bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infrared spectroscopic study of the conformations assumed, in solution, by β‐diamides considered as model compounds for the repeating unit in poly amides synthesized from β‐amino and β‐imino acids
Authors: Marraud M. , Neel J. 
Published: June 2010

AbstractIn order to get a closer understanding of the conformational features displayed by poly‐amides obtained from different β‐amino and β‐imino acids, a systematic investigation was carried out with three sets of model β‐diamides.
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Very dilute solutions in carbon tetrachloride were studied by infrared spectroscopy in the 3200‐3500 cm−1 frequency range which includes the vNH stretching absorption bands.Depending on the substitution of the middle aliphatic sequence, molecules I (R, R') mainly assume either a stretched form (when R = H in β‐alanine derivatives) or a folded six‐membered ring conformation (when R = Me in the compounds synthesized from β‐aminobutyric acid). This latter conformer is stabilized by an intramolecular hydrogen bonding.A similar behavior was evidenced with N‐dimethylated species III(R). The β‐alanine derivative III(H) was found to be in an open form, whereas, the β‐aminobutyric analogous diamide III(Me) assumed a folded structure. In this latter case, however, it was shown that the folding is mainly governed by a NH…π interaction between the NH group and the π orbital of the tertiary amide function.On the other hand, the N‐methylation of the acetylamino group in models II(R) produces preferentially an eight‐membered ring chelate which is stabilized by an intramolecular hydrogen bonding involving the NH of the C‐terminal amide function and the highly nucleophilic CO in the N‐methylated acetylamino group.Each of the evidenced conformers is described by a set of three rotational angles and is experimentally characterized by its specific spectroscopic features.
Postgelation relationships for number fraction distribution after polyfunctional polymerization
Authors: Luby P. 
Published: June 2010

AbstractCorrelations between weight and number fraction distributions of a reaction mixture obtained by polyfunctional homopolymerization of a single kind of repeat unit under postgelation conditions are derived by virtue of an inter‐ and intramolecular bonds balance. An expression for the number average degree of polymerization was derived by means of the probability generating function of the first generation. Number fractions of a specific group of topologically distinguishable structures corresponding to a certain class of molecular trees defined by a vector u may be calculated in this way. Relations were established in terms of the link distribution function which allows for a substitution effect. Gelation phenomenon is shown to cause the number distribution mathematical relations to take two different forms while the weight fraction distribution equations remain valid throughout the whole conversion range.
Spin labeling studies on constituents of wood. II. Correlation times of spin probes and rigidity of network structure in isolated lignin
Authors: Lindberg J. Johan , Bulla Ivan , Tö;rmälä Pertti 
Published: June 2010

AbstractThe correlation times, T, of stable pyrroline nitroxyl radicals were determined in solutions of thioglycolic acid lignin from birch pulp dissolved in dioxane, pyridine, or dimethyl sulfoxide‐water at 298 and 325 K. It was found that T decreases continously with temperature, but increases with increasing lignin concentration. In pyridine and dimethyl sulfoxide‐water, the lignin seems to behave as a nearly compact sphere, whereas in dioxane a more loose structure occurs in accordance with the correlation time data. However, the rigidity of the lignin network is evident in all cases investigated.
Polymerization of trans‐7‐oxabicyclo[4.3.0]nonane
Authors: Kops J. , Larsen E. , Spanggaard H. 
Published: June 2010

AbstractThe polymerization of trans‐7‐oxabicyclo[4.3.0]nonane in bulk has been investigated in connection with PF5 initiation. Complete reversability of the polymerization of this system has been demonstrated. The ceiling temperature is around 12°C, and thermodynamic parameters have been calculated from the temperature dependence of the equilibrium composition. The rate of polymerization decreases rapidly with temperature and becomes very slow below −30°C, particularly at higher degrees of conversion where a glassy state is approached. The molecular weights increase as expected with decreasing temperature, and products with molecular weights above 100,000 are obtained. In the upper range of polymerization temperatures, an appreciable oligomer fraction is formed which has been analyzed. The chain propagation occurs by predominant breakage of the O‐C8 bond, leading to an all‐trans configuration as shown by NMR. Polymerization may also be carried out in solution in toluene; however, the presence of solvent lowers both conversion and molecular weight. The polymers are elastomeric solids at room temperature (Tg ∼ 0°C).
Synthesis, hydrolytic reactivity, and polymerization of 2,6‐ and 2,7‐dioxabicyclo[2.2.1]‐heptanes
Authors: Hall H. K. , Deblauwe F. , Carr L. J. , Rao V. S. , Reddy G. S. 
Published: June 2010

