bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chain structure of homogeneous ethylene‐propylene copolymers showing inversion, described on the basis of 13C‐NMR data. II. Application
Authors: Mathot V. B. F. , Fabrie Ch. C. M. , Tiemersma‐Thoone G. P. J. M. , Van Der Velden G. P. M. 
Published: April 2003

AbstractFor a series of homogeneous ethylene‐propylene copolymers with mole fraction ethylene (x1) ranging between 0.40 and 0.85, the inversion (I) independent propagation probabilities (Pijs) and reactivity ratios ( rijs) and the methylene, ethylene, and propylene sequence length distributions have been determined from 13C nuclear magnetic resonance (NMR) data, using a first‐order Markovian terpolymer [ethylene (1), inverted propylene (2), and normal propylene (3)] model. For each sample, the limiting values of I (Imin, Imax) are given. Calculations of the common parameters for 19 samples show that the polymerization direction characterized by the r set and I is statistically more probable than the opposite direction, which is characterized by the r′ set and I′. Further, I = Imin appears to be close to the most probable value of I. The resulting r set is r12 = 119, r13 = 19.7 and, for I = Imin, r21 = 0, r31 = 0.034, r32 = 2.98. In the limited range 0.60 < x1 < 0.85, there appears to be no preference for either polymerization direction, so that the solutions characterized by the r set and I = Imin and by the r′‐set and I = I′max, respectively, are about equally probable. If the copolymer reactivity ratios re and rp are defined in the usual manner, it follows that for the limited range re = 17. In the model used here, rp is found to be dependent on the ethylene‐propylene ratio in the reactor. Nevertheless, it can be stated that rp ≅ 0.029 and re rp ≅ 0.50.
Quasiharmonic treatment of infrared and raman vibrational frequency shifts induced by tensile deformation of polymer chains
Authors: Tashiro Kohji , Wu Gang , Kobayashi Masamichi 
Published: April 2003

AbstractStress‐induced vibrational frequency shifts in the infrared and Raman spectra of polymer chains are interpreted theoretically on the basis of the quasiharmonic lattice dynamical treatment. The calculated frequency shifts are in good agreement with experiment for planar‐zigzag polyethylene and helical polyoxymethylene. The anharmonic terms of the force constants are estimated numerically in order to obtain the parameters of anharmonic potential functions such as the Morse potential. The close relationship between stress‐induced frequency shifts and molecular deformation mechanisms is discussed in terms of the force field and the geometry of the polymer chain.
Characterization of orientation clustering in short‐fiber composites
Authors: Ranganathan Sridhar , Advani Suresh G. 
Published: April 2003

AbstractDuring flow of concentrated fiber suspensions, the proximity of the fibers induces interactions in their orientation space. These fiber‐fiber interactions may lead to clustering in orientation of fibers and a nonhomogeneous fiber orientation field. An orientation cluster is a group of fibers in a specific neighborhood sharing the same orientation state. It is important to characterize clustering to understand and quantify fiber‐fiber interactions. Such characterization will also be useful in the prediction of the mechanical and physical properties of the resulting composite material. An image of the fiber distribution at a location in a composite is divided into a number of partitions, and the variance of the fiber orientation states within the partitions, between the partitions and of the entire sample are compared to establish the existence and the extent of clustering in the orientation space. Statistical methods such as analysis of variances and techniques analogous to the scale of segregation used in mixing theory are modified and adopted to identify and quantify orientation clusters. Simulated examples that describe clustering quantitatively in magnitude and direction of planar orientations are presented. This method is then extended to identify clustering in model injection molding experiments performed in a center‐gated square mold with suspensions of 1% and 10% volume fractions.
An improvement in the flory corresponding‐states theory of polymer solutions
Authors: Li Pantong , Krause Sonja , Hollinger Henry B. 
Published: April 2003

