bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lactone polymers. II. Hydrodynamic properties and unperturbed dimensions of poly‐ε‐caprolactone
Authors: Koleske J. V. , Lundberg R. D. 
Published: April 2003

AbstractPoly‐ε‐caprolactone prepared by a dibutylzinc‐catalyzed bulk polymerization process was fractionated, and the solution properties of the fractions were studied in benzene and in dimethylformamide. In these solvents at 30°C the Mark‐Houwink relations were [η] = 9.94 × 10−5 M and [η] = 1.91 × 10−4 M, respectively. The value of KΘ was found to vary from 1.1 to 1.2 × 10−3 when determined by three known extrapolation techniques. Poly‐ε‐caprolactone chains appear to be quite flexible in solution, and the steric hindrance parameter σ had the low value of 1.37. Root‐mean‐square end‐to‐end dimensions were approximated from the experimental data and calculated from the Debye‐Bueche and the Kirkwood‐Riseman theories.
Rheological properties of ionic and nonionic polyacrylamide solutions
Authors: Bruce C. , Schwarz W. H. 
Published: April 2003

AbstractNon‐Newtonian shear viscosities were measured over six decades of strain rate k for 13 solutions of both the ionic and nonionic forms of polyacrylamide. By using the Weissenberg rheogoniometer with both the cone‐and‐plate and the parallel‐plate attachments, the normal stress functions σ1 (k2) and σ2(k2) were obtained for four of the solutions. From the measurements of the shear viscosity and the normal stresses at low rates of strain, characteristic times τ and τN, respectively, were determined for each solution. The quantity τ was then used to nondimensionalize the strain rate τk, and when plotted versus the reduced shear viscosity, found successfully to correlate the experimental data for all the polyelectrolyte solutions over the entire range of τk and the data for the concentrated solutions of the nonionic polymer over a smaller range of τk. However, in order to correlate the normal stress data for the polyelectrolyte solutions, a second reduced strain rate (τNk) was used. Thus, two different times were required to correlate all the observed data. The shear viscosity data for the dilute solutions of the nonionic polymer were well represented by the two‐parameter, non‐Newtonian intrinsic viscosity function that has been computed by Fixman.
Rotating frame proton spin‐lattice relaxation measurements of poly(ethylene oxides)
Authors: Connor T. M. , Hartland A. 
Published: April 2003

AbstractMeasurements of T1ρ as a function of temperature have been made on three polyethylene oxides (PEO) with molecular weights of 550, 6000, and 2.8 × 106 in order to try to elucidate various problems arising in the interpretation of previous T1 measurements on PEO. In contrast to the T1 measurements, the T1ρ measurements show discontinuities at the melting or softening points of the respective polymers concerned, and also show nonexponential magnetization decay in the case of PEO 6000 and 2.8 × 106, which is presumbly due to the existence of “mobile” and “crystalline” regions, in qualitative agreement with NMR studies and x‐ray measurements. Motional correlation frequencies and activation energies have been derived where possible by using the BPP theory adapted to the rotating frame and also the strong collision Slichter‐Ailion theory. There is reasonable correlation with other data on motional frequencies where it is available, although the overall situation for the so‐called α transition in PEO 6000 and 2.8 × 106 is still not clear. It is suggested that spin‐diffusion is an important mechanism for all three polymers; for PEO 550 because it contains CH3 endgroups which act as sinks, and for the other two polymers where the mobile fraction performs the same function.
Relation between melting behavior and physical structure in polymers
Authors: Bell J. P. , Dumbleton J. H. 
Published: April 2003

AbstractThe phenomenon of double melting, as manifested by two characteristic endotherms in the melting region on a differential thermal analysis (DTA) scan, has been studied in nylon 66 and polystyrene as a function of sample treatment by annealing or drawing. A variety of techniques were used in these studies including DTA, x‐ray diffraction, electron microscopy, and mechanical testing. It is shown that the two endotherms are not caused by a bimodal crystal size distribution, by recrystallization, by orientation changes, or by phase changes. It is proposed that one endotherm is caused by the melting of foldedchain crystals, while the other is due to the melting of less perfect bundle crystals. This view is well supported by the results, especially by the DTA measurements made at different heating rates. Published data on the thermal behavior of annealed and drawn poly(ethylene terephthalate) and on polyethylene crystallized at various pressures may also be explained on this basis if it is allowed that in polyethylene the chains may be more extended.
Infrared studies of cryogenic transitions in poly(ethylene terephthalate)
Authors: Hannon M. J. , Koenig J. L. 
Published: April 2003

