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A novel diamine (FAPDA) bearing rigid planar fluorene and amide groups was successfully synthesized. Using such diamine and pyromellitic dianhydride (PMDA), a high-barrier polyimide (FAPPI) was obtained. FAPPI exhibits an outstanding gas barrier. Its water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) are as low as 0.51 g·m–2·day–1 and 0.43 cm3·m–2·day–1, respectively. Additionally, FAPPI shows excellent thermal stability with a coefficient of thermal expansion (CTE) of 5.8 ppm·K–1 and a glass transition temperature (Tg) of 416 °C. Molecular simulations, positron annihilation, and X-ray diffraction were utilized to gain insight on the microstructures for the enhanced barrier properties. Introducing fluorene moieties and amide groups improves the regularity and rigidity of molecular chains and increases interchain interaction of PI, resulting in low free volumes and decreased movement capacity of the chain. The low free volumes of FAPPI restrain the gas diffusivity and solubility. Meanwhile, the decreased chain movement reduces the diffusivity of gases. Consequently, barrier performances of FAPPI are improved. The polyimide possesses widespread application in the microelectronics packaging fields.

In order to meet the increasingly stringent requirements for heat resistance and barrier properties in the packaging and electronic device encapsulation field. A high-barrier polyimide (NAPPI) contains naphthalene ring and amide group was prepared by polymerization of a novel diamine (NAPDA) and pyromellitic dianhydride. The structure and properties of diamine monomers and polymers were characterized. Results show that the NAPPI exhibits superior barrier properties with extremely low water vapor and oxygen transmission rate values of 0.14 g·m−2·day−1 and 0.04 cm3·m−2·day−1, respectively. In addition, the NAPPI presents outstanding mechanical properties and thermal stability as well. This article attempts to explore the relationship between NAPPI structure and barrier properties by combining experiment and simulation. Studies on positron annihilation lifetime spectroscopy, Wide angle X-ray diffractograms and molecular dynamics simulations prove that the NAPPI has smaller interplanar spacing and higher chain regularity. In addition, the strong chain rigidity and interchain cohesion of NAPPI due to the presence of the rigid naphthalene ring and a large number of hydrogen bond interactions formed by amide groups result in compact chain packing and smaller free volume, which reduces the solubility and diffusibility of small molecules in the matrix. In general, the simulation results are consistent with the experimental results, which are important for understanding the barrier mechanism of NAPPI.

This work focused on the influence of UV radiation on the structures and performances of ethylene-propylene-diene rubber (EPDM). The exposure of EPDM to UV radiation was performed for various times (0, 7, 14, 21 and 28 days). The surface chemical structure and free volume of EPDM before and after UV ageing were determined by infrared spectroscopy (IR) and positron annihilation lifetime spectroscopy (PALS), respectively. The surface morphology, crosslink density, mechanical and gas permeability properties of EPDM were also analyzed. Under UV radiation, oxidation reactions occur on the EPDM surface and oxygenated species are formed. With prolonging ageing time, the oxidative degree increases, leading to more and denser microcracks on the surface. The plausible ageing mechanism of EPDM is suggested. At the initial 14 days of UV irradiation, the crosslink density of EPDM reduces due to the chain scission reaction, causing the increase of free volumes and thereby the enhancements of gases permeabilities. When the ageing time is longer than 14 days, crosslinking dominates and the free volumes decrease, bringing about the reductions of gases permeabilities. With prolonging ageing time, the tensile strength, glass transition temperature (Tg) and storage modulus of EPDM initially decrease and then enhance, in agreement with the change trends of crosslinking density.

A novel diamine (3,6-CAPDA) bearing carbazole and amide group was prepared. On the basis of 3,6-CAPDA and pyromellitic dianhydride (PMDA), a high-barrier polyimide (3,6-CAPPI) was obtained through a two-step polymerization method. The 3,6-CAPPI displays excellent barrier performances and thermal stability. Its oxygen permeability (OP) and water vapor permeability (WVP) are low to 2.63 cm3·mil·m−2·day−1 and 3.22 g·mil·m−2·day−1, respectively. The 5% weight-loss temperature (Td5%) and glass transition temperature (Tg) are up to 526 °C and 431 °C, respectively. Through a combination of molecular simulation, X-ray diffraction and positron annihilation test, the effet of polymer structure on the barrier properties are fully explored. The results demonstrate that the introduction of carbazole and amide groups not only improves the chain order and rigidity, but also enhances the interchain force of polyimide, which thereby bring about enhancement of crystallinity and decreases of free volume and chain movement of 3,6-CAPPI. These factors lower the gas diffusivity and solubility in polymer matrix. Simultaneous decreases of gas diffusivity and solubility give rise to the notable enhancement of gas barrier for 3,6-CAPPI.

