bluuebunny/crossref_metadata_2025 huggingface dataset:
An ab initio study of the relative stabilities of the isomers of CH2N2 and SiH2N2
Authors: Thomson Colin , Glidewell Christopher
Published: December 2004

Ab initio SCF calculations of the equilibrium geometries have been carried out on nine possible isomers of MH2N2, where M = C or Si, and compared with the results of MNDO calculations. The results for the carbon compounds are in good agreement with available experimental data, but in the case of the silicon compounds, the molecules are predicted to be unstable with respect to decomposition to SiH2 and N2. The inclusion of electron correlation at the MP3 level does not alter the order of the relative stabilities, although the importance of the correlation contribution varies substantially between the different isomers.
Ab initio studies on calicene
Authors: Hess B. A. , Schaad L. J. , Ewig C. S. , Čársky P.
Published: December 2004

Optimum geometries of planar and 90°‐twisted C2v calicene are calculated with single‐configuration STO‐3G and 3‐21‐G wavefunctions. The barrier to ring–ring rotation is computed. Bond alternation is pronounced in the planar form and decreases in the twisted form, while dipolar character increases on twisting.
Computation of electron repulsion integrals using the rys quadrature method
Authors: Rys J. , Dupuis M. , King H. F.
Published: December 2004

Following an earlier proposal to evaluate electron repulsion integrals over Gaussian basis functions by a numerical quadrature based on a set of orthogonal polynomials (Rys polynomials),

a computational procedure is outlined for efficient evaluation of the two‐dimensional integrals Ix, Iy, and Iz. Compact recurrence formulas for the integrals make the method particularly fitted to handle high‐angular‐momentum basis functions. The technique has been implemented in the HONDO molecular orbital program.
Molecular symmetry. IV. The coupled perturbed Hartree–Fock method
Authors: Takada Toshikazu , Dupuis Michel , King Harry F.
Published: December 2004

Symmetry methods employed in the ab initio polyatomic program HONDO are extended to the coupled perturbed Hartree–Fock (CPHF) formalism, a key step in the analytical computation of energy first derivatives for configuration interaction (CI) wavefunctions, and energy second derivatives for Hartree–Fock (HF) wavefunctions. One possible computational strategy is to construct Fock‐like matrices for each nuclear coordinate in which the one‐ and two‐electron integrals of the usual Fock matrix are replaced by the integral first derivatives. “Skeleton” matrices are constructed from the unique blocks of electron‐repulsion integral derivatives. The correct matrices are generated by applying a symmetrization operator. The analysis is valid for many wavefunctions, including closed‐ or open‐shell spin‐restricted and spin‐unrestricted HF wavefunctions. To illustrate the method, we compare the computer time required for setting up the coupled perturbed HF equations for eclipsed ethane using D3h symmetry point group and various subgroups of D3h. Computational times are roughly inversely proportional to the order of the point group.
Proton and lithium cation affinities calculated with floating orbital geometry optimization (FOGO)
Authors: Huber Hanspeter , Latajka Zdzisław
Published: December 2004

The FOGO method is used to calculate proton affinities and lithium cation affinities. The molecules of primary interest in this study are the methyl‐substituted amines. In addition, the lithium cation affinity of HF, H2O, CH3OH, H2CO, and HCN are calculated for comparison. Geometries of all species are fully optimized with a double‐zeta (DZ) basis set, including polarization on hydrogen and the first‐row elements by floating orbitals. Comparison with experimental values demonstrates that structural data and proton affinities resulting from this type of ab initio calculation are of chemical accuracy. The lithium cation affinities are also reasonably well reproduced, but the small experimental differences are not within the accuracy, which can be expected from this type of calculation.
A technique for determining the symmetry properties of molecular graphs
Authors: Davis Michael I. , Ellzey M. Lawrence
Published: December 2004

A procedure has been devised to determine the automorphism partition and the automorphism group for nondirected graphs. The general approach is to reveal the permutational symmetry by means of its systematic destruction. Symmetry decomposition pathways are created by numerically weighting specific series of vertices. Each pathway leads to a discrete ordered vector. Each pair of pathways that match reveals an element of the automorphism group. Results are presented for two molecular graphs. Further potential applications of this approach to problems of isomorphism, canonical labeling, and structural indexing are discussed.
Molecular mechanics studies of enthalpies of formation and strain energies of azoxyalkanes
Authors: Byström Katarina
Published: December 2004

A force field has been developed, on the basis of available experimental and partial retention of diatomic differential overlap (PRDDO) data, to permit molecular mechanics calculations on azoxyalkanes. The calculated structures and enthalpies of formation are in fair agreement with experimental results. The calculated enthalpies of formation and strain energies are compared with the corresponding quantities for analogous azoalkanes.
Nonrelativistic and quasirelativistic model potential calculations on AgH and Ag2
Authors: Klobukowski M.
Published: December 2004