Abstract2,6‐Dioxabicyclo[2.2.1]heptane (3), the parent of a new ring system, has been synthesized by acid‐catalyzed bicyclization of 1,1‐diethoxy‐3‐hydroxymethyl‐4‐butanol. Conditions which were crucial to success included working in dilute dioctyl phthalate under high vacuum with vigorous stirring and distilling 3 as formed.2,7‐Dioxabicyclo[2.2.1]heptane (4) was synthesized by similar acid‐catalyzed cyclization of either 5‐hydroxy‐2‐methoxytetrahydropyran or 1,1‐diethoxy‐4,5‐pentanediol.In acid‐catalyzed hydrolysis, 3 was almost one million times as reactive as dimethyl acetal, and 4 was only slightly less. General acid catalysis was observed for both during studies of hydrolysis in presence of buffers.Polymerization of 3 occurred very readily with a variety of cationic initiators. Protonic acids gave high conversion to soluble polymer which was of moderate molecular weight (ζinh = 0.35), liquid (rubber), and consisted of a 60:40 mixture of isomers (probably trans:cis) detected by NMR.Cationic polymerization of 4 also occurred readily. Again, high conversions to moderate molecular weight liquid polymer were obtained. At −78°C, the polymer contained exclusively tetrahydrofuran links; at a higher temperature, several initiators gave significant amounts of tetrahydropyran links.
The oxidative thermal degradation of polypropylene containing various 2,6‐di‐t ert‐butyl‐4‐alkylphenols
Authors: Holčík J. , Košík M. 
Published: June 2010

AbstractThe oxidative thermal stability of isotactic polypropylene stabilized by a series of 2,6‐di‐tert‐butyl‐4‐alkyl (aralkyl, cycloalkyl)phenols by means of a thermoanalytical technique was investigated. The inhibition and the course of the oxidative thermal reaction was determined. The influence of the structure of antioxidants on active thermal decomposition in an oxygen atmosphere was compared. The effect of substituents in the applied type of antioxidants on the oxidative thermal reaction and the active thermal decomposition is discussed in detail.
Solvent effect on decomposition of hydroperoxides with dithiophosphates
Authors: Ivanov S. K. , Kateva J. D. 
Published: June 2010

AbstractDecomposition of tetralin hydroperoxide in the presence of zinc diisopropyldithiophosphate and N‐phenyl‐β‐naphthylamine has been performed in solvents such as n‐decane, decalin, tetralin, cumene, anisole, acetophenone, nitrobenzene, chlorobenzene, and quinoline. The decomposition of hydroperoxide to molecular products and free radicals has been studied by means of the inhibitor method. The effect of solvent on the rate of oxidation of cumene and on the rate and course of decomposition of hydroperoxide is discussed.
Hypersound propagation in oriented polymethylmethacrylate
Authors: Lindsay S. M. , Shepherd I. W. 
Published: June 2010

AbstractThe hypersonic elastic properties of oriented polymethylmethacrylate (PMMA) have been studied using high contrast (>108) multipass Fabry‐Perot techniques. Four samples of different degrees of orientation (birefringence Δn = −4, −9, −15, −24 × 10−4) were prepared by drawing at 130°C. Measurements of longitudinal sound velocity, VL, as a function of ϕ, the angle between the draw and propagation directions, show an anisotropy which scales with Δ and amounts to 6% in the sample having Δn = 24 × 10−4. At ϕ = 0, VL = 2.80 kilometers per second, (KMS−1), the same as the value in an isotropic sample. The elastic constants C11 and C33 are measured as a function of Δn. Data as a function of sound wavelength, Λ, show dispersive effects in both VL and attenuation αΛ, for Λ > 0.7 μ. Over the range 0.7 μ < Λ < 1.3 μ, αΛ increases from 0.1 to 0.5 and VL increases by 8%. Attenuation is consistently higher for ϕ = 0. The data are interpreted in terms of densification (up to 15%) accompanied by void formation on orientation, the structure having characteristic dimensions of approximately 1.5 μ. The structure may be asymmetric with the longer dimension perpendicular to the draw direction. Additional Brillouin peaks may result from sound propagation in the voids (VL = 5.8 KMS−1) in which case the density is approximately 0.3 g cm−3. Measurements of the Landau‐Placzek ratio support these ideas, but evidence from electron micrographs is inconclusive. Dispersion measurements should in principle help determine details of the structure shape.
Melt‐spun polypropylene fibers with helical orientation. I. Morphology and mechanical properties characterization
Authors: Pakułl T. , Morawiec J. , Swiȩtosławski J. , Kryszewski M. 
Published: June 2010

