Functionalization of terminal carbon atoms of hydroxyl terminated polybutadiene by polyazido nitrogen rich molecules

We report a novel synthetic approach for the attachment of the polyazido nitrogen rich molecule on to the hydroxyl terminated polybutadiene (HTPB) backbone. The terminal carbon atoms of the HTPB are functionalized by attaching cyanuric chloride (CYC) covalently on the HTPB backbone. Further reaction of this modified HTPB with sodium azide yields polyazido nitrogen rich HTPB. The unique physico-chemical properties and the microstructure of the HTPB do not get affected upon modification. IR, gel permeable chromatography (GPC) and absorption spectroscopy studies prove that the polyazido nitrogen rich molecules are covalently attached at the terminal carbon atoms of the HTPB. The π electron delocalization owing to long butadiene chain, strong electron withdrawing effect of the triazine molecules are the major driving forces for the covalent attachment of the triazine at the terminal carbon atoms of the HTPB. The disruption of the intermolecular hydrogen bonding between the terminal hydroxyl groups of the HTPB chains and the presence of hydrogen bonding between the N atoms of the triazine ring with OH group of the HTPB are observed. Theoretical study also reveals the existence of the hydrogen bonding between the OH and N. Theoretical calculation shows that the detonation performance of the polyazido nitrogen rich HTPB are very promising.     

低分子量HTPB聚氨酯弹性体的制备及其性能

为改善高固含量高聚物黏结炸药(PBX)和丁羟推进剂的工艺性能,以低分子量的端羟基聚丁二烯(HTPB)、异佛尔酮二异氰酸酯(IPDI)为主要原料,选用一缩二乙二醇(DEG)为扩链剂,采用二步法制备了聚氨酯弹性体。研究了催化剂用量对浆料黏度的影响,固化参数R及扩链剂用量对HTPB聚氨酯弹性体力学性能的影响。试验结果表明,当催化剂质量分数为0.004%时,适用期可达5 h;R值为1.1,DEG羟基含量占反应总羟基量的60%时,聚氨酯弹性体力学性能较好,拉伸强度达7.60 MPa,断裂伸长率达540.21%。动态力学分析(DMA)测试结果显示,低分子量HTPB聚氨酯弹性体有两个明显的玻璃化转变温度,说明样品存在明显的微相分离结构。     

Zwitterionic Conjugated Surfactant Functionalization of Graphene with pH‐Independent Dispersibility: An Efficient Electron Mediator for the Oxygen Evolution Reaction in Acidic Media

The functionalization of graphene has been extensively used as an effective route for modulating the surface property of graphene, and enhancing the dispersion stability of graphene in aqueous solutions via functionalization has been widely investigated to expand its use for various applications across a range of fields. Herein, an effective approach is described for enhancing the dispersibility of graphene in aqueous solutions at different pH levels via non‐covalent zwitterion functionalization. The results show that a surfactant with electron‐deficient carbon atoms in its backbone structure and large π–π interactive area enables strong interactions with graphene, and the zwitterionic side terminal groups of the molecule support the dispersibility of graphene in various pH conditions. Experimental and computational studies confirm that perylene diimide amino N‐oxide (PDI–NO) allows efficient functionalization and pH‐independent dispersion of graphene enabled by hydration repulsion effects induced by PDI–NO. The PDI–NO functionalized graphene is successfully used in the oxygen evolution reaction as an electron mediator for boosting the electrocatalytic activity of a Ru‐based polyoxometalate catalyst in an acidic medium. The proposed strategy is expected to bring significant advances in producing highly dispersible graphene in aqueous medium with pH‐independent stability, thus broadening the application range of graphene.     

Hydroxyl groups and a-C:H and a-C:H(Me) structures

IR absorption spectra of hydroxyl groups in a-C:H and a-C:H(Me) (Me = Cu, Co) films grown by magnetron cosputtering of graphite and metal targets in argon-hydrogen plasma were studied. The hydroxyl band shape was analyzed using published data on the dependence of the O-H stretching vibration frequency on the distance from the nearest oxygen atom. It is demonstrated that the hydroxyl band shape is related to the character of interaction between an encapsulated metal and a carbon backbone of the film.     

GAP/HTPB粘合剂固化胶片力学性能研究

选用主链柔顺性好,可在推进剂中单独用作粘合剂的端羟基聚丁二烯(HTPB),通过化学共聚的方法来改善叠氮缩水甘油醚(GAP)的力学性能.反应活性对比表明,二者与异佛尔酮二异氰酸酯(IPDI)的反应速度有较大差异,进而影响粘合剂固化胶片的网络结构.实验结果表明:加入扩链剂和交联剂,所得粘合剂力学性能有较大提高,拉伸强度可达1.43MPa,延伸率为382.37%.     