The major relativistic effects are included into the model potential (MP) method of Bonifacic and Huzinaga. The effects are incorporated on the level of Cowan and Griffin's relativistic Hartree–Fock (RHF) method. The model potential parameters are determined using the results of nonrelativistic Hartree–Fock (NHF) and RHF calculations. A new scheme of selection of the basis functions for use in atomic and molecular MP calculations is proposed. To obtain agreement with the Hartree–Fock calculations on AgH and Ag2, the 4p shell has to be included explicitly in the MP calculations. The explicit treatment of the 4p electrons and the resulting reduction of the core size are necessary in order to overcome difficulties with approximate representation of the large 4p–4d core‐valence interactions on the MP level.
A method for the calculation of normal‐mode vibrational frequencies using symmetry coordinates. Application to the calculation of secondary deuterium isotope effects on carbocations
Authors: Hout Robert F. , Levi Beverly A. , Hehre Warren J.
Published: December 2004

A method is introduced for the calculation of normal‐mode vibrational frequencies of polyatomic molecules based on numerical differencing of analytical gradients in symmetry coordinates. This procedure requires a number of gradient evaluations equal to the largest number of symmetry coordinates belonging to any single irreducible representation of the molecular point group (plus a single gradient evaluation at the equilibrium configuration), which is fewer than the 3N‐6 (N atoms) gradient evaluations needed for schemes based on Cartesian or internal coordinates. While the proposed method will not generally be as efficient as procedures which involve the direct calculation of energy second derivatives analytically (as are now available for single‐determinant wavefunctions) it appears to be equally accurate, and it should be the method of choice for frequency calculations involving multideterminant wavefunctions for which analytical second‐derivative algorithms have yet to be developed. The method is illustrated by the calculation of equilibrium secondary deuterium‐isotope effects on a number of reactions involving simple carbocations.
Ground states of molecules. 64.MNDO Calculations for compounds containing bromine
Authors: Dewar Michael J. S. , Healy Eamonn
Published: December 2004

MNDO has been parametrized for bromine. Since d atomic orbitals (AOS) are not included, the calculations are restricted to BrI. Heats of formation, molecular geometries, ionization energies, and dioole moments are reproduced with useful accuracy.
Orbital relaxation in the Rydberg series of the lithium atom. An excited state SCF calculation
Authors: Chang Tse‐Chiang
Published: December 2004

Self‐consistent‐field (SCF) calculations for a series of Rydberg states (1s2ns)2S of the Li atom are performed using the generalized Brillouin theorem (GBT) method. The calculated energy is a proper upper bound to the excited state energy. The SCF term values of the Rydberg states are almost the same as those of the frozen‐core approximation ones. The orbital behavior shows that the core is slightly expanded by the penetration of the Rydberg orbitals, and the higher Rydberg orbitals can be very well represented by the modified hydrogen‐like orbitals.
Remarks on the molecular mechanical calculations of functionalized hydrocarbons
Authors: Meyer A. Y.
Published: December 2004

Molecular mechanical calculations for hetero‐substituted hydrocarbons present certain difficulties that are not encountered in dealing with hydrocarbons. Ways are proposed to overcome such difficulties, sometimes by two‐step or iterative computation. The following topics are considered: fitting the force field by using data from studies in solution; ways to estimate atomic charges or, alternatively, bond moments; ways to account for field effects upon atomic charges and bond moments.
Conformational studies of octalene and its benzo‐derivatives
Authors: Favini Giorgio , Moro Giorgio , Todeschini Roberto , Simonetta Massimo
Published: December 2004

Theoretical calculations by the combined empirical force‐field (EFF)‐extended Hückel molecular orbital (EHMO) approach confirm that octalene and benzo‐|c|‐octalene present π‐bond fixation with a common single bond between the cyclooctatetraene and cyclooctatriene fragments, whereas the structure of dibenzo‐|c, j|‐octalene is characterized by a central double bond. The dynamic behavior of these compounds is discussed and the interconversion energy barriers are calculated; the inversion of the cyclooctatriene ring is faster than that of the cyclooctatetraene ring in octalene, but it is slower in benzo‐|c|‐octalene.
Electron density and related properties in stereoregular polymers and biopolymers
Authors: André Jean‐Marie , Vercauteren Daniel P. , Fripiat Joseph G.
Published: December 2004

Formulas fully exploiting the periodicity symmetry of the electron density of polymers are deduced. They are shown to lead to efficient algorithms for the evaluation of Coulomb and exchange interactions in those systems.
Ab initioMO calculations on the acidities of water and methanol, and hydrogen bond energies of the conjugate ions with a water molecule
Authors: Ikuta Shigeru
Published: December 2004

The acidities, deprotonation energies, of water and methanol were calculated by the use of the ab initio self‐consistent‐field (SCF) molecular orbital (MO) method with electron correlation computed by the thirdorder Møller–Plesset perturbation method and configuration interaction with double excitations. Zero‐point vibrational energy correction translational energy change, and the PV work term were included to evaluate the accurate acidities. The calculated acidity difference including these corrections was 7 kcal/mol, which is somewhat smaller than the experimental ones (9.5–12.5 kcal/mol) recently determined. The hydrogen bond energies of the conjugate ions (OH− and CH3O−) with a water molecule were calculated to be 2.3 kcal/mol near the Hartree–Fock limit; this energy only amounts to 25% of the (total) hydration energy difference between the two negative ions. The aqueous solvation effect on the acidity scale was discussed.
Ab initio calculations of the electronic structure of helical polymers
Authors: André J. M. , Vercauteren D. P. , Bodart V. P. , Fripiat J. G.
Published: December 2004