A high-barrier polyimide (2,7-CPI) was synthesized through the polymerization of pyromellitic dianhydride (PMDA) and a novel diamine (2,7-CDA) containing carbazole moiety. The synthesized diamine and polyimide were fully characterized by elemental analyses, FTIR and NMR. The 2,7-CPI displays very attractive barrier performances, with oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) low to 0.14 cm3&middot, m&minus, 2&middot, day&minus, 1 and 0.05 g&middot, 1, respectively. Meanwhile, 2,7-CPI also exhibits exceptional thermal stability with a glass transition temperature (Tg) of 467 &deg, C, 5% weight-loss temperature (Td5%) of 550 &deg, C under N2 and coefficient of thermal expansion (CTE) of 3.4 ppm/K. The barrier performances of 2,7-CPI are compared with those of a structural analogue (2,7-CPPI) and a typical polyimide (Kapton). Their barrier performances with respect to microstructure were investigated by molecular simulations, wide angle X-ray diffraction (WAXD), and positron annihilation lifetime spectroscopy (PALS). The results show that 2,7-CPI possesses better coplanar structure and more number of intermolecular hydrogen bonds among the three PIs, which result in tight chain packing and thereby high crystallinity, low free volume, and decreased chains mobility. That is, the high crystallinity and low free volume of 2,7-CPI reduce the diffusion and solubility of gases. Meanwhile, the poor chains mobility further decreases the gases diffusion. The reduced diffusion and solubility of gases consequently promote the improvement of barrier properties for 2,7-CPI. The polyimide has a wide application prospect in the field of flexible electronic packaging industries.

Diffusion and sorption of five gases (H2, N2, O2, CO2, CH4) in hydrogenated nitrile butadiene rubber (HNBR) have been investigated via molecular dynamics and grand canonical Monte Carlo (GCMC) simulations. According to the simulation results, the diffusion coefficients of gas molecules in HNBR decrease in the penetrant order D(H2) > D(O2) > D(N2) > D(CH4) > D(CO2), which are well correlated with effective penetrant diameter except for CO2. The decrease of D(CO2) is due to the interaction between CO2 and HNBR and the linear shape of CO2. The sorption isotherms for H2, N2, O2 and CH4 in HNBR fit the Henry model, while that of CO2 matches well with dual sorption model. Solubility coefficients of gas molecules in HNBR decrease in the sequence S(CO2) > S(O2) > S(CH4) > S(N2) > S(H2), which are associated with the effective Lennard-Jones interaction constant (e/k) apart from CH4. The weak interaction between CH4 with HNBR decreases S(CH4), while the high compressibility and strong interaction between CO2 with HNBR improve S(CO2). The permeability calculated using diffusion and solubility coefficients decrease in the order P(H2) > P(CO2) > P(O2) > P(CH4) > P(N2). The high permeabilities of H2 and CO2 are mainly resulted from the high diffusivity and solubility, respectively.

A diamine (WuFDA) containing vertical rigid non-planar conjugated fluorene moiety and low polarizability group (C―F) was designed and synthesized through three steps of reactions (halogenated reaction, Suzuki coupling reaction, and reduction reaction). Four kinds of high performance functional polyimides (WuFPI-6F, WuFPI-BP, WuFPI-BT, and WuFPI-PM) were thus prepared by the condensation polymerization of WuFDA with four commercial dianhydride 6FDA, BPDA, BTDA, and PMDA, respectively. The polyimides exhibited low dielectric constant, excellent thermal stability, outstanding solubility, good film-forming property, and mechanical properties. The dielectric constants of the polyimides were in the range of 2.28−2.88 (f = 104 Hz). The 5% weight-loss temperatures (Td5%) in nitrogen were in the range of 555−584 °C, and the glass transition temperatures (Tg) were in the range of 408−448 °C. The weight loss of WuFPI-BP maintaining at 450 and 500 °C for half an hour was only 0.33% and 1.26%, respectively. All the WuFPIs could be dissolved in almost all organic solvents, even chloroform. The tensile strength and tensile modulus of these films were in the ranges of 78.6−85.7 MPa and 3.1−3.2 GPa, respectively. In addition, the polyimides displayed light color with special fluorescent and resistive switching (ON-OFF) characteristics; the maximum fluorescence emission was observed at 422−424 nm in NMP solution and at 470−548 nm in film state. The memory devices with the configuration of indium tin oxide/WuFPIs/aluminum (ITO/WuFPIs/Al) exhibited distinct volatile memory characteristics of static random access memory (SRAM), with an ON/OFF current ratio of 105−106. These functional polyimides showed attractive potential applications in the field of high performance flexible polymer photoelectronic devices or polymer memory devices.

