New synthetic route to diaminonitropyrazoles as precursors of energetic materials

Treatment of nitropyrimidine derivatives with (N-substituted) hydrazines (2 equiv.) gave 1-(substituted)-3,5-diamino-4-nitropyrazole, providing a very mild conversion of pyrimidines into pyrazoles. This reaction provided a convenient route to precursors for new efficient and insensitive explosives.     

PTFE nanoemulsions as ultralow-k dielectric materials

Modern integrated circuits require insulating materials with a dielectric constant as low as possible in order to obtain device speed improvements through lower RC delay. We have investigated the electrical and structural properties of PTFE thin films obtained from Algoflon^®-PTFE nanoemulsions, via spin coating deposition, followed by sintering. Films as thin as 160 nm with dielectric strength better than 4 MV/cm have been obtained.     

Molecular design of porphyrin-based nonlinear optical materials

Nonlinear optical chromophores containing (porphyrinato)Zn(II), proquinoid, and (terpyridyl)metal(II) building blocks were optimized in a library containing approximately 10(6) structures using the linear combination of atomic potentials (LCAP) methodology. We report here the library design and molecular property optimizations. Two basic structural types of large beta(0) chromophores were examined: linear and T-shaped motifs. These T-shaped geometries suggest a promising NLO chromophoric architecture for experimental investigation and further support the value of performing LCAP searches in large chemical spaces.     

Molecular design of supramolecular polymers with chelated units and their application as functional materials

This article summarizes the basic concepts and synthetic strategies leading to various types of supramolecular polymers with chelated units, including linear, branched, cross-linked, and heterometallic polymers. Particular attention is paid to such new synthetic approaches to supramolecular polymers as hierarchical and orthogonal self-assembly based on a combination of metal–ligand interaction with hydrogen bonds and host–guest interactions. Metallosupramolecular polyelectrolytes, supramolecular polymer gels, self-assembled metallosupramolecular monolayers, and supramolecular metal chelate dendrimers are analyzed. The stimuli-responsive, self-healing, and shape memory supramolecular polymers with chelated units are considered. The bibliography includes articles published over the past five years.     

Electrospinning as a route to advanced carbon fibre materials for selected low-temperature electrochemical devices: A review

Electrospinning has been proven as a highly versatile fabrication method for producing nano-structured fibres with controllable morphology,of both the fibres th...     

Molecular design of star-shaped benzotrithiophene materials for organic electronics

Progresses in the design and application of conjugated small molecules, oligomers and polymers have empowered rapid development of organic electronic technology as an alternative to conventional devices. Among the numerous organic electronic materials, benzotrithiophene (BTT)-based oligomers and polymers have recently come in the limelight demonstrating great potential in organic electronics as high performance photovoltaic devices, field-effect transistors, electrochromic materials, high-area capacitors and charge carrier discotic liquid crystals. In this digest, we propose an overview of the organic electronic materials based on BTT isomers, highlighting the structure-performance relationship. The results obtained so far clearly indicate that the BTT isomers are among the most promising building blocks for the development π-extended materials for optoelectronic applications in the near future.     

Molecular design of hybrid organic-inorganic materials with electronic properties

The synthesis of two classes of hybrid organic-inorganic nanocomposites with electronic properties is reported. One is made of PDMS units cross linked with vanadium oxo-species where the vanadium coordination depends on the hydrolysis pH. Tetrahedral coordination is retained at neutral pH, while acidic conditions promote the segregation of five coordinated vanadium oxo-species. The reduction process depends also on the vanadium coordination. The second system is made of siloxane T units and polypyrrole oligomers, grafted and interpenetrated at a nano size level.     

Silica dissolution as a route to octaanionic silsesquioxanes

The octaanion, [OSiO_1.5]₈^8? (OA) is a low cost, discrete nano silica particle that can be made directly from high surface area, amorphous silica reacted with Me₄NOH in water alcohol mixtures. It would be ideal if Me₄NOH could be formed in situ from, for example, Me₄NCl and NaOH, as long known in the literature. This process would reduce costs and enable recycling of Me₄NCl produced in the functionalization of OA with chlorosilanes, RMe₂SiCl, to form [RMe₂SiOSiO_1.5]₈ organic/inorganic hybrid nanobuilding blocks. Kinetic studies were conducted to assess base‐promoted dissolution of fumed silica (25 m 2 /g) as a function of concentrations, times, etc., to form the octaanion [OSiO_1.5]₈^8? using Me₄NOH, NaOH and mixtures of NaOH/Me₄NCl. Surprisingly, we find that small amounts of Me₄NCl greatly inhibit the dissolution reaction for reasons that are as yet unknown. Copyright © 2005 John Wiley & Sons, Ltd.     

