In Situ Generation of Cationic Methylzirconium Complexes from rac-(EBI)Zr(NMe2)2 and NMR-Scale Polymerization of Propylene

ABSTRACT

Sequential NMR-scale reactions have been carried out in order to generate cationic methylzirconium complexes by the reaction of rac-(EBI)Zr(NMe₂)₂ (rac- 1 , EBI = Et(indenyl)₂) with methylaluminoxane (MAO) or various anionic compounds. By reacting 40 equiv. of MAO with rac- 1 in an NMR tube containing CD ₂CI₂ as a solvent at room temperature, rac- 1 is completely activated to give stable cationic methylzirconium complexes, [(EBI)ZrMe]⁺[MAO]^? which polymerize propylene to isotactic polypropylene (iPP). The formation of the cationic species is achieved after rac- 1 is methylated to form rac-(EBI)ZrMe₂ (rac- 2 ) by MAO and/or free Al₂Me₆ contained in MAO. The same sequential reaction has been performed by using rac(EBI)ZrCl₂ (rac- 3 ) for the comparison. MAO cannot generate the cationic species at the same reaction conditions in the reaction of rac- 3 and MAO, mainly due to the difficulties of methylation of rac- 3. Ansa ziconocene amide rac- 1 is stoichiometrically methylated by 2 equiv. of Al₂Me₆ to give rac- 2. Introduction of 1 equiv. of noncoordinating to the solution mixture of rac- 1 and 2 equiv. of Al₂Me₆ leads to the formation of stable cationic methylzirconium species, [rac-(EBI)Zr(μ-Me)₂AlMe₂]⁺. NMR-scale polymerizations have been carried out by adding a small amount of liquid propylene to these cationic species. The meso pentad values of iPP isolated in these polymerizations are in the range of 80.2–84.7%. By changing the order of sequential reaction, i.e., by reacting rac- 1 with noncoordinating anions prior to methylation by Al₂Me₆, the yield to give cationic methylzirconium species is decreased. Coordinative anions such as [HNMe₂Ph][BPh₄] and [HNBu₃][BP₄] are less effective for the generation of the active zirconium cations than noncoordinating anions. The amount of MAO needed to activate rac- 1 can be decreased by the pre-methylation of rac- 1 by Al₂Me₆.     

New Diarylheptanoid from the Barks of Alnus japonica Steudel

A new diarylheptanoid glycoside, 1,7-bis-（3,4-dihydroxyphenyl）-5-hydroxyheptane- 3-O-β-D-xylopyranoside （1）, together with nine known diarylheptanoids （2-10） were isolated from the fresh bark of Alnus japonica which is a species of the genus Alnus species, growing throughout Korea.     

ANALYSIS OF SOUND TRANSMISSION THROUGH PERIODICALLY STIFFENED PANELS BY SPACE-HARMONIC EXPANSION METHOD

An analysis method is developed to study sound transmission characteristics of a thin plate stiffened by equally spaced line stiffeners. The dynamic equation that describes the vibro-acoustic response of the system is derived by expanding the structural and acoustic responses in terms of the space harmonics and by using the virtual energy method. The series solution can be considered as the exact solution because the structural and acoustic-structural coupling effects in the system are fully considered and the solution converges. Parameter studies are conducted for major design parameters to understand the characteristics of the system.     

VIBRATION-BASED DAMAGE IDENTIFICATION USING RECONSTRUCTED FRFS IN COMPOSITE STRUCTURES

This work aims to establish a vibration-based damage identification method for fiber-reinforced laminated composites and their sandwich construction. This new on-line structural damage identification technique uses the structural dynamic system reconstruction method exploiting the frequency response functions (FRFs) of a damaged structure. To verify the effectiveness of this damage identification method, the frequency responses obtained by vibration testing of fatigue-damaged laminated composites and honeycomb sandwich beams with debonding are examined according to the extent of the damage via the fatigue-damage load cycle for laminated composites, and via the debonding extent for honeycomb sandwich beams. The changes of the peaks and valley of the FRFs according to the debonding extent and the fatigue load cycles are examined, and the area changes in the FRFs are also discussed as the damage index. The residual FRFs or the difference between intact and damaged FRFs are newly defined for application of the on-line damage identification method. Finally, the delamination extent for the sandwich beams and the fatigue damage level for the laminated composites can be easily identified in terms of the changes in natural frequencies and damping ratios of the reconstructed FRFs for these damaged composite structures.     

HEALTH-MONITORING METHOD FOR BRIDGES UNDER ORDINARY TRAFFIC LOADINGS

A method for damage estimation of a bridge structure is presented using ambient vibration data caused by the traffic loadings. The procedure consists of identification of the operational modal properties and the assessment of damage locations and severities. An experimental study is carried out on a bridge model with a composite cross-section subjected to vehicle loadings. Vertical accelerations of the bridge deck are measured while vehicles are running. The modal parameters are identified from the free-decay signals extracted using the random decrement method. The damage assessment is carried out based on the estimated modal parameters using the neural networks technique. As input to the neural networks, the ratios of the resonant frequencies between before and after damages and the mode shapes after the damages are used to take into account the mass effect of the traffic on the bridge. The identified damage locations and severities agree reasonably well with the inflicted damages on the structure.     

Synthesis of 3-Benzyloxy-6-methyl-7-methoxyphenanthrene-9-carboxaldehyde with Utilize Intramolecular Heck Reaction as the Key Step

The substituted phenanthrene-9-carboxyaldehydes are very important intermediates for the syntheses of phenanthroindolizidine and phenanthroquinolizidine alkaloids. The novel title compound was prepared from the reaction of 5 steps starting from the condensation of 3-methoxyl-4-methyl-phenylacetic acid and 4-（benzyloxy）-2-iodobenzaldehyde, followed by esterification, cyclization, reduction, and oxidation. A new method for the preparation of phenanthrene ring via palladium-catalyzed intramolecular Heck reaction was described. The title compound was characterized by IR, ^1H NMR, ^13C NMR, elemental analysis, and MS.     

柠檬酸盐法制备(Na0.5 Bi0.5)1-xBaxTiO3压电陶瓷的极化特性研究

采用柠檬酸盐法合成了具有单一钙钛矿结构的(Nao5Bio5)1-xBaxTiO3(x=0,x=0.04)超细粉料,并研究了陶瓷样品的极化特性、压电性能和铁电性能.研究结果表明,柠檬酸与金属离子的摩尔比(C/M)控制在1.2～1.6、前驱体液的pH值控制在7～9范围内可以得到均匀透明的溶胶和凝胶,凝胶在600℃下热处理1h后可形成单一钙钛矿结构的超细粉料.XRD研究结果表明,x=0和x=0.04时陶瓷样品均为三方钙钛矿结构.极化电压和极化温度对陶瓷样品的压电性能有很大影响,而极化时间对压电性能的影响则不显著.Ba2+的固溶改善了陶瓷样品的铁电性能,有利于材料极化性能和压电性能的提高.与常规固相法制备的同种组成样品相比,柠檬酸盐法制备的(Nao5Bi0.5)1-xBaxTiO3(x=0,x=0.04)陶瓷具有较好的压电性能.     

Demi-linear analysis Ⅱ——demi-distributions

In this paper, we develop the theory of demi-distributions which generalizes the usual distribution theory. In particular, we show that many results on differentiations, Fourier transforms, and convolutions can be generalized to demi-distributions theory.