In this article, novel side chain liquid crystalline polymers (SCLCPs) based on cyanostilbene were synthesized to obtain luminescent liquid crystalline materials. The fluorescent luminescence behavior and liquid crystallinity of SCLCPs were evaluated and characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), X-ray diffraction (XRD), ultraviolet spectroscopy (UV) and photoluminescence (PL) measurements. Testing results showed that all polymers exhibited good thermo-stability and stable double-layer smectic A phase below the clearing point temperature. The liquid crystalline properties of polymers were affected by the spacer length. The clearing point temperature (Ti) of SCLCPs decreased with increasing spacer length. All polymers were weakly emissive in good solvent but emitted stronger fluorescence in the aggregation state, showing aggregation-induced emission enhancement (AIEE) behavior. The fluorescent luminescence behavior of polymers was closely linked with chemical structure and the fluorescence quantum yield of polymers in solid phase, which increased with increasing spacer length.

A high-performance polyimide was prepared by the dipolymerization of 4,4'-diaminobenzanilide (DABA) and pyromellitic dianhydride (PMDA). Due to the introduction of rigid planar moieties and amide groups, the polyimide shows outstanding properties, such as high glass transition temperatures (435 °C), excellent thermal stability (Td5%, 542 °C, coefficient of thermal expansion, −3.2 ppm K−1), and superior mechanical properties. Most importantly, the polyimide exhibits excellent barrier properties, with oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) low to 7.9 cm3 (m2 day)−1 and 5.1 g (m2 day)−1, respectively. Wide angle X-ray diffractograms (WAXD), positron annihilation lifetime spectroscopy (PALS) and molecular dynamics simulations reveal that the excellent barrier properties are mainly attributed to the high crystallinity, high extent of in-plane crystalline orientation, and low free volume, which are resulted from the rigid planar structure and strong interchain hydrogen bonding. The high-barrier and thermally stable polyimide has an attractive potential application prospect in the fields of micro-electronics encapsulation and high grade packaging industry.

An aromatic polyimide (3,6-CPI) was prepared by the polymerization of pyromellitic dianhydride and diamine (3,6-CDA) containing a rigid planar carbazole moiety. The synthesized polyimide shows outstanding barrier properties with oxygen permeation rate and water vapor permeation rate low at 7.9 cm3 m−2 day−1 and 9.8 g m−2 day−1, respectively. Wide angle X-ray diffraction, positron annihilation lifetime spectroscopy and molecular dynamics simulations reveal that the excellent barrier properties of 3,6-CPI are mainly due to the crystallinity and low free volume of the polymer, which result from the rigid planar backbone structure and strong interchain hydrogen bonding. In addition, the polyimide exhibits excellent thermal stability and favorable mechanical properties with a 5 wt% weight-loss temperature of 559 °C in nitrogen, a glass transition temperature (Tg) of 397 °C and a tensile strength of 115.4 MPa. The as-synthesized polyimide shows potential packaging applications in the field of flexible electronics and displays, flexible and thin film photovoltaics, and light-emitting diodes. © 2017 Society of Chemical Industry

A novel aromatic diamine monomer (4,4′-(dibenzofuran-2,8-diyl) dianiline (DFPDA)) derived from the rigid planar dibenzofuran was synthesized through Suzuki coupling reaction. The aromatic polyimide...