AbstractThe original Flory corresponding‐states theory of polymer solutions requires an entropic correction parameter Q12, the sign and value of which seem to be arbitrary, and the physical meaning of which is obscure. Moreover, calculated excess volumes of mixing for many polymer solutions are often in significant disagreement with experimental data. In order to eliminate these problems, we have modified the kinetic part of the partition function, introduced an effective mass for the mixture segment, and adopted the nonlinearity of the number of degrees of freedom with respect to the composition for the mixture segment. In addition, the effect of nonrandom configurations of the segments in the mixture has been included. In the improved equations, derived in this work, the Flory interaction parameter χ can be considered to comprise three parts: (a) a kinetic part due to the contribution of the average number of degrees of freedom and the effective mass of the mixture; (b) a free volume part; and (c) an interaction part including the contributions due to the contact interaction and the nonrandom configuration of the segments in the mixture, caused by the interaction. The improved theory is in good agreement with literature data on polystyrene solutions and poly (dimethyl siloxane) solutions.
Gas transport properties of annealed polyimide films
Authors: Hachisuka H. , Tsujita Y. , Takizawa A. , Kinoshita T. 
Published: April 2003

AbstractSorption and permeation of CO2 in various annealed polyimide (PI) films were investigated. Dual‐mode sorption and partial immobilization models were used to analyze the data. Sorption of CO2 in PI film quenched from above the glass transition temperature (Tg) is greater than in film as received. In fact, sorption is decreased over the entire pressure range by cooling the film slowly. These changes in sorption of CO2 can be attributed to a change in the Langmuir sorption capacity C′H by annealing, since the other dual‐mode sorption parameters, kD and b, are almost independent of annealing. The value of C′H is increased by quenching, and decreased by slow cooling from above Tg. The two diffusion coefficients DD and DH according to the Henry and Langmuir modes, respectively, for CO2 also depend markedly on annealing. Diffusion coefficients of quenched PI films are increased and those of film cooled slowly are decreased compared with values for PI film as received. The change in DH is larger than that in DD. The permeability coefficient of quenched PI films at 100 cmHg is about 1.7 times that of PI film as received. The film structure formed by quenching can enhance permselectivity.
The evolution of the viscoelastic retardation spectrum during the development of an epoxy resin network
Authors: Plazek Donald J. , Chay In‐Chul 
Published: April 2003

AbstractThe evolution of the viscoelastic behavior of an epoxy resin at various stages of curing has been followed with the changes in the retardation spectrum. The creep J(t) and recoverable creep compliance Jr(t) curves of the neat epoxy resin Epon l00lF (Shell) were determined at temperatures between 30 and 77°C. The viscosity decreased over 8 orders of magnitude as the temperature was increased. Specimens with eight stages of network development were prepared by reacting all of the epoxy resin's oxirane rings with amine hydrogens from varying ratios of a monofunctional amine (methyl aniline) and a tetrafunctional amine 4,4′‐diamino diphenyl sulfone (DDS). Preparations in which 25, 35, and 40% DDS were used did not result in a molecular network, so they were viscoelastic liquids. With 45% DDS, the product had a nascent network and was judged to be just beyond the point of incipient gelation. The remaining preparations from 0.50, 0.60, 0.70, and 1.0 DDS yielded tighter less compliant molecular networks. The creep and recoverable compliance curves were measured over a range of temperatures above the glass transition temperature, Tg. They were reduced to Tg, and retardation spectra L(ln τ) were calculated.
Dependence of slow crack growth in polyethylene on butyl branch density: Morphology and theory
Authors: Huang Yan‐Ling , Brown Norman 
Published: April 2003

AbstractA theoretical equation has been developed to described the rate of slow crack growth in an ethylene‐hexene copolymer in terms of the basic morphological parameters. These parameters are spacing of the butyl branches, number of tie molecules, and the thickness of the lamellar crystal. Experimentally, the thickness of the lamellae and the long period were determined as functions of the branch density. The calculation of the number of tie molecules is based on the values of the molecular weight and the long period. The model of slow crack growth is based on the rate of disentanglement of the tie molecules. The rate of disentanglement varies inversely with the number of tie molecules and directly with the number of tie molecules that are not pinned by the branches.
Single‐molecule single crystals
Authors: Bu Haishan , Pang Yanwan , Song Dandan , Yu Tongyin , Voll T. M. , Czornyj George , Wunderlich B. 
Published: April 2003

