bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aspects of plastic scintillators. II. Energy transfer studies in polymerizing media
Authors: Neilson R. D. M. , Soutar I. , Steedman W. 
Published: April 2003

AbstractChanges in scintillation efficiency during formation of plastic scintillator compositions have been studied. The separate roles of energy transfer and solute fluorescence efficiencies in the determination of the observed luminescence output of the systems were elucidated. Bis‐1,4‐2‐(5‐phenyloxazolyl)benzene(POPOP); 1,1′,4,4′‐tetraphenylbutadiene(TPB), and 9‐methyl anthracene (MAN) were employed as scintillator solutes. The increased scintillation yield of polymerizing solutions of POPOP is primarily a consequence of increased energy transfer efficiency from solvent to solute. Solutions of TPB exhibit enormous increases in luminescence output upon formation of polymers. The major contributor to the overall effect is the great enhancement of the fluorescence efficiency of TPB which occurs when the microviscosity of the medium is increased. MAN solutions exhibit a decreasing luminescence yield upon polymerization despite increasing energy transfer efficiency. Structural rearrangements of the fluor, consequent upon involvement in the polymerization kinetic chain, are responsible for the decreased scintillation efficiency.
Internal viscosity in the dynamics of polymer molecules. II. A new model for the Lamb–Matheson–Philippoff increment
Authors: Macinnes D. A. 
Published: April 2003

AbstractWe propose a new model for the Lamb–Matheson–Philippoff (LMP) increment in the dynamical viscosity of polystyrene solutions. The crucial difference between the new model and the currently accepted models is that our model predicts that at least a large part of the LMP increment relaxes at a particular frequency, whereas the conventional models predict a nonrelaxing increment. In order to derive our model, we reformulate the internal viscosity (IV) concept, for a fluid undergoing shear, in such a way that the shear filed appears explicitly in the IV resistance. Since the derivation of this IV model is nonrigorous and produces a result which may be surprising, we rederive the dynamical viscosity using a correlation function technique, into which the flow field does not enter explicitly. We show that our model predicts the principal experimental results on the LMP increment as well as the conventional models do, but that our model gives a result which is more in line with current thinking (i.e., that the increment might be expected to undergo relaxation). We also show that our model accurately predicts an “anomalous” result obtained recently on the viscoelastic absorption spectrum of poly(propylene glycol) melts, the description of which is quite outside the scope of the Rouse–Zimm model or the currently accepted IV model.
Effects of diluent on molecular motion and glass transitions in polymers. III. The system poly(vinyl acetate)–toluene
Authors: Adachi Keiichiro , Hattori Mitsuhiro , Ishida Yoichi 
Published: April 2003

AbstractDielectric measurements, differential thermal analyses (DTA), and broad‐line proton magnetic resonance (NMR) measurements are reported on the system poly(vinyl acetate)–toluene. Four dielectric relaxations were observed between 80 and 400°K. From proton NMR measurements on solutions in toluene and in deuterated toluene, the relaxation processes can be assigned, respectively, to segmental motion of poly(vinyl acetate), α; motion of side group, β′ rotation of toluene, β; local motions of poly(vinyl acetate) and toluene, γ, in order of appearance with decreasing temperature. Two stepwise changes in DTA traces have been observed and can be assigned as glass transition points TgI and TgII. Comparison of these glass transition points with temperatures at which dielectric relaxation times for the α and β processes are 100 sec, indicate that segmental motion of poly(vinyl acetate) and rotation of toluene are frozen‐in at TgI and TgII, respectively. Activation plots for the α process conform to the Vogel–Tamman equation. In terms of the parameters A, B, and T0 of the equation, TgI can be represented by an expression of the form TgI ≈ T0 + B/(A + 3). In the range of concentration above 50% by weight, A and B are almost independent of concentration but T0 varies strongly. The nature of the secondary dispersions is also discussed.
A new method for the study of molecular motion in polymeric solids: Thermally stimulated creep
Authors: Monpagens J. C. , Chatain D. G. , Lacabanne C. , Gautier P. G. 
Published: April 2003

