 containing six hexadecyloxy side groups. The long alkyl chains of the acceptor dissolve perfectly in the side chain region of the discs. No asymmetry is induced and the columns formed can be arranged on a hexagonal lattice resulting in a D_ho phase.     

Theoretical investigations on Ziegler-Natta catalysis: Alkylation of the TiCl4 catalyst

Theoretical ab initio methods have been used to study the alkylation reaction of the MgCl₂-supported TiCl₄ catalyst. Investigation of the reaction path indicated that the Al(CH₃)₃ co-catalyst inserts into the coordination sphere of the titanium atom of the catalyst so that a methyl group of Al(CH₃)₃ interacts with the titanium. The methyl group migrates from Al(CH₃)₃ to the vacant coordination site of the catalyst. When the catalyst loses one of its chlorine atoms to the co-catalyst during this reaction, the catalyst maintains its vacant site, but the position of the vacant site changes. The presence of the external electron donor coordinated to the co-catalyst makes the alkylation reaction energetically more favourable.     

Studies on the Copolymerization of Propylene and Butadiene with Supported Titanium Catalysts (I)——Copolymerizat ion and Characterizat ion of the Products

Copolymerizations of propylene and butadiene in various ratios with two kinds of supported catalysts, i.e. TiCl4/MgCl2/AlEt3 and TiCl4/MgCl2/AlEt3/ethyl Bonzoate(EB). have been investigated. The results show that these two catalysts are quite effective for propylene-butadiene copolymerization but behave in different features. Characterizations of the copolymerization products by solvent extraction, IR, 13C NMR, X-ray diffraction and DTA show that blocked propylene-propylene and butadiene-butadiene sequences exist in polymer chain and the butadiene units are exclusively in trans-1,4 configuration.     

NMR study of nickel(II) Schiff base complexes with benzoyl groups and long alkyl chains

The nickel(II) Schiff base complexes with 2-methylbutyl or 2-methylpentyl groups and their benzoyl derivatives have been prepared and characterized by ¹H and ¹³C NMR spectroscopy. The structure of the benzoyl derivatives in chloroform solution can be estimated as follows: the donor set of N₂O₂ has a square planar coordination, the benzoyl substituents are perpendicular to the chelate plane and the long alkyl chains (2-methylbutyl or 2-methylpentyl groups) move segmentally to aproach the benzoyl substituents.     

含稀土的钛系催化剂进行乙烯聚合动力学及ZnCl2调节分子量的研究

以SN-1催化剂进行乙烯常压聚合动力学研究表明,催化剂高效的主要原因是活性中心浓度明显增大、表观活化能△E较低。研究了ZnCl₂对乙烯聚合反应的影响。发现ZnCl₂能有效地降低聚乙烯的分子量,并能显著地提高催化效率,当ZnCl₂浓度过大时,则对聚合反应有抑制作用。     

用负载型钛系催化剂进行丙烯-丁二烯共聚合的研究(Ⅰ)——共聚反应及共聚产物的表征

本文首次用负载型钛系催化剂TiCl₄/MgCl₂/AlEt₃和TiCl₄/MgCl₂/AlEt₃/苯甲酸乙酯(EB)进行了丙烯-丁二烯共聚合的研究,考察了不同单体比对共聚合的影响。结果表明,两种催化体系均能有效地进行丙烯-丁二烯的共聚合并各具特点。共聚产物经用溶剂萃取和IR、¹³CNMR、X-光衍射、DTA等方法进行分析和表征,证明共聚物中存在有丙烯-丙烯和丁二烯-丁二烯长序列的结构。丁二烯链节的微观结构基本上是反式-1,4构型。     

Synthesis of new-type donor–acceptor π-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole fluorescent dyes and their photovoltaic performances of dye-sensitized solar cells

New-type donor–acceptor π-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole fluorescent dyes with various lengths of non-conjugated alkyl chains containing a carboxyl group at the end position have been developed and their photovoltaic performances of dye-sensitized solar cells are investigated. It is found that in spite of the lengths of the alkyl chains, due to flexibility of alkyl chain, the cyano group of the dyes is located in close proximity to TiO₂ surface and thus a good electron communication between the dyes and TiO₂ surface is established.     

