bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereospecific hydride transfer under NCI/OH− conditions. 2—Origins of the C2H4O elimination from stereoisomeric alkoxyketal derivatives1
Authors: Tabet Jean‐Claude , Hanna Issam , Fetizon Marcel 
Published: May 2005

AbstractA new stereospecific intramolecular hydride transfer, induced by an alkoxide, has been demonstrated under NCI/OH− conditions using unimolecular and collision‐induced decomposition spectra.
Elemental compositions from daughter ion spectra of m1+ and [m1 + 1]+: Some applications of the method
Authors: Bozorgzadeh M. H. , Lapp R. L. , Gross M. L. 
Published: May 2005

AbstractThe elemental compositions of ions can be determined in tandem mass spectrometry by comparing the daughter ion spectra of the m1+ and [m1 + 1]+ ions. The method is demonstrated for mass‐analyzed ion kinetic energy spectra but is applicable to all types of daughter ion spectra, including complex collisionally activated dissociation spectra. In this work, the method is applied to compounds that produce daughter ions of known elemental compositions, and the errors and limitations are evaluated. Following that test, the procedure is applied to a compound that may produce daughters of more than one possible elemental composition. The method is sometimes useful even if the formula of the parent is not known; that is, the formulae of unknown parent and daughter ions may be found. Locating a specific atom in an isotopically labeled molecule is another capability of the method. The basic equation of the method was generalized and incorporated into a computer program for performing the calculations.
Mass spectra of aliphatic dicarboxylic acids and their dimethyl esters: Cyclic structures for the [M − H2O]+˙ ions from the diacids and [M − MeOH]+˙ ions from the dimethyl esters
Authors: Harrison Alex G. , Kallury R. Krishna Mohan Rao , Krull Ulrich J. , Thompson Michael 
Published: May 2005

AbstractMethyl 2‐oxocycIoalkane carboxylate structures are proposed lor the [M − MeOH]+˙ ions from dimethyl adipate, pimelate, suberate and azelate. This proposal is based on a comparison of the metastable ion mass spectra and the kinetic energy releases for the major fragmentation reaction of these species with the same data for the molecular ions of authentic cyclic β‐keto esters. The mass spectra of α,α,α′,α′‐d4‐pimelic acid and its dimethyl ester indicate that the α‐hydrogens are involved only to a minor extent in the formation of [M − ROH]+˙ and [M − 2ROH]+˙ ions, while these α‐hydrogens are involved almost exclusively in the loss of ROH from the [M − RO˙]+ ions (R = H or CH3). The molecules XCO(CH2)7COOMe (X = OH, Cl) form abundant ions in their mass spectra with the same structure as the [M − 2MeOH]+˙ ions from dimethyl azelate.
Electron impact ionization of ethylene–methanol heteroclusters: Stable configurations and mechanisms in intracluster ion–molecule reactions
Authors: Choi Chang Ju , Jung Kwang Woo , Kang Wee Kyung , Youn Dae Young , Jung Kyung‐Hoon , Kim Dongho 
Published: May 2005

AbstractReactions that proceed within mixed ethylene–methanol cluster ions were studied using an electron impact time‐of‐flight mass spectrometer. The ion abundance ratio, [(C2H4)n(CH3OH)mH+]/[(C2H4)n(CH3OH)m+], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope‐labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C2H4)n(CH3OH)m+ and (C2H4)n(CH3OH)m–1CH3O+ ions are interpreted as a consequence of the ion–neutral complex and intracluster ion–molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C2H4)n(CH3OH)mH+ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion–molecule condensation reactions, leading to the formation of fragment ions, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $\end{document} and (CH3OH)H3O+, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C2H4)n(CH3OH)mH+(n + m ≤ 3) using semi‐empirical molecular orbital calculations.
Negative‐ and positive‐ion chemical ionization mass spectra of aromatic amines: Surface‐assisted reactions involving oxygen
Authors: Stemmler Elizabeth A. , Buchanan Michelle V. 
Published: May 2005