AbstractWe propose a new method for the investigation of molecular motion in polymeric solids. In a mechanical step‐function experiment, we thermally stimulate the response to a constant stress. The high resolving power of this technique permits detailed study of the complex retardation modes observed in polymers. As an example, we consider the thermally stimulated creep of low density polyethylene. The experimental resolution of the thermally stimulated creep spectra shows the existence of elementary processes well fitted by the assumption of single retardation times.
Structural changes on hot‐rolling of polyethylene. I. Crystallite orientation and lamellar deformation
Authors: Yoda Osamu , Kuriyama Isamu 
Published: April 2003

AbstractThe crystallite orientation and lamellar deformation produced by hot‐rolling in polyethylene have been investigated. In the lightly rolled stage, the [110]* axis of polyethylene crystals orientates in the plane perpendicular to the rolling direction and the c axis becomes aligned with the rolling direction. In the heavily rolled stage the a, b, and c axes coincide with the macroscopic directions in the sample. These orientational changes are interpreted in terms of a slip mechanism. Small‐angle x‐ray scattering (SAXS) investigations of hot‐rolled polyethylene show the following. (1) There are two kinds of lamellar structures; one in which inclined lamellae give a four‐point diagram in the SAXS photograph and another in which lamellar normals are oriented around the rolling direction even at the lightly rolled stage. The latter structure is attributed to the mechanism of unfolding and recrystallization. (2) The chain‐fold length in the original structure remains unchanged in the lamellae up to a roll ratio of four although the apparent long period decreases. This is explained by inclination of polymer chains in the lamellae. Further rolling aligns the polymer chains with the rolling direction and the fold length decreases.
Effect of drawing on the melting point and heat of fusion of polyethylene
Authors: Sumita Masao , Miyasaka Keizo , Ishikawa Kinzo 
Published: April 2003

AbstractThe melting point and the heat of fusion were measured by differential scanning calorimetry (DSC) as a function of draw ratio for linear polyethylene. Both the melting point and the heat of fusion increased with an increase in draw ratio. The plot of the heat of fusion against the melting point was approximately linear. The linear relation is explained theoretically using the assumption that the increases in the melting point and the heat of fusion are due to the orientation of the amorphous phase caused by drawing. The excess free energy of the amorphous phase derived from the orientation increases the melting point, and the amorphous phase absorbs heat for its randomization at the melting point. Hence for drawn samples having an oriented amorphous phase not only the crystal phase but also the amorphous phase contribute to the heat of fusion.
General properties of secondary relaxations in polymers as determined by the thermally stimulated current method
Authors: Vanderschueren J. 
Published: April 2003

AbstractThe method of thermally stimulated current (TSC) has been used to study the low‐temperature dielectric β relaxations of several polymers including especially poly(vinyl chloride), poly(vinyl acetate), polyamide 6, 6,6,poly(t‐butyl acrylate), poly(methyl methacrylate), poly(ethyl methacrylate), poly(phenyl methacrylate), and poly(t‐butyl methacrylate). The distribution characteristics of the relaxation processes have been determined from the corresponding TSC peaks by a fractional polarization technique which consists of applying the electric field in several discrete steps during a slow cooling. Several common features have been found in all the polymers investigated: the β peaks are characterized by a distribution of relaxation times resulting from a distribution in activation energy and this distribution is quasisymmetrical and continuous. These facts are in agreement with the hypothesis of a relaxation involving local motions of small polar groups undergoing various interactions with the environment. Some discrepancy remains, however, between our calculated values of the mean activation energy and those obtained from the dielectric loss.
Dielectric study on copolymers in dilute solution. Relaxation behavior of methyl methacrylate–styrene and methyl methacrylate–α‐methylstyrene copolymers
Authors: Iwasa Yasuo , Chiba Akio 
Published: April 2003

