bluuebunny/crossref_metadata_2025_split huggingface dataset:
Permeation of dimethyl sulfoxide through polyethylene membraness
Authors: Stern S. A. , Britton G. W. 
Published: April 2003

AbstractPermeability and diffusion coefficients for dimethyl sulfoxide (DMSO) in polyethylene have been measured by the “time‐lag” technique and found to be affected by the adsorption of DMSO vapor in the low‐pressure side of the apparatus. An analytical method is described for correcting the apparent permeability coefficients for such adsorption effects. “True” permeability coefficients for DMSO in polyethylene, expressed in units of cm3(STP) – cm/(sec‐cm2‐cmHg), vary from 0.92 X 10‐7 at 30°C to 1.7 X 10‐7 at 45°C, and their dependence on relative DMSO pressure appears to be small. The energy of activation for the permeation process is 7.1 kcal/mole. The described correction method is also applicable to the permeation of water vapor through polyethylene and poly‐(phenylene oxide). The apparent diffusion coefficients could not be corrected by this method. The solubility of DMSO in polyethylene was measured with a Bakr‐McBain balance and found to be very small; solubility coefficients are less than 0.8 cm3(STP) DMSO/(cm3 polymer‐cmHg). It is concluded that the transport and solution behavior of DMSO in polyethylene is more similar to that of water vapor than to the corresponding behavior of organic vapors.
Crystallization and melting of poly(2,6‐dimethyl‐1,4‐phenylene oxide) in ternary mixtures with toluene and polystyrene
Authors: Shultz A. R. , McCullough C. R. 
Published: April 2003

AbstractThe crystallization and melting temperatures of an unfractionated poly(2,6‐dimethyl 1,4‐phenylene oxide) (PPO) sample, PM2, were determined at 0.25°C/min cooling and heating rates in five binary toluene—PM2 and fifteen ternary toluene—polystyrene—PM2 solutions. The total polymer weight fraction range studied was 0.12–0.40 and the PM2 weight fraction range was 0.026–0.40. The heat of fusion Hf of the PM2 was computed to be 10.1 cal/g from the melting point depressions. A toluene—PM2 pair interaction parameter χ13 = 0.890 – 223.5/T was found. Although a reliable polystyrene–PM2 interaction parameter could not be computed, the data are consistent with χ23 = 0. Setting χ23 = 0 we calculate the toluene—polystyrene interaction parameter to be χ12 = 0.495 – 15.46/T. This χ12 is in remarkable agreement with values reported in osmotic pressure studies.
Laser‐raman study of crystallinity changes in poly(ethylene terephthalate)
Authors: Melveger A. J. 
Published: April 2003

AbstractThe bandwidth at one‐half maximum intensity of the Raman‐active CO stretching vibration was found to correlate with density in poly(ethylene terephthalate). This correlation is valid for unoriented as well as highly oriented materials. It is suggested that a number of rotational states of the terephthalate segment occur in the amorphous polymer. Crystallization causes a resonance‐stabilized planar conformation.
Relation between the refractive index increment and the density increment of binary mixtures: Application to the determination of partial specific volumes of polymers in solution
Authors: Scholte Th. G. 
Published: April 2003

AbstractStarting from the Lorentz‐Lorenz equation, Heller, a few years ago, advanced a method for calculating the partial specific volume of a substance in a dilute solution from the refractive index increment of the solution and the specific refraction of the solute. It is shown that this method, based on graphical extrapolation, can be considerably simplified. Further, a method is indicated by which the partial specific volume of a substance over the whole range of concentrations can be calculated in an analogous manner. The method is checked and elucidated with reference to some experimental examples.
Molecular fracture in natural rubber during tensile testing at low temperatures
Authors: Natarajan R. , Reed P. E. 
Published: April 2003