石墨烯吸附TiCl4分子的条件控制及光电性能的理论研究

为研究石墨烯吸附TiCl₄分子的影响因素及其光电性能,探索复合物应用于传感器及透明导电薄膜的可能性,采用第一性原理与蒙特卡罗方法研究TiCl₄气体分子在石墨烯表面的吸附条件控制与光电性能。结果表明：(1)石墨烯对TiCl₄气体分子具有较强的物理吸附作用,Cl原子吸附在其附近相距质心位置最远的碳原子顶位最稳定;(2)温度升高不利于TiCl₄气体分子吸附,气体逸度增加有利于吸附,TiCl₄气体分子插入石墨/双层石墨烯/多层石墨烯时宜将温度维持在TiCl₄沸点附近,并增加气体的压力;(3) TiCl₄的吸附对石墨烯的电子结构进行了调控,使费米能级附近的态密度显著提高,赝能隙减小,有效提高了导电性能;(4)在可见光区域,TiCl₄的吸附对体系的吸收性能影响不大,在提升透明导电薄膜导电性的同时未影响薄膜的光学性能。     

The crystalline and liquid crystalline structures of benzyl-tri-octadecylammonium bromide complete the puzzle: how do Group VA halide salts with one-four long n-alkyl chains pack?

The first single crystal structure of a Group VA halide salt with three equivalent long n-alkyl chains, benzyltrioctadecylammonium bromide (BzN18Br), is reported. It consists of alternating interdigitated and non-interdigitated regions of alkyl chains separated by ionic planes. Two chains per molecule are paired and extend to one side in a non-interdigitated region. The third chain is on the opposite side of the ionic plane and pairs intermolecularly to form an adjacent, interdigitated region. The thickness of two nearly extended molecules defines the bilayer unit-two ionic planes flanked by a region with intramolecularly paired chains and separated by an interdigitated chain region. Powder X-ray diffraction and optical microscopy data of liquid crystalline BzN18Br are consistent with an enantiotropic smectic A₂ (SmA₂) phase: the three n-alkyl chains of each molecule are projected from one side of an ionic plane, and head groups of neighbouring molecules are oriented head-to-head, in a non-interdigitated bilayer assembly. The structure of BzN18Br fills an important gap in our knowledge about the crystal packing of ammonium and phosphonium salts with one-four equivalent long n-alkyl chains. A comparison of their packing arrangements is made and the transitional nature of the BzN18Br structures is demonstrated. Although salts with one, two, or three long n-alkyl chains form SmA₂ phases, each is distinctive in its molecular packing. A large molecular reorganization accompanies the crystal-to-liquid crystal transition of BzN18Br.     

The effect of fluorinated terminal chains on the mesomorphic properties of 4,4'-disubstituted phenyl benzoates

A variety of 4,4'-disubstituted phenyl benzoates having a terminal chain containing multifluorine atoms, attached directly to the benzene ring or through an ester group, have been synthesized and their mesomorphic properties determined by hot stage polarizing optical microscopy. These properties were compared to those of the corresponding hydrogenated esters and to other esters containing rigid terminal chains. Usually transition temperatures were higher and mesophase ranges wider than those observed for the parent compounds but no nematic phases were found. Any mesophase seen was usually a smectic A phase sometimes accompanied by a smectic C phase. Crystal E phases were found along with the smectic A phase in alkyl or alkoxy esters having a C₉F₁₉CO₂ chain on the acid side. A first order smectic A-smectic C transition was observed in the ester with CN on the acid side and O₂CC₇F₁₅ on the phenol side. A comparison of the effect of a terminal fluorinated chain and a lateral fluorine group on one set of esters is also included.     

Synthesis of titanium(IV) complexes that contain the Bis(silylamide) ligand of the type [1,8-C10H6(NR)2], and alkene polymerization catalyzed by [1,8-C10H6(NR)2]TiCl2-cocatalyst system

[1,8-C₁₀H₆(NR)₂]TiCl₂ (3; R=SiMe₃, SiⁱBuMe₂, SiⁱPr₃) complexes have been prepared from dilithio salts [1,8-C₁₀H₆(NR)₂]Li₂ (2) and TiCl₄ in diethyl ether in moderate yields (60–63%). These complexes showed significant catalytic activities for ethylene polymerization and for ethylene/1-hexene copolymerization in the presence of methylaluminoxane (MAO), methyl isobutyl aluminoxane (MMAO), AlⁱBu₃– or AlEt₃–Ph₃CB(C₆F₅)₄ as a cocatalyst. The catalytic activities performed in heptane (cocatalyst MMAO) were higher than those carried out in toluene (cocatalyst MAO): 709 kg-PE/mol-Ti·h could be attained for ethylene polymerization by using [1,8-C₁₀H₆(NSiⁱBuMe₂)₂]TiCl₂–MMAO catalyst system.     