AbstractDielectric measurements were made on some methyl methacrylate (MMA)‐related polymers in dilute solution, in the frequency range of 1–150 MHz. Effects of the solvent viscosity upon the relaxation behavior were carefully examined. The dielectric relaxation of MMA–styrene copolymers with a high content of MMA units as well as that of the MMA–α‐methylstyrene copolymer was little affected by the solvent viscosity. With the aid of Kramers'rate constant for small friction, it was found that their dipolar relaxation is very similar to that caused by the internal rotation of a flexible side‐chain. On the other hand, MMA–styrene copolymer with a low content of MMA units showed a diffusion‐controlled relaxation process, which can be interpreted in terms of Kramers' theory for large friction. In the latter case, the dipolar relaxation appears to reflect a molecular motion such as sweeping out solvent molecules. These results indicate that it is not the dipole itself but its environment, or rather the local molecular structure containing dipoles, that principally controls the relaxation process. On this basis, we propose a criterion, for quantitatively distinguishing the two relaxation mechanisms from each other.
Hydrogen catalysis of alkyl radical decay in single crystalline polyethylene
Authors: Patel V. M. , Dole Malcolm 
Published: April 2003

AbstractAlthough hydrogen gas is about tenfold more soluble in hot‐filtered mats of polyethylene (PE) single crystals (SC) than in bulk linear PE, we found that no hydrogen solubility at all could be measured in freeze‐dried SC. Despite this, hydrogen gas still exerts a catalytic effect on alkyl radical decay on both the fast and slow first‐order decay reactions in the freeze‐dried samples. Above 40°C the first‐order decay constants of the slowly decaying component decrease with increasing fold period.
Study of the viscoelastic behavior of uncrosslinked (gum) rubbers in moderately large deformations
Authors: Chang W. V. , Bloch R. , Tschoegl N. W. 
Published: April 2003

AbstractTwo models, one for materials possessing a well‐defined reference state (solid‐like behavior, model S), the other for materials lacking such reference (liquid‐like behavior, model L) were tested with the aid of experimental data obtained in various strain histories in simple tension on an uncrosslinked styrene–butadiene rubber (SBR) gum rubber over the temperature range from −20 to 23°C.The models resulted from the introduction of the nonlinear n‐measure of strain into the Boltzmann superposition integral. Both gave excellent predictions of the response of the SBR to step and to ramp functions of strain. Published data on the response of polyisobutylene to an exponential stretch ratio excitation were in similarly good agreement with both models. Sensitive tests in which small deformations were superposed on a finite stretch allowed a distinction to be made in favor of model S.In uncrosslinked materials the strain parameter n was found to be small (typically about 0.5) and sensibly independent of temperature in the range investigated. By contrast, in crosslinked rubbers, n is typically between 1 and 2 at room temperature and generally decreases with temperature. The dependence of n on the nature of the material, crosslink density, temperature, and crosslinking conditions was examined.
Plastic fracture
Authors: Cornes P. L. , Smith K. , Haward R. N. 
Published: April 2003

AbstractIt has been previously shown that when rigid poly(vinyl chloride) is extended by fully necking the test‐piece, subsequent fracture takes place by a novel mechanism. Surface crazes grow into “diamond” ‐shaped cavities which slowly expand while retaining their shape. We have now found that this new mechanism is of general applicability to a wide range of plastics which fracture after yielding. Examples are given from polycarbonate, poly(ether sulfone), and poly(methyl methacrylate) broken at elevated temperatures. The form of the diamond cavity is determined by the continuation of plastic deformation in the whole test‐piece while the diamond grows bigger. After fracture a characteristic cavity is left behind on the fracture surface which demarcates the zone of slow growth. At a given point, which is generally easily observable on the fracture surface, the crack speeds up. This change is believed to correspond to a situation where enough elastic energy is available to propagate a crack. It is favored, not only by the increase in size of the diamond in the test‐piece but also by an increase in the average energy stored per unit volume of material.
Thermoluminescence of irradiated poly(methyl methacrylate)
Authors: Radhakrishna S. , Murthy M. Rama Krishna 
Published: April 2003

