bluuebunny/crossref_metadata_2025_split huggingface dataset:
An endochronic prediction of the variability in fracture times of polymers
Authors: Valanis K. C. , Yilmazer Ulku 
Published: April 2003

AbstractA theory of variability in lifetimes of identical polymer specimens under identical test conditions is formulated, using the theory of fracture of amorphous crosslinked polymers developed previously by the authors. Variability in fracture times follows from the assumption that the critical number Ncr of bonds that must fail in order to cause fracture of a specimen varies from specimen to specimen. A plausible physical explanation for the variation in Ncr may well lie in the variability of the spatial distribution of weak local regions. The scale of locality may vary from molecular to grosser dimensions. The theory is applied to styrene–butadiene rubber (SBR) under creep conditions and fares well in its prediction of observed results. Most notably, it predicts that the shape of the distribution curve of the observed lifetimes remains invariant with changes in the levels of stress and temperature and that the effects of these manifest themselves through shifts of the curve on the logarithmic time axis. The theory also predicts correctly that the fracture process is accelerated if the creep test is interrupted by unloading–reloading cycles at high strain rates. This last result is shown to be a direct consequence of the concept of “the endochronic time to fracture,” previously introduced by the first author.
Microvoid formation during deformation of high‐impact polystyrene
Authors: Steger T. R. , Nielsen L. E. 
Published: April 2003

AbstractSmall‐angle x‐ray scattering (SAXS) has been used to study the formation of microvoids in polymers which craze or stress‐whiten extensively. Specimens are subjected to a stepwise uniaxial strain, with scattering curves being obtained at each step. The increase in scattering intensity upon crazing is attributed to the formation of microvoids, and the relative size, shape, and concentration of the scattering elements are determined by a Porod analysis of the SAXS curves. The major portion of our work has been on high‐impact polystyrene which shows a large increase in SAXS intensity as crazing occurs. We are able to follow the changes in void size and concentration during craze initiation and growth. Effects of temperature, molecular orientation, and matrix molecular weight have also been studied. The results add to the information on craze growth and microstructure known from electron microscopy and dilatometry. In addition, a qualitative physical model for microvoid nucleation is proposed, and the implications for toughness are discussed.
Dielectric properties of maleic acid–ethylene copolymer in salt‐free aqueous solutions
Authors: Paoletti S. , Van Der Touw F. , Mandel M. 
Published: April 2003

AbstractThe dielectric behavior of maleic acid–ethylene copolymer solutions has been investigated at different polymer concentrations and two degrees of neutralization α′. It is shown that this behavior is analogous to that of ordinary polyacids. Also the experimental data can be explained in terms of the van der Touw–Mandel theory, but at low α′ a possible contribution from motion of negative charges (in turn related to bound proton fluctuations) has to be taken into account. The dielectric results suggest that the formation of intramolecular hydrogen bonds has an influence on the change of the average dimensions of the chain with increasing α′. This seems to be confirmed by viscosity data.
Solubility of carbon dioxide in cellulose acetate at elevated pressures
Authors: Stern S. A. , De Meringo A. H. 
Published: April 2003

AbstractThe solubility of carbon dioxide in symmetric (dense) cellulose 2.4‐acetate has been measured at temperatures from 0 to 70°C and pressures up to 45 atm. The polymer samples were prepared by slowly drying asymmetric reverse osmosis membranes. The solubility isotherms can be described satisfactorily up to 60°C by the “dual‐sorption” model for glassy polymers. The model cannot represent the experimental data above 60°C, possibly because of a second‐order transition in the polymer between 60 and 70°C. An analysis of the dual‐sorption parameters and of the heats of solution and “hole filling” suggests that the polymer samples contained a relatively large volume of microcavities. Gas solution appears to occur predominantly in microcavities, a large fraction of the penetrant moleculers being immobilized or partially immobilized. The solubilities obtained in this work are compared with similar data computed from time‐lag measurements of other investigators, and the validity of the dual‐sorption model is examined for the present case.
Thermodynamic properties of phenol–formaldehyde resin
Authors: Harwood C. , Wostenholm G. H. , Yates B. , Badami D. V. 
Published: April 2003

