Materials Literature
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The physical and thermal properties of hand-cast polyurethane and polyurethane/polyurea elastomers prepared from prepolymers of 20 and 97% trans,trans-4,4′-diisocyanatodicyclohexyl methane (t,t-rMDI) and C3- and C4-polyethers chain extended with either 1,4-butanediol (XB) or a commercial mixture of diethyl toluenediam…
Excellent yields of the carbaporphyrin 1 are obtained by application of the “3 + 1” methodology for the reaction of 1,3-indenedicarboxaldehyde with a tripyrrane in the presence of 5% CF3CO2H in CH2Cl2. The related formylcarbaporphyrin 2 was prepared similarly. In contrast to earlier claims, no unusual tautomers or con…
Through “electronic separation” of the seven-membered ring the formally cross-conjugated, azulene-containing macrocycle (limiting structure A) becomes a porphyrinlike species with a weak, diamagnetic ring current (limiting structure B). This aromatic character is further accentuated upon twofold protonation.
Abstract It is a great challenge to synthesize compounds containing planar‐tetracoordinate carbon that are stable enough to be isolated, investigated, and handled under ambient conditions. There have therefore been many attempts to construct hydrocarbon frameworks that can incorporate and stabilize tetravalent carbon…
Isothermal melt crystallization of poly(L-lactide) (PLLA) has been studied in the temperature range of 90 to 135°C. A maximum in crystallization kinetic was observed around 105°C. A transition from regime II to regime III is present around 115°C. The crystal morphology is a function of the degree of undercooling. At c…
Soft chemical methods were used for preparing the new class of composite materials presented here. One example is [{Cu(4,4′-bpy)}4Mo8O26] (4,4′-bpy = 4,4′-bipyridine), whose unique structure (shown on the right) consists of [Mo8O26]4− clusters embedded in a web of {Cu(4,4′-bpy)} one-dimensional chains.
Abstract Some chemical and mechanical properties of intermediate products obtained in the production of PE heat shrinkable tubes were studied, seeking correlations between the composition and the properties. Different PE granulates were mixed with antioxidant (amine or phenol derivative), flame retardant agent and, fo…
Three modified bismaleimide resin systems (designated as systems I, II, and III) for high-performance radomes are introduced. Their glass transition temperatures are 274°, 268°, and 265°C, respectively; and their dielectric loss tangents at 10 GHz are 0.0117, 0.0108, and 0.0118, respectively. System I and system II ar…
The excited states of many organic molecules are sufficiently long lived so that excitation gives rise to a change in the absorption spectrum that persists for seconds or even longer. The author is unaware of any perfect crystal for which this is true. Vacancies are essential to the appearance of photchromism in alkal…
Cryogenic refrigeration could be realized by using the electrocaloric effect (i. e. inverse pyroelectric effect) of ferroelectric materials. Recent progresses implied that ferroelectric refrigeration may be a possible new technique of cryogenic refrigeration operated near room temperature. The analyses and syntheses o…
Thermal decomposition during pyrolysis of poly(vinyl alcohol) (PVA) was investigated using off-line pyrolysis gas chromatography mass spectrometry (Py-GCMS). Observation of a yellow-brown smoke produced when PVA was heated at elevated temperatures indicated that the liquid products may contain highly conjugated chromo…
A two-dimensional analysis of horizontal Bridgman crystal growth is presented. Material properties are close to those of lithium calcium aluminium fluoride (LICAF), while operating parameters resemble, on average, those used during growth of fluorides via vertical techniques. Estimates of characteristic timescales, as…
One of the key requirements for optical switching apertures for ophtalmic, building and automobile glazing is long lived product. However, oxidation of a spirooxazine yields photoproducts such as oxindoie derivatives, naphthoxazole, dihydro-2,6-quinolone and 1-N-formylimino-2-naphthoquinone devoid of photochromic acti…
The formation of porous silicon is investigated by the Monte Carlo method in a model that takes account of the nonuniformity of the charge distribution over the silicon-electrolyte interface, hole diffusion, generation, and recombination processes, and size quantization. The structures obtained in a computer simulatio…
The theory of CSL and DSC has been applied for grain boundaries of quasicrystals. Particular features of special grain boundaries of quasicrystals are underlined. The Frank–Rodrigues representation of rotations is used to classify disorientations and to find the degeneracy of different values of the coincidence index.
The magnetic properties and structure of hydrogen-amorphized RFe 2 H x compounds (R=Y, Gd, Tb, Dy, Ho, Er) have been studied. It is shown that amorphization of the RFe 2 H x hydrides results in an increase of Fe-Fe, and a decrease of R-Fe exchange interaction energy compared to their crystalline hydride counterparts.…
In order to understand the behaviour of ceramics and minerals at an atomic level a wide variety of modelling techniques are presently used, and one of the purposes of this workshop is to bring these together. At the most expensive end of the spectrum are the ab initio electronic structure calculations, which can accur…
In a previous study (B. Reihl and K.O. Magnusson, Phys. Rev. B 42 (1990) 11 839) no change was observed in the LEED pattern from the 2 × 1 pattern of the clean Si(111) surface upon potassium adsorption. In contrast to this paper, we observe six surface phases during room temperature dosing of K on the cleaved Si(111)…
The reactions of ana-anthraquinones with nucleophiles have been studied in order to find the photochromic compounds with the lowest fatigue. The primary stage of the reaction between 9-aryloxy-1,10-anthraquinones and nucleophiles (water, alcohols, primary amines) is the reaction of nucleophilic 1,4-addition. The elect…
Multilayer amorphous selenium-based photoreceptors were prepared by thermal evaporation in a vacuum at . Amorphous multilayers of Se/CdSe, as well as a combination of a thin film and multilayers were used as photogeneration layers. `Pure' Se or were the transport layers. The xerographic properties of the photoreceptor…