An ab initio self‐consistent‐field (SCF) algorithm taking into account all the features of the one‐dimensional translational periodicity and the helical symmetry is presented. This algorithm includes the long‐range correction to the Coulomb potential and is designed to calculate the band structure of periodic one‐dimensional polymers (planar or helical). Its efficiency in terms of computing time and numerical accuracy is tested via applications on a (LiH)n chain, polyethylene, and four conformers of polypropylene.
Classical conformational analysis of strained organic molecules. I. [l,m,n]Propellanes with l,m,n equal to 2, 3, and 4
Authors: Dodziuk Helena
Published: December 2004

Classical conformational analysis was applied to the study of the variation of heats of formation (HOF) and geometrical parameters of small‐ring propellanes. As expected, the calculated HOF is the smallest for [4,4,4] propellane I and the largest for [2,2,2]propellane X. In spite of the different trends exhibited by the strain energy components, the calculated HOF values may be reproduced within a simple additivity scheme. The calculated bridgehead–bridgehead bond length is the longest for [2,2,2]propellane (1.655 Å), lowers with increasing molecular size, and is equal to 1.558 Å for [4,4,4]propellane. In agreement with experimental findings the latter value is significantly larger than the standard value of 1.54 Å typical for unstrained hydrocarbons. Other calculated geometrical parameters as well as HOF values cannot be compared with experimental and/or theoretical results since there is a lack of reliable experimental data. Surprisingly, [2,2,2]propellane was found to be more flexible than the less strained bicyclo[2,2,2]octane.
Unique description of chemical structures based on hierarchically ordered extended connectivities (HOC procedures). V. New topological indices, ordering of graphs, and recognition of graph similarity
Authors: Mekenyan Ovanes , Bonchev Danail , Balaban Alexandru T.
Published: December 2004

The vertex numbering obtained by application of the HOC algorithm can be converted into two sequences of numbers: If each vertex starting with vertex 1 is only counted once, the sums of numberings of adjacent vertices form sequence Si (i = 1−N), while the sums of Si values form sequence Mi (i = 1−N). These two sequences can be used for (i) two new topological indices, ℳ︁ and 𝒩, the latter being of extremely low degeneracy, and the former correlating with boiling points of alkanes; (ii) a criterion based on sequence Si for ordering graphs which possess the same number N of vertices; and (iii) a quantitative measure, also based on sequence Si, for appreciating the similarity or dissimilarity of pairs of graphs. Comparisons with other topological indices, ordering criteria, and similarity measures for graphs show that the newly devised procedures compare favorably with those known previously.
Application of an ion‐fitted pseudopotential to HF, H2O, NH3, BeO, and HCl in a Gaussian lobe basis
Authors: Nguyen T. T. , Raychowdhury P. N. , Shillady D. D.
Published: December 2004

The core potentials for atoms of atomic numer 1–18 fitted to ion spectra by Chang, Habitz, Pittel, and Schwarz have been extended to the molecular case in a Gaussian lobe basis by using a six‐Gaussian (6G‐POT) representation for the exponential factors of the atomic core potentials. In a (9s/5p/1d) basis the 6G‐POT one‐electron energies, dipole moments, and Mulliken charges are improved over a one‐Gaussian potential form for HF, NH3, and H2O; BeO also yields good agreement within 2.6% of the experimental bond length. For HCl, the core potential shows larger errors in the dipole moment (7%) and one‐electron eigenvalues (2%), but a 75% saving in computer time is realized for HCl compared with only about 35% for first‐row systems using the 6G‐POT core potentials. Analytical expressions are given to extend the 6G‐POT method up to s, p, d, f, and g valence shells.
Studies of a proposed mechanism for the reaction between 2H‐pyran‐2‐ones and organomagnesium compounds
Authors: Dreux J. , Lhoste P. , Moreau M. , Royer J.
Published: December 2004

Part of the reaction between 2H‐pyran‐2‐ones and organomagnesium compounds has been investigated by means of MNDO and ab initio calculations. Criteria for the mechanism of reaction are provided by the stereoselectivity observed and calculations are consistent with this stereoselectivity. Conformations of the reaction intermediates are given.
Operational method of data treatment
Authors: Silver G. L.
Published: December 2004

A new instrument of exploration can be used to develop unrecognized connections among points in a variety of geometric designs. Operational methods are used to derive the relationships, and a new approach to extremum location is demonstrated. The technique is suitable for interpolation problems which arise in experimental design and the treatment of data.
Comparison between 6‐31 + bond functions and 6‐31 G* basis sets in UMP calculations of dissociation energies of the first row element compounds. I
Authors: Mach P. , Kysel O.
Published: December 2004

A basis set with bond functions (6‐31G + BF) has been tested for its applicability to calculation of dissociation energies of single and multiple bonds by Moeller‐Plesset perturbation theory at the second and third orders. Results have been compared with those calculated in the 6‐31G* basis set. The 6‐31G + BF basis at the MP2 and MP3 levels yields better results than 6‐31G* basis and the time consumption is less as well. Consideration of the bond functions on the bonds neighboring the bond being broken has no significant influence on the dissociation energies either at the SCF or at the MP2 levels. If both reactants and products can be characterized by two‐center bonds, the 6‐31G + BF basis and UMP2 variant of perturbation theory can be recommended for practical calculation of De values, especially for the systems where the use of more exact bases is rather difficult.
Geometrically feasible binding modes of a flexible ligand molecule at the receptor site
Authors: Ghose Arup K. , Crippen Gordon M.
Published: December 2004

