Flexibility and hydrodynamic properties of poly(vinylpyrrolidone) in non-ideal solvents

At 298.15K, intrinsic viscosity [] has been measured for poly (vinylpyrrolidone), PVP, samples of different relative molar masses M in pure water and eight different binary solvents. These solvents were water/acetone mixtures having different volume fractions of acetone (ACT). The solvation power of these mixtures showed a cosolvancy effect. The maximum solvation power was found for the mixture containing 0.2 volume fraction of ACT. The value of K=74×10^-3 dm³kg^-1 was utilized for calculating the unperturbed dimensions, u.d., steric factor, , the characteristic ratio, C, and the persistence length, a_p. Values of 0.666 A^o, 2.28, 10.38 and 8.76 A^o, respectively, were obtained for PVP in theta-solvent. The calculated values of the effective radius (R_e), effective unit length (b) and the effective hydrodynamic radius of monomeric unit (r_o) showed the complete impermeability of polymer molecules. Some errors in the polymer handbook and CRC, water-soluble synthetic polymers, were demonstrated with its logical corrections.     

Properties ofSrMO 3-δ(M=Fe,Co) as oxygen electrodes in alkaline solution

Strontium ferrates and cobaltates with compositions SrFeO_3- (0.060.40) and SrCoO_3- (0.040.30) were synthesized. The dependence of the oxygen electrode properties on the value was examined in 1 mol dm^–3 KOH solution. In the SrFeO_3- series, the samples with 0.24<<0.29, showed the highest activity in both oxygen evolution and reduction reactions. In contrast, no strong dependence on the value was observed in SrCoO_3-, which also showed a high catalytic activity for oxygen evolution.     

The electrochemical properties of polyaniline derivatives: poly(4,4′-diphenylamine methylenes) and poly(4,4′-diphenylimine methines)

Summary The electrochemical properties of poly(4,4-diphenylamine methylenes) and poly(4,4-diphenylimine methines) were investigated by cyclic voltammetry. A dehydrogenation reaction occured when poly(4,4-diphenylamine methylenes) underwent a electrochemical reaction and transformed to poly(4,4-diphenylimine methines). The fully oxidized poly(4,4-diphenylimine methines) had the electrochemical band gaps of 1.60–1.72 eV, which were found to significantly smaller than those of the fully reduced poly(4,4-diphenylamine methylenes).     

Convective Regime of Filtration Combustion of Energetic Materials in a Cocurrent Flow of Their Combustion Products

The convective regime of filtration combustion of energetic materials in a cocurrent flow of their combustion products is studied using a model with extremely simplified kinetics and heat transfer, which shows instability of the process. It is shown that the more accurate twotemperature model describes a steadystate regime. In this regime, the gas temperature on the hot boundary of the heating zone is well below the combustion temperature, and the solidphase temperature is well below the temperature proposed in recent studies on this topic. It is pointed out that the twotemperature approach is unjustified and intragranular nonisothermicity must be taken into account for convective regimes. It is shown that the threetemperature model, which takes into account this effect, does not give a stable steadystate solution.     

Quasi‐Homogeneous and Pseudospin Modes of Zirconium‐Wire Combustion in Air

A novel experimental technique is proposed for examining the transition mechanism from quasihomogeneous to heterogeneous combustion — burning of a variablepitch spring. Depending on the pitch of aircombustible zirconium springs, two combustion modes are possible. Quasihomogeneous (layerbylayer) combustion is observed in the case of smallpitch springs; as the spring pitch increases, quasihomogeneous combustion transforms into heterogeneous (pseudospin) combustion. Conditions for the occurrence of various combustion modes, depending on the spring diameter and pitch, are studied.     