AbstractCharacterization measurements of a commercial phenol‐formaldehyde resin prepared from constituents including phenol and formaldehyde in the molar ratio 1:1.33 are reported. The measurements consist of (1) the linear thermal expansion coefficient between approximately 85 and 270°K; (2) the specific heat capacity between approximately 6 and 100°K; (3) the Young's modulus at room temperature. A critical examination of the data reveals that: (1) the vibrational behavior is predominantly that of a three‐dimensional assembly; (2) as far as data available from other sources permit an assessment to be made, the principle of additivity appears to be applicable to the specific heat capacity between approximately 50 and 100°K; and (3) the data lie near the limit of an empirical relationship observed between the Young's modulus and linear thermal expansion coefficient of other polymers.
Morphology and rheology of peel of model adhesives
Authors: Parsons W. F. , Faust M. A. , Brady L. E. 
Published: April 2003

AbstractThe morphology of surfaces produced during peel experiments was studied to increase the understanding of peel phenomena. Thin films of polystyrenes of narrow molecular‐weight distribution and a polydisperse polyester on flexible supports were peeled from rigid substrates at temperatures above their glass transitions with equipment that also permitted quenching and preservation of the peeled surfaces which then could be studied by scanning electron microscopy. The results show many types of cavitation including foams and the coalescence of cavities to form fibers. Cavitation occurred throughout and beyond the region of transition from cohesive to interfacial failure where peel force decreased abruptly; however, cavity growth was abruptly restricted as the failure mode changed. The master curves and shift factors obtained in this work provided strong evidence that the quenching used to preserve the peeled surfaces did not introduce large perturbations in the results. The reason was that failure occurred at or close to the heated substrate.
Effect of ozone on creep of vulcanizates
Authors: Metherell C. 
Published: April 2003

AbstractIn‐service secondary creep rates of natural rubber (NR) vulcanizates at ambient temperature are known to be low. However, in tests on thin strips of NR vulcanizates in tension, secondary creep at rates of up to 120%/week were observed. From an examination of the effect of antioxidants, antiozonants, waxes, and specimen thickness it was shown that the anomalous creep was due to ozone attack on the vulcanizate, which only becomes serious in tests on thin strips in tension.
Fourier transform infrared studies on the thermal degradation of polyacrylonitrile
Authors: Coleman M. M. , Petcavich R. J. 
Published: April 2003

AbstractFourier transform infrared studies of the thermal degradation of polyacrylonitrile (PAN) conducted at 200°C in air and under reduced pressure are presented. The spectra are markedly superior to those published previously. A mechanism consistent with the infrared results obtained under reduced pressure is advanced, and assignments for the infrared bands occuring in the spectrum of both the reduced pressure and air degraded PAN are given.
Solid‐state polymerization of a diacetylene crystal: Thermal, ultraviolet, and γ‐ray polymerization of 2,4‐hexadiyne‐1,6‐diol bis‐(p‐toluene sulfonate)
Authors: Chance R. R. , Patel G. N. 
Published: April 2003

AbstractResults are presented for the thermal, ultraviolet, and γ‐ray polymerization of 2,4‐hexadiyne‐1,6‐diol bis‐(p‐toluene sulfonate) (PTS). Monomer extraction is used to obtain polymer conversion‐vs.‐time curves at 30, 50, and 80°C. In agreement with previous work over a narrower temperature range, the curves all display a dramatic autocatalytic effect with an onset at about 10% conversion to polymer. Although the polymerization rate undergoes a 200‐fold change over this temperature range, the shape of the conversion curves does not change. These data yield an activation energy (E) of 22.2 ± 0.4 kcal/mole when interpreted in terms of the time required to reach 50% polymer. An annealing technique is used to provide a closer look at the autocatalytic region. In that case, E = 22.5 ± 0.8 kcal/mole is determined from measurements of the time required to go from 10 to 50% polymer at temperatures ranging from 23 to 80°C (a 500‐fold change in rate). Thermal polymerization rates measured in the low‐conversion limit using a spectroscopic method based on diffuse reflectance yield E = 22.8 ± 0.6 kcal/mole. Thus E is independent of polymer conversion and the autocatalytic effect can be best understood as arising from a large increase in the propagation length of the polymer chains. The autocatalytic effect is shown to be present in both UV and γ‐ray polymerization. In the case of γ‐ray polymerization, conversion‐vs.‐time and spectroscopic measurements are consistent with inhomogeneities in the polymer concentration caused by particle tracks. Activation energies for UV and γ‐ray polymerization are quite low (2‐3 kcal/mole) and confirm that the chain initiation event makes the major energetic contribution to E. The polymerization mechanism is discussed in detail. The photopolymerization experiments can be consistently interpreted with a model based on the triplet excited state of the diacetylene monomer as the chain initiation species.
Epitaxial crystallization of polyesters on inorganic and organic substrates
Authors: Rickert S. E. , Baer E. , Wittmann J. C. , Kovacs A. J. 
Published: April 2003

