Cyanated liquid crystals with trans-stilbene structure: Syntheses and their cyclotrimerizations

Liquid crystalline aromatic monocyanate ( M ) and dicyanates ( D1 and D2 ) with trans-stilbene ( Ph CHCH Ph ) structure were synthesized and their cyclotrimerization reactions were studied by differential scanning calorimetry and infrared spectroscopy. Monocyanate M underwent cyclotrimerization to yield a trimerized material with discotic properties. Dicyanate D2 and its cured product failed to exhibit any mesophase. In contrast, polycyclotrimerization of dicyanate D1 obtained a liquid crystalline thermoset with its schlieren texture prolonged over a wide temperature range. © 1995 John Wiley & Sons, Inc.     

Dynamic mechanical properties of aluminum nitride/cyanate ester composites for high performance electronic packaging

Viscoelastic ature is one of the key features of polymeric composites. A series of cyanate ester (CE)‐based composites with different aluminum nitride (AlN) contents for high performance electronic packaging, coded as AlN/CE, were developed; the viscoelastic nature of AlN/CE composites was intensively investigated by employing dynamic mechanical analysis (DMA). Results show that the AlN content has a great effect on dynamic mechanical properties of AlN/CE composites. The storage modulus in the glassy region increases linearly with the addition of AlN as well as the increase of AlN content. Meanwhile, all composites also exhibit notably higher loss modulus than cured CE resin due to the appearance of new energy dissipation forms. In addition, the incorporation of AlN has a significant effect on damping factor peak. All reasons leading to these phenomena are analyzed from the view of structure–property relationship. Copyright © 2009 John Wiley & Sons, Ltd.     

NCOCH2(CF2)6CH2OCN cyanate ester resin. A detailed study

The NCOCH₂(CF₂)₆CH₂OCN fluoromethylene cyanate ester monomer and resin are synthesized and characterized. The monomer is prepared by a large‐scale bench‐top synthesis, characterized by differential scanning calorimetry, infrared, ¹H‐, ¹³C‐, ¹⁵N‐, and ¹⁹F‐NMR spectroscopies and analyzed for catalytically active impurities. Conversion of the monomer to prepolymer and cured resin is characterized by IR and NMR spectroscopies and kinetically analyzed. Resin properties characterization includes thermal, tensile, dynamic mechanical, dielectric, refractive index, thermodielectric and thermogravimetric stabilities, and water absorption. Relevant property comparisons with the commercial AroCy F cyanate ester resin (6F bisphenol A dycyanate) and a Jeffamine‐bisphenol diglycidyl ether epoxy are made. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 135–150, 1999     

Total Synthesis of (+)‐Rubriflordilactone A

Two enantioselective total syntheses of the nortriterpenoid natural product rubriflordilactone A are described, which use palladium‐ or cobalt‐catalyzed cyclizations to form the CDE rings, and converge on a late‐stage synthetic intermediate. These key processes are set up through the convergent coupling of a common diyne component with appropriate AB‐ring aldehydes, a strategy that sets the stage for the synthetic exploration of other members of this family of natural products.     

Resveratrol still has something to say about aging!

A votre Santé! The mechanism by which resveratrol, a hydroxystilbenoid polyphenol found in grapes and present in wine, exerts antiaging metabolic benefits has been uncovered. Chung and co-workers have found that it works by inhibiting cAMP phosphodiesterases, thus triggering a signaling cascade that leads to the possible activation of the mammalian enzyme sirtuin?1.     

Total Synthesis of Resveratrol‐Based Natural Products Using a Palladium‐Catalyzed Decarboxylative Arylation and an Oxidative Heck Reaction

Controlled access to resveratrol‐based natural products is offered by a novel, modular concept. A common building block readily available on a large scale serves as the starting material for the introduction of structurally important aryl groups by a Pd‐catalyzed decarboxylative arylation and an oxidative Heck reaction with good yields and high stereoselectivity. The modular approach is convincingly documented by the successful synthesis of three racemic resveratrol‐based natural products (quadrangularin A, ampelopsin D, and pallidol).     

