bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nylon 66 polymers. I. Molecular weight and compositional distribution
Authors: Burke J. J. , Orofino T. A. 
Published: April 2003

AbstractResults from characterization of melt‐polymerized nylon 66 by various solution property measurements are reported and employed in analysis of typical molecular weight and compositional distributions for these systems. Critical attention is paid to application of standard procedures including light scattering, viscosity, membrane osmometry and other colligative property measurements in arriving at satisfactory specification of polymer molecular weight averages. Particular consideration is given to polymers extending appreciably beyond the lower and higher limits in molecular weight normally encountered. The conclusions drawn are: (1) in the range of number‐average molecular weights less than about 25 000, nylon 66 as ordinarily prepared by melt condensation consists principally of linear species approximating the “most probable” distribution; (2) small amounts of cyclic oligomers are present in all samples: (3) increase in the extent of the melt polycondensation to progressively higher stages is accompanied by secondary reactions and the formation of branched components terminating ultimately in crosslinked, insoluble gels. Intrinsic viscosity–molecular weight relationships in seven solvents, applicable to nylon polymers meeting the requirements of (1) above, are derived.
Poly(1,2‐dimethyl‐5‐vinylpyridinium methyl sulfate). IV. Flocculation of crystalline silica
Authors: Shyluk W. P. , Smith R. W. 
Published: April 2003

AbstractSilica flocculated with a high molecular weight poly(DMVPMS) contains aggregates that are stable enough to permit size measurement with a Coulter counter. The average size of these aggregates increases up to a critical level of added polymer; the primary particles reappear at higher levels of added polymer. The aggregate size is reduced by continued mixing and the particle size distribution before flocculation is approached. Subsidence rates, equilibrium sediment volumes, and refiltration rates give somewhat different estimates of the degree of flocculation. Additional aggregation beyond that measured by the Coulter counter must be considered in the interpretation of these data. The decrease in floc strength during continued agitation is attributed to a disaggregation of the bridging polymer, to a decrease in the interparticle bonding of the bridging polymer, and to an increase in the surface coverage with polymer.
Weight distribution approach to the theory of random depolymerization of heterogeneous chains
Authors: Lee Sung Won 
Published: April 2003

AbstractThe random depolymerization model of Montroll and Simha for originally homogeneous polymers is derived analytically by utilizing a weight distribution function approach not requiring the use of any approximations. The model is then extended to consider heterogeneous initial chains having an arbitrary chain length distribution. The probabilities for breakage are assumed to be identical for all bonds joining monomeric elements in the system and to be independent of chain length and position in the chain, assumptions also used in the model of Montroll and Simha. An expression is found for estimating the probability of bond breakage.
Morphology of poly(vinylidene chloride) and of the carbons resulting from its pyrolysis
Authors: Bailey A. , Everett D. H. 
Published: April 2003

AbstractThis paper reports an electron microscopy study of the morphology of crystals of poly(vinylidene chloride) prepared under a variety of conditions and of the carbons resulting from the pyrolysis of the polymer. The structure of the polymer carbons prepared under conditions such that the polymer does not pass through a plastic phase is closely related to the morphology of the original polymer. The shapes of the crystals and of the crystal pseudomorphs are indexed in terms of the unit cell proposed by Narita and Okuda. Morphological studies of this kind are important in discussing the graphitizability of polymer carbons, their mechanical properties and pore structure, and the kinetics of the dehydrochlorination reaction.
Form birefringence in biaxially oriented polypropylene
Authors: Normandin L. M. , Legrand D. G. 
Published: April 2003

AbstractThe birefringence of several biaxially oriented polypropylene films swollen with a number of fluids has been measured and found to exhibit a minimum when plotted against the fluid refractive index, as predicted by the theory of Wiener. However, a discrepancy in the form birefringence behavior is observed when samples of different degrees of crystallinity but the same total birefringence are compared. These results are interpreted in terms of Bullough's theory and suggest that this discrepancy arises because of different morphologies. A refractometric technique was employed that makes possible the simultaneous determination of birefringence and the volume fraction of fluid.
Unperturbed dimension of poly‐N‐vinylcarbazole
Authors: Kuwahara Nobuhiro , Higashida Shiro , Nakata Mitsuo , Kaneko Motozo 
Published: April 2003