AbstractVarious approaches to the preparation and verification of single‐molecule single crystals are discussed for polyethylene and poly (oxyethylene). Analytic tools are electron microscopy, electron diffraction, and differential scanning calorimetry. The main difficulty in producing a single‐molecule single crystal is to keep crystals from joining during growth.
Third virial coefficient of polystyrene in benzene
Authors: Nakamura Yo , Norisuye Takashi , Teramoto Akio 
Published: April 2003

AbstractSecond virial coefficients A2 and third virial coefficients A3 for benzene solutions of ten polystyrene fractions ranging in weight‐average molecular weight Mw from 104 to 2 × 107 at 25°C were determined by light scattering. The third coefficient is represented approximately by A3 = 8.0 × 10−6 M mol g−3 cm6 for Mw above 105. In this molecular weight region, the factor g defined by A3/AMw/ This trend of g is consistent with predictions of early two‐parameter theories but not with those of renormalization group theories. In particular, quantitative agreement is observed between the present experiments (for Mw ≳ 2 × 105) and the mean‐field two‐parameter theory of Stockmayer and Casassa.
Interfacial effects on stress distribution in model composites
Authors: Fan Cun Feng , Waldman David A. , Hsu Shaw Ling 
Published: April 2003

AbstractRaman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x‐ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface.
Nonintegral and integral folding crystal growth in low‐molecular mass poly (ethylene oxide) fractions. II. End‐group effect: α,ω‐methoxy‐poly (ethylene oxide)
Authors: Cheng Stephen Z. D. , Chen Jianhua , Zhang Anqiu , Heberer Daniel P. 
Published: April 2003

AbstractDifferential scanning calorimetry (DSC) and in situ small‐angle x‐ray scattering (SAXS) indicate that in an α ω‐methoxy‐poly(ethylene oxide) (MPEO) fraction (MW 3000) a transient nonintegral folding (NIF) crystal initially forms during crystallization throughout a wide range of crystallization temperatures. Subsequent transformations of the NIF to IF (integral folding) crystals at low temperatures occur mainly through isothermal thickening or thinning via perfection processes or, at higher temperatures, through primary crystal formation. The NIF crystal is thermodynamically the least stable state among the crystal forms, but its growth is the most rapid. The overall crystallization and crystal melting of this MPEO fraction reveal that the NIF crystal and the NIF → IF crystal transformations are common to low‐molecular mass PEO fractions without regard to the end group. Nevertheless, diffusion coefficient and viscosity measurements provide clear evidence of an end‐group effect in PEO and MPEO fractions. The difference in the overall crystallization and isothermal thickening and thinning kinetics of low‐molecular mass PEO and MPEO fractions can lead to further understanding of end‐group effects.
Nonintegral and integral folding crystal growth in low‐molecular mass poly (ethylene oxide) fractions. III. Linear crystal growth rates and crystal morphology
Authors: Cheng Stephen Z. D. , Chen Jianhua 
Published: April 2003

AbstractCorrelations of the linear crystal growth rates with the change in crystal morphology for poly (ethylene oxide) (PEO) (MW 3000) and α,ω‐‐methoxy‐poly (ethylene oxide) (MPEO) (MW 3000) fractions have been established over a wide range of supercooling (ΔT= 25 K). Two linear crystal growth rates were measured, namely, the linear crystal growth rate of spherulites or hedrites and the lateral (linear) crystal growth rate of single lamellar crystals along different crystalline planes (below ΔT= 11–12 K). At a low supercooling of 5 K, the crystal growth rate of the MPEO fraction passes through a minimum. Subsequently, the rate increases abnormally and reaches a maximum at even lower supercooling. This crystal growth retardation has been attributed to the competition between differing chain conformations during crystal growth. In this case, particularly, these conformations are the extended chain and the once‐folded chain conformations. This retardation is not observed in the PEO fraction, since in this low supercooling region any once‐folded chain conformations formed during crystal growth are of the double‐layer lamella type. The change in morphology in this region supports this judgement. Above ΔT= 7.6 K, the crystal growth behavior in these two fractions can be described by the present nucleation theory on flat crystal growth faces. Below that ΔT, however, different crystal growth mechanisms can be clearly seen. This may be associated with the crystal growth on the highly serrated growth faces in these two fractions.
Fatigue crack propagation in high‐density polyethylene
Authors: Yeh J. T. , Runt J. 
Published: April 2003