Pore Propagation Directions in P+ Porous Silicon

A comparative study is presented on the pore propagation directions of porous silicon layers (PSL) formed on p⁺-type substrates of different orientations. PSLs were formed on plain (0 0 1) and (1 1 1) silicon wafers as well as on structured (0 0 1) wafers containing facets of various orientations. During anodization, regular pores follow the 0 0 1 direction on the (0 0 1) planes. While on the (1 1 1) planes fewer regular pores develop and seemingly propagate closely to the 1 1 1 direction. These results indicate that the pores propagate perpendicular to the surface i.e. along the field lines when the surface orientation is either (0 0 1) or (1 1 1).When the silicon surface provided (1 1 0) orientation (Chuang, Collins, and Smith, 1989), or its position is in between the (0 0 1) and (1 1 1) planes then the pores do not propagate perpendicular to the surface but along the 0 0 1 direction.All the phenomena exhibited might be explained by presuming that during formation, the pores propagate along the 1 0 0 directions, and that those 1 0 0 directions are preferred which are closely to the field lines. In PSLs formed on (0 0 1) surfaces the field lines and the 0 0 1 crystallographic direction are coincident. However, in the (1 1 1) oriented wafer where three equally probable 1 0 0 directions exist around the field lines, more irregular structure of PSLs will develop.     

Synthesis of monocarboxylic polyoxyethylenes

Summary The various methods of synthesis which can be used to prepare -carboxy polyoxyethylenes are reviewed. The synthesis and the purification of -methoxy -carboxy polyoxyethylenes ( ) are reported. The process consists of the reaction of halogenoacetic acids with an -methoxy -sodium hydroxylate polyoxyethylene followed by a purification by extraction. ,-dimethoxy and -methoxy -ethyl carboxylate polyoxyethylenes were synthesized.     

Aphid deterrence by glucose esters in glandular trichome exudate of the wild tomato,Lycopersicon pennellii

Settling of the potato aphid,Macrosiphum euphorbiae, on feeding membranes was deterred by methanolic leaf rinses ofLycopersicon pennellii, or of its F₁ with tomato,L. esculentum. The active compounds in theL. pennellii rinsates were identified as 2,3,4-tri-O-acylglucoses bearing short to medium chain length fatty acids. These compounds are localized in the glandular exudate of the type IV trichomes and may accumulate to levels in excess of 400 g/cm². In choice assays, purified glucose esters fromL. pennellii reduced aphid settling at concentrations as low as 25 g/cm²; at concentrations of 150 g/cm² or more, all aphids avoided treated areas. Glucose esters were also active in deterring aphid settling in no-choice assays. At 100 g/ cm², these esters resulted in increased levels of mortality after 48 hr.     

Synthesis of novel telechelic monodispersed nonconjugated dienes

Summary The synthesis of novel telechelic monodispersed nonconjugated dienes from commercially available , -dithiols and dienes is presented. The batch reaction produced a polydispersed. mixture separable with difficulty whereas a dropwise addition of dithiol onto an excess of , -diene in the presence of peroxide led selectively and quantitatively to the addition product: diene-dithiol-diene.     

Weak Gel Behaviour of Poly(vinyl alcohol)-Borax Aqueous Solutions

Thermal transition of PVA-borax aqueous gels with a PVA concentration of 60 g/L and a borax concentration of 0.28 M was investigated at temperatures ranging from 15 to 60C using static light scattering (SLS), dynamic light scattering (DLS), and dynamic viscoelasticity measurements. Three relaxation modes, i.e. two fast and one slow relaxation modes, were observed from DLS measurements. Two fast relaxation modes located around 10^–310¹ sec, with one fast mode (_f1) being scattering vector q-dependent and the other fast mode (_f2, with _f2>_f1) being q-independent. The _f1 mode was attributed to the gel mode whilst the _f2 mode could be due to the hydrodynamics of intra-molecular hydrophobic domains formed by uncharged segments of polymer backbones. The slow relaxation mode with relaxation time located around 10¹10³ sec in DLS data was due to the motion of aggregated clusters and was observed only at temperatures above 40C. The amplitude and relaxation time of slow mode decrease as temperature is increased from 40 to 60C. At temperatures below 40C, no slow relaxation mode was observed. The SLS measurements showed PVA-borax-water system had fractal dimensions D _f2.4 and D _f2.0 as temperature was below and above 40C, respectively. The simple tilting test indicated gel behaviour for the PVA-borax aqueous system at temperatures below 40C with a creep flow after a long time exposure in the gravity field. But the dynamic viscoelasticity measurements demonstrated a solution behaviour for PVA/borax/water at temperatures below 40C, the critical gel point behaviour for G() and G() was not observed in this system as those reported for chemical crosslinked gels. These results suggest that the PVA-borax aqueous system is a thermoreversible weak gel.     

