Materials Literature
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A two-step process for lactic acid polymerization is studied: in the first step the lactic acid is condensation-polymerized to a low-molecular-weight hydroxyl-terminated prepolymer; and then the molecular weight is raised by joining prepolymer chains together using diisocyanate as the chain extender. The resulting pol…
The thermal recovery of the stored stress in crosslinked polyethylene has been commercially exploited in the preparation of heat shrinkable materials. The study on thermally recoverable crosslinked polyethylene compositions is reported in this paper. Thermally recoverable compositions were prepared by cross-linking of…
The porphyrin–prophyrin distance and the spatial requirements of the porphyrin substituents are parameters that influence the rotatability of the ligands in metal bis(porphyrinate)s (shown on the right): the chiral cerium complexes were much easier to racemize than the zirconium complexes. The porphyrin ligands in the…
The heavy-metal chelating properties of a soy protein based hydrogel, prepared by crosslinking an ethylenediaminetetraacetic acid dianhydride (EDTAD) modified soy protein isolate (SPI), have been studied. The equilibrium binding capacities of the divalent calcium, zinc, mercury, and lead ions by the gel were 0.70, 0.6…
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.…