AbstractSulfur‐cured natural rubber and other elastomers subjected to tensile tests at low temperatures and low strain rates are found to swell and “foam” after testing when brought to room temperature. The conditions under which this phenomenon can occur are established and related to load‐extension curves. Free radicals formed during tensile testing are studied by electron spin resonance (ESR) techniques. It is found that the free radicals observed at the low temperatures are stable below the glass transition temperature of the material, and it is suggested that these radicals arise from mainchain fracture occurring during yielding of the material. The subsequent swelling at higher temperatures is found to be due to the expansion of environmental gases absorbed during tensile testing and to the release of hydrogen in certain cases from the materials tested. It is also suggested that yielding of the material which gives rise to these characteristics occurs by crazing of the material; the voids in the craze bands absorbing the environmental gases which subsequently cause the foaming at higher temperatures.
Empirical probability‐density functions for the radii of gyration of linear random‐flight chains
Authors: Hoffman Robert F. , Forsman W. C. 
Published: April 2003

AbstractA number of empirical equations are presented that are good approximations to computed probability density functions of the one, two and three‐dimentional radii of gyration of linear random‐flight chains. Equations are given that are in good agreement with the distributions over the range of the radii of most physical interest. Alternative equations are presented that give especially good fit for small values of the one and two‐di‐mensional radii.
Molecular weight and long‐chain branching distributions of some polybutadienes and styrene–butadiene rubbers. Determination by GPC and dilute solution viscometry
Authors: Kraus Gerard , Stacy C. J. 
Published: April 2003

AbstractA method described for the determination of molecular weight and long‐chain branching distributions of polymers requires no prior knowledge of the functional relation between branching frequency and molecular weight. It is based on preparative fractionation and viscometric and gel‐permeation chromatographic measurements on both fractions and whole polymer. The technique is applied to several polybutadienes and butadiene‐styrene copolymers differing widely in method of synthesis and pattern of long‐chain branching.
Dilute solution characterization of polyfluoroalkoxyphosphazenes
Authors: Hagnauer G. L. , Schneider N. S. 
Published: April 2003

AbstractResults from the dilute solution characterization of polyfluoroalkoxyphosphazenes in Freon ether (E2) solutions are reported. Anomalous viscosity data suggest that polymer aggregation sometimes occurs in E2 and may be caused by the presence of relatively few anomalous polar groups on the polymer backbone. Since small amounts of acetone added to the E2 solutions inhibit aggregate formation, samples are also characterized in an E2‐acetone mixed solvent. Light scattering and osmometry indicate that E2 and E2‐acetone (9.09% by volume) are theta solvents for the polymers. High molecular weights (M̄w < 3 × 106) and unusually broad molecular weight distributions (M̄w/M̄n < 16) are found. One polymer is fractionated by extracting solutions in 1,1,2‐trichloro‐1,2,2‐trifluoroethane with acetone. Although the samples are highly polydisperse, intrinsic viscosities correlate with number‐average molecular weights satisfying the Mark‐Houwink relation with the exponent a ≈ 1/2. The z‐average mean‐square radius of gyration increases linearly with molecular weight so that 〈S2〉g/M̄w ≈ 0.098. Because of the large polydispersity and unknown form of the distribution function, a quantitative interpretation of characterization results relating dilute solution parameters to polymer skeletal structure is not possible. The tentative conclusion is that the fluoroalkoxy‐substituted phosphazene polymers are relatively linear and therefore that the broad distribution of molecular weights must be due to some polymerization mechanism other than branching.
Structure of unsaturated polyester resins crosslinked with styrene as studied by raman spectroscopy
Authors: Koenig J. L. , Shih Peter T. K. 
Published: April 2003

AbstractAn unsaturated polyester resin and the styrene‐crosslinked polyester were studied with laser Raman spectroscopy. Following the polyesterification reaction, Raman measurements showed that the polyester contained 55% fumarate and 45% maleate unsaturation. Additionally, the glycol fragment was indicated to exist as the gauche isomer. The 1213 cm−1 line is assigned to the glycol‐ester linkage and can be measured to follow the conversion to polymer. After the crosslinking reaction, styrene was found to copolymerize preferentially with the fumarate unsaturation. There was no evidence of forming long‐chain polystyrene crosslinks. Our results indicate that, after crosslinking, 41% of the fumarates have reacted with styrene and there is an average of two styrene molecules in each link.
Conductivity of some semiconducting polyazophenylenes
Authors: Heleskivi J. , Löfgren B. 
Published: April 2003