A very efficient algorithm for determining the geometrically feasible binding modes of a flexible ligand molecule at the receptor site is presented. It is based on distance geometry but maintains the requirements of three dimensions. The distance geometry manipulation can superimpose two bodies without explicitly calculating the necessary rigid rotation and translation. The whole conformation space of a flexible molecule can be efficiently examined by considering only a finite number of conformational points. The method is suitable only when the criterion for superposition is some minimum distance limit. It cannot, however, give the exact distance between two points in two different bodies.
Unique description of chemical structures based on hierarchically ordered extended connectivities (HOC procedures). III. Topological, chemical, and stereochemical coding of molecular structure
Authors: Balaban Alexandru T. , Mekenyan Ovanes , Bonchev Danail
Published: December 2004

A topological code is devised on the basis of the unique topological representation of the molecule described in the preceding two parts of this series.1 By adding to the topological code additional chemical information on atoms and/or bonds, as well as stereochemical information, a chemical and respectively stereochemical code (SHOC) are also constructed. The advantages of the new linear codes are that they are convention‐free codes, preserving the symmetry of molecular graph, and easily implemented either manually or by means of computer programs. By concentrating all topological, chemical, and stereochemical information, our code (SHOC) is more compact and more general than the codes based on several separate lists.
Unique description of chemical structures based on hierarchically ordered extended connectivities (HOC procedures). VIII. General principles for computer implementation
Authors: Ralev Nikolai , Karabunarliev Stoyan , Mekenyan Ovanes , Bonchev Danail , Balaban Alexandru T.
Published: December 2004

The computer implementation of the HOC procedures presented in Parts I, II and III of this series is based on the module principle. It contains a main program and seventeen subroutines in Fortran IV. The system is able to provide unique atom numbering and code for all kinds of chemical compounds in their tremendous variety of structures.
Systematic errors in the total energy of molecular wave functions calculated within the PRDDO approximations
Authors: Throckmorton Linda , Marynick Dennis S.
Published: December 2004

We compare calculated total energies for 150 open‐chain molecules using ab initio methodology and the PRDDO approximations. The bulk of the errors implicit in the PRDDO approximations are apparently of a one‐center nature, i.e., they are due to the number and type of atoms in the molecule, and not the details of the molecular geometry. Atomic correction factors are developed which reduce the errors in the calculated total energy of PRDDO wave functions by a factor of eight relative to the ab initio reference calculations. PRDDO calculations on ring and cage compounds are shown to have additional systematic errors in the total energy.
The effect of including polarization functions on the geometrical parameters calculated for pyridine
Authors: Bock Charles W. , Trachtman Mendel , George Philip
Published: December 2004

Geometrical parameters for pyridine have been calculated using the 6‐31G, 6‐31G*(5D), 6‐31G**(6D), and 6‐31G(2 × 6D) basis sets. Comparisons are made with a microwave substitution structure and with results of other ab initio calculations reported in the literature. Particular attention is paid to the influence of polarization functions on the magnitude of the ring angle, 〈C6N1C2, which is analogous to the ipso angle in monosubstituted benzene derivatives.
A minimal multiconfigurational technique
Authors: Fernández Rico J. , Paniagua M. , GarcíA De La Vega J. M. , Fernández‐alonso J. I. , Fantucci P.
Published: December 2004

A direct minimization method previously presented by the authors is applied here to biconfigurational wave functions. A very moderate increasing in the time by iteration with respect to the one‐determinant calculation and good convergence properties have been found. So qualitatively correct studies on singlet systems with strong biradical character can be performed with a cost similar to that required by Hartree‐Fock calculations.
An all atom force field for simulations of proteins and nucleic acids
Authors: Weiner Scott J. , Kollman Peter A. , Nguyen Dzung T. , Case David A.
Published: December 2004

We present an all atom potential energy function for the simulation of proteins and nucleic acids. This work is an extension of the CH united atom function recently presented by S.J. Weiner et al. J. Amer. Chem. Soc., 106, 765 (1984). The parameters of our function are based on calculations on ethane, propane, n−butane, dimethyl ether, methyl ethyl ether, tetrahydrofuran, imidazole, indole, deoxyadenosine, base paired dinucleoside phosphates, adenine, guanine, uracil, cytosine, thymine, insulin, and myoglobin. We have also used these parameters to carry out the first general vibrational analysis of all five nucleic acid bases with a molecular mechanics potential approach.
Kinetics of particle growth VII. NH4NO3from the NH3‐O3 reaction in the presence of air and water vapor
Authors: Olszyna Kenneth J. , De Pena Rosa G. , Heicklen Julian
Published: December 2004

Our earlier work on the formation of particulate NH4NO3 in the NH3O3 reaction at 25°C is extended to include air as a diluent and H2O vapor as an additive. More extensive data at different values of [NH3]/[O3]0 were obtained also, where [O3]0 is the initial O3 concentration. In our earlier work we concluded that NH4NO3 vapor was dissociated to NH3 + HNO3 and that the HNO3 was removed by diffusion to the walls with a rate coefficient kdiff = 0.4 min−1 or by condensation on the suspended particles. Particles were nucleated by 8 NH3HNO3 pairs when their concentration product reached 5.8 × 1027 molec2/cm6 with a rate coefficient knucl of 6.2 × 10−224 cm45/min and removed by coagulation with a rate coefficient kcoag of 1.3 × 10−7 cm3/min. A corrected calculation modifies the number of pairs required to 6–7 with a correspondingly changed value of knucl.