An intrinsic high-barrier and thermally stable polyimide (2,7-CPPI) was prepared by the polymerization of pyromellitic dianhydride (PMDA) and novel diamine (2,7-CPDA), which consists of rigid planar carbazole moiety. The resulted 2,7-CPPI exhibits excellent barrier properties, with oxygen transmission rate and water vapor transmission rate low to 0.2 cm3 m−2·day−1 and 0.1 g m−2·day−1, respectively. Wide angle X-ray diffractograms (WAXD), positron annihilation lifetime spectroscopy (PALS) and molecular dynamics simulations reveal that the excellent barrier properties of 2,7-CPPI are mainly ascribed to the crystallinity, high chain rigidity and low free volume, which are resulted from the rigid planar structure and strong hydrogen bonding among molecular chains. Meanwhile, 2,7-CPPI also presents outstanding thermal stability and mechanical properties with a glass transition temperature of 437 °C, 5 wt % loss temperature of 556 °C under N2, coefficient of thermal expansion of 2.89 ppm/K and tensile strength of 143.8 MPa. The polyimide shows attractive potential applications in flexible electronics and high-grade packaging area, especially using as the substrates for top-emitting OLEDs display.

Diffusion and sorption of five gases (H2, N2, O2, CO2, CH4) in hydrogenated nitrile butadiene rubber (HNBR) and ethylene–propylene–diene rubber (EPDM) have been investigated by molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The diffusion coefficients of gas molecules in HNBR and EPDM are well correlated with the effective penetrant diameter except for CO2. CO2 shows a lower diffusion coefficient due to its linear shape. Additionally, the favorable interaction between CO2 and HNBR is another factor for its lower diffusion coefficient in HNBR. HNBR shows lower diffusion coefficients than EPDM. This is because the polar –CN groups in HNBR chains increase interchain cohesion and result in tight intermolecular packing, low free volume and poor chain mobility, which decreases the diffusion coefficients of HNBR. The solubility coefficients of CH4, O2, N2 and H2 in HNBR are lower than those in EPDM, which is a result of the weak HNBR–penetrant interactions and low free volume of HNBR. However, the solubility coefficient of CO2 in HNBR is higher than in EPDM. This is attributed to the strong interaction between CO2 and HNBR. H2, O2, N2 and CH4 show lower permeability coefficients in HNBR than in EPDM, while CO2 has higher permeability coefficients in HNBR. These molecular details provide critical information for the understanding of structures and gas transport between HNBR and EPDM.

A novel carbazole-containing diamine (M-2,7-CPDA) isomer of our previously reported diamine 2,7-CPDA, has been synthesized using a two-step synthesis. Compared with 2,7-CPDA, the substituted position of amino is changed from para to meta for M-2,7-CPDA. The two diamines were polymerized with pyromellitic dianhydride (PMDA) to prepare two isomeric polyimides (M-2,7-CPPI and 2,7-CPPI), respectively. The effects of para/meta isomerism on microstructures and gas barrier performances of the two isomeric polyimides were studied by positron annihilation test, X-ray diffraction and molecular simulation. The results display that meta-connected M-2,7-CPPI has less ordered chain structure and weaker hydrogen bonding than para-connected 2,7-CPPI, which leads to loose chain stacking and thereby increased free volumes of M-2,7-CPPI. The higher free volumes promote the solubility and diffusivity of gas in M-2,7-CPPI. As a result, the meta-linked M-2,7-CPPI shows a lower gas barrier than its para-linked analog. The work provides guidance for the design and synthesis of high-performance barrier polymers.

A series of high-performance multifunctional polyimides with exceptional thermostability and solubility (Tg as high as 494 °C and, at the same time, well soluble in common organic solvents) were successfully designed and synthesized by introducing a typical aromatic rigid trifluoromethyl-containing moiety with special non-planar and conjugated characteristics into the polymer backbone. Additionally, these polyimides show light color (one even colorlessness) and transparency, intrinsic ultralow dielectric constant (k, k ≈ 1.93), and electrical bistability characteristics (ON/OFF ratio as high as 107, working voltage as low as 1.5 V) simultaneously. The excellent thermal stability and solubility allow them to undergo the high temperature process (over 400 °C) in the preparation of photoelectric devices (like PVD or PECVD), or the highly efficient, continuous roll-to-roll process. The as-synthesized polymers are ideal potential candidates for practical applications in the fields of ultra-large-scale integration (ULSI), high-performance polymer memory devices, flexible displays, thin film PV industries, and wearable electronics.