AbstractA series of low‐molecular‐weight linear polyesters were epitaxially crystallized from dilute solution and the melt on a variety of organic and inorganic substrates. The rod‐like polyester crystals which were formed assumed general orientations in alignment with substrate geometry. This yielded monodirectional orientation of these crystals on one of the organic substrates, and bidirectional orientation on the other surfaces. Heterogeneous nucleation on the organic substrates, trioxane and naphthalene, induced the growth of much larger epitaxial crystals than have previously been observed on inorganic substrates. Those polyesters, with a high percentage of methylene units per chain repeat, crystallized in an unusual polymorphic form when in contact with the organic substrates. Polymorphic transformation to the normal form was not possible under thermal treatment or with increased crystal thickness. The expected relationship between dipolar alignment in the polymer crystal and this polymorphism was established.
Observations on the dielectric anisotropy of solutions of flexible polymers in flow
Authors: Block H. , Ions W. D. , Walker S. M. 
Published: April 2003

AbstractMeasurements of the increase in the relative permittivity for solutions of polystyrenes, poly(p‐ethoxystyrene), poly(methyl methacrylate), and poly(N‐vinyl carbazole) when subjected to shear gradients are reported. The influences of such factors as shear rate, concentration, viscosity, solvent permittivity, polymer dipole moment, and polymer molecular weight on the phenomenon are described. An empirical correlation for the diverse data obtained with polystyrenes and poly(p‐ethoxystyrene) has been established, but this relation does not entirely match the theoretically predicted effects. We discuss the various physical processes which may have an influence on the observed phenomenon.
Properties of polyethylene modified with phosphonate side groups. II. Dynamic mechanical behavior
Authors: Weiss R. A. , Lenz R. W. , Macknight W. J. 
Published: April 2003

AbstractThe viscoelastic behavior of phosphonate derivatives of phosphonylated low‐density polyethylene (LDPE) was studied by dynamic mechanical techniques. The polymers investigated contained from 0.2 to 9.1 phosphonate groups per 100 carbon atoms and included the dimethyl phosphonate derivative and two derivatives for which the phosphonate ester group was an oligomer of poly(ethylene oxide) (PEO). The temperature dependences of the storage and loss moduli of the dimethyl phosphonate derivatives were qualitatively similar to those of LDPE. At low phosphonate concentrations, the α, β, and γ dispersion regions characteristic of PE were observed, while at concentrations greater than 0.5 pendent groups per 100 carbons atoms, only the β and α relaxations could be discerned. At low degrees of substitution, the temperature of the β relaxation Tβ decreased from that of PE, but above a degree of substitution of 0.1, Tβ increased. This behavior was attributed to the competing influences of steric effects which tend to decrease Tβ and dipolar interactions between the phosphonate groups which increase Tβ. For the phosphonate containing PEO, a new dispersion region designated as the β′ relaxation was observed as a low‐temperature shoulder of the β relaxation. The temperature of the β′ loss was consistent with Tg(U) of the PEO oligomers as determined by differential scanning calorimetry, and it is suggested that the β′‐loss process results from the relaxation of PEO domains which constitute a discrete phase within the PE matrix.
Raman spectroscopic method for determining the crystallinity of polyethylene
Authors: Strobl G. R. , Hagedorn W. 
Published: April 2003