With the more extensive data of the present study the indications are that the vapor‐phase NH4NO3 monomer is not dissociated and that its diffusion constant for loss to the walls varies between 0.3 and 0.9 min−1 for different reaction conditions. Nucleation occurs when the NH4NO3 vapor concentration reaches 1.0 × 1012 molec/cm3 via.

where r is 9 and the nucleation rate coefficient knucl is 3 × 10−108 cm24/min. With 5.0 or 9.5 torr of H2O vapor present, there is an excess of particles produced over that expected from this rate coefficient, indicating an additional nucleation step in which H2O vapor participates directly to produce a hydrated salt. The coagulation coefficient of (1.87 ± 0.14) × 10−7 cm3/min found here is in good agreement with that found previously.
Recommendations for measuring second‐order rate constants and kinetic solvent isotope effects on acid‐catalyzed reactions
Authors: Jensen James L. , Carr Michael D. , Yamaguchi Kenneth S.
Published: December 2004

Kinetic solvent isotope effects (KSIE) were measured for the hydrolyses of acetals of benzaldehydes in aqueous solutions covering the pH (pD) range of 1–6. For p‐methoxybenzaldehyde diethyl acetal, k/k = 1.8–3.1, depending on the procedure used to calculate the KSIE and on the pH (pD) range used as the basis for k(k). It is shown that this variation is an experimental artifact, and is a characteristic of KSIE measurements in general. It is recommended that k be calculated from a least‐squares fit of data to the equation kobs = k[L+], and that the KSIE be reported as k/k. The limitation remains, however, that the KSIE measured for a variety of substances over quite different pH (pD) ranges may not be comparable to more than ℜ20%. The source of these observations is discussed in terms of small changes in the activity coefficient ratios (a specific salt effect), including the solvent isotope effect on the activity coefficient ratio [eq. (3)].
Rate constants for the reactions of alkyl radicals with 1,4‐cyclohexadiene
Authors: Hawari J. A. , Engel P. S. , Griller D.
Published: December 2004

An electron paramagnetic resonance (EPR) technique was used to show that simple alkyl radicals readily abstract hydrogen from 1,4‐cyclohexadiene. Rate constants for the reaction were ca. 104–105 M−1 s−1 at 300 K and activation energies 5–7 kcal mol−1. For the stabilized radicals, allyl and benzyl, the rate constants were <102 M−1 s−1 at 300 K. The data suggest that 1,4‐cyclohexadiene could be used as an effective trap to probe rearrangement reactions of carbon centered radicals and biradicals.
Kinetic studies on the oxidation of carbon monoxide over pure, reduced, and doped indium sesquioxides
Authors: Lee Sung Han , Heo Gweon , Kim Keu Hong , Choi Jae Shi
Published: December 2004

Kinetic studies on the oxidation of carbon monoxide have been carried out between 413 and 473 K at different partial pressures of carbon monoxide and oxygen by means of the static method using vacuum‐activated, hydrogen‐reduced, and NiO‐doped In2O3 semiconductors as catalysts. A strong carbon dioxide inhibiting effect is observed. The experimental data satisfactorily fit an equation derived by assuming the controlling step to be the adsorption of gaseous oxygen on the surface of catalyst. CO and CO2 adsorb on the lattice oxygens (O), while O2 adsorbs on the oxygen vacancies (V) formed by vacuum‐activation, H2‐reduction, and NiO‐doping of In2O3. When CO2 formed during the reaction is removed by means of liquid nitrogen trap, the oxidation is found to be first‐order with respect to CO and to be half‐order with respect to O2. The concentration of oxygen vacancy in the solid catalyst is shown to be the controlling factor for the oxidation of carbon monoxide. A possible reaction mechanism can be explained by the n‐type character of In2O3 and proposed from the experimentally obtained kinetic data and conductivities.
Kinetics of the acyl migration in some adducts of acyl‐1, 4‐benzoquinones: Part I
Authors: Dabbagh Abdul Majeed , Al‐Hamdany Raad
Published: December 2004

The rates of migration of acetyl, propionyl, isobutyryl, and benzoyl substituent in Diels‐Alder adducts of acyl‐1, 4‐benzoquinones, (enediones), (I), to form the corresponding 2‐acyl hydroquinones, (II), in 50% (v/v) ethanolic pyridine have been studied in detail. Rate dependence on pyridine concentration has been established and maximum rate was found at pyridine a volume percent of 25 in an ethanolic reaction mixture. The study indicated first‐order dependence on reactants and fractional dependence on pyridine concentration. The effect of substituents of the acyl group on the rate showed that electronic factors play an important role on the stability of the transition state. A plausible mechanism, which is consistent with the results has been postulated and suitable rate law in consonance with the postulated mechanism have been derived.
Reinigung von Metalloberflächen
Authors: Schultze G.
Published: December 2004