AbstractThe O2–N2 and O2–Ar negative‐ion chemical ionization mass spectra of aromatic amines show a series of unusual ions dominated by an addition appearing at [M + 14]−˙. Other ions are observed at [M – 12]−˙, [M + 5]−˙, [M + 12]−˙, [M + 28]−˙ and [M + 30]−˙. Ion formation was studied using a quadrupole instrument equipped with a conventional chemical ionization source and a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. These studies, which included the examination of ion chromatograms, measurement of positive‐ion chemical ionization mass spectra, variation of ion source temperature and pressure and experiments with 18O2, indicate that the [M + 14]−˙ ion is formed by the electron‐capture ionization of analytes altered by surfaceassisted reactions involving oxygen. This conversion is also observed under low‐pressure conditions following source pretreatment with O2. Experiments with [15N]aniline, [2,3,4,5,6‐2H5] aniline and [13C6]aniline show that the [M + 14]−˙ ion corresponds to [M + O − 2H]−˙, resulting from conversion of the amino group to a nitroso group. Additional ions in the spectra of aromatic amines also result from surface‐assisted oxidation reactions, including oxidation of the amino group to a nitro group, oxidation and cleavage of the aromatic ring and, at higher analyte concentrations, intermolecular oxidation reactions.
Differentiation among some isomeric di‐ and trifunctional aromatic amines by plasma desorption mass spectrometry
Authors: Bouchonnet Stéphane , Hoppilliard Yannik , Maret Agnès 
Published: May 2005

AbstractIsomeric di‐ and trifunctional aromatic amines are easily differentiated on the basis of their plasma desorption (PD) mass spectra. Six series of aromatic amines were studied in the positive‐ion mode. In each series, the differences observed in the PD mass spectra allow each isomer to be characterized. In the formation of molecular ions, these differences proceed from the competition between electron impact ionization and protonation. Several chemoselective or regioselective reactions such as hydrogenation, hydration, dimerization and some fragmentations also allow isomeric aromatic amines to be differentiated.
Stress measurement in graphite/epoxy uniaxial composites by X‐rays
Authors: Barrett Charles S. , Predecki Paul 
Published: May 2005

AbstractX‐rays can be used to measure residual as well as applied stresses in polymers and reinforced polymeric composites by diffracting from filler particles that are embedded before curing. We have investigated various fillers that exhibit suitable stress‐induced shifts of diffraction angle when embedded in uniaxial graphite fiber/epoxy composites. Stresses in the particles determined by X‐rays are proportional to the corresponding composite stresses, in agreement with the model of H. T. Hahn. Results indicate that the stress sensitivity (change in X‐ray strain per MPa applied to the composite) increases in the order W, CdO, Ni, Ag, Nb, Al. The elastic range terminates at a yield point beyond which the stress sensitivity is markedly reduced for metallic fillers, but no such yield point has appeared with CdO particles. Oppositely directed particle strains are seen after unloading from stress levels that have exceeded the yield point. Theoretical predictions for these findings are discussed. Residual stresses in the particles were determined after curing and storage under ambient conditions. In the fiber direction the residual stresses were always found to be positive and larger than the principal stresses orthogonal to these.
Spectroscopic determination of the in‐situ composition of epoxy matrices in glass fiber reinforced composites
Authors: Antoon M. K. , Zehner B. E. , Koenig J. L. 
Published: May 2005

AbstractComputerized infrared analysis is applied to the characterization of a glass‐reinforced crosslinked polyester. The method of factor analysis determines the number of independent components which constitute the polymeric matrix. Subsequently, the spectra of those components are fitted by a least‐squares criterion to spectra of the multicomponent matrix, or, if the glass spectrum is included as an additional component, to the spectra of composites. The least‐squares coefficients yield the matrix composition in terms of the initial reactant composition and the extent of crosslinking.
Mica composites of improved strength
Authors: Newman S. , Meyer F. J. 
Published: May 2005