Dynamics and self-organization of catalytic systems

The kinetics of a catalytic reaction is frequently formulated in terms of simple concepts of the Langmuir type. Apart from limitations arising from the non-uniformity of the catalyst's surface and from the coverage dependence of the rate constants, several other complications may come into play. These may arise on the quantum level where energy flow between the various degrees of freedom may cause failure of simple transition state theory, as well as on the continuum level where formulation of rate equations in terms of coupled non-linear differential equations may give rise to a rich scenario of spatio-temporal self-organization, including kinetic oscillations, chaos, and formation of concentration patterns. Several of these phenomena are illustrated by selected examples.     

Effects of crystallinity and supermolecular formations on the interfacial shear strength and adhesion in GF/PP composites

Aim of this study was to screen the morphological effects on the interfacial shear strength (i) in glass fibre (GF) reinforced isotactic polypropylene (iPP) model composites. i was determined by a modified single fibre pull-out technique. It was established that the relation between i (5–6 MPa) and the yield stress of the iPP (y30 MPa) is at about 1:6 and that the i values were not influenced by the mophological superstructure set under isothermal crystallization conditions. Increased i was only observed when specimens were produced non-isothermally, by quenching (i9 MPa). This improvement could not be related to thermal shrinkage stresses. The enhancement in i was attributed to better wetting and improved adhesion due to the enlarged amorphous PP (aPP)-phase. A schematic adhesion model considering the wetting behaviour of aPP and iPP was proposed.     

Estimation of α and β peptide bonds in thermal poly(aspartic acid) by potentiometric titration

Summary A potentiometric titration method for the estimation of the configuration ( and peptide bonds, I and II) of poly (aspartic acid) prepared by thermal polycondensation is presented. Experimental results of the potentiometric titration of various samples differing in the molar fraction of I and II are confronted with the results of ¹³C NMR spectroscopy. Both methods lead to comparable results.     

Ethynylene-disilanylene copolymers

Polymers of structure (SiR₂SiR₂-C C-SiR₂SiR₂-C C) _n , in which ethynylene units alternate with disilylene units, have been prepared by two routes: (a) condensation of dichlorodisilanes with dilithium derivatives of 1,2-diethynyldisilanes and (b) ring-opening polymerization of strained cyclic disilanylene-acetylnes, (SiR₂SiR₂C C)₂. The polymers display UV absorption near 240 nm indicative of – conjugation between the Si₂ and the C C moieties. Polymers with R=R=n-Bu or R=n-Bu, R=Ph, undergo solid-state transitions to form liquid crystalline mesophases resembling those observed for many poly(silylenes). Single crystals were obtained for the polymer with R=R=CH₃, by precipitation from dilute cyclohexane solution. The solid-state properties and structures of this family of polymers are discussed.This paper was presented at the Second International Topical Workshop, Advances in Silicon-Based Polymer Science.     

Gasless Combustion of Ti–Al Bimetallic Multilayer Nanofoils

Ti–Al multilayer foils were produced magnetron vacuum deposition. The microstructure period varied in the range of 5–110 nm, the number of layers was 150–4700, and the total thickness of a multilayer foil reached 15–20 m. The gasless combustion of the foils was studied. Steadystate and pulsating combustion regimes were revealed; combustion temperatures were determined for both regimes. It was shown that the most probable mechanism of the selfpropagating reaction is the diffusion of Al in Ti at a temperature close to the temperature of the transition.     

Variable‐temperature IR spectroscopic studies of CO adsorbed on Na‐ZSM‐5 and Na‐Y zeolites

CO interacts with extraframework alkali metal cations (M⁺=) of zeolites to form both M⁺CO and M⁺OC species. By using variabletemperature FTIR spectroscopy, these Cbonded and Obonded species were found to be in a temperaturedependent equilibrium. For the same cation, the difference in interaction energy depends upon the zeolite framework. Thus, for the equilibrium process ZNa⁺=CO ZNa⁺OC, where Z represents the zeolite framework, H ⁰ was found to take the values 3.8 and 2.4 kJ mol^– for CO/NaZSM5 and CO/NaY, respectively. The Cbonded species show always the highest cation–CO interaction energy.     