AbstractMeasurements of infrared absorbance as a function of temperature down to 77°K have been made on poly(ethylene terephthalate). Transitions observed by other techniques such as torsion pendulum measurements are reflected in the infrared measurements by an abrupt change in the slope of the absorbance versus temperature. The infrared measurements are made on bands of known structural origin so the structures contributing to each transition can be determined. The β transition is shown by infrared to be a composite of two peaks with the lower‐temperature portion arising from the amorphous regions and the higher‐temperature portion from the crystalline regions.
Swelling of crosslinked poly‐4‐vinylpyridine
Authors: D'Aprano Alessandro , Fuoss Raymond M. 
Published: April 2003

AbstractPolyvinylpyridine of molecular weight 0.77 × 106 was crosslinked by 2.5, 5, and 10% BrCH2C6H4CO(CH2)8COC6H4CH2Br and by 10% ClCH2C6H4CH2Cl; quaternization of the gel was completed with n‐butyl bromide. Swelling ratios in aqueous solutions of lithium, sodium, and 4‐isopropyl‐N‐n‐butylpyridinium bromide and in methanolic lithium bromide were determined. Selectivity increased in the sequence Li+ <Na+ <PrN+−C5H5. The Flory parameter χ1, which measures interaction between solvent and polymer, decreased from 1.5 kT to nearly zero with increasing density of crosslinks in the aqueous solutions, and from 3 kT to 0.5 kT in the methanol solutions. The inverse proportionality of q2/3 (q = swelling ratio) to the crosslinking density was approximately verified for swelling of the resins in water, methanol, and dimethylformamide.
Stress‐optical coefficient of cis‐1,4‐polybutadiene and cis‐1,4‐polyisoprene networks. Measurements on cis‐1,4‐polybutadiene networks and theoretical interpretation
Authors: Ishikawa Toshihide , Nagai Kazuo 
Published: April 2003

AbstractStress, strain, and birefringence measurements have been carried out on swollen and unswollen networks of ′cis‐1,4‐polybutadiene polymers. Neither stress‐strain nor birefringence‐strain relations of unswollen specimens obey the Gaussian network theory, but both can be fitted by the Mooney‐Rivlin equation. On the contrary, data on specimens swollen in tetralin, decalin, benzene, and carbon tetrachloride strictly obey the Gaussian network theory. Existing methods for evaluating the temperature coefficient of the unperturbed dimensions, d In 〈r2〉/dT, from the stress‐temperature relation are applied to the present data and discussed in some detail. It is concluded that reliable values of d In 〈r2〉/dT are not obtainable from data on unswollen samples because of the pronounced non‐Gaussian effect. The value 7.5 Å3 for the optical anisotropy Å3 (an alternative to the stress‐optical coefficient) for unswollen specimens is markedly larger than values (5.8 Å3 on the average) for swollen specimens. This is interpreted as due to the shortrange orientational order among polymer segments. The quantities 〈r2〉, ΔΓ, and their temperature coefficients are calculated for both cis‐1,4‐polybutadiene and cis‐1,4‐polyisoprene chains, on the basis of the rotational isomeric state approximation for bond rotations. Values of ΔΓ for cis‐1,4‐polybutadiene calculated using Clément and Bothorel's set of anisotropic bond polarizabilities are in good agreement with observed values for swollen specimens. Those for cis‐1,4‐polyisoprene obtained using the same set of anisotropic bond polarizabilities are somewhat smaller than observed values for unswollen specimens. This departure is in the direction expected from the behavior of ΔΓ upon swelling (i.e., a decrease in ΔΓ upon swelling).
Thermodynamic interpretation of domain structure in solvent‐cast films of A–B type block copolymers of styrene and isoprene
Authors: Inoue Takashi , Soen Toshiichi , Hashimoto Takeji , Kawai Hiromichi 
Published: April 2003