An intrinsic high-barrier polyimide (9-OH-FPPI) was prepared through the polycondensation reaction of pyromellitic dianhydride (PMDA) with a novel diamine (9-OH-FPDA) containing fluorenol moiety. The synthesized polyimide displays superior barrier performances, possessing water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) low to 1.64 g·m−2·day−1 and 0.66 cm3·m−2·day−1, respectively. Meanwhile, 9-OH-FPPI also demonstrates high thermal stability with a glass transition temperature (Tg) of 410 °C, 5% weight-loss temperature (Td5%) of 577 °C under N2 and coefficient of thermal expansion (CTE) of 5.65 ppm/K. A detailed molecular simulation study as well as positron annihilation lifetime spectroscopy (PALS) and wide angle X-ray diffraction (WAXD) analysis have been carried out to reveal the barrier mechanism. The results reveal that the introduction of fluorenol moiety not only enhances the rigidity and regularity of polymer backbone, but also improves the interchain cohesion of PI matrix, which in turn lead to high crystallinity, low free volume and poor chains mobility of 9-OH-FPPI. The high crystallinity and low free volume decrease the diffusion and solubility of gases in polyimide matrix. In addition, the poor chains mobility further suppresses the gases diffusion. Simultaneous reductions of gases diffusion and solubility promote the barrier properties of 9-OH-FPPI. The as-synthesized polyimide exhibits wide application prospects in the flexible electronic packaging industry.

A bulk dielectric polymer film with an intrinsic ultralow k value of 1.52 at 10 kHz has been successfully synthesized based on a novel polyimide FPTTPI. More importantly, such outstanding dielectric properties remain stable up to 280 °C. The excellent ultralow dielectric properties are mainly because of the larger free volume (subnanoscale), which intrinsically exists in the amorphous region of polymeric materials. Meanwhile, FPTTPI also shows excellent thermal stability and mechanical properties, with a glass-transition temperature (Tg) of 280 °C, 5 wt % loss temperature of 530 °C, and a residual of 63% at 800 °C under N2. It was soluble in common solvents, which made it possible to undergo simple spin-on or efficient, low-cost, and continuous roll-to-roll processes.

This paper is concerned with the attitude control of a three-axis-stabilized spacecraft which consists of a central rigid body and a flexible sun-tracking solar array driven by a solar array drive assembly. Based on the linearization of the dynamics of the spacecraft and the modal identities about the flexible and rigid coupling matrices, the spacecraft attitude dynamics is reduced to a formally singular system with periodically varying parameters, which is quite different from a spacecraft with fixed appendages. In the framework of the singular control theory, the regularity and impulse-freeness of the singular system is analyzed and then admissible attitude controllers are designed by Lyapunov’s method. To improve the robustness against system uncertainties, an H ∞ optimal control is designed by optimizing the H ∞ norm of the system transfer function matrix. Comparative numerical experiments are performed to verify the theoretical results.

We have designed and synthesized a novel deep-blue luminescent compound (WuFDA), which can emit efficiently both in solution and in the aggregated state; the fluorescence emission maximum of WuFDA in the aggregated state shows a remarkable blue-shift from that shown in the dilute solution. Moreover, WuFDA shows interesting fluorescent behaviour in mixed solvent systems of THF–H2O, and a solvent effect in different polar solvents. These unusual phenomena have been interpreted by studies of the single crystalline structure of WuFDA and density functional theory (DFT) investigations. The special chemical structure (containing a planar conjugated fluorene core and strong polar groups (–NH and –F)) and their location in the molecule formed a typical non-planar D–π–A molecule with strong internal charge transfer (ICT). Such a polar molecule possesses the ability to form hydrogen bond interactions with itself, as well as with the polar solvents. Both the ICT effect and the intermolecular hydrogen bond interactions play very important roles in the geometrical manner of aggregation and the fluorescent behaviours of the WuFDA. In addition, WuFDA exhibited good thermal stability, with 5% and 10% weight-loss temperatures (Td) of WuFDA in nitrogen of 399 and 414 °C, respectively, and the glass transition temperature (Tg) was about 161 °C.

Nitrogen-incorporated titanium silicalite-1 (NTS-1) was used to prepare a supported gold catalyst for direct gas-phase epoxidation of propylene using H2 and O2. The NTS-1 was synthesized by direct calcination of the TS-1 powder in a flow of NH3 at high temperature. Gold catalyst supported on NTS-1 was synthesized by the deposition-precipitation method. The samples were characterized by X-ray diffraction, N2 adsorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy, inductively coupled plasma optical emission spectrometry, elemental analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy. The results indicated that nitrogen was incorporated into the TS-1 framework, and that the NTS-1 preserved the multidimensional fatigue inventory (MFI) structure well. It was found that NH3-treatment resulted in decreased acidity of the TS-1 zeolite support and improved both the Au capture efficiency and dispersion, which remarkably improved the catalytic performance. The enhanced activity was ascribed to the decrease in acidic surface sites and the ligand effect of the terminal NH2 groups on the support surface.