AbstractMineral fillers of flake configuration such as mica can, in principle, produce large increases in modulus and strength especially if the flake is oriented predominantly in a plane. Additionally, the resulting composites have the advantage of possessing isotropic properties in the plane of orientation, thereby minimizing the warpage normally associated with the injection molding of fiber‐reinforced thermoplastics. However, to properly transmit stress from the matrix to the mica and minimize the effect of defects in morphology, a ductile matrix is required with adequate interaction or adhesion between phases. Many of the above conclusions are documented in the literature and are confirmed by our investigations of the system mica‐polypropylene. The novelty of this effort rests upon (1) successful attempts to identify specific non‐silane additives which by co‐blending suitably modify the mica‐polypropylene interface, (2) to demonstrate the remarkable effects of time‐temperature during melt processing on the behavior of this system; and, (3) to show the relation between composition and time‐temperature effects on resultant mechanical, physical, and thermal properties. Most notably, large improvements in tensile and flexural strength and heat distortion temperature can be attributed to the use of small amounts of chlorinated organic compounds blended under carefully selected melt process conditions. Some speculation concerning the mechanism of interaction will be discussed and the resultant potential for increased application will also be outlined.
Test method evaluation for fiber‐reinforced molding materials
Authors: Taggart David G. , Pipes R. Byron , Mosko John C. 
Published: May 2005

AbstractStandard test methods ASTM D‐651 for determining tensile properties and ASTM D‐790 for flexure properties are evaluated. Heterogeneous fiber distributions due to molding flow conditions are shown to yield test specimens wherein fiber orientation near surfaces is highly collimated while orientations in central regions are oriented approximately transverse to the specimen axis. In addition, the converging and diverging flow fields in the dog bone (ASTM D‐651) specimen with end gate are shown to yield a variation in fiber orientation along the specimen length. Finite element analysis of the dog bone (ASTM D‐651) reveals that stress concentrations and a non‐uniform stress distribution are introduced due to the required gripping arrangement of the test standard. The flexural specimen is decomposed into two elements of a collimated and transverse fiber orientations and a mathematical model is developed which reflects the composite behavior of the beam specimen. Finally, it is concluded that the D‐651 and D‐790 test methods do not reveal intrinsic design data for fiber reinforced molding materials.
Flow and flow orientation of composites containing anisometric particles
Authors: Utracki L. A. 
Published: May 2005

AbstractThere is a growing commercial and academic interest in polymeric composites filled with short fibers and/or glass or mica flakes. Here, the properties depend strongly on the flow induced morphology and on the distribution of residual stresses. To optimize processing and properties, it is important to know both the melt rheology and the orientation of the dispersed phase. The industrial formulations are notoriously very complex. However, it is possible to understand, and sometimes predict, their behavior by a systematic comparison with simpler, better known systems, i.e., suspensions. This review concentrates on two main aspects of flow of polymer melts containing anisometric particles, namely yield phenomena and orientation.
Determination of the orientation of mica in composites
Authors: Malik T. M. , Prud'Homme R. E. , Rémillard B. 
Published: May 2005

AbstractA wide angle x‐ray diffraction technique has been used to determine the orientation of mica flakes in composites. The mica used was a fine grade Phlogopite, and the polymers were polystyrene, polycarbonate and poly(vinyl chloride). Composite samples of varying mica contents and orientations were prepared. The x‐ray method can give the orientation distribution function of mica flakes across and parallel to the surface of the sample. From this function, an average orientation parameter was calculated. The results show that there is no orientation of mica across the surface of the sample (the x‐ray beam is normal to the surface), but that there is a strong orientation in a direction parallel to this surface, the average orientation parameter being strongly dependent upon the particle size of mica and mode of preparation.
Measurement of fiber and matrix orientations in fiber reinforced composites
Authors: Kamal Musa R. , Song Li , Singh Peter 
Published: May 2005