Synthesis and characterization of new phosphorus and other heteroatom containing aryl cyanate ester monomers and networks

Several aromatic dicyanate monomers have been synthesized bearing para-linked strong electron withdrawing groups, such as phenylphosphine oxide, sulfone, and carbonyl. These groups increased the reactivity of the cyanate functional groups and eliminated the need for curing catalysts. However, an undesirable decrease in the processing window between the monomer melting point and the onset of cure was also generally observed. An arylene ether phenyl phosphine oxide system was designed that displayed several attractive characteristics such as a low softening point, a wide processing window, cure with no catalyst, high T_g and high char yield in air, suggesting that these new thermosets might show good fire resistance. The dicyanate ester monomers were synthesized in high yield by reacting various bisphenols with cyanogen bromide in the presence of triethylamine. The high reactivity of the cyanate functional groups required that the cyanation reaction be conducted at temperature below 0°C in order to prevent imidocarbonate side reactions. Proton NMR and FT-IR were used to characterize these monomers. The cyclotrimerization curing process was monitored by the disappearance of the carbon-nitrogen triple bond stretch (2270 cm⁻¹). An optimal cure schedule was determined and the cured polycyanurate networks were characterized by DSC, DMTA, and TGA. Tg values were typically > 250°C and 5% weight loss values were observed by TGA in air above 400°C. Several of the dicyanate monomers with sufficiently large processing windows were cured into single lap shear adhesive bonds onto titanium 6/4 and the measurements are reported herein. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 977–987, 1997     

Immunosuppressive Resveratrol Aneuploids from Hopea chinensis

Two novel resveratrol aneuploids, hopeachinols A ( 1 ) and B ( 2 ), as well as a potent immunosuppressive polyphenol diptoindonesin G ( 3 ) were characterized from the ethanol extract of Hopea chinensis stem barks. The structure of the polyphenols was accommodated by comprehensive spectroscopic analysis with the absolute stereochemistry determined by the CD approach coupled with theoretical ECD spectra computer‐generated through the Gaussian 03 program. The distinct structure and biological profile of 3 recommended it as a starting molecule for the relevant drug discovery.     

A Study on the Ballistic Performance of Composites

The mechanical behaviour and ballistic performance of carbon, glass (E and S type), aramid and polyethylene fabric reinforced composites with different epoxy resins were studied. The specimens – produced by hand lay-up method – were characterized by low velocity (Charpy and drop-weight tests) and high velocity (two different calibre ballistic) impact tests. The energy absorption capacity of the composites was found to be strongly affected by the material properties of the reinforcing fiber, by the type of fabric structure and by the elasticity of resin.     

A new ultrasonic measurement system for the cure monitoring of thermosetting resins and composites

Measurements of the ultrasonic sound speed of thermosetting resins and composites can be used as an in-process cure monitoring technique. Ultrasonic measurements have an advantage over other in-process techniques in that ultrasonic sensors do not make contact with the part (thus leaving no imbedded sensor or witness mark) and can make true bulk measurements of the part. A new commercially available ultrasonic cure monitoring system has been developed which easily enables ultrasonic measurements to be made in compression molding, resin transfer molding, and autoclave processes. Advancements in ultrasonic sensor technology enable the sensor to maintain good coupling to the part during thermal cycling to 260C. Data is presented showing the change in ultrasonic sound speed during the compression molding of a graphite-epoxy prepreg. The data shows a good relationship to the ionic conductivity and resistivity data collected via dielectric cure monitoring.This effort was sponsored by the Manufacturing Technology Directorate, Wright Laboratory (WL/MTX), Air Force Material Command, USAF, under cooperative agreement award(s) to NCMS. The U. S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Wright Laboratory or the U.S. Government.     

氰酸酯树脂改性热固性丁苯树脂的固化及其动力学

利用傅里叶变换红外光谱法(FT-IR)和差示扫描量热法(DSC)研究了氰酸酯树脂改性热固性丁苯树脂的固化反应特性及其动力学.以温度-升温速率外推法计算得到固化反应起始温度(Ti0)、峰顶温度(Tp0)和终止温度(Tf0)分别为414.2、444.5、460.6 K,对改性树脂的固化过程进行优化.采用Freeman-Ca...     