A simple diamine (TetraPEDA) containing rigid nonplanar conjugated tetraphenylethylene (TetraPE) moieties was designed and synthesized through Wittig–Horner and Suzuki coupling reactions. Four kinds of high-performance functional polyimides (PI) were thus prepared by the polymerization of TetraPEDA and four dianhydrides, respectively. Because of the introduction of the aromatic rigid nonplanar TetraPE structure, the PI exhibited special fluorescent characteristics, as the maximum fluorescence emission of the four PI was observed at 425–505 nm in NMP solution and at 470–491 nm in film state. Also these organo-soluble PI showed outstanding properties, such as low dielectric constant (even without fluorinated substituent), light color, high glass transition temperatures (382–443 °C) and thermal stability in air (Td5% up to 565 °C), and excellent mechanical properties. The polymer memory devices with the configuration of indium tin oxide/PI/aluminum (ITO/PI/Al) exhibited distinct volatile memory characteristics of static random access memory, with an ON/OFF current ratio of 1 × 104 to 1 × 105. These functional PI showed attractive potential applications in the field of high performance flexible polymer photoconducting devices or fluorescent polymer memory devices. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

A novel, simple but efficient diamine (TriPEDA) containing rigid nonplanar conjugated triphenylethylene moieties was designed and synthesized through Wittig–Horner and Suzuki coupling reactions. Four kinds of high-performance functional polyimides were thus prepared by the dipolymerization of TriPEDA and four dianhydrides, respectively. Because of the introduction of the aromatic rigid nonplanar triphenylethylene structure, the polyimides exhibited special fluorescent and resistive switching (ON-OFF) characteristics, as the maximum fluorescence emission of the four polyimides was observed at 472–505 nm in NMP solution and at 473–541 nm in film state. Also these organo-soluble polyimides showed outstanding properties, such as low dielectric constant (even without fluorinated substituents), light color, high glass transition temperatures (359–409 °C), thermal stability, and excellent mechanical properties. The memory devices with the configuration of indium tin oxide/polyimides/aluminum (ITO/PI/Al) exhibite...

Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the consideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of centroid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid location and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel- and 5-pixel-windows’ centroid estimation are less than 2×10−3 pixels and 2×10−4 pixels respectively.

Mesoporous molecular sieves MCM-41 modified by bimetal (Zr and Ti) ions with ordered hexagonal arrangement were prepared by direct synthesis under microwave–hydrothermal conditions at 403 K. FT-IR, N2 adsorption–desorption, scanning electron microscope, high-resolution transmission electron microscope, element mapping, X-ray photoelectron spectroscopy, diffuse Reflectance UV–Visible Spectra etc. were used to characterize as-prepared materials. The results showed that Zr and Ti were introduced into MCM-41 and bonds of Zr–O–Si and Ti–O–Si were formed in framework of the MCM-41. Moreover, their structures with ordered arrangement were still retained. The microwave–hydrothermal method might shorten the synthesis time from days to hours and the as-prepared catalyst had a high catalytic activity and selectivity for the liquid-phase epoxidation of styrene.

Mesoporous molecular sieve Al-MCM-41 with Si/Al ratio = 5, was in situ synthesized under hydrothermal condition using tetraethylorthosilicate (TEOS) and metakaolin as silica and aluminum sources and cetyl trimethylammonium bromide as structure directing agent. Powder X-ray diffraction (XRD), solid-state magic-angle spinning (MAS) NMR spectroscopy, Fourier transform infrared spectroscopy (FT-IR), N 2 isothermal adsorption–desorption, SEM and TEM are used to characterize the samples. Metakaolin used as source of aluminum and silicon allowed the formation of well-ordered Al-MCM-41 mesoporous materials. Thus, inexpensive metakaolin is probably a better Al and Si source for MCM-41 samples with low Si/Al ratios than other aluminum sources.