AbstractElectron microscopic textures of A–B type block copolymers of styrene and isoprene cast from several solvents were investigated by means of the osmium tetroxide fixation technique. The two‐phase structure, i.e., the semimicro heterogeneous structure due to the microphase separation of block segments, was observed to change systematically with the fraction of block segments and the kind of solvent. Three types of fundamental domain structure were found. With the assumption that domain structure originates from micellar structure at a critical concentration in relatively dilute solution during solvent casting, the formation of the three types of domain structure and the sizes of their elements were treated in terms of the equilibria governing the formation of micelles at the critical concentration. This analysis takes into account such thermodynamic and molecular parameters as the incompatibility between the A and B segments, the solvation of the segments, the casting temperature, the total chain length of the block copolymer, and the weight fraction composition of the block copolymer. It was concluded that the block segments are preferentially oriented along the direction perpendicular to the interface between the two phases. This particular orientation‐aggregation of the block segments must make the bulk properties of the block copolymer much different from those of merely mechanical mixtures of the corresponding homopolymers, even if the same semimicro heterogeneous structures are formed in the mechanical mixtures.
Origin of the γ relaxations in polyethylene and polytetrafluoroethylene
Authors: Gray R. W. , McCrum N. G. 
Published: April 2003

AbstractMechanical relaxation has been studied at 0.67 cps in linear polyethylene (LPE) and polytetrafluoroethylene (PTFE) between −190 and −20°C. Specimens were prepared by use of various thermal treatments to produce in LPE a range of crystalline fractions from 0.690 to 0.825 and in PTFE from 0.615 to 0.870. An empirical theory is proposed relating the modulus of the crystalline–amorphous composite solid to the moduli and the volume fractions of the two phases. The empirical theory is shown to be in accord with the bounds of Hill and of Hashin and Shtrikman. The theory is used to determine the magnitudes of the crystalline and amorphous components of the low temperature relaxations in LPE and PTFE from measurements of logarithmic decrement and shear modulus. In PTFE the γ relaxation occurs in the amorphous fraction alone. In LPE the γ relaxation is a composite one, formed from the superposition of a small crystal relaxation and a large amorphous relaxation. For the crystal relaxation in LPE the ratio of relaxed to unrelaxed modulus equals 0.78; for the amorphous relaxation, the ratio equals 0.23. In a specimen of LPE with crystal fraction 0.69 the crystal contribution to the relaxation is 25% of the total. The magnitude of the unrelaxed modulus of the crystal fraction of LPE (modulus of polycrystalline LPE at −190°C) is in reasonable agreement with theoretical calculations of Odajima and Maeda.
Fractionation of styrene–acrylonitrile copolymers
Authors: Lovrić Ljerka 
Published: April 2003

AbstractThree types of commercial styrene–acrylonitrile copolymer were fractionated by coacervate extraction and by column‐elution techniques. Both methods were studied with two different solvent–nonsolvent pairs. Glass wool was used as the support material in the column. Fractionation by the coacervate extraction method was studied with benzene–triethylene glycol as a solvent–nonsolvent system at 60°C and with dichloromethane–triethylene glycol at 25°C. Column elution was carried out with acetone–methanol as the solvent–nonsolvent system at 30°C, and with dichloromethane–methanol at 20°C. Results of excellent reproducibility were obtained by these two methods. Characterization of fractions involved determination of both the molecular weight and chemical composition. It was established that the fractionation of the samples tested was dependent upon molecular weight only. The two methods described above are compared. Each gives an efficient procedure for fractionation of styrene–acrylonitrile copolymers.
Electron microscopy of crazes in glassy polymers: Use of reinforcing impregnants during microtomy
Authors: Kambour R. P. , Holik A. S. 
Published: April 2003

AbstractAttempts to prepare undamaged microtomed sections of crazes without reinforcement have failed. Several methods of reinforcing crazes in glassy polymers with impregnants prior to microtomy have been tried. Generalized characteristics of successful impregnant systems are suggested on the basis of this experience. The most successful system has involved the infusion of liquid sulfur into crazes in poly(2,6‐dimethyl‐1,4‐phenylene oxide). After quenching, the solid sulfur reinforces the crazes successfully during microtomy but subsequently sublimes away under vacuum. The resultant, largely undamaged craze structure is seen by transmission electron microscopy to resemble an open‐cell foam, the holes and polymer elements of which uniformly average ∼200 Å in diameter. A moderate degree of orientation in the original tensile stress direction is observed. Implications drawn from craze structure for the existence of order in the glassy state are discussed.
Dielectric relaxations in poly(vinylidene fluoride)
Authors: Sasabe Hiroyuki , Saito Shogo , Asahina Mitsuo , Kakutani Haruko 
Published: April 2003