AbstractA new method of melt‐spinning of fibers with a twist is presented. The analysis of the dynamics of the spinning process shows differences in the distributions of rotational and longitudinal velocity gradients along the distance from the spinneret. The morphology of polypropylene fibers spun with the twist was examined by various techniques. It was shown that the applied method of spinning produces the distinct helical orientation inside the fibers. The overall and crystalline orientation was observed by birefringence and X‐ray diffraction techniques. The light diffraction patterns have shown the periodic helical unhomogenities inside the fibers. Measurements of mechanical properties have shown the dependence of the stress‐strain behavior of fibers on the twist rate. It was established that the fibers spun with intermediate rotational speed have the maximal tensile and sonic modulus and the ultimate strength.
A comparison of the supermolecular structure of wholly‐aromatic and aliphatic polymer fibers
Authors: Slutsker L. I. , Utevskii L. E. , Yu. Chereiskii Z. , Perepelkin K. E. 
Published: June 2010

AbstractThis paper considers specific features of the supermolecular structure of wholly‐aromatic polymer (WAP) fibers as compared with that of aliphatic polymer (AP) fibers revealed by small‐ and wide‐angle X‐ray diffraction and acoustic methods. Long periods of 150‐230 Å in size were observed in many WAP fibers. Special studies showed these periods to consist of crystalline and intercrystalline amorphous regions alternating along the fiber axis. These intercrystallite regions represent, just as in AP fibers, “weak” spots in the structure with respect to deformation and are responsible for the sorption properties. Acoustic measurements permitted the evaluation of the fraction of load‐holding chains in intercrystallite regions from the number of chains in the crystallite per the same section. It can reach 60‐80% for WAP, while only 10‐15% for the strongest AP fibers. Besides, in WAP fibers all tie molecules in intercrystallite regions are load‐holding, while only a small fraction of them hold the load in AP fibers. A study of poly‐p‐benzamide fibers showed their structures to be close to homogeneous. This accounts for the unusually high elastic modulus of this fiber (16,000–17,000 kg/mm2) which is close to that of crystallites (18,600 kg/mm2) and to the theoretical modulus of the molecule. Such a homogeneous supermolecular structure of oriented polymers is observed for the first time.
Properties of oriented block copolymers
Authors: Skoulios A. 
Published: June 2010

AbstractIn this paper, we shall be concerned with single crystals of block copolymers. As we shall have occasion to note later, these are highly oriented specimens of block copolymers in the mesomorphic state. The present condensed review of the subject is based mainly on published evidence worked out conjointly at Bristol and Genoa; it also refers, however, to unpublished work carried on in Strasbourg at Ecole d'Application des Hauts Polymères and at Centre de Recherches sur les Macromolécules. It is proper to specify immediately that the only copolymers found so far to produce “single crystals” are formed of polystyrene and polydiene blocks.
Styrene‐diene triblock copolymers: Orientation conditions and mechanical properties of the oriented materials
Authors: Weill A. , Pixa R. 
Published: June 2010