AbstractThermoluminescence of poly(methyl methacrylate) (PMMA) irradiated with x rays, has been studied in the temperature range 100 to 460°K. Two glow peaks with maxima at 136 and 368°K have been observed. These are analyzed by three methods and the results are compared. Both curves obey second order kinetics and correspond to activation energies of 0.17 and 0.88 eV, respectively. It is possible to identify the centers responsible for the two peaks by correlation with electron spin resonance and optical data obtained for the same samples irradiated under the same conditions. Spectral studies of the emission show that the low temperature peak has its maximum at 365 nm while the high temperature peak has its maximum at 480 nm.
The effect of molecular weight heterogeneity on the second virial coefficient of linear polymers in good solvents
Authors: Noda Ichiro , Kitano Toshiaki , Nagasawa Mitsuru 
Published: April 2003

AbstractThe effect of molecular weight heterogeneity on the second virial coefficient A2 in good solvents is studied for binary mixtures of monodisperse poly(α‐methylstyrenes). It is concluded that A2 for polymer mixtures passes through a maximum with variation of the mixing ration. From comparison with the data, it is concluded that no available theory quantitatively explains both the molecular weight dependence of A2 of monodisperse polymer and the variation of A2 of mixtures with the mixing ratio. The interpenetration function for two polymer coils with different molecular weights is discussed on the assumption that the thermodynamic interaction between two polymer coils in good solvents can be approximated by a hard‐sphere model.
A fourier transform infrared spectroscopic investigation of polyethylene single crystals. II. Fine structure of the CH2 rocking mode
Authors: Painter P. C. , Havens J. , Hart W. W. , Koenig J. L. 
Published: April 2003

AbstractThe application of the spectral subtraction routine to an analysis of the CH2 rocking mode of polyethylene single crystals is discussed. A difference band at 716 cm−1 characteristic of a local monoclinic arrangement of chains is detected. Oxidation of crystal mats by nitric acid indicates that these defect structures are located inside the crystal and are not associated with the fold surface.
Thermoluminescence of irradiated polystyrene
Authors: Radhakrishna S. , Murthy M. Rama Krishna 
Published: April 2003

AbstractThermoluminescence of irradiated polystyrene has been studied in the temperature range 100 to 440°K. Three glow peaks with maximum at 160, 221, and 378°K have been observed. These peaks are analyzed by different methods and the activation energies which were obtained are compared. The activation energies are found to be 0.22, 0.48, and 1.45 eV for the peaks with maxima at 160, 221, and 378°K, respectively. Second‐order kinetics is appropriate to all these cases. The glow peaks are attributed to the decay of the free radicals formed on irradiation and subsequent thermal stimulation. The peak with the maximum at 160°K is attributed to electron trapping by the carbonyl groups or peroxy radicals formed on irradiation. The curve with the peak at 221°K is attributed to the cyclohexadienyl radical, and the curve with the peak at 378°K is attributed to the chain radical CH2C (C6H5)CH2. The centers responsible for the observed thermoluminescence are identified by correlation with electron spin resonance (ESR) data obtained on the same samples.
Crystallization of bisphenol‐A polycarbonate. II. Melting behavior and equilibrium melting temperature of the plasticized polymer
Authors: Legras R. , Mercier J. P. 
Published: April 2003

AbstractThe melting behavior of bisphenol‐A polycarbonate samples plasticized by tritolyl phosphate (TTP), pentaerythritol tetranonanoate (PETN), and trimellitic acid–tridecyloctyl ester (TMDO) has been investigated and discussed on the basis of current theories. Using the Hoffman and Weeks approach modified for finite chain length, the variation of the equilibrium melting temperature has been determined as a function of the plasticizer concentration. Extrapolation of these data yields an equilibrium melting temperature of 317°C for the pure polycarbonate of infinite molecular weight. This figure greacly exceeds the value so far reported in previous publications. It is also shown that the compatibility of the plasticizer affects the melting temperature just as it controls the glass transition. The cryoscopic effect observed, however, is much more pronounced than anticipated on the basis of the Flory–Huggins theory.
Solid‐state relaxations in poly(ethylene oxide). I. Study using the differential scanning calorimetry method
Authors: Lang M. C. , Noël C. , Legrand A. P. 
Published: April 2003