AbstractThe electrical conductivity of a series of semiconducting polyazophenylenes was studied as a function of temperature and molecular weight in the temperature range 293–493°K and for molecular weights between 9500 and 62800. The compounds studied included poly‐2,4‐diminotoluene and poly‐2,5‐diaminotoluene. The temperature dependence of conductivity obeys the exponential law σ = σ0 exp {–Ea/kT}. All of the compounds studied show a break in the conductivity curve at a temperature of about 380°K with the slope of the curve greater at temperatures above 380°K. The activation energies Ea determined from the higher slopes are in the range 0.63–0.89 eV, and the corresponding σ0 values are in the range 10−4‐10° (ohm‐cm)−1. Both Ea and σ0 show a tendency to increase with increasing molecular weight such that the compensation law was valid. Activation energies and σ0 values determined from the (smaller) slope below the temperature of the break point showed a tendency to decrease with successive measurements on new samples. This indicates some kind of orientation effect, and conclusions concerning the properties of the material on basis of results below the break point are therefore difficult.
Sorption of propane and propylene in polyethylene
Authors: Santos Marcos Luiz Dos , Leitão Dorodame Moura 
Published: April 2003

AbstractMeasurements are reported of the solubility and concentration of propane and propylene in polyethylene, at temperatures from −30°C to +30°C and pressures from 1.68 to 3.52 atm. Solubility of both gases in polymer depends on penetrant activity. Henry's law is not obeyed at high values of the penetrant activity, i.e., in the vicinity of the condensation point of the gas. The interaction between the solvent and the polymer is independent of pressure and a function of temperature. The propylene‐polyethylene interaction seems to reach a maximum at 10°C within the range investigated. A physical mechanism, based on opposite effects of temperature upon polymer and penetrant, is suggested to explain the results.
Melting behavior of isotactic polystyrene
Authors: Lemstra P. J. , Kooistra T. , Challa G. 
Published: April 2003

AbstractThe melting behavior of isotactic polystyrene, crystallized from the melt and from dilute solutions in trans‐decalin, has been studied by differential scanning calorimetry and solubility measurements. The melting curves show 1, 2, or 3 melting endotherms. At large supercooling, crystallization from the melt produces a small melting endotherm just above the crystallization temperature Tc. This peak originates from secondary crystallization of melt trapped within the spherulites. The next melting endotherm is related to the normal primary crystallization process. Its peak temperature increases linearly with Tc, yielding an extrapolated value for the equilibrium melting temperature Tc° of 242 ± 1°C as found before. By self‐seeding, crystallization from the melt could be performed at much higher temperature to obtain melting temperatures as high as 243°C, giving rise to doubt about the value of Tc° found by extrapolation. For normal values of Tc and heating rate, an extra endotherm appears on the melting curve. Its peak temperature is the same for both melt‐crystallized and solution‐crystallized samples, and independent of Tc, but rises with decreasing heating rate. From the effects of heating rate and partial scanning on the ratio of peak areas and of previous heat treatment on dissolution temperature, it is concluded that this peak arises from the second one by continuous melting and recrystallization during the scan.
Interdependence of enthalpic and entropic contributions to the second osmotic virial coefficient
Authors: Wolf B. A. 
Published: April 2003

AbstractThe interdependence of the enthalpic contribution A2, H and the entropic contribution A2, s to the second osmotic virial coefficient for a given polymer‐solvent system has been investigated from the experimental and the theoretical point of view. Experimentally, the following common facts were observed for various systems at temperatures and pressures below the critical values for the solvent. Both the isobaric and isothermal dependences can be approximated over relatively wide ranges of A2, H by linear relations with a slope deviating only slightly, but in a characteristic manner from a value of −1. When the temperature is increased at constant pressure one moves along an isobar towards higher A2, H; when the pressure is increased at constant temperature, one moves along an isotherm in the opposite direction, i.e., towards lower A2, H. Theoretically this behavior can be described in a qualitative manner, starting from a relation derived by Patterson and Delmas on the basis of the Prigogine corresponding‐states theory. The reasons for the lack of quantitative agreement are discussed.
Measurement of surface area of polymer shavings
Authors: Salloum Robert J. , Eckert Roger E. 
Published: April 2003