Für die Entfernung von Oberflächenverunreinigungen von Metallen stehen heute verschiedenartige Behandlungsmethoden zur Verfügung, die kurz umrissen wurden. Die chemische Reinigung dürfte an Bedeutung gewinne, und zwar um so mehr, je allgemeiner die Bedeutung der sauberen Metalloberfläche für den weiteren Einsatz erkannt wird. In immer höherem Maße wird der sauren Beizung der Vorzug gegeben und trotz der bisher erreichten überraschenden Ergebnisse dürfte bei systematischer Bearbeitung der Schutzeffekt noch wesentlich umfassender gestaltet werden können.
Effects of orientation on dynamic mechanical properties of ABS
Authors: Daane J. H. , Matsuoka S.
Published: December 2004

Mechanical properties of a composite of glassy and rubbery polymers, ABS, were studied. Orientation induces two effects: (1) the intensity of the loss dispersion attributed to the rubbery component initially increases, then is reduced, and (2) a new loss peak at a temperature approximately 40°C below the original loss peak for the rubbery component appears. Assuming that this new peak is due to the dilated rubber particles embedded in the glassy matrix under strain, it is judged from the theory of Newman and Strella that a built‐in strain of 6% would be sufficient to cause this shift in Tg. Above the Tg of the rubbery component, the strain energy required to break increases with temperature. The reinforcement through incorporation of rubber particles is accomplished by enhancing the ability of the glassy matrix to draw on a local, microscopic scale. Such a local cold drawing may well be identified with crazing of glassy polymers.
Viscous dissipation in capillary flow of rigid PVC and PVC degradation
Authors: Morrette R. A. , Gogos C. G.
Published: December 2004

The steady state, non‐isothermal behavior of rigid polyvinyl chloride melt, flowing in capillaries of circular cross‐section, was investigated by solving, with the aid of a digital computer, the momentum and energy balance equations. It was assumed that the polymer melt can be described by the “Power Law” constitutive equation. The shear rate, temperature and pressure dependent properties of the fluid were obtained experimentally. The effects of the thermal degradation of PVC on its viscosity, were also introduced in the equations of momentum and energy.

The velocity, temperature and pressure profiles, obtained for both adiabatic flow and flow through a tube of constant wall temperature, indicate that considerable heating of the melt, due to viscous dissipation, can be achieved at moderate flow rates. Thermal degradation occurs in the capillary under certain conditions of temperature history and residence time of the fluid. The results of this work are in fair agreement with experimental results in this area.
The interfacial stresses in particulate composite systems
Authors: Matonis V. A.
Published: December 2004

It is postulated that property gradients exist at the interface forming an “interphase” between the insert and the matrix. Such gradients might be caused by partial solubility and diffusivity of the two phases comprising a composite. For simplicity, the “interphase” is replaced by a shell exhibiting averaged properties (Eshell = 1/2 Einsert + 1/2 Ematrix, etc.). An exact linear elastic solution was employed to evaluate stress fields throughout all regions. The possible effect of the “interphase” and its thickness on several physical properties of the composite are evaluated in terms of the particular stress fields.
Folded chain model of highly drawn polyethylene
Authors: Peterlin A.
Published: December 2004

Neither the fringed‐micelle, fringed‐fibril or extreme folded‐chain models explain the morphological and mechanical properties of highly drawn polyethylene. The modified folded‐chain model, assuming that a substantial fraction (between 5 and 30 percent) of the molecules do not fold back at the crystal surface but go through the “amorphous” surface layer and enter the next crystal, avoids the insufficiencies of the above mentioned models.

The elastic modulus and tensile strength of drawn polyethylene, both increasing with draw ratio, are to a large extent the consequence of the molecules bridging the quasi‐amorphous layers and interconnecting the folded‐chain lamellae oriented more‐or‐less perpendicular to the machine direction. The folds create enough space for the accommodation of more‐or‐less extended tie molecules in the quasi‐amorphous layers between the lamellae. Electron microscopy and calorimetry of samples as drawn, annealed and/or etched with fuming nitric acid support the model.
Interpretation of the tensile creep response of an ABS polymer
Authors: Moore R. S. , Gieniewski C.
Published: December 2004

Tensile creep measurements were carried out on a commercial ABS polymer over a temperature range from 40 to 100°C at stress levels from 0.6 to 1.8 × 108 dynes/cm2. Experiments were conducted in a prototype of an apparatus designed to be compatible with digital acquisition systems. Analysis of the data indicated that application of the time‐temperature super‐position principle was of limited value due to the use of test temperatures near and below the effective glass transition temperature of the acrylonitrile‐styrene component of the polymer. A strong stress dependence of the compliance was observed, even at relatively short times after loading. This was analyzed in terms of a model in which the height of the potential energy barrier to motion of the molecular flow unit is lowered by the application of stress. Analysis of the temperature dependence of the compliance at low stress levels indicated that the effective Tg of the acrylonitrile‐styrene phase is about 85°C. The temperature dependence of the magnitude of the activation energy is considered as is the stress dependence of the glass transition temperature. Implications of short‐time response in creep with regard to response under impact loading are pointed out. Practical application of results to the prediction of dimensional stability of molded parts is discussed as well as the limitations involved in extrapolation of experimental data to long times and high stress levels.
Strength ‐Composition relationships of random short glass fiber ‐thermoplastics composites
Authors: Lee Lieng ‐Huang
Published: December 2004