Specific features of the phase transformations occurring during the sintering process of the beta-alumina based ceramics and their properties

Conclusions During the sintering process of beta-alumina obtained using the method of plasmochemical synthesis, the structural transformation occurs and it is accompanied by the separation of the excess Na₂O and the formation of an intergranular meltlike phase that is saturated with sodium and is characterized by high dielectric properties.The quantity of the meltlike phase and the magnitude of the /( + ) ratio determine the degree of stabilization (stability) and the final resistivity of the material and depend on the initial chemical composition and the heating rate maintained during the sintering process.It was shown that when the duration of residence of the material in the hot zone of the furnace is increased or when the specimens sintered maintaining high heating rates are subjected to additional heat treatment, one observes the occurrance of the reverse structural transformation that is characterized by an increase of the phase ratio /( + ) 1, a reduction in the quantity of the meltlike phase right up to its complete disappearance, and a decrease of the electrical resistivity of the material.In the materials having a large excess quantity of sodium oxide, the process of crystallization of the intergranular NaAlO₂ phase occurs simultaneously with the second phase transformation.The best ceramic and electrophysical parameters were obtained when sintering the material contained 7.9% Na₂O.Translated from Ogneupory, No. 3, pp. 13–18, March, 1990.     

State and prospects of development of domestic equipment for manufacture of needle-punched,nonwoven materials from polymer melts

Conclusions Domestic equipment has been devised for the production of needle-punched nonwoven geotextile materials from second-grade polycaproamide or fibre-forming polypropylene.The geotextile materials produced are promising for use in construction of roads, foundations of buildings, in hydrotechnology, and in land reclamation.Promising trends in the development of equipment for preparing spun nonwoven materials have been noted (light-duty needle-punched or heat-bonded materials, bulky spun articles, etc.).Coworkers of the Kemerovskii and Kamenskii Khimvolokno IAs the Khimtekstil'mash SIA, the VNIISV, the GIPROtyumenneftegaz, the SoyuzdorNII, and the Plastpolimer SIA took part in this work.Translated from Khimicheskie Volokna, No. 4, pp. 8–10, July–August, 1989.     

Preparation of poly(alkylvinylether)s for nonlinear optical applications

Summary 3,5-Dimethoxy-4-(2-vinyloxyethoxy)-4-nitrostilbene 2 and 3,5-dimethoxy-4-(2-vinyloxyethoxy)-2,4-dinitrostilbene 5 were prepared by the reactions of 2-iodoethyl vinyl ether with 3,5-dimethoxy-4-hydroxy-4-dinitrostilbene 1 and 3,5-dimethoxy-4-hydroxy-2,4-dinitrostilbene 4, respectively. Monomers 2 and 5 were polymerized with cationic initiators to obtain polymers with the NLO-phores 3,5-dimethoxy-4-oxy-4-nitrostilbene and 3,5-dimethoxy-4-oxy-2,4-nitrostilbene in the side chain. The resulting polymer 3 and 6 were soluble in DMSO and DMF. The inherent viscosities of polymers were in the range of 0.28–0.33 dL/g in DMSO. Polymers 3 and 6 showed good thermal stabilities in their TGA thermograms, and the T_g values from DSC thermograms were in the range of 81–87°C.     

Pheromone biosynthesis in lepidoptera

Pheromone components for many lepidopteran species are produced by the use of unique chain-shortening and 9, 10, and 11 desaturase systems. Correlations in the Tortricidae indicate that the pheromone components derived from 9 and 01 desaturases are found in the more primitive species (those possessing morphological plesiomorphies). The precise blend ofZ andE acetates in a number of species is regulated in the final reduction sequence from acyl intermediates. Preliminary research has been conducted on the characterization of the various desaturase enzymes used and on the important blend regulating sequence. Initial purification work on the 11 desaturase enzyme found in the cabbage looper moth is reported.