AbstractOsmotic‐pressure, viscosity, and light‐scattering measurements have been carried out on dilute solutions of poly‐N‐vinylcarbazole fractions (4 < 10‐4M < 230) in toluene, dioxane, and benzene. The theta temperature for poly‐N‐vinylcarbazole in toluene solutions has been found to be 37 ± 1°C. The intrinsic viscosity of poly‐N‐vinylcarbazole in toluene at 37°C is represented by [η]θ = 76.2 × 10−3M̄n0.50. Values of the characteristic ratios (〈L2〉0/M)1/2 and σ = (〈L2〉0/〈L2〉0f)1/2 have been obtained as 633 × 10−11 and 2.85, respectively. It appears that the large σ value is due to the steric repulsion between large side groups.
A new method for determination of intrinsic viscosity
Authors: Maron Samuel H. , Reznik Richard B. 
Published: April 2003

AbstractThe Huggins and Kraemer equations generally used to determine intrinsic viscosity frequently do not yield identical results, and their constants often do not add up to 1/2 as is mathematically required. To overcome these difficulties an equation has been deduced which through linear plots gives unambiguous intrinsic viscosities, constants which meet the 1/2 condition, as well as two other flow constants. Extensive tests of the equation with precise data on solutions of poly(methyl methacrylates) and polystyrenes in benzene and toluene confirm the validity of the new equation in every respect. It is further shown that the four constants involved are interrelated, and that it is possible to express the values of three of these in terms of the fourth.
Thermodynamics of swelling of polymer‐network gels. Analysis of excluded volume effects in polymer solutions and polymer networks
Authors: Mijnlieff P. F. , Jaspers W. J. M. 
Published: April 2003

AbstractThe assumed analogy between polymer solutions and polymer‐network gels as regards the thermodynamics of swelling—a fundamental assumption implicit in all previous analyses of swelling measurements on gels, aimed at checking the statistical theories of rubber elasticity—is shown in fact to be rather limited. In particular, excluded volume effects, which play a dominant role in both solutions and gels, are quite different in the two types of systems. A new thermodynamic description of swelling equilibria, taking account of differences in excluded volume effects, is given, and analogies and differences between gels and solutions are pointed out.
Study of low‐frequency molecular motions in polydimethylsiloxane polymers by neutron inelastic scattering
Authors: Henry A. W. , Safford G. J. 
Published: April 2003

AbstractThe intrachain and interchain vibrations below 900 cm−1 of polydimethylsiloxane (PDMS) have been studied by slow neutron inelastic scattering. A composite motion observed at +25°C for the methyl groups corresponds to nearly free rotation about the threefold axis of symmetry together with a large‐amplitude rotation of the entire methyl group. At −123°C, rotation about the threefold axis evolves to a torsional oscillation. The large‐amplitude rotation evolves to the skeletal vibrations of a helical conformation. Vestiges of the cooperative skeletal vibrations of the conformation at −123°C persist into the 25°C spectrum. The results indicate the presence of interrupted helical conformations at 25°C, which result from thermal disordering of the low temperature helices. The effects of crosslinking, low molecular‐weight oils, and silica filler on the freedom of the methyl group motions and on skeletal vibrations have been determined. The effects of different crosslinking agents and different relative amounts of filler and oil on both the macroscopic physical properties and the observed molecular motions of PDMS can also be interpreted in terms of an interrupted helix.
Energy transfer in polymer films: The nylon 66–proflavine system
Authors: Dearman H. H. , Lang F. T. , Neely W. C. 
Published: April 2003