Twelve polymers and copolymers reinforced with random short glass fibers are used for the study of the strength ‐composition relationship. Six of these reinforced systems are new and have not been reported elsewhere. The effect of fiber volume fraction on tensile and flexural strengths is related to the Kelly and Tyson equation. For each composition the strengthening factor, F, is calculated and discussed with respect to the structure of the polymer. One factor pertaining to the actual performance of fiber glass, fiber efficiency, K, has been extrapolated for the fiber glass used for this study. The effects of fibers on toughness and the Izod notched impact strength are discussed. It is the impact strength ratio and not the toughness which is used to describe the net result of reinforcement.

The deviations between the wet and the dry strengths are used to illustrate the effect of the fiber ‐matrix interfacial bond. A new parameter, Δθ, is introduced to describe the effect of structure on the fiber ‐matrix interface. The effect of water at the fiber ‐matrix interface is further demonstrated through the determination of dielectric constant and dissipation factor of the composite before and after water immersion. The rule of mixtures was found to apply to dry electrical properties of composites.
Thermodynamic and physical properties of crystals formed from dilute solutions
Authors: Mandelkern L.
Published: December 2004

Some of the thermodynamic and physical properties of crystals of linear polyethylene, formed from dilute solution are discussed. These properties include density, enthalpy of fusion, infrared absorption spectrum, selective oxidation and dynamic mechanical measurements. Despite the fact that electron microscopic examination reveals an apparent geometric regularity to these crystals, all these physical measurements yield a consistent interpretation in that they require about 15–20% of the chain units to be in a non‐random conformation, and to form a disordered amorphous overlayer.

Detailed studies of the experimentally observed relations between the crystallite thickness, crystallization temperature, and dissolution temperature (melting temperature in a dilute solution) are also presented. A thermodynamic analysis of the dissolution temperature‐size relations, based on independently determined equilibrium solubility temperatures, indicates that the interfacial free‐energy characteristic of the mature crystallites is significantly different from that involved in nucleation. The interfacial structures of the nucleus and the crystallites must, therefore, also be different. Size control by a nucleation process can be demonstrated from very general theoretical considerations. However, the detailed molecular structure characteristic of the nucleus cannot be specified solely from the fact that this process is size controlling.
Flexural fatigue of glass‐reinforced thermoplastics
Authors: Cessna L. C. , Levens J. A. , Thomson J. B.
Published: December 2004

The fatigue failure of thermoplastics and glass‐reinforced thermoplastics is a function of cyclic stress or deflection level, test frequency, viscoelastic polymer parameters and matrix‐to‐fiber stress transfer. This paper reports an investigation of the modes of high frequency fatigue failure in glass‐reinforced and unreinforced thermoplastics. In particular the effects and control of dissipative heating of a working specimen and the role of efficient matrix‐to‐fiber stress transfer are considered. A test procedure with which the severity of dissipative heating can be continuously followed and controlled during an accelerated fatigue test is described.
Brabender viscometry: I. Conversion of brabender curves to instron flow curves
Authors: Lee G. C. N. , Purdon J. R.
Published: December 2004

Equations have been derived to convert Brabender flow curves to Instron flow curves for practical application purposes. The technique involved is simple and has been described and discussed in detail. Nine pairs of Brabender and Instron flow curves of three different high polymers, each at three operating temperatures, have been found to fit each other quite well. The converted Brabender flow curves overlap a part of the Instron curves and extend the shear range toward the Newtonian flow region. An important consequence of this work is that the Brabender Plastograph can now be regarded as a formal viscometer while still functioning as a miniature of the Banbury mixers used in industry. More work is being done to take advantage of this consequence.
Post extrusion heat and solvent transfer from polymeric film
Authors: Shih N. C. , Middleman S.
Published: December 2004

The problem of heat and solvent transfer from plasticized film is considered. The transport equations are solved by a numerical method. The formulation of the model includes the temperature dependence of diffusivity, the dependence of diffusivity on decreasing solvent concentration, as solvent leaves the film, and the latent heat of vaporization of the solvent. The Flory‐Huggins theory is used as a model for vaporliquid equilibrium. Heat and mass transfer coefficients are taken either as constants (to simulate extrusion with blowing at the film surface) or from analytical solutions to the appropriate boundary layer equations (to simulate extrusion into a stationary medium.) The boundary layer theory takes into account the effect of rapid vaporization on heat and mass transfer coefficients. Several numerical solutions were obtained for cases corresponding to extrusion of polyvinylacetate, plasticized with acetone, extruded into air.
Rates of molecular vaporization of organic plasticizers
Authors: Wall L. A. , Flynn J. H. , Straus S.
Published: December 2004