AbstractMolecular motions in poly(vinylidene fluoride) were studied by the dielectric technique. Three distinct absorption peaks (αc, αa, and β) were observed in the frequency range from 0.1 cps to 300 kcps and in the temperature range from −66 to 100°C. The molecular mechanisms for these absorptions and their temperature dependence are discussed, and results are compared with x‐ray diffraction and the NMR measurements. It is concluded that the αc absorption located at 97°C (1 kcps) is related to molecular motion in the crystalline region. The αa absorption located at −27°C (1 kcps) can be interpreted as due to the micro‐Brownian motion of the amorphous main chains. The β absorption located at −47°C (1 kcps) is attributed to local oscillation of the frozen main chains.
Mechanical and dielectric absorption of poly(vinyl chloride) and some related polymers
Authors: Kakutani Haruko , Asahina Mitsuo 
Published: April 2003

AbstractThe mechanical and dielectric low temperature absorptions of poly(vinyl chloride) (PVC) and several modified PVC's have been studied over the temperature range from −60 to +60°C. with some tests extending to −150°C. and others to +170°C. The results indicate that the low‐temperature absorption near −50°C (β2 absorption) decreases in intensity with chlorination, while the absorption at a higher temperature near 0°C (β1 absorption) decreases in intensity with hydrogenation. The apparent activation energies of the β1 and β2 absorptions were calculated to be 16 kcal/mole and 10.7 kcal/mole, respectively. Besides, the β2 absorption markedly decreases in intensity with addition of plasticizer, while the intensity of β1 absorption is not much affected by increasing plasticizer content. From these results, the β1 and β2 processes are concluded to be the results of molecular motion in crystalline and amorphous region in PVC, respectively. For samples of reduced Cl content, another low‐temperature absorption was located near −120°C (γ absorption) and attributed to the presence of short sequences of ethylene units. It has also been observed that the temperature location of the high temperature absorption near 100°C (α absorption) shifts linearly to higher temperature with increasing chlorine content and to lower temperature with increasing hydrogen content.
Study of the side‐chain relaxation of methacrylate homopolymers and copolymers by the dielectric method
Authors: Kawamura Yasuaki , Nagai Satoshi , Hirose Juichi , Wada Yasaku 
Published: April 2003

AbstractDielectric constant and dielectric loss of copolymers of methyl methacrylate (MMA) with n‐butyl methacrylate (nBMA) and isobutyl methacrylate (iBMA) have been measured in the frequency range 30 cps to 1 Mcps at temperatures from 70°K to 370°K. Results lead, together with those of previously published investigations on copolymers of MMA, to the following conclusions. (1) The loss‐peak temperature attributed to side‐chain relaxation (β peak) of PMMA varies with the comonomer ratio when the comonomer does not have an α‐methyl group, but remains almost unchanged for comonomers having an α‐methyl group. (2) In both cases, the β peak height of PMMA decreases with increasing ratio of comonomer B and completely vanishes for poly‐B, and the loss peak temperature plotted against the fraction of B does not extrapolate to the β peak of poly‐B. It is suggested on the basis of the above facts that the moving unit in the side‐chain relaxation consists of a single side chain with a segment of the backbone chain and that the change in mobility of the side chain upon copolymerization results from the distortion of the helical structure of the backbone chain due to random distribution of α‐methyl groups. Dielectric studies of the low‐temperature side‐chain relaxation (β2 peak) in PnBMA, poly(n‐octyl methacrylate), and poly(n‐dodecyl methacrylate) (130°K at 1 kcps) have been made and an interpretation is offered for the molecular nature of this relaxation.
Elasticity and structure of chemically crosslinked polyurethanes
Authors: Blokland R. , Prins W. 
Published: April 2003