AbstractTriplet → singlet energy transfer in nylon 66 film (donor) dyed with proflavine (acceptor) is demonstrated by a decrease of the nylon phosphoresence lifetime and an increase in the proflavine delayed fluorescence/nylon phosphoresence ratio with increasing proflavine concentration. Although the observed donor phosphorescence decay is apparently exponential, the transfer is probably via a long‐range dipole–dipole (Förster) interaction, rather than by triplet exciton migration. Arguments are advanced to support this view. Proflavine delayed fluorescence produced by a direct excitation process is also observed. The decay time for this process is roughly an order of magnitude less than that for the sensitized process. All emission intensities are shown to vary linearly with exciting light intensity. Finally, temperature dependence of proflavine delayed fluorescence under different excitation conditions is shown. The efficiency of direct excitation process increases markedly near −50°C as the temperature is increased; the sensitized delayed fluorescence intensity follows that of the nylon phosphorescence with increasing temperature, as expected.
Thermal analysis of polydimethylsiloxanes. I. Thermal degradation in controlled atmospheres
Authors: Thomas T. Howard , Kendrick T. C. 
Published: April 2003

AbstractThermogravimetric analyses (TGA) of catalyst‐free polydimethylsiloxanes (PDMS) have been carried out in controlled atmospheres and a kinetic analysis of the results has enabled the various decomposition processes to be separated and identified. The calculated activation energy for thermal depolymerization is 42 ± 3 kcal/mole, while thermo‐oxidation has an apparent activation energy of 30 ± 2 kcal/mole. Quantitative analyses of the major degradation products and molecular weight distribution studies of the residues from degradation studies under isothermal conditions have shown that in vacuo, PDMS fractions depolymerize to cyclic dimethylsiloxanes and low molecular weight linear residues by a randomly initiated mechanism which, it is postulated, involves the formation of an intramolecular, cyclic, four‐centered transition state followed by siloxane bond rearrangement. This mechanism is a basic property of linear PDMS fractions and is independent of molecular weight. Molecular weight distribution (MWD) changes observed from further isothermal investigations on hydroxy endblocked PDMS fractions, have shown the presence of a chain‐lengthening process in vacuo below the depolymerization temperature. This process, with an apparent activation energy of 8.6 ± 1 kcal/mole, is attributed to the intermolecular condensation of terminal hydroxyl groups.
Ultimate tensile properties of elastomers. V. Rupture in constrained biaxial tensions
Authors: Smith Thor L. , Rinde James A. 
Published: April 2003

AbstractThe strength and extensibility of an unfilled styrene‐butadiene rubber vulcanizate were determined in constrained biaxial tension (essentially pure shear) by stretching thinwalled cylindrical specimens in the axial direction with an Instron tester while gas pressure was admitted to maintain constant the outside diameter of a specimen. The rupture stress, λ1b, and the extension ratio, λ1b, in the axial direction and the rupture stress, σ2b, in the circumferential direction were determined at extension rates from 0.0031 to 3.1 min−1 and temperatures from 25 to 90°C. Rupture data in simple tension were also obtained by testing ring specimens under similar test conditions. The time‐temperature shift factor, aT, obtained by superposing rupture data at different temperatures, gives a constant activation energy of 35 kcal. Doubly logarithmic plots were prepared showing the dependence of σ1b/λ1b, σ2b, and λ1b from the biaxial tensile tests and of σb/λb and λb from the simple tensile tests on the temperature‐reduced extension rate, \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \lambda a_T $\end{document}. (The quantities σ1b/λ1b, σ2b, and σb/λb are rupture stresses based on the dimensions of undeformed specimens.) At equal values of \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \lambda a_T $\end{document}, the extension ratios λ1b and λb are sensibly identical. The ratios σ1b/σb and σ2b/σb, as well as λbσ2b/σb, were obtained from rupture data read from the composite curves at selected values of \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \lambda a_T $\end{document}. Also, similar ratios were derived from stress data at equal extensions in biaxial and simple tension for 1.25 ≤ λ ≤ 3.0, the range comparable to that in which rupture data were obtained. A consideration of the ratios given by both the rupture and the stress data shows that the von Mises failure criterion is not applicable, although the departure is small except at the larger values of λb.
Ultimate tensile properties of elastomers. VI. Strength and extensibility of a styrene–butadiene rubber vulcanizate in equal biaxial tension
Authors: Dickie Ray A. , Smith Thor L. 
Published: April 2003