Synthesis, characterization and catalytic activity of CdO nanocrystals

In this paper, we report the synthesis of nanocrystalline cadmium oxide (CdO) and its characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Its catalytic activity was investigated on the thermal decomposition of 1,2,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), ammonium perchlorate (AP), hydroxyl terminated polybutadiene (HTPB) and composite solid propellants (CSPs) using thermogravimetric analysis (TG), simultaneous thermogravimerty and differential scanning calorimetry (TG-DSC) and ignition delay measurements. Kinetics of thermal decomposition of AP + CdO has also been investigated using model free (isoconversional) and model-fitting approaches which have been applied to data for isothermal TG decomposition. All these studies show enhancement in the rate of decomposition of AP, HTPB and CSPs but no effect on HMX. The burning rate of CSPs has also been found to be increased with CdO nanocrystals.     

Preferential interactions of calcium ions in poly(2-hydroxyethyl methacrylate) hydrogels

An investigation of the preferential interaction of calcium ions with oxygen atoms in poly(2-hydroxyethyl methacrylate) (PHEMA)-based hydrogels has been carried out. The formation of polymer–Ca complexes was achieved by exposing powdered or fully hydrated samples with 5 mM, 0.1–0.5 M, or saturated CaCl₂ solutions for certain periods of time. The characteristics of the polymer–Ca complexes were deduced from the effect of the solute on the equilibrium water content, and from NMR, atomic absorption and infrared spectroscopies. The absence of significant changes in the NMR chemical shift and infrared vibrational wavenumbers for the various functional groups confirmed that polymer complexation with Ca²⁺ ions involves only weak interactions, possibly electrostatic or ion–dipole interactions. Among the three types of oxygen atoms in PHEMA, hydroxyl oxygen atoms seem to be the most sensitive to the presence of Ca²⁺ ions. Complexation at the ester oxygen atoms was also evidenced by a new band in the infrared spectra at 1,550 cm^-1. On the other hand, there were no indications that the hydrophobic domains in the backbone and the methyl groups at the side chain of PHEMA interact significantly with Ca²⁺ ions.     

Novel molecular device based on electrostatic interactions in organic polymers

A number of researchers have reported attempts to design molecular level devices. One approach is to make use of electrostatic interactions in different parts of a polymeric molecule. This paper reports a means to achieve this by adding space charge to a molecule consisting of symmetric and asymmetric subgroups. Physically, space charge residing in a subgroup produces a dipolar charge layer thereby creating a potential trough in the polymer backbone. By lifting or lowering this potential minimum, it is possible to modify the terminal current. The effect of space charge on the potential profile in the polymer backbone was examined and the change correlated to data on carrier mobilities for OC1C10-PPV reported in the literature. Modulation of space charge in the subgroup allows the manipulation of current flow along the polymer backbone, forming the basis for the development of a molecular device. A first-order analysis suggested that such a device could have current-voltage (I-V) characteristics similar to those of a MOSFET at subthreshold, with an estimated transconductance approximately 1-2 pAV and a cutoff frequency approximately 10(15) Hz.     

The position of nitrogen in N-heteropentacenes matters

An exploratory study on novel silylethynylated N-heteropentacenes, which have their N atoms on the terminal rings of the pentacene backbone, is reported. This study leads to both p- and n-channel organic thin-film transistors with high field-effect mobility and also reveals that the position of the N atoms plays an important role in tuning the structures and properties of organic semiconductors based on N-heteropentacenes.     

Effects of backbone conformation and surface texture of polyimide alignment film on the pretilt angle of liquid crystals

Polyimides (PIs) with different inclination angle of polymer backbones, together with polar hydroxyl group and/or nonpolar trifluoromethyl group at various sites of the backbone were synthesized and used as liquid crystal alignment layers. The molecular conformation, surface chemistry, surface energy, surface morphology, and pretilt angle of the PI film were investigated. The distributions of fluorinated group and hydroxyl group at different depths of the PI surfaces were analyzed by X-ray photoelectron spectroscopy. Effects of the conformation of the PI molecular backbone on the surface morphology of the rubbed PI layer, the pretilt angle and surface energy of the alignment film were studied. The PI which contains both nonpolar fluorinated groups sticking out of the surface and the polar hydroxyl groups on the surface exhibits high pretilt angle.     