Carbene-carbene rearrangements as a route to 1,5-dihydropentalene

1,5-Dihydropentalene (4) is formed as the main product on treatment of trans-1,2-bis(2,2-dibromocyclo-propyl)ethene 3 with methyllithium at −40°. In addition the reaction affords 1- and 2-propadienylcyclopentadienes (5a) and (5b), and trans-1,2,4,6,7-octapentaene (6), new C₈H₈ isomers. Diels-Alder adducts of 4, 5a and 5b were obt in the reaction with perfluorobut-2-yne. The formation of 1,5-dihydropentalene 4 is explained by a double ring expansion sequence involving consecutive carbene-carbene rearrangements with 1,3-carbon and subsequent 1,2-hydrogen shifts, supported by the reaction of double labelled (¹³C-depleted) 3. From readily available 3 at low temperatures formation and fusion of two 5-membered rings are achieved in one step.     

Transmetalation as a route to novel styryllithium reagents

[structure: see text] Transmetalation of beta-tributyl(styryl)stannanes with n-BuLi gives the functional equivalents of the corresponding styryllithium intermediates. Reaction of the intermediates with chlorotrimethylsilane, iodomethane, or dimethyl sulfate gives the substituted styryl products in moderate to good yields. In all cases, the configuration about the double bond was retained in the products.     

Directed deprotonation-transmetalation as a route to substituted pyridines

Regioselective C-4 deprotonation of 3-bromopyridine, followed by Li/Zn transmetalation and Pd-mediated coupling processes, provides a flexible entry to 4-substituted and 3,4-disubstituted pyridines. Application of a similar sequence to 2-bromopyridine (with LDA as base) provides 2,3-disubstituted pyridines, but using lithium 2,2,6,6-tetramethylpiperidide (LiTMP) provides access to both the 2,3- and 2,4-disubstituted isomers.     

Anionic oligomerization as a route to chain clusters

The combination of two old concepts (the "sigma-donor" capability of M-H bonds and the propensity of unsaturated complexes for addition reactions) has led to the first example of addition oligomerization of an organometallic analogue of olefins: chains containing cis-[Re(CO)4] units joined by Re-H-Re interactions have been obtained through the oligomerization of the unsaturated complex [Re2(micro-H)2(CO)8] promoted by anionic "initiators". The limits of the method and the possible extension to other substrates are discussed.     

Helicate extension as a route to molecular wires

We describe the preparation of a helicate containing four closely spaced, linearly arrayed copper(I) ions. This product may be prepared either directly by mixing copper(I) with a set of precursor amine and aldehyde subcomponents, or indirectly through the dimerization of a dicopper(I) helicate upon addition of 1,2-phenylenediamine. A notable feature of this helicate is that its length is not limited by the lengths of its precursor subcomponents: each of the two ligands wrapped around the four copper(I) centers contains one diamine, two dialdehyde, and two monoamine residues. This work thus paves the way for the preparation of longer oligo- and polymeric structures. DFT calculations and electrochemical measurements indicate a high degree of electronic delocalization among the metal ions forming the cores of the structures described herein, which may therefore be described as "molecular wires".     

Use of Stille-type cross-coupling as a route to oligopyridylimines

The new tin reagents, 2-(n-Bu₃Sn)-6-{C(R)OCH₂CH₂O}-C₅H₃N, (R=H a, Me b), have been employed in Stille-type cross-coupling reactions with a range of oligopyridylbromides generating, following a facile deprotection step, a series of formyl- and acetyl-functionalised oligopyridines. Condensation reactions with 2,6-diisopropylaniline has allowed access to families of novel sterically bulky multidentate N,N,N,N (tetradentate), N,N,N,N,N (pentadentate), N,N,N,N,N,N (sexidentate) and N,N,N,N,N,N,N (heptadentate) nitrogen donor ligands. This work represents a straightforward and rapid synthetic route for the preparation of oligopyridylimines, which are expected to act as useful components for the self-assembly of polymetallic complexes.     