AbstractA modified BET apparatus has been developed to measure the surface area of polymer samples in the range 0.2–3.0 m2. The sample holder is designed to permit easy entry for bulky samples, such as polymer shavings, which cannot be loaded through a capillary or exposed to the high temperature required to seal glass. Other apparatus modifications, which allow the accurate measurement of surface area, include the addition of a dibutyl phthalate differential manometer in conjunction with a pressure reservoir. Corrections for the dead volume, nonideality of nitrogen, and the thermal gradient in the sample holder are developed. Calibrations of the equipment with inorganic samples of known areas from 1.81 to 11.8 m2 gave highly accurate values of 1.74 to 11.6 m2. Results on high‐density polyethylene shavings showed precision in determinations and very close agreement in the value of 49.7 for C in the BET equation with the published value, 47.7.
Proposed GPC and intrinsic viscosity analyses of randomly crosslinked polymers having primary distributions of the schulz‐zimm form
Authors: Shultz A. R. 
Published: April 2003

AbstractA mathematical treatment is presented for the gel‐permeation chromatographic and intrinsic viscosity behavior of randomly crosslinked polymers having primary molecular weight distributions of the Schulz‐Zimm form. Kimura's serial solution of the integro‐differential equation derived by Saito for randomly crosslinked polymers is employed for the distribution function. The intrinsic viscosity of a molecule containing i crosslinks is assumed related to that of a linear molecule of the same number of units through [η]br/ = gi½[η]l where gi = (Rbr2)i/Rl2 = {[1 + (i/6)]½ + (4i/3π)}−½. Rbrand Rl denoting the root‐mean‐square radii of gyration of branched and linear chains of the same mass. It is also assumed that GPC elution is controlled by the hydrodynamic volumes of the molecules. Representative calculation results are displayed for polymers with a narrow primary distribution and the “most probable” primary distribution. Results for the latter polymers are compared with those previously obtained by a somewhat different mathematical approach.
Crazing of polystyrene containing two rubber balls: A model for ABS plastics
Authors: Matsuo M. , Wang Tsuey T. , Kwei T. K. 
Published: April 2003

AbstractIn order to study the crazing behavior in rubber‐toughened glassy polymers, polystyrene samples containing two rubber balls of the same diameter with varying separations have been prepared. They were subjected to simple tension, and their crazing behavior was observed. When the two balls are close together, the craze‐initiation stress is considerably lower than that of single‐ball samples. With increase in the distance between the two balls the craze‐initiation stress increases at first almost linearly and levels off when l/d reaches about 1.45, where l and d are the center‐to‐center distance and the diameter of the balls, respectively. When l is sufficiently small, the crazes are seen to develop extensively at the inner surfaces of the balls and finally bridge with each other. The crazes bridged between the balls expand largely in the plane perpendicular to the applied load.
Multiple melting transitions in natural rubber
Authors: Kim Hyo‐gun , Mandelkern L. 
Published: April 2003

AbstractDetailed studies of the fusion of natural rubber, following isothermal crystallization, has revealed a hitherto undetected low temperature transition which depends on the crystallization temperature. This transition is shown to be a melting phenomenon which is not caused by any polymorphic structural changes. It can be attributed to the formation of less stable crystallites which develop as the transition progresses.
Polymorphism in polymers. I. The equilibrium melting temperature of two crystalline modifications of trans‐1,4‐polyisoprene
Authors: Flanagan R. D. , Rijke A. M. 
Published: April 2003