AbstractShort glass fiber reinforced polypropylene was employed in a study to determine the effect of molding and mold design variables on the distrubution of fibers and their orientations, and consequently, on the distributions of mechanical properties in the molded article. In this paper, a variety of experimental techniques were employed to evaluate the distributions of fibers and their orientations. Moreover, techniques were developed to evaluate the orientation and crystallization of the matrix. The results yield significant information regarding the development and control of both the microstructure and the properties of short fiber reinforced composites.
Use of grafted aspen fibers in thermoplastic composites: IV. Effect of extreme conditions on mechanical properties of polyethylene composites
Authors: Kokta Bohuslav V. , Daneault Claude , Beshay Alphons D. 
Published: May 2005

AbstractHardwood fibers of aspen in the form of chemithermo‐mechanical pulp (CTMP) have been used as reinforcement in linear low density polyethylene (LLDPE). The effect of composite treatment (immersion in boiling water, heat exposure at 105°C for seven days or at a temperature of −40°C) on resulting mechanical properties were evaluated. The grafted aspen CTMP composites showed by far the best results with regard to secant modulus, tensile strength, energy, and strain when compared to those of wood flour, mica or glass–fiber filled LLDPE, as well as to virgin LLDPE. Finally, the dimensional stability of CTMP aspen‐filled LLDPE composites immersed for four hours in boiling water was better than that of mica or glass–fiber filled LLDPE.
Ultrasonic evaluation of filled polymers: I. Techniques and models for the elastic moduli of a resin filled with iron spherical inclusions
Authors: Piché L. , Hamel A. 
Published: May 2005

AbstractThe ultrasonic technique for the nondestructive evaluation of elastic moduli is described. Its use in the application to polymers, whereby viscoelastic effects are eliminated, is discussed. Experimental results are given for composites containing high contrast (iron) spherical inclusions. The measurements are discussed in terms of available theoretical models. It is clearly demonstrated that models that account for the microscopic details of the material offer the best description of the bulk properties.
Buckling of composite cylinders under external pressure
Authors: Ouellette P. , Hoa S. V. , Sankar T. S. 
Published: May 2005

AbstractExperimental results from buckling tests on thin shell structures made of filament‐wound glass fiber reinforced plastic are compared to values calculated with three different procedures. These procedures are: (1) a linear stability analysis for anisotropic, heterogeneous, thin, cylindrical shells, (2) a proposed design code, and (3) a national standard. Imperfection surveys in the circumferential direction were conducted and were found to be much larger than imperfections typical for metallic thin shells. All three procedures yield design pressures lower than observed buckling pressures. The analytical method and the standard are less conservative than the proposed design code and may possibly permit the fabrication of safe and more economical structures.
Crystallization and fiber/matrix interaction during the molding of PEEK/carbon composites
Authors: Denault J. , Vu‐Khanh T. 
Published: May 2005

AbstractThe objective of this work was to investigate the effects of molding conditions (molding temperature, residence time at melt temperature, and cooling rate) on the crystallization behavior and the fiber/matrix interaction in PEEK/carbon composites made from both prepreg and commingled forms. In order to investigate the crystallization behavior of the PEEK matrix, the molding process was simulated by differential scanning calorimetric analysis, DSC. The results show that the prepreg and commingled systems do not have the same matrix morphology; prepreg tape was found to be at its maximum of crystallinity, whereas the commingled system was found to be only partially crystalline. The results show that processing must be carried out at a temperature sufficiently high to destroy the previous thermal history of the PEEK matrix; this is an essential requirement to produce efficient fiber/matrix adhesion in the commingled fabric system. Optical microscopic observations also suggest that matrix morphology near the fibers is dependent on the melting conditions; a well‐defined transcrystalline structure at the interface is observed only when the melt temperature is sufficiently high. However, the high temperature of molding can easily result in degradation of the PEEK matrix such as chain scission and crosslinking reactions. Thermal degradation of the matrix during processing is found to affect the crystallization behavior of the composites, the fiber/matrix adhesion, and the matrix properties. This effect is more important in the case of a commingled system containing sized carbon fibers because the sizing agent decomposes in the molding temperature range of PEEK/carbon composites. This produces a decrease of the matrix crystallinity and an elimination of the nucleating ability of the carbon fibers. A transition between cohesive and adhesive fracture is observed when the cooling rate increases from 30°C/min to 71°C/min for the composite made from the commingled fabric. This critical cooling rate is found to closely correspond to a change in the mechanism of crystallization of the PEEK matrix.
Blends of semicrystalline and amorphous polymeric matrices for high performance composites
Authors: Torre L. , Kenny J. M. 
Published: May 2005