AbstractThe ultimate properties of an unfilled styrene‐butadiene rubber vulcanizate in equal biaxial tension were determined by inflating a circular membrane into a bubble. Tests were made at several extension rates (evaluated at the pole) from about 0.15 to 4 min−1 and at temperatures from −43 to 90°C. The stress in the vicinity of the pole when rupture occurred was evaluated from the pressure, the radius of curvature, and the extension ratio λ, the latter two quantities being obtained from photographic data. Below 70°C, the ultimate extension ratio λb is approximately 5.2 and is essentially independent of extension rate and temperature, in striking contrast to the behavior in simple and constrained biaxial tension (pure shear). Likewise, the rupture stress is manyfold greater than in either simple or constrained biaxial tension. From the extremum points of failure envelopes, the maximum extension ratio (λb)max in equal biaxial tension is 5.7 and in simple tension is 7.2. An examination of ruptured membranes showed that, except at 70 and 90°C, rupture began away from the pole in a region where the stress state is unequal biaxial tension. Hence, values of the ultimate properties in truly equal biaxial tension are no doubt somewhat greater than those obtained from the membrane tests. However, it is shown that (λb)max in truly equal biaxial tension must be lower than that in simple tension by at least 10%. A consideration of rupture data in simple, constrained biaxial, and equal biaxial tension leads to the conclusion that no simple failure criterion is applicable for interrelating data obtained under the several states of combined stress. The rupture patterns and factors that affect the site of rupture initiation and the mode of crack growth are also discussed.
General description of optical (dichroic) orientation factors for relating optical anisotropy of bulk polymer to orientation of structural units. Part II. Fourth moments of orientation distribution and polarized fluorescence
Authors: Kimura Itsuro , Kagiyama Mitsuyasu , Nomura Shunji , Kawai Hiromichi 
Published: April 2003

AbstractA general description is given for relations among the optical quantities obtained from fluorescence polarization measurements on bulk polymer stained by fluorescent groups: the moments of distribution of orientations of the fluorescent groups, and those of the structural units of the polymer (chain segments) on which the groups are adsorbed. Two assumptions as to the biaxial symmetry of the bulk polymer and the cylindrical symmetry of the optical anisotropy of the fluorescent element, both for the absorption and emission processes, reduce the intensities of the polarized fluorescence to a 3 × 3 matrix L which is asymmetric (Lij ≠ Lji), as has frequently been observed in experiments. The components of the L matrix are related to those of the J matrix which is so defined as to describe the fourth moments of the distribution of orientations of the structural units on the basis of a random distribution of the rotational angle of the unit about the segment axis. It is found that the use of the method of fluorescence polarization combined with absorption dichroism and/or emission gives the values of the optical anisotropy ratios of the fluorescent unit, and that the effects of the thermal agitation of the structural unit can be separated from the moments of the orientation distribution for the simplest case.
Stress relaxation of natural rubber during irradiation
Authors: Evans D. , Morgan J. T. , Sheldon R. , Stapleton G. B. 
Published: April 2003

AbstractThe site of chain scission and crosslinking in vulcanized natural rubber irradiated with 4 MeV electrons has been determined by analysis of stress relaxation data. Sulfur and peroxide vulcanizates of different crosslink densities were prepared and the crosslink densities determined from stress‐strain measurements. Stress relaxation was measured during irradiation using modified commercial relaxometers. The specimens were maintained in an atmosphere of nitrogen to minimize oxidative side effects. Scission is deduced to take place in the vicinity of crosslinks, since the rate of continuous stress relaxation is independent of crosslink density. Scission may be associated both with crosslinks initially present and with those subsequently introduced by irradiation. Crosslinking by radiation is largely a random process. However, there is a crosslinking reaction dependent to a slight extent on crosslink density as well as a small contribution from random scission reactions. G values for the random reactions are given.
Yielding of oriented poly(vinyl chloride)
Authors: Rider J. G. , Hargreaves E. 
Published: April 2003