Matrix-block negative-factor-counting treatment of electron correlation in long alkane chains

Ab initio matrix-block negative-factor-counting calculations including electron correlation effects at the quasi-particle level have been performed on long linear alkane chains. Explicit results are given for C₃₆H₇₄, C₇₂H₁₄₆ and C₆₀₀H₁₂₀₂. It was found that the band edges in the photoelectron spectra for the CC and CH regions are already converged for these oligomers. On the other hand, band-shape formation inside the CH-regions is not yet complete for C₃₆H₇₄ from the theoretical point of view.     

以TiCl4为共引发剂的阳离子聚合体系的络合竞争

通过聚合物的GPC谱图分析以及紫外光谱测试证明了以TiCl₄为共引发剂的阳离子聚合体系中微量水与引发剂和TiCl₄之间存在着络合竞争,提出了抑制水对阳离子聚合影响的方法.     

Investigation of surface anchoring strength and pretilt angle in NLC on rubbed polythiophene surfaces with alkyl chain lengths

A high pretilt angle for the nematic liquid crystal, 4-n-pentyl-4'-cyanobiphenyl (5CB), was observed on rubbed polythiophene (PTP) surfaces having alkyl chains with more than ten carbon atoms. We consider that this is due to a surface-excluded volume effect caused by the long alkyl chains between the LC molecules and the PTP surfaces. The polar anchoring strength in 5CB on rubbed PTP surfaces with long alkyl chains has also been successfully evaluated. The extrapolation length d_e of 5CB increases with increasing alkyl chain lengths above the seven carbons of alkyl chain R7; that is, it may be attributed to the high pretilt angle. An extrapolation length of 5 nm is observed in 5CB for the seven carbons alkyl chain R7 on the PTP surface; this indicates high anchoring strength.     

A study of ortho- and para-siloxyanilines for the synthesis of mono-, bi-, and tetra-nuclear early transition metal–imido complexes

The siloxyanilines o-Me₃SiOC₆H₄NH₂ (1) and p-RMe₂SiOC₆H₄NH₂ (R=H (2); R=Me (3)), and their N-silylated derivatives p-Me₃SiOC₆H₄NHSiMe₃ (4) and p-Me₃SiOC₆H₄N(SiMe₃)₂ (5) have been prepared from ortho- or para-aminophenol and used in the synthesis of imido complexes. Thus, binuclear [{Ti(η⁵-C₅H₅)Cl}{μ-NC₆H₄(p-OSiMe₃)}]₂ (6) and mononuclear [TiCl₂{NC₆H₄(p-OSiMe₃)}(py)₃] (7) imido complexes have been obtained from the reaction of 3 and [Ti(η⁵-C₅H₅)Cl₃] or [TiCl₂(N^tBu)(py)₃], respectively. In contrast, the reaction of 1 with TiCl₄ and ^tBupy affords the titanocycle [TiCl₂{OC₆H₄(o-NH)---N,O}(^tBupy)₂] (8). Compound 5 has also been used to prepare the niobium imide complex [NbCl₃{NC₆H₄(p-OSiMe₃)}(MeCN)₂] (9), by its reaction with NbCl₅ in CH₃CN. These findings have been applied to the synthesis of polynuclear systems. Thus, chlorocarbosilane Si[CH₂CH₂CH₂Si(Me)₂Cl]₄ (CS–Cl) has been functionalized with the ortho- and para-aminophenoxy groups to give 10 and 11, respectively. The use of 11 has allowed the formation of the tetranuclear compound 12. Attempts to synthesize terminal imido titanium complexes from 10 and TiCl₄ in the presence of ^tBupy and Et₃N, give complex 8 and carbosilane CS–Cl.