Theoretical investigation of metal-molecule interface with terminal groups

The effects of terminal groups on the electron transport between metal electrodes and molecule are investigated through metal-molecule-metal systems using the first principles method, which is based on the density functional theory, with norm-conserving nonlocal pseudopotentials and nonequilibrium Green's functions. Eight Au-molecule-Au open systems are constructed and numerically examined, where gold atoms are used as electrode, benzene and borazine as core molecules, and sulphur (S), oxygen (O), selenium (Se), and cyano-group (CN) as terminal groups. Gold electrodes are described through a three-dimensional atomic model. The current-voltage (I-V) characteristics, density of states, and transmission functions of constructed systems are calculated and analyzed. Results show that the transmission properties of the systems are affected greatly by the terminal groups and are dependent on the core molecule as well. Se is demonstrated as the best terminal group to couple borazine to Au electrodes and CN is the best one to couple benzene to Au electrodes.     

Polystannanes: Polymers of a Molecular,Jacketed Metal–Wire Structure

Organometallic polymers comprising a backbone of covalently connected metal atoms can be regarded as molecular metal wires surrounded by a jacket of organic matter. Such polymers are rare and their materials properties are largely unexplored. Here, we report on polystannanes, (SnR₂)_n, that is, polymers with a backbone of tin atoms, which are synthesized by dehydropolymerization of dialkylstannanes (H₂SnR₂) with the catalyst [RhCl(PPh₃)₃]. The polystannanes feature reversible phase transitions into liquid‐crystalline states, remarkably, even below room temperature, and, interestingly, oriented either parallel or perpendicular to external driving forces, depending on the length of the alkyl substituents.     

Vertical Charge Transport via Small Polaron Hopping within TIPS‐Pentacene Lamellar Single Crystal

A modified liquid method is employed to grow an ultralarge 6,13‐bis(triisopropylsilylethynyl)pentacene crystal, ensuring fabrication and measurements of the two terminal devices. The hole transport mechanism is studied by analyzing the space charge limited currents (SCLCs) at various temperatures. Modified SCLC theory with a small polaron hopping model is developed and employed to successfully simulate the I–V curves. Values of effective hopping distance, transfer integral, and reorganization energy are extracted and reasonably discussed. A scenario is suggested that hopping transport takes place from one molecule to its nearest neighbor along the c‐axis, with every molecule acting as a trapping center.     

Extraction of U(VI) and Th(IV) from nitric acid solutions with tetraaryl-substituted (<Emphasis Type="Italic">o</Emphasis>-phenyleneoxymethylene)diphosphine dioxides

Extraction of U(VI) and Th(IV) from HNO₃ solutions in the form of complexes with tetraarylsubstituted (o-phenyleneoxymethylene)diphosphine dioxides is studied. The effect of substituents at the P atoms in the extractant molecule on its extraction ability and selectivity is considered. The stoichiometry of the extractable complexes is determined. The possibility of U(VI) and Th(IV) preconcentration with a complexing sorbent prepared by noncovalent immobilization of tetra-p-tolyl-substituted (o-phenyleneoxymethylene)-diphosphine dioxide on a polymeric matrix is demonstrated.     

Development by Hydrazine

The reduction of silver bromide in alkaline solution by hydrozine yields four atoms of silver per molecule of hydrazine. Development of a (lne-grain bromide emulsion takes place at pH levels obove 12 at a rate proportional to the concentration of hydrazine and to the hydroxyl ion concentrotion. The (lrst and rate-determining step is the loss of a single hydrogen ion and an electron from the hydrozine. The density-time plots are sigmoid with a deep toe curvature. E/ectronmicrographs of the developed particle population ot various stages show that the density grows by the increase in the number af centres reaching the developable stage.     

Organometallic Bonding in an Ullmann‐Type On‐Surface Chemical Reaction Studied by High‐Resolution Atomic Force Microscopy

The on‐surface Ullmann‐type chemical reaction synthesizes polymers by linking carbons of adjacent molecules on solid surfaces. Although an organometallic compound is recently identified as the reaction intermediate, little is known about the detailed structure of the bonded organometallic species and its influence on the molecule and the reaction. Herein atomic force microscopy at low temperature is used to study the reaction with 3,9‐diiododinaphtho[2,3‐b:2′,3′‐d]thiophene (I‐DNT‐VW), which is polymerized on Ag(111) in vacuum. Thermally sublimated I‐DNT‐VW picks up a Ag surface atom, forming a C? Ag bond at one end after removing an iodine. The C? Ag bond is usually short‐lived, and a C? Ag? C organometallic bond immediately forms with an adjacent molecule. The existence of the bonded Ag atoms strongly affects the bending angle and adsorption height of the molecular unit. Density functional theory calculations reveal the bending mechanism, which reveals that charge from the terminus of the molecule is transferred via the Ag atom into the organometallic bond and strengths the local adsorption to the substrate. Such deformations vanish when the Ag atoms are removed by annealing and C? C bonds are established.     