Molecular weight-dependence of free volume in polystyrene studied by positron annihilation measurements

Positron annihilation lifetime measurements are reported for four monodisperse polystyrenes with molar mass M = 4,000, 9,200, 25,000, and 400,000. The temperature dependences of orthopositronium (o-Ps) lifetime (τ₃) and intensity (I₃) were measured from 5°C to T_g + 30°C for each sample. From these data, the free volume hole size, 〈v_f(τ₃)〉, and fractional free volume h_ps=CI₃〈v_f(τ₃)〉 were calculated. The temperature dependences of τ₃, 〈v_f(τ₃)〉 and h_ps show a discrete change in slope at an effective glass transition temperature, T_g,ps, which is measurably below the conventional bulk T_g. This suggests that τ₃ is sensitive to large holes which retain their liquid-like mobility in the glassy state. Good agreement was found for T > h_g,ps between h_ps and the theoretical free volume fraction h_th deduced from experimental P-V-T data for polystyrene using the statistical mechanical theory of Simha and Somcynsky. Below T_g,ps, deviations between h_ps and h_th are observed, h_ps falling increasingly below h_th as temperature decreases. Whereas h_ps and h_th depend strongly on M in the melt, each essentially independent of M in the glass. A free volume quantity, computed from the bulk volume, which is in good numerical agreement with the Simha-Somcynsky h-function in the melt, gives improved agreement with h_ps in the glassy state. © 1994 John Wiley & Sons, Inc.     

Synthesis and structural investigation of new triptycene-based ligands: en route to shape-persistent dendrimers and macrocycles with large free volume

Triptycene was used to build a series of ligands containing pyrazine groups for use in forming coordination frameworks and as model compounds toward target shape-persistent dendrimers and macrocycles. The phenylenediamine precursors are formed by controlled double nitration/reduction of triptycene, followed by condensation with triptycenyl o-quinone to form the ligands. Solid-state structures show that the ligands favor packing in layered structures with intermolecular pi stacking. Increasing the length of the wings still allows for effective packing, but increasing the number of pyrazine groups or adding more triptycenyl moieties reduces packing efficiency. To demonstrate the potential of these molecules to function as ligands, a coordination complex of 15 with copper(I) iodide was obtained and found to form dimers that pack into a layered arrangement.     

Solvent‐free neat synthetic route to tetrahydroacridinones

An environmentally benign approach for the synthesis of acridines using inorganic solid supports and “neat reaction'' technology is described. These methodologies completely eliminate the use of solvent during the course of reaction. Moreover, microwave‐assisted reactions reduce the reaction time from hours to minutes with improved yield. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:138–222, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20080     

Melt drawing as a route to high performance polyethylene

Well established routes for obtaining stiff and strong polyethylene (PE) involve solid state drawing either of solution crystallized gel films or melt crystallized spherulitic PE. The aim of this work is to show the potential of melt deformation as an alternative route for obtaining highly oriented products. Our previous work on the melt deformation route showed that oriented PE fibers could be directly extruded under appropriately controlled conditions [8,9]. Here, we show that PE films (or filaments) can also be melt drawn in the temperature window 130–160 °C, thus yielding oriented products. The advantage of melt drawing over direct melt extrusion is that it allows a wider operational latitude and thus does not require such carefully controlled conditions.The morphology produced by melt deformation is different from solid state deformation and consists of extended chain fibrils with platelet overgrowths. The relative amount of fibrils and platelets depends on operating parameters. The temperature window of PE melt drawing is identified with the regime where some flow induced crystallization takes place. The conditions for melt drawability are of wider generality for crystallizable flexible chain polymers. They are: (i) adequate strain rate to overcome entropie resistance to chain extension, (ii) but not high enough to activate the elastic response of the transient networks in the entangled system, (iii) sufficient strain to fully extend the chain, (iv) appropriate temperature for flow-induced crystallization and strain hardening, and (v) cooling to freeze the oriented structure.Ultra high molecular weight PEs were not the most suitable for melt drawing due to their high recoverable elongation in the melt (melt elasticity) in addition to added limitations imposed by their nascent grain systeme. Our work suggests that an optimum molecular weight for melt drawing is¯M _w(400–900)×10³ with further possibilities for improvement through multimodal distributions.