热固性聚合物基复合材料废弃物回收利用进展

综述了目前国内外热固性聚合物基复合材料废弃物的回收利用的方法,着重论述了物理粉碎回收法和化学热解回收法,并对不同方法的回收料用于团状模压料（bulk molding compound,BMC）、片状模压料（sheet molding compound,SMC）以及热塑性塑料的产品性能进行了对比。     

Cure kinetics of thermosetting bisphenol E cyanate ester

Resin injection repair is a common method to repair delamination damage in polymer matrix composites (PMCs). To repair high-temperature PMCs, the resin should have a very low viscosity, yet cure into a compatible adhesive with high temperature stability. Normally, thermosetting polymers with high glass transition temperatures (T _g) are made from monomers with high room temperature viscosities. Among the high temperature resins, bisphenol E cyanate ester (BECy, 1,1’-bis(4-cyanatophenyl)ethane), is unique because it has an extremely low viscosity of 0.09–0.12 Pa s at room temperature yet polymerizes as a cross-linked thermoset with a high T _g of 274°C. BECy monomer is cured via a trimerization reaction, without volatile products, to form the high T _g amorphous network. In this study, the cure kinetics of BECy is investigated by differential scanning calorimetry (DSC). Both dynamic and isothermal experiments were carried out to obtain the kinetic parameters. An autocatalytic model was successfully used to model isothermal curing. The activation energy from the autocatalytic model is 60.3 kJ mol⁻¹ and the total reaction order is about 2.4. The empirical DiBenedetto equation was used to evaluate the relationship between T _g and conversion. The activation energy of BECy from the dynamic experiments is 66.7 kJ mol⁻¹ based on Kissinger’s method, while isoconversional analysis shows the activation energy changes as the reaction progresses.     

Cyanate ester tethered POSS/BACY nanocomposites for low‐k dielectrics

Low‐k dielectrics have been developed as an interlayer insulating material in the large scale integrated circuitry devices by the copolymerization of various weight percentages (10, 20, 30, and 40 wt%) of cyanate ester tethered POSS (POSS‐OCN) and bisphenol‐A cyanate ester (BACY) to obtain BACY/POSS‐OCN nanocomposites. The reinforcement of POSS‐OCN significantly contributes to the reduction in the value of dielectric constant and dielectric loss as well, which might be due to the presence of porous structured POSS‐OCN. The 30 wt% POSS‐OCN/BACY nanocomposite possesses the lowest value of dielectric constant of 1.81 at 1 MHz. Copyright © 2016 John Wiley & Sons, Ltd.     

酚醛型氰酸酯与双酚A型环氧共固化反应的FTIR研究

在恒温固化条件下,通过FTIR跟踪方法,研究了酚醛型氰酸酯与双酚A型环氧共固化反应的路径及其反应机理.共固化体系的反应过程包括在150℃及其以下温度,主要发生的是氰酸酯的三嗪环化固化反应,其中三嗪环化固化反应由于环氧的加入,反应速率被极大地提高了;同时,酚醛型氰酸酯中的氨基甲酸酯类杂质与环氧发生开环聚合反应,引起环氧官能团产生弱而持续的消耗.但在此阶段,酚醛型氰酸酯与环氧之间没有化学反应发生;在180℃及其以上温度,三嗪环和环氧发生反应,异构为异氰脲酸环结构,并进一步反应生成唑啉酮环结构,由于该反应的发生,促进了环氧官能团的消耗速度,在环氧官能团的转化率-时间图中,出现倒S曲线;在三嗪环的转化率图中,出现一个极大值后再降落的曲线.反应温度的提高有利于促进酚醛型氰酸酯与环氧之间的共固化反应,特别是当反应温度为220℃时,氰酸酯官能团和环氧官能团的消耗、三嗪环和唑啉酮环的生成均以较快的速率进行,—OCN生成三嗪环的转化率可以较容易地达到1,而唑啉酮环的转化率不超过0.5.     

Antifungal activity of cinnamic acid and benzoic acid esters against Candida albicans strains

Candida albicans is an important opportunistic fungal pathogen capable of provoking infection in humans. In the present study, we evaluated the antifungal effect of 23 ester derivatives of the cinnamic and benzoic acids against 3 C. albicans strains (ATCC-76645, LM-106 and LM-23), as well as discuss their Structure–Activity Relationship (SAR). The antifungal assay results revealed that the screened compounds exhibited different levels of activity depending on structural variation. Among the ester analogues, methyl caffeate (5) and methyl 2-nitrocinnamate (10) were the analogues that presented the best antifungal effect against all C. albicans strains, presenting the same MIC values (MIC = 128 μg/mL), followed by methyl biphenyl-2-carboxylate (21) (MIC = 128, 128 and 256 μg/mL for C. albicans LM-106, LM-23, and ATCC-76645, respectively). Our results suggest that certain molecular characteristics are important for the antifungal action.