AbstractThe Raman spectrum of partially crystalline polyethylene can be described as a superposition of three components, which originate from the orthorhombic crystalline phase, a meltlike amorphous phase, and a disordered phase of anisotropic nature, where chains are stretched but have lost their lateral order. The mass fractions involved in the three phases can be derived directly from the integral intensities of characteristic bands without an additional calibration procedure. A comparison of the results obtained for a variety of samples shows agreement with the crystallinities derived from the density, and the small‐angle and wide‐angle x‐ray diagrams. Data indicate that the disordered anisotropic phase is located at a transition zone between crystalline and amorphous layers. Application of the method in a temperature‐dependence experiment permits a detailed examination of partial melting.
Growth kinetics of solvent crazes in glassy polymers
Authors: Kramer Edward J. , Bubeck Robert A. 
Published: April 2003

AbstractThe kinetics of craze growth from sharp cracks in polystyrene (PS) and poly(methyl methacrylate) (PMMA) in contact with liquid methanol were measured with time‐lapse photography as a function of the stress intensity factor KI. At high KI the craze length in both systems increases as √t if the sides of the craze are protected from methanol and as t if they are not, where t is the elapsed time after loading. If such a side‐protected craze is dried under load and then methanol is reintroduced to the crack tip, the methanol front advances with the same kinetics as the original craze growth. This experiment Proves that solvent crazing velocities are limited by the hydrodynamic transport of solvent through the porous craze structure under a capillary pressure driving force (which can be as high as 100 atm). An improved model of fluid flow through the craze is developed and shown to predict craze growth kinetics in good agreement with those observed. The hydraulic permeability of methanol crazes in PS was found to be independent of craze length at small craze length and to be independent of KI except at very low KI. Although increases in molecular weight in the range Mw = 200,000 to Mw = 670,000 do not markedly affect the crazing kinetics, they greatly increase the time to fracture of the craze.
Ion‐aggregation and thermal expansion in styrene‐based ionomers
Authors: Eisenberg A. , Trepman E. 
Published: April 2003

AbstractThe linear thermal‐expansion coefficients (α) of styrene–sodium methacrylate copolymers were studied as a function of the concentration of sodium methacrylate comonomer. Over the concentration range studied (0.61–9.0 mole % sodium methacrylate), the expansion coefficients of the glass αg and of the liquid αl were independent of ion concentration. Average values for these quantities were αg = (6.9 ± 0.9) × 10−5 deg−1 and αl = (16.0 ± 2.0) × 10−5 deg−1. When samples of concentrations above 6 mole % were heated from room temperature, a low value for the liquid‐expansion coefficient αl was observed in the first runs. This quantity had an average value of (12.0 ± 1.9) × 10−5 deg−1. Heating of the 6.5 mole % sample from room temperature followed by cycling from the glass transition temperature Tg to successively higher temperatures resulted in a gradual increase in liquid‐expansion coefficient. The results are consistent with the hypothesis of the existence of various types of ionic aggregates in these polymers, with the state of aggregation changing at approximately (5–6) % of ions. Experimental Tg values, which increase with ion concentration over the entire range, are consistent with the results of previous studies.
The structure and properties of oriented fibers of poly(pentamethylene terephthalate). I. Synthesis of polymer and preparation of two different crystalline phases
Authors: Hall I. H. , Pass M. G. , Rammo N. N. 
Published: April 2003

AbstractThe synthesis of poly(pentamethylene terephthalate) and its subsequent drawing into highly oriented fiber has proved difficult for two reasons. First, it was difficult to produce polymers of sufficiently high molecular weight to withstand subsequent drawing; and second, because of the slow rate of crystallization of the material, the spun fiber coalesced on the windup bobbin, becoming useless for drawing. Methods are described which overcome these difficulties. Two crystalline phases of the oriented fiber have been discovered. The α form is obtained by annealing under zero or small tension and has a crystallographic repeat along the fiber axis of 24.7 Å compared with a chemical repeat of 14.5 Å. There are evidently two monomers per crystallographic repeat, each appreciably contracted. The β form is obtained by annealing either under high tension or at constant extended length, but in the relaxed fiber it always exists in mixture with the α form. Its crystallographic repeat is 28.2 Å, and so again consists of two monomers; but their conformation is more highly extended than that of the α form. An α‐form fiber will transform reversibly to the β form under the influence of mechanical stress.
Structural relaxation in poly(vinyl acetate)
Authors: Sasabe Hiroyuki , Moynihan Cornelius T. 
Published: April 2003