AbstractDifferential scanning calorimetry (DSC) studies show that poly(ethylene oxide) (PEO) exhibits three transition regions below its melting point. The effects of annealing on the intensity and temperature of these transitions enable us to locate T < Tg (Tγ) Tg, and Tα at about 130–140. 190–240, and 263–313°K, respectively. Our results argue for a small transition Tg (L) at 190–200°K with a second Tg (U) above 233°K, the temperature of which increases on annealing. The shape of DSC derivative curves reveals that T < Tg and Tα are complex and suggests the possibility of two steps in these processes. In addition, a splitting of Tα is observed every time a multiple melting endotherm appears as a result of annealing. Up to three separate melting endotherms can be observed. One of them is related to the normal primary crystallization process. Its peak temperature increases linearly with the annealing temperature, yielding an extrapolated value for the equilibrium melting temperature T of 347°K as found before.
Fluorine magnetic relaxation in poly(p‐fluorostyrene) and poly(m‐fluorostyrene)
Authors: Matsuo Keizo , Kuhlmann K. F. , Yang H. W.‐H. , Gény F. , Stockmayer W. H. , Jones Alan Anthony 
Published: April 2003

AbstractThe spin‐lattice relaxation time and the nuclear Overhauser enhancement (NOE) of 19F nuclei in dilute solutions of poly(p‐fluorostyrene) and poly(m‐fluorostyrene) were measured as a function of molecular weight, concentration, temperature, solvent, and field strength. Models for local motion of the chain backbone based on independent internal rotations or on one‐dimensional defect diffusion failed to provide a quantitative description of both T1 and the NOE. A model based on three‐bond crankshaft motions and a cutoff of coupling along the backbone gives a consistent account of these results as well as 13C nuclear magnetic resonance (NMR) relaxation data on polystyrene from the literature. The model provides a finite set of exponential correlation times to describe local motion, the center of the distribution lying in the nanosecond region for dilute solutions of polystyrenes in normal solvents. The apparent activation energy for the backbone motion obtained from the temperature dependence of the average correlation time based on NMR data is about 20 kJ mole−1. The local correlation times based on NMR are appreciably shorter than those determined by dielectric relaxation. This discrepancy points to the existence of several different local motions which make different contributions depending upon the experimental technique employed.
Thermally induced conformational changes in poly(vinyl chloride)
Authors: Koenig J. L. , Antoon M. K. 
Published: April 2003

AbstractFourier transform infrared spectroscopy has been used for the detection of thermally induced conformational changes in atactic poly(vinyl chloride) (PVC). Difference spectra emphasize changes in the distribution of gauche defects in the chains as functions of temperature and annealing. Specific bands in the ν(CCl) and δ(CH2) regions varied with inverse temperature, allowing a calculation of the activation energies of the rotamer species. Conformational changes were also detected in quenched PVC films as a result of annealing below the glass transition temperature, Tg.
Monomer distributions and number‐average sequence lengths in hydrogenated butadiene–styrene copolymers from carbon‐13 nuclear magnetic resonance
Authors: Randall James C. 
Published: April 2003

AbstractMonomer distributions and number‐average sequence lengths are determined from 13C nuclear magnetic resonance (NMR) data for 1,4‐ and 1,2‐butadiene additions and styrene additions in a series of four hydrogenated butadiene–styrene copolymers. The monomer distribution is expressed in terms of the six unique days from which it is possible to calculate the number‐average sequence length of each monomer type. Carbon‐13 NMR spectral assignments are given and the techniques for making the assignments are discussed. The method presented could, in principle, be applied to any copolymer or terpolymer. Limitations that are encountered in the analysis of hydrogenated butadiene–styrene copolymers high in 1,2 additions are discussed.