AbstractPoly(vinyl chloride) sheet was oriented by hot drawing. The yield behavior of the oriented sheet was then investigated under uniaxial tension at room temperature as a function of the angle between the tensile axis and the molecular alignment direction. The onset of yield was localized in deformation bands. The variation of yield stress with direction and the direction in which the deformation bands formed were found to be satisfactorily accounted for in terms of a yield criterion based on that of von Mises, provided that a term representing internal compressive stress in the molecular alignment direction was included. The internal stress was found to increase from zero with increasing draw ratio of the prior hot drawing. It is pointed out that other workers have found polymers to obey the yield criterion of Coulomb rather than that of von Mises.
Diffusion in glassy polymers. II
Authors: Frisch H. L. , Wang T. T. , Kwei T. K. 
Published: April 2003

AbstractThe Fickian diffusion coefficient of methylene chloride in a glassy epoxy polymer is calculated with the use of Crank's model of discontinuous change of D with concentration C. The diffusion constant is obtained as 1.93 × 10−6 cm2/sec. The swollen layer behind the advancing solvent front is essentially in the rubbery state of the same polymer. The case II swelling by benzene is discussed in terms of a convective transport arising from the partial stress (internal) tensor of the penetrant. The superposition of Fickian and case II diffusion found with mixtures of methylene chloride and benzene is also discussed briefly.
Diffusion and solubility of methane in polyisobutylene
Authors: Lundberg J. L. , Mooney E. J. , Rogers C. E. 
Published: April 2003

AbstractDiffusion coefficients and solubilities of methane in polyisobutylene have been measured at four temperatures between 102 and 188°C. in the pressure range 23–341 atm. Diffusion coefficients extrapolated to atmospheric pressure range from 1.72 × 10−6 cm.2/sec. at 102°C. to 1.5 × 10−5 cm.2/sec. at 188°C. corresponding to an activation energy for diffusion of 8.7 ± 0.4 kcal./mole. Solubilities are small, about one molecule of methane for every forty carbon atoms in the polyisobutylene at 300 atm. partial pressure of methane. Solubilities vary little with temperature, but show an apparent minimum between 127 and 188°C. With improved methods of data analysis, diffusion coefficients and solubilities have been recalculated from previously reported studies on nitrogen in branched polyethylene and methane in branched polyethylene, linear polyethylene, and polystyrene. Recalculated diffusion coefficients are essentially the same as those reported previously, but the recalculated solubilities are decreased from 2 to 30%. The solubilities of all five systems show strong deviations from Henry's law, i.e., increases in partial pressure of methane and nitrogen with respect to solubility exceed linearity. The partial pressure (or fugacity)—solubility data may be interpreted in terms of a sorption model in which sorbed molecules are accommodated in widely dispersed, unoccupied volumes or sites in the polymer. An almost equivalent, solution model in which the first sorbed molecules to enter the polymer are accommodated to a large extent in existing volumes in the polymer, with successively sorbed molecules swelling the polymer to a greater extent (i.e., partial molal volume of sorbed molecules, V1, increasing with concentration) can also account for these data.
Effect of the internal field on the birefringence of polymer crystals
Authors: Stein Richard S. 
Published: April 2003

AbstractThe discrepancy between the values of the anisotropy of methylene groups determined from crystal refractive indices, stress‐optical data, and gas and liquid light‐scattering depolarization is explained on the basis of the effect of the internal field on the polarizability of the isolated molecule. The internal field may arise from intermolecular or intramolecular interactions which depend upon molecular conformation and state of aggregation. A simple continuum calculation based upon an extension of the calculation of the Lorenz‐Lorentz field is shown capable of accounting for the discrepancy.