AbstractThe organization of the hexagonal structure of some block copolymers has been obtained directly from the melt. We have pointed out the temperature and shear conditions which give a well‐organized and oriented structure. In order to represent the viscous and elastic behavior of the melt, we have drawn flow curves and have measured the die swell ratio. A flow mechanism, corresponding to grain structure, is proposed. The results obtained enabled us to build a molding device. Fracture tests under tension on ABA poly(styrene‐b‐isoprene) samples exhibiting hexagonal structure showed a highly anisotropic behavior: If the crack propagates in a plane perpendicular to the isoprene cylinder axes or parallel with it, the fracture is either brittle or ductile accordingly. In the latter case, branching also occurs on both sides of the main crack. By using optical and scanning electron microscopy, the corresponding fracture surface morphologies have been studied. The brittle fracture surface shows a pattern of alternating rough and smooth bands which is characteristic of pure polystyrene. On the other hand, the ductile fracture surface is composed of an array of elongated “chips.” They are disposed practically parallel to the fracture propagation direction. Moreover, indentations made with a spherical steel penetrator led to residual ellipsoidal impressions. By measuring their dimensions, the anisotropy of the mechanical properties was displayed.
Molecular motion, thermal expansion, and phase transitions in paraffins: A model for polymers
Authors: Strobl G. R. 
Published: June 2010

AbstractOwing to their simple chemical structure paraffins are generally regarded as representing a system which is especially suitable for a model study of the thermal behavior of oligomeric and polymeric solids. Extensive investigations on the properties of n‐tritriacontane (C33H68) provide an example. For this system an identification of several types of motional mechanisms become possible. Their presence leads to peculiarities in the thermal expansion and to the occurrence of solid‐solid phase transitions.Paraffins and polyethylene exhibit a marked anisotropy in the lateral thermal expansion. An analysis of the molecular background can be based on a modified Grüneisen theory which connects expansion coefficients with elastic constants and Grüneisen constants. The Grüneisen constants describe anharmonic properties of the lattice vibrations and can be derived from a temperature dependent measurement of the frequencies of a number of Raman active lattice modes. The analysis shows that the observed anisotropy is mainly a consequence of the uniaxial orientation of the strong thermal pressure originating from the rotational and torsional oscillations of the chains.In the case of C33H68, the transition from the well ordered crystalline state to the melt occurs in several consecutive steps. Three solid‐solid phase transitions occur before melting and each one leads to a steplike decrease in the degree of order. Applying a combination of x‐ray and spectroscopic techniques it was possible to follow on a molecular level the changes in the state of order by specifying the defect structure. It is found that coupled 180°‐jumps, flip‐flop screw jumps, and defect diffusion along a chain set in successively, the onset of each mechanism of motion being accompanied by a phase transition.The measured melting entropy is indicative for a coiled chain conformation in the melt with slight deviations from a random coil owing to the occurrence of limited short range order. This follows from theoretical considerations.
State conditions of polymer and monomer with liquid crystalline phases
Authors: Cser F. , Nyitrai K. , Hardy Gy. 
Published: June 2010

AbstractResults are presented for studies of p‐substituted p'‐acryloyloxy‐azoxy‐benzene, cholesteryl vinyl‐succinate, and cholesteryl vinyl fumarate in systems containing monomers and polymers in different mesomorphic states.
Analysis of exponential clipped photon autocorrelation spectra
Authors: Nieuwenhuysen P. , Clauwaert J. 
Published: June 2010

AbstractSeveral fitting procedures were applied to the analysis of experimentally obtained mono‐exponential clipped photon autocorrelation spectra to find out how small distortions of individual measurements can best be taken into account. An iterative method seems unsatisfactory. The interpretation of a plot of the combined results of unweighted and weighted linear least square fits to straight lines and quadratic curves is more successful. This prevents a possible bias caused by using only one kind of fit. A smoothed weighting procedure was compared with the direct use of weighting factors from the raw data.
Spectral broadening of light scattered from alginate gels
Authors: MacKie W. , Sellen D. B. , Sutcliffe J. 
Published: June 2010

AbstractLight scattering Rayleigh linewidth measurements have been made on calcium alginate gels using the autocorrelation method. The degree of broadening has been found to be small (∼2%) although two relaxation times (∼7 and 50 msec) within the broadened component have been measured. Oscillations were generally found to be superimposed upon the autocorrelation function and these have been positively identified with bulk oscillations of the specimen. By scanning through the gel with the focused laser beam it has been shown that there are long range (tenths of millimeters), long term (tens of minutes), fluctuations in alginate density.Experiments were also carried out in which the diffusion constants of dextran fractions and globular proteins within the gel were measured by investigating the heterodyne beat spectrum. It was found that the movement of macromolecules with hydrodynamic diameters less than 10 nm was virtually unimpeded by the gel. Diffusion constants fell to about one third of those in aqueous solution for hydrodynamic diameters of ∼30 nm.
On the theory of polymer adsorption at an interface
Authors: Hoeve C. A. J. 
Published: June 2010