AbstractStructural relaxation in poly(vinyl acetate) (PVAc) in and slightly above the glass‐transition region has been studied by monitoring the time dependence of enthalpy using differential scanning calorimetry and the frequency dependence of electric polarization by dielectric loss measurements. The results have been analyzed to yield the kinetic parameters characterizing the structural relaxation and are compared with similar analyses of previously published shear compliance and volume relaxation experiments. Relaxation of enthalpy, electric polarization, volume, and shear stress in PVAc all appear to be characterized by somewhat different relaxation times. The difference between the volume and enthalpy relaxation times, coupled with the fact that PVAc exhibits a Prigogine–Defay ratio greater than unity, is evidence for a previously proposed connection between the thermodynamics and kinetics of structural relaxation in terms of an order parameter model.
Time‐resolved fluorescence spectroscopy of polystyrene and poly(1‐vinylnaphthalene)
Authors: Ghiggino K. P. , Wright R. D. , Phillips D. 
Published: April 2003

AbstractAn apparatus is described which enables the rapid recording of time‐resolved emission spectra on a nanosecond time scale. The instrument permits detailed study of the time‐dependent photo‐physical processes occurring in many polymer systems. The technique has been used to investigate the kinetics of excimer formation in methylene chloride solutions of polystyrene and poly(1‐vinyl‐naphthalene). Unambiguous evidence for excimer dissociation is observed in poly(1‐vinylnaphthalene) but the process appears unimportant in solutions of polystyrene.
Study of the molecular motions of polyethylene by line‐shape analysis of broad‐line proton NMR spectra
Authors: Bergmann Klaus 
Published: April 2003

AbstractThe broad‐line proton NMR spectra of polyethylene are separated into three components (broad, medium, and narrow) corresponding to the crystalline and two kinds of amorphous protons, respectively. All amorphous protons are found to be mobile above 210°K. The unusually low molecular mobility in the amorphous regions of polyethylene compared to purely amorphous and other partially crystalline polymers is considered to be adequately described by the network model of Edwards and De Gennes. In this model the chain motions are anisotropic and restricted to small tubular volumes. The medium and the narrow component are believed to result from two different modes of chain motion within these tubes, depending on the free volume available. Two motions in the crystalline regions are observed. One at temperatures below 110°K involves 2%–5% of the protons, depending on the crystallinity of the material, and the other beginning at 290°K involves all crystalline protons (α‐process). Coupling of the amorphous and crystalline motions is found above 290°K. Several line shapes have been tested as representations of the three components. Of these the low‐temperature spectrum, the Gauss–Lorentz product curve, and the Lorentz curve proved to be the most suitable shapes for the broad, medium, and narrow component, respectively. Using these line shapes, the best fit of the experimental spectra and the expected agreement of the broad and the crystalline fraction are obtained over a very broad temperature range. Above 310°K the low‐temperature spectrum must be replaced by the convolution of a Gauss curve and a rectangular function to take into account the line‐shape transition of the α‐process. The modulation broadening of all components is considered, and this allows line‐shape analysis close to the melting point.
An approximate method of determination of birefringence of circular fibers from intensity distribution of backscattered light
Authors: Holoubek Jaroslav 
Published: April 2003

AbstractA method proposed for determination of high birefringence values of circular fibers is based on an analysis of the intensity of backscattered light for two orthogonal polarization directions of the incident light. The method has been used in the determination of birefringence of nylon 6‐6 fiber from a circular photographic recording of scattered light. The values thus obtained are compared with those obtained by polarized light microscopy.