AbstractAn investigation of the influence of crystalline microstructure on fatigue crack propagation (FCP) in high‐density polyethylene (HDPE) is reported. Various thermal histories were used to generate samples with the same crystallinity and supermolecular structure for three different molecular weight HDPEs. Estimation of tie chain densities were obtained from measurements of brittle fracture stress and predicted from the estimated chain dimensions of the polymers using the modified version of the approach originally taken by Huang and Brown. A significant decrease in FCP resistance and a clear transition to a more brittle fracture surface was observed with decreasing molecular weight. Detailed studies of damaged zones preceding the growing crack show a transition to a more highly branched crack structure for those samples associated with a higher FCP resistance. These results strongly suggest that the branched damaged zone structure improves the FCP resistance by enlarging and blunting the crack tip and, therefore, consuming more energy during the fatigue crack propagation. Additional efforts were made to prepare samples with the same crystallinity and tie chain density, but different supermolecular structure. However, in contrast to reports in the literature, no significant difference in FCP resistance was observed for specimens with different average spherulite sizes. This is probably because the propagating crack front is preceded by a significant zone of plastic deformation and is not expected to directly encounter the spherulites.
Nuclear magnetic relaxation of α‐13C nuclei of helical poly(γ‐hexyl‐L‐glutamate) and poly(γ‐benzyl‐L‐glutamate)
Authors: Raby Philip , Budd Peter M. , Heatley Frank , Price Colin 
Published: April 2003

AbstractSpin‐lattice relaxation times (T1), spin‐spin relaxation times (T2), and nuclear Overhauser enhancements (NOE), at 75.5 MHz are reported for α‐13C nuclei of poly (γ‐benzyl‐L‐glutamate) in deuterated dimethylformamide at 60°C and of poly(γ‐hexyl‐L‐glutamate) in cyclohexanone at 48 and 79°C. It is shown that for molecular weights above 105, the polypeptides cannot be considered as essentially rigid helices with internal librational motions; additional backbone flexing motions contribute to the relaxation behavior.
Theories for network formation in multistage processes
Authors: Tiemersma‐Thoone G. P. J. M. , Scholtens B. J. R. , Dušek K. , Gordon M. 
Published: April 2003

AbstractTwo different theoretical approaches have been developed to describe network formation in a six‐component, three‐stage process with the stochastic theory of branching processes. Both approaches make use of probability‐generating functions and cascade substitutions. In the POLYM approach, the products of the previous stage, namely, complete (branched) molecules, are used as building units in the subsequent stage. The molar masses and unreacted functionalities are identified by means of dummy variables. In the resulting formulas the sequence of the three stages is clearly visible. In the MONOM approach, the system is treated as a quasi‐one‐stage process; the original monomers are the building units in all three stages, the sequence of which is only apparent from the input parameters. In the MONOM approach the original monomers are used as building units, irrespective of the stage in which they react. A separate dummy variable is chosen for each possible reaction in each stage in the MONOM approach, so that the two approaches give analytically identical results, but along completely different derivations. This avoids correlation errors in the MONOM approach. Both approaches have incorporated kinetic effects by way of substitution effects in two of the monomers. The two approaches are prefaced by the treatment of several paradigms of increasing complexity to show the unity and strength of the theory and to warn against typical pitfalls.
Crystal transition and structure of poly (γ‐n‐alkyl glutamate)s
Authors: Sasaki Shintaro 
Published: April 2003