The kinetics of the molecular vaporization process of 21 plasticizers were investigated in detail. By both isothermal and nonisothermal kinetic methods, it was evident that 11 were quite pure single compounds, while 10 were clearly mixtures of compounds. For the single component species internal energies for vaporization and rates of volatilization are listed. The internal energies of vaporization are about one‐half or less of values one can estimate from the additive factor method of Small. Thus, solubility parameters based on our experimental values are low by about 30 percent. From this and previous work on linear alkanes, it is concluded that in the molecular vaporization process, the large organic molecules studied evaporate approximately as spheres and hence low values for the energy of vaporization are obtained. Consequently, the difference between our experimental energy and that estimated from solubility parameters is the energy for extending the molecule in a vacuum environment.
Compression, bending, and shear of bonded rubber blocks
Authors: Gent A. N. , Meinecke E. A.
Published: December 2004

An approximate theoretical treatment is given for small compressions of bonded rubber blocks. The component of the compressive force arising from the bonded condition at the loaded surfaces is obtained from a pressure distribution within the block, given by the solution of the corresponding torsion problem. The bending of blocks is treated in a similar way, the pressure distribution in this case being derived from the corresponding bending stress function. The apparent shear of relatively thick blocks is then treated as a combination of shear and bending displacements. The location of an internal rupture and the deformation at which it occurs are also derived from a critical (negative) value of the pressure developed within the block, at which a small cavity increases indefinitely in size. The corresponding critical deformations are calculated for extension and bending displacements. The shear stresses developed at the bonded surfaces under extension, compression or bending displacements are also evaluated.
Flow behavior of concentrated solutions of an SBS block copolymer
Authors: Paul D. R. , St. Lawrence J. E. , Troell J. H.
Published: December 2004

The non‐Newtonian viscosity of concentrated solutions of a styrene‐butadiene‐styrene, SBS, block copolymer was measured with a novel capillary viscometer. Polymer concentrations ranged from 0.165 to 0.306 g/cc. Apparent shear rates ranged from 1 to 105 sec−1. Five different solvents were employed. All of the flow curves can be reduced to a single master curve with the same shape exhibited by monodisperse polystyrenes and the Graessley theory. The shift factor for the shear rate axis, τ0, approximately parallels the Rouse relaxation time, τR, but shows a residual concentration and solvent dependence not predicted by the Rouse form. For different solvents at the same concentration, better solvents show a minimum relative zero shear viscosity, η0/ηs, and a maximum ratio τR/τ0. It is concluded that all solvent effects are not adequately incorporated into the zero shear viscosity for the purposes of constructing master plots; however, the shape of the master plot is not affected by the solvent or the polymer block structure.
Effect of processing history on melt flow defects
Authors: Rudin A.
Published: December 2004

The two main flow defects which appear to originate in the processing machine or die are melt fracture and sharkskin. Both are associated with the elastic nature of the polymer melt. Processing variations that decrease the elastic nature of the melt diminish the severity of the effects of melt fracture. These include increased die length and temperature and shear at temperatures at which polymer segmental mobility is not too high. The sheared, less elastic melt structure may sometimes be stabilized by polymeric additives. A simple model is presented to account for this behavior, which is illustrated with examples of polyethylene and plasticized PVC.
Cause and effect in the weathering of plastics
Authors: Kamal M. R.
Published: December 2004

In most instances, the study of the weatherability of plastics follows empirical schemes that show little correlation with the actual effects of outdoor exposure. A more reliable analysis must be based on a knowledge of the factors in the weather which affect plastic properties and of the modes of interaction between these factors and the plastic material. It is shown that both the factors of the weather and the kinetics of polymer degradation may be expressed in a quantitative manner suitable for analytical treatment. Furthermore, it is shown that the analytical approach yields predictions which are in qualitative agreement with the results of actual outdoor exposure. Finally, some new techniques are proposed for more reliable predictions of long‐term outdoor weatherability on the basis of laboratory studies.
Melt fracture of polystyrene
Authors: Vlachopoulos J. , Lidorikis S.
Published: December 2004

The results of an experimental study of melt fracture using polystyrene samples of narrow and broad molecular weight distribution are presented. The weight average molecular weight (M̄w) ranged from 9.72 × 104 to 1.80 × 106 and the distribution breadth M̄w/M̄η from 1.06 to 9.21. The critical shear stress varies linearly with 1/M̄w, increases slightly with temperature and is independent of the distribution of molecular weights. This type of behavior is satisfactorily explained in terms of Graessley's entanglement theory.
Force requirements in forging of crystalline polymers
Authors: Wissbrun K. F.
Published: December 2004

The forces required to compress billets of crystalline polymers below their melting points were determined and related to the initial billet dimensions and amount of deformation. The studies involved the use of three high‐density polyethylenes and an acetal copolymer. The results were found to obey an equation derived from plasticity theory using, at each temperature and for each material, a single parameter very nearly equal to the yield strength determined in ordinary tensile tests, and having the same temperature dependence. An empirical equation that describes the pressure required to form cups by backward extrusion of metal billets is also successful for the same process with polymers, using the yield parameter from the compression experiments. Cold working causes a high degree of orientation, increased clarity, and greatly increased tensile strength.