AbstractDilatometric, calorimetric, and dissolution studies have been made of two crystalline modifications of trans‐1,4‐polyisoprene in order to determine their equilibrium melting temperatures. This parameter is of fundamental importance in the formal treatment of polymorphism in crystalline polymers. A consistent set of thermodynamic parameters has been derived for both crystalline modifications. The equilibrium melting temperature of the polymorph, which was previously observed to melt from carefully crystallized bulk material at 64°C, was calculated to be at least 82.4°C. The other form, which melts from the bulk at 74°C, has an equilibrium melting temperature of 79.5 ± 0.5°C. The trans‐1,4‐polyisoprene, crystallized by stirring n‐butyl acetate solutions at 49°C, was found by x‐ray diffraction to be in the first form and melts at 81.2 ± 0.5°C when very slow heating rates are applied. This melting temperature is very close to the independently derived equilibrium melting temperature and lends support to the possibility that extended chain crystals are present in these solution crystallized crystals. Using the newly found melting temperatures of the two crystalline modifications it can be derived from the free energies of fusion that the first crystalline form is more stable at temperatures above approximately 66°C, whereas the other form is more stable below this temperature.
Dynamic mechanical behavior of lightly crosslinked networks of poly(n‐butyl methacrylate) and poly(n‐butyl acrylate) in the rubberlike region
Authors: Hrouz J. , Janáček J. 
Published: April 2003

AbstractAn investigation was made of the dynamic mechanical behavior in the rubberlike region of poly(n‐butyl methacrylate) (PBuMA) and poly(n‐butyl acrylate) (PBuA) networks lightly crosslinked with ethylene dimethacrylate to concentrations from 10−6 to 10−4 mole/cm3. The measurements were carried out by use of an apparatus for low‐frequency forced vibrations working in the frequency range 2.5 × 10−4 to 1 Hz. With parameters c1 and c2 of the Williams‐Landel‐Ferry equation, obtained from data in the main transition region, the data did not reduce in the rubberlike region for the poly(butyl methacrylate) networks; the spread of the deviations decreases with increasing concentration of the crosslinking agent. Superposition could be achieved in all cases when a shift factor was used on the vertical axis. At sufficiently low reduced frequencies and at high temperatures the storage compliance decreases in both series of polymers with increasing concentration of the crosslinking agent as expected. At higher reduced frequencies and at higher temperatures of measurement, however, anomalous behavior was observed with uncrosslinked samples having a lower compliance than those crosslinked to a very low degree. This finding was explained as due to very long relaxation times of the untrapped entanglements present in the noncrosslinked polymer, which are absent in the same polymer crosslinked already to very low degrees. The retardation spectra of both PBuMA and PBuA exhibited secondary relaxation mechanisms which were shifted by four logarithmic decades toward higher retardation times in comparison with the primary retardation maximum.
Fracture behavior in nylon 6 fibers
Authors: Lloyd B. A. , Devries K. L. , Williams M. L. 
Published: April 2003

AbstractA reaction rate model of fracture in polymer fibers is described. This model assumes that bond rupture is governed by absolute reaction rate theory with a stress‐aided activation energy. It is demonstrated that the key in obtaining good agreement between the model and experiment lies in taking proper account of the variation of stress on the tie‐chain molecules. The more taut chains rupture first, and the load is redistributed among the remaining unruptured tie chains. The effect of varying the temperature both in the model and in experiments on fracture in fibers is explored. Good agreement between predictions of the model and experiment is possible only with an undeterstanding of the distribution in stress on the tie chains. The distribution in stress on the chains was experimentally determined by monitoring the kinetics of bond rupture with electron paramagnetic resonance (EPR) spectroscopy. Temperature is found to have two effects on macroscopic strength. (1) The thermal energy aids the atomic stress in breaking the atomic bonds; as a consequence the rate of bond rupture of a family of bonds under a given molecular stress is increased. In this respect temperature might be viewed as decreasing the “strength” of a bond. (2) Temperature also serves to “loosen” the molecular structure and in this way modify the distribution in stress on the tie chains. To explain bond rupture and macroscopic fracture behavior quantitatively, account must be taken of both effects.