AbstractA combination of electron‐microscopy, light‐scattering, and stress‐birefringence studies on chemically crosslinked polyurethanes point toward the existence of rodlike regions (“bundles”), approximately 3000–8000 Å in length and involving about 5% of the volume, in which molecular orientations are correlated. The elastic behavior of these networks—as indeed that of most rubberlike networks—deviates substantially from the Gaussian behavior. The empirical representation of the data in Mooney‐Rivlin plots yields C1 and C2 constants which depend on the type of imposed strain. It is thus impossible to identify C1 with the Gaussian behavior and C2 with the deviation there‐from. Instead, it is found that the elastic behavior can be adequately described if it is assumed that, as a result of the bundle structure, about 5% of the segments of each chain are not free to assume the normal random‐walk configurations. The determination of the number of chains in the network from the elastic behavior remains ambiguous, however, and the behavior upon swelling is not (yet) adequately reproduced by the theory. It is conceivable that in many cases deviations from Gaussian elasticity behavior may be caused by an intermolecular structuring effect, rather than by various minor deficiencies in the Gaussian model for the single chain statistics or by anisotropic excluded volume effects, as has been proposed in the past. In the present case, the amount of bundle structure, as well as the C2/C1 values, increase with the number of urethane couplings per chain, and this suggests that the interaction of the highly polar urethane couplings is responsible for the structuring. In other networks one often finds a dependence of C2/C1 on the previous history of the sample, which suggests that an accidentally trapped order may be responsible for the elastic behavior.
Influence of an interfacial free‐energy correction on the expansion of a polymer coil in a solvent
Authors: Vrij A. 
Published: April 2003

AbstractA new type of long‐range interaction between chain segments and solvent molecules in a polymer molecule is introduced. It can be depicted as an “interfacial” free energy, due to the more or less diffuse interface between the interior of a polymer coil and the surrounding solvent. Flory's calculation of the coil expansion α is extended for this effect, by using theoretical approaches developed by van der Waals, Cahn and Hilliard, and Debye for inhomogeneous systems (interfaces). It is found that Flory's equation for α is replaced by:

where the last term is due to the “interfacial” free‐energy correction. The Debye molecular interaction length l is also found in theories on light scattering of binary mixtures near the critical solution temperature. An important result of this equation is that at T = θ, α is not equal to unity, as before, but somewhat larger, depending on the molar mass of the polymer and the solvent type. A calculation shows that the “interfacial” free energy correction may contribute substantially to the “solvent” effects on the expansion of a polymer molecule at the θ temperature, as has recently been reported in the literature.
Rates of crystallization of polyethylene fractions by calorimetry
Authors: Fatou J. M. G. , Barrales‐Rienda J. M. 
Published: April 2003

AbstractRates of crystallization of polyethylene fractions have been studied at high undercoolings by differential calorimetry to demonstrate the utility of this technique for fast crystallization analysis. It has been shown that there is continuity in the crystallization kinetics from low to high undercoolings. On the other hand, the influence of molecular weight on the crystallization rates, as the undercooling increases, is very moderate, as would be expected.
Fast gel‐permeation chromatography. I. A study of operational parameters
Authors: Little James N. , Waters James L. , Bombaugh Karl J. , Pauplis William J. 
Published: April 2003

AbstractA systematic study of factors affecting the GPC separation showed that peak spreading with increasing flow rate was much less than predicted from the Van Deemter equation. Viscous fingering decreased and peak symmetry improved at increased flow rates. As a result, fast GPC analysis was shown to be readily attainable through optimization of operating parameters.
Calculation of molecular weight distributions for polymers undergoing random crosslinking and scission
Authors: Kells D. I. C. , Guillet J. E. 
Published: April 2003

AbstractA simple, practical calculation procedure has been developed for predicting the changes in molecular weight distribution of a polymer undergoing random crosslinking and/or degradation. Simulations of the random crosslinking and degradation of narrow and broad Poisson‐type distributions have been made. The results agree with those calculated from Kimura's analytical solutions to Saito's general equations after a correction has been made for a mathematical error in Kimura's solution. This method can be applied to determining the probabilities of crosslinking and scission for any arbitrary molecular weight distribution expressed in tabular form. The importance of using narrow distribution samples to estimate crosslinking from changes in molecular weight distribution is graphically demonstrated.