AbstractExact results are given for the grand partition function of a single model chain adsorbed at an interface. The model chosen corresponds to a walk on a 5‐choice, instead of a 6‐choice, simple cubic lattice by disallowing step reversals. The flexibility of this model is rendered variable by assigning different weights to consecutive steps made in the same direction. The obtained results are compared to those of a previous model for Gaussian chains. Satisfactory agreement between the models allows the previously undetermined flexibility parameter to be determined. The segment density in the vicinity of the interface is obtained as a function of this parameter. Correspondence with polymer chains is established through this parameter. We conjecture that the volume fraction of segments in the diffuse layer resulting from the loops does not exceed 0.1, even when the volume fraction in the interface is unity.
Some domain‐size effects in polymer transitions
Authors: Couchman P. R. , Karasz F. E. 
Published: June 2010

AbstractSize‐dependent changes of transition temperatures in polymers are shown to derive from two principal sources: the effect of surface energy (or interfacial tension) and the role of the interface in the mixing of foreign material with the system. The formal elements and physical insight necessary for a description of the influence of domain size on the two main polymer transitions, the glass transition and melting, are discussed in some detail.
Radical ring‐opening polymerization and copolymerization with expansion in volume
Authors: Bailey William J. , Endo Takeshi 
Published: June 2010

AbstractAlthough ring‐opening polymerization involving ionic intermediates and Ziegler catalysts are quite extensively used in polymer chemistry, free radical ring‐opening polymerization is extremely rare. We have been able to show that unsaturated spiro ortho carbonates will undergo double ring‐opening polymerization under radical conditions. In addition these monomers will undergo ready copolymerization with common monomers, such as styrene, methyl methacrylate, and diallyl carbonate.Since this process involves a double ring‐opening, a slight expansion in volume occurs. For a number of industrial applications, such as precision castings, strain‐free composites, binders for solid propellants, high strength adhesives, dental fillings, and rock‐cracking materials, it is highly desirable to have monomers that expand on polymerization. In the formation of composites, such a monomer might minimize poor adhesion between the matrix and the reinforcing agent or eliminate microcracks. Formation of additional polymers usually involves shrinkage since the monomer undergoes a transition from a van der Waals distance to a covalent distance in the polymeric material. Ring‐opening polymerization usually involves somewhat less shrinkage because for every new bond that is formed involving a shift from a van der Waals distance to a covalent distance, another bond is broken involving a shift from a covalent distance to a near van der Waals distance. Thus, if monomers are utilized in which two bonds are broken for every new bond that is formed in the polymerization process, near zero shrinkage or expansion takes place.
Mechanochemical syntheses
Authors: Simionescu Cristofor , Oprea Cleopatra Vasiliu , Negulianu Claudia 
Published: June 2010

AbstractIn the present paper some main directions in mechanochemical synthesis are developed, based on the mechano‐destructive process induced under different conditions in homo‐ and heterochain solid polymers (polyethylene, cellulose and derivatives, polyesters and polyamides). The fact is known that the elastic energy conferred to crystalline amorphous polymers focuses on structural and composition defects distributed statistically, causing molecular ruptures of the homolytic type which generate nascent microcracks propagating and increasing within the solid leading finally to a fracture. The nascent microcrack represents in fact the existence within small volumes of a number of active macroradicals (or of a number of reactive functional groups after the stabilization of the destruction fragments) capable of reacting with appropriate chemical reagents existing in the working medium. On this basis became possible the initiation of graft polymerization, block copolymerization, polycondensation, and complexing reactions. The concentration of the elastic energy not on molecular underlayers but on metallic surfaces, even when these are the reaction vessel walls, leads to the formation of active centers of a particular type, capable of initiating homo‐ or copolymerization reactions.