Magnetism in oxidized graphenes with hydroxyl groups

The magnetic properties of three oxidized graphene structures with hydroxyl groups (cases A, B and C) have been investigated through spin-polarized density functional theory. The results reveal that in a graphene hexagonal ring structure, chemical bond formation by two non-neighbored hydroxyl-bonded carbon atoms with one carbon atom between (case B) can cause unpaired spins to produce a magnetic moment of 1.2 μ(B), while chemical bond formation by two neighbored hydroxyl-bonded carbon atoms (case A) or non-neighbored hydroxyl-bonded carbon atoms with two carbon atoms between (case C) cannot generate unpaired spins for nonmagnetic states. These magnetic oxidized graphenes have great promise for new spintronics. This work provides fundamentals to controllably synthesize or/and oxidized graphene with hydroxyl groups at specific carbon positions for magnetic properties.     

<Emphasis Type="Italic">Ab initio</Emphasis> studies on [bmim][PF<Subscript>6</Subscript>]-CO<Subscript>2</Subscript> mixture and CO<Subscript>2</Subscript> clusters

Ab initio molecular dynamics studies have been carried out on the room temperature ionic liquid, 1,n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) and supercritical carbon dioxide mixture at room temperature and experimental density. Partial radial distribution functions (RDF) for different sites have been computed to see the organization of CO₂ molecules around the ionic liquid. Several partial RDFs around the carbon atom of CO₂ molecule are compared to find out that the CO₂ has specific interaction with a carbon atom present in the imidazolium ring. The CO₂ is also found to be very well organized around the terminal carbon atom of the butyl chain. The partial RDFs for the oxygen atoms around oxygen and carbon atoms of the CO₂ suggests that there is very good organization of CO₂ molecules around themselves even in the [bmim][PF₆]-CO₂ mixture. The instantaneous quadrupole moment tensor has been calculated for the anion and the cation. The ensemble average of diagonal components of quadrupole moment tensor of the cation have finite values, whereas the off-diagonal components of the cation and both the diagonal and off-diagonal components of the anion have the value of zero with a large standard deviation. The CPMD studies performed on CO₂ clusters reveals the greater tendency of the clusters with more CO₂ units, to deviate from the linear geometry.     

A thermovisco-hyperelastic constitutive model of HTPB propellant with damage at intermediate strain rates

The uniaxial compressive tests at different temperatures (223–298 K) and strain rates (\(0.40\mbox{--}63~\mbox{s}^{-1}\)) are reported to study the properties of hydroxyl-terminated polybutadiene (HTPB) propellant at intermediate strain rates, using a new INSTRON testing machine. The experimental results indicate that the compressive properties (mechanical properties and damage) of HTPB propellant are remarkably affected by temperature and strain rate and display significant nonlinear material behaviors at large strains under all the test conditions. Continuously decreasing temperature and increasing strain rate, the characteristics of stress-strain curves and damage for HTPB propellant are more complex and are significantly different from that at room temperature or at lower strain rates. A new constitutive model was developed to describe the compressive behaviors of HTPB propellant at room temperature and intermediate strain rates by simply coupling the effect of strain rate into the conventional hyperelastic model. Based on the compressive behaviors of HTPB propellant and the nonlinear viscoelastic constitutive theories, a new thermovisco-hyperelastic constitutive model with damage was proposed to predict the stress responses of the propellant at low temperatures and intermediate strain rates. In this new model, the damage is related to the viscoelastic properties of the propellant. Meanwhile, the effect of temperature on the hyperelastic properties, viscoelastic properties and damage are all considered by the macroscopical method. The constitutive parameters in the proposed constitutive models were identified by the genetic algorithm (GA)-based optimization method. By comparing the predicted and experimental results, it can be found that the developed constitutive models can correctly describe the uniaxial compressive behaviors of HTPB propellant at intermediate strain rates and different temperatures.     

HTPB/增塑剂共混物的介观动力学模拟

高分子粘接剂与小分子增塑剂癸二酸二辛酯(DOS)的相分离会严重影响端羟基聚丁二烯(HTPB)固体推进剂的使用性能.文中应用分子动力学(MD)和介现动力学(MesoDyn)模拟方法研究了不同增塑剂含量和温度对HTPB/DOS共混物的相容性和介现形貌的影响.结果表明,在室温时当增塑剂DOS的含量为6%时,HIPB和DOS的...