AbstractThe compatibility and crystallization behavior of blends of semicrystalline and amorphous polymers, traditionally used as matrices of high performance composites, has been studied. The analysis has been focused on blends of semicrystalline poly(etheretherketone) (PEEK) with amorphous poly(etherimide) (PEI) prepared by melt mixing. Differential scanning calorimetry and thermogravimetric analysis have been used to analyze the influence of blend constituents and processing conditions on the compatibility, on the crystallization kinetics and on the final crystalline content. An Avrami model has been applied to the crystallization of PEEK in a PEEK/PEI 50/50 blend and the results have been compared with the behavior of the neat PEEK resin. The results of the characterization can be applied to predict the behavior of such blends when processed as matrix of composites or when used in the “amorphous bonding” procedure.
Structure and properties of poly(p‐xylylene) composites made by electrochemical and vapor deposition polymerization
Authors: Li Hong , Moshonov Aharon , Muzzy John D. , Olsen Roger A. 
Published: May 2005

AbstractPoly(para‐xylylene)(PPX)/carbon fiber towpregs were produced by two different in‐situ polymerization processes: Electrochemcal polymerization (ECP) and vapor deposition polymerization (VDP). The monomer used for the ECP process was α, α′ ‐dibromo‐para‐xylylene and di‐para‐xylylene was the starting material for the VDP process. A series of tests, including FTIR, WAXD, DSC, TG, and SEM were carried out to identify and compare these two composite towpregs. It has been confirmed that the PPX samples obtained by the two different polymerization processes were basically chemically identical. However, the polymer coating on the fiber surface produced by the VDP process was much smoother than that produced by the ECP process, which produced a porous coating.
Impact modification of poly(vinyl chloride) with chlorinated polyethylene I. Blend morphology
Authors: Siegmann A. , Hiltner A. 
Published: May 2005

AbstractThe solid state morphology of chlorinated polyethylene (CPE)‐modified poly(vinyl chloride) (PVC) and the relationship of blend structure to impact strength and mode of fracture have been investigated. Selective staining of the CPE phase showed that the morphology of the two phase system changes with increasing CPE content from a dispersion of discrete CPE particles to a network structure enveloping the primary PVC particles. The network formation coincides with a transition from brittle to ductile impact fracture. When the blend was mixed for too long a time or above the fusion temperature of the primary PVC particles, the CPE network was destroyed. The resulting indistinct domain structure is associated with a reduction in the impact properties.
Analysis of the evolution of microcreep during physical aging and mechanical deformation in poly(methyl methacrylate) using a microstructural model
Authors: Shankar N. Gowri , Bertin Y. A. , Gacougnolle J. L. 
Published: May 2005

AbstractThe evolution of poly(methyl methacrylate) (PMMA) during physical aging at 90°C is followed by torsional microcreep tests. On the aged specimen a longitudinal stress is applied which induces a strain of 5 percent after 30 days of creep. The torsional microcreep tests are performed during the longitudinal creep in order to compare the structure evolution of PMMA caused by straining with its evolution measured during aging. The microcreep, for the first 800s, follows a reversible logarithmic law. In this stage the mobile defects achieve their activated form which is perfectly reversible when unloaded. The physical aging reduces this logarithmic part of microcreep. This is due to the decrease of either the number or the volume of the mobile defects. Beyond a critical elongation ϵ = 1 percent, the longitudinal straining has just the opposite influence, i.e., the logarithmic part of microcreep increases. This critical elongation ϵ = 1 percent corresponds to the beginning of the steady state longitudinal creep. The transient that precedes this steady state has no detectable influence on the structure of the specimen.