AbstractThe nature of the crystal transition of the α‐helical forms of poly (γ‐n‐alkyl glutamate)s (alkyl = ethyl, propyl, and butyl) is described. The transition is thermally reversible, and its temperature T2 is much higher than the glasslike transition temperature T1 associated with the side‐chain motion. The main chains undergo large‐scale motion (librational about the chain axis and translational along the axis) above T3 ≈ 200°C. The structure observed below T2 is anomalously disordered compared with that observed between T2 and T3. The crystal structure emerging above T2 is analyzed for a typical sample of poly(γ‐n‐propyl L‐glutamate). The trigonal unit cell contains three α‐helices so that each helix is surrounded by other helices in the same fashion, but the helices are not interrelated by a crystallographic symmetry element. The side chains suffer no particular change at T2. The main‐chain motion gives rise to the T2 transition by inducing attractive forces between interpenetrating side chains.
Light‐scattering studies on solutions of cellulose in the ammonia/ammonium thiocyanate solvent system. I. Classical light‐scattering
Authors: De Groot A. W. , Guinnup D. E. , Theil M. H. , Cuculo J. A. 
Published: April 2003

AbstractThis article reports the use of classical light scattering to study cellulose in the NH3/NH4SCN solvent system. Three solvent compositions were used, 27.01 73.0,25.5/ 74.5, and 24.51 75.5 weight ammonia/weight ammonium thiocyanate. The coefficient, (dn/dc)υ, was determined by back calculating using the molecular weight determined by solution viscometry in the solvent system cupriethylenediamine and the classical light‐scattering results. Second virial coefficients were found to be similar to those values measured for cellulose in the FeTNa and LiCl/DMAC solvent systems. The characteristic ratios were found to vary with solvent composition with the highest values being at a composition of 25.5/74.5 weight ammonia/ weight ammonium thiocyanate. Persistence lengths were also found to vary with solvent composition with the highest value being 264 × 10−8 cm at solvent composition 25.5/74.5.
A composite methodology for multistage degradation of polymers
Authors: Nam Jae‐do , Seferis James C. 
Published: April 2003

AbstractFive different analytical schemes for examining isothermal and nonisothermal degradation of polymers were reviewed and found inadequate for describing multistage decomposition. The different schemes were experimentally tested using thermogravimetric analysis data for an ethylene‐vinyl acetate (EVA) copolymer, which exhibited a well‐behaved two‐step decomposition process in a nitrogen environment. Based on these experimental and analytical findings, a generalized methodology was developed capable of describing the exhibited complex decomposition behavior of polymers by combining two or more kinetic mechanisms in a series or parallel arrangement. This composite of combinational methodology thus extends established analytical schemes for describing complex decomposition of polymers in a rational manner, incorporating both experimental and theoretical considerations.
Thermal, dielectric, and mechanical relaxation in poly(benzimidazole)/poly(etherimide) blends
Authors: Liang Kuiming , Bánhegyi György , Karasz Frank E. , MacKnight William J. 
Published: April 2003

AbstractThermal, dielectric, and mechanical relaxation measurements on miscible blends of polybenzimidazole (PBI) and a polyetherimide (PEI, Ultem 1000) prepared by solution casting from dimethylacetamide (DMAc) reveal a number of structurally related features. Annealing below the glass transition temperature induces an enthalpy relaxation process typical of single‐phase glasses of nonequilibrium structure. Dielectric relaxation experiments on samples annealed at ambient conditions reveal two relaxation processes below 400°C. At lower temperatures (50–200°C), the desorption of water is observed. Above 200°C in the first run, a composition‐dependent relaxation is seen at the highest frequencies (100 kHz) while a relaxation approximately independent of composition appears in the second run. The latter corresponds to the glass transition of the PEI phase. The glass transition of PBI at this frequency is above the degradation temperature. At lower frequencies a strongly dispersive electrode polarization process masks the high‐temperature relaxations. Dynamic mechanical results show similar features with respect to phase separation; the main difference is that the tan δ curves in the first run are complicated by the desorption of residual solvent.