Tungstophosphoric acid (H3PW12O40) (PW) catalysts supported on mesoporous Mn-MCM-41(n Si/n Mn = 25) with various (10, 20 and 30 wt%) acid loadings were prepared by impregnation, and their physical chemical properties were characterized by powder X-ray diffraction (XRD), N2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM), and X-Ray Photoelectron Spectroscopy (XPS). The host material suffers severe structural distortions at higher loading, which lead to a considerable loss of long-range orders. Their catalytic performances were evaluated in the epoxidation of styrene with dilute H2O2 (30%) as an oxidizing agent under liquid phase reaction conditions over PW/Mn-MCM-41 catalysts for selective synthesis of styrene oxide. The influences of various reaction parameters such as temperature, time, solvents, PW loading and catalyst amount, styrene to H2O2 mmol ratios and acetonitrile (MeCN) to N,N-dimethylformamide (DMF) volume ratios on the conversion of styrene and yield as well as selectivity of styrene oxide have also been studied in details. The results revealed that 20% PW/Mn-MCM-41 (n Si/n Mn = 25) was more active than other catalysts. The PW/Mn-MCM-41, moreover, was found to be reusable and environmentally benign for the epoxidation of styrene.

Mesoporous Ti-MCM-41 molecular sieve was synthesized under hydrothermal conditions. 5, 10, 20, 30 and 50 wt.% phosphotungstic acid (H 3 PW 12 O 40 ) (PW) were supported on Ti-MCM-41 and the resulting catalysts were characterized by powder X-ray diffraction (XRD), N 2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). The host material suffers severe structural distortions at higher loading, which lead to a considerable loss of long-range orders. Their catalytic performances were evaluated in the epoxidation of styrene with dilute H 2 O 2 (30%) as an oxidizing agent under liquid-phase reaction conditions over PW/Ti-MCM-41 catalysts for selective synthesis of styrene oxide. The influences of various reaction parameters such as temperature, time, solvents, PW loading and catalyst amount, styrene to H 2 O 2 mmol ratios and acetonitrile (MeCN) to N , N -dimethylformamide (DMF) volume ratios on the conversion of styrene and yield as well as selectivity of styrene oxide have also been studied in details. The results revealed that 20% PW/Ti-MCM-41 was more active than other catalysts. The PW/Ti-MCM-41, moreover, was found to be reusable and effective for the epoxidation of styrene.

Mesoporous molecular sieves Mn-Ti-Al-MCM-41 prepared by in situ microwave hydrothermal synthesis were studied for the epoxidation of styrene with H 2 O 2 under microwave irradiation. Characterization by XRD, 29 Si MAS NMR, N 2 physisorption, SEM-EDS, and HRTEM revealed that the materials had a typical hexagonally arranged mesoporous structure with high surface area and narrow pore size distribution. The novel synthesis method of Mn-Ti-Al-MCM-41 shortened the synthesis time from days to hours, and the as-synthesized materials had a higher catalytic activity in the liquid-phase epoxidation of styrene and greatly improved the selectivity for styrene oxide.

Appropriate modeling for a controlled plant has been a remarkable problem in the control field. A new modeling theory, i.e. characteristic modeling, is roundly demonstrated. It is deduced in detail that a general linear constant high-order system can be equivalently described with a two-order time-varying difference equation. The application of the characteristic modeling method to the control of flexible structure is also introduced. Especially, as an example, the Hubble Space Telescope is used to illustrate the application of the characteristic modeling and adaptive control method proposed in this paper.

Mesoporous molecular sieves MCM-41 modified by single (Ti) and bimetal (Ti-V) ions with highly ordered hexagonal arrangement of their cylindrical channels were prepared by direct synthesis under microwave–hydrothermal (M–H) conditions at 403K. Characterizations with powder X-ray diffraction (XRD), 29Si magic-angle spinning (MAS) NMR, N2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelcctron spectra(XPS) and transmission electron microscopy (TEM) showed that Ti and V ions were introduced into MCM-41 under M-H conditions and Ti/V-Si bond was formed. Results revealed that all the samples were of a typical hexagonal arrangement of mesoporous structure. The modified materials were high active and selective in the epoxidation of styrene at 343 K in comparison with single-functional MCM-41. Moreover, compared to conventional method, the presented microwave hydrothermal synthesis of molecular sieves greatly improved the selectivity to styrene oxide, e.g., it reached 58.6% at styrene conversion of 18.7% over Ti-V-MCM-41 (50).

A transient temperature field of thin-walled beam in the condition of sudden flux is analyzed by using flourier expansion. And the frequency of the structure which depends on temperature is gotten. The vibration of the beam is divided into quasi-static and dynamic displacement which makes it available to the analytic solution. The temperature effect of material is concerned in the process of solution, which makes this analysis more accurate and more widely used.