bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plastic deformation of polyethylene II. Change of mechanical properties during drawing
Authors: Meinel G. , Peterlin A. 
Published: April 2003

AbstractThe crystallinity, elastic modulus, and tensile strength of samples of various draw ratios together with the true stress—strain curves of high‐density polyethylene were determined to establish correlations with morphological changes occurring during deformation. Changes of crystallinity at draw ratios below 5, i.e., constancy during drawing of quenched film and a decrease during drawing of annealed film, are explained by the formation of microfibrils with crystallinity independent of the thermal history of the film. The microfibrils slide past each other at higher draw ratios, generating an increasing number of interfibrillar tie molecules, which is reflected in the increasing number of interfibrillar tie molecules, which is reflected in the increase of crystallinity, elastic modulus, and tensile strength. From the true stress—strain curves, the differential work density for the deformation of the volume element was calculated as a function of the draw ratio. It contains two components which reflect two different mechanisms of deformation. The first component, decreasing with increasing draw ratio, can be associated with the destruction of the original microspherulitic structure; the second one, increasing with increasing draw ratio, can be associated with the deformation of the new fiber structure, i.e., with the sliding motion of the microfibrils formed during the first deformation step.
Correlation between the temperature dependence of apparent specific volume and the conformation of oligomeric propylene glycols in aqueous solution
Authors: Sandell L. S. , Goring D. A. I. 
Published: April 2003

AbstractThe apparent specific volumes, ϕ2, of a series of poly(propylene glycol) and poly(ethyleneglycol) oligomers in aqueous solution were determined as a function of temperature from 4 to 25°C. The slope, dϕ2/dT, was taken as a measure of the extent of interaction between the hydrophobic portions of the oligomer and water, higher values of dϕ2/dT representing diminished hydrophobic interaction. It is suggested that the observed increase in dϕ2/dT with chain length for the poly(propylene glycol) oligomers can be attributed to the previously proposed disk coiled conformation of the chain which reduces the degree of contact between the side‐chain methyl groups and water as the chain length increases. This interpretation is supported by (1) the direct relationship between the difference in the thermal expansion behavior of the two oligomer series and the accessibility of the methyl groups in the poly(propylene glycol) disk‐coil, and (2) the agreement between the calculated volume changes on mixing for the methyl groups and the values predicted for the disk‐coil model from the Némethy and Scheraga theory.
Ethylene‐propylene copolymers: Degree of crystallinity and composition
Authors: Ver Strate G. , Wilchinsky Z. W. 
Published: April 2003

AbstractX‐ray, differential scanning calorimeter, and density measurements of the degree of crystallinity have been made on ethylene—propylene copolymers which range in composition from 60 to 100 mole‐% ethylene. At 23°C the degree of crystallinity was found to vary from zero to approximately 75 wt‐% in a regular manner with composition. A systematic difference exists between the x‐ray and heat of fusion measurements if a simple two‐phase model is assumed in order to calculate the per cent crystallinity from heats of fusion. The apparent heat of fusion of the crystalline fraction detected by the x‐ray method is as low as 30 cal/g. This discrepancy increases with comonomer content. It is suggested that large surface or defect energies are present. The broad melting behavior of the samples is also consistent with such a description of the system.
γ–α transformation in isotactic polypropylene
Authors: Newman B. A. , Song S. 
Published: April 2003

AbstractA γ‐phase to α‐phase transformation in a specimen of isotactic polypropylene crystallized under conditions of high pressure was induced by drawing at 100°C. X‐ray studies showed that the unoriented component remained in the γ‐phase, and that the oriented component was found only in the α‐phase. This evidence supports a previous suggestion that the phase transformation is martensitic in character. The consequences of such an assumption are discussed. The role of dislocations in polymeric systems is generally believed to be not too significant, but since martensitic reactions involve cooperative movements of atoms, an exception in this case is suggested. A possible mechanism for the phase transformation is suggested.
Viscoelastic behavior of low molecular weight polystyrene
Authors: Plazek Donald J. , O'Rourke V. Michael 
Published: April 2003

AbstractThe shear creep and creep recovery behavior of narrow molecular weight distribution polystyrene samples of low molecular weight, 1.1 × 103, 3.4 × 103, and 1.57 × 104 are reported as a function of temperature, near and above the glass temperature. Time‐temperature equivalence for the total creep compliance is found to be nonapplicable, and in fact the steady‐state recoverable compliance, Je, is a strong function of temperature. The time‐scale shift factors for the recoverable compliance are analyzed in the light of free volume theory. Viscosity data are presented for samples with molecular weights between 1.1 × 103 and 6.0 × 105. The temperature dependence of the characteristic time constant ηJe can be explained in terms of free volume concepts whereas that of viscosity η cannot. Effects of residual molecular weight heterogeneity are demonstrated.
Light scattering by cellulose. III. Morphology of wood
Authors: Borch Jens , Sundararajan P. R. , Marchessault R. H. 
Published: April 2003

AbstractRadial, tangential and cross cuts of Eastern spruce are examined by a solid‐state light‐scattering method which allows study of light scattering due to fluctuations in density and fluctuations in anisotropy. All of the samples investigated show well‐defined scattering maxima which are related to their anisotropic texture with limited contributions from random density fluctuations. The radial cuts give rise to scattering similar to that by a grating with orthogonal characteristic spacings. The gratinglike character is due mainly to the pit structure and their periodic spacings, which can be deduced from the “unit‐cell” dimensions of the scattering pattern. The scattered intensity is maximum when the fiber direction is at 45° to the polarization direction; when it is either horizontal or vertical, a distinct “spherulitic” scattering is observed from which size and asymmetry of the pits can be deduced.
Crystallization of polyethylene at elevated pressures
Authors: Rees D. V. , Bassett D. C. 
Published: April 2003

AbstractThe crystallization from the melt of three sharp polyethylene fractions has been studied at 5 kbar. It has been shown that the thickness of so‐called extended‐chain lamellae is a function of time, temperature, and molecular weight. There is by no means just the fully extended molecular configuration present. Crystallization is qualitatively similar to that of chain‐folded crystals at 1 bar, giving an optimum lamellar thickness which increases with time and decreasing supercooling. Fractional crystallization is widespread and is a major cause of disparate lamellar thickness. Isothermal thickening of lamellae during crystallization has been established directly. Morphological detail suggests further that layers can increase their thickness tenfold over their initial size.
Long‐chain branching in low‐density polyethylene
Authors: Cote J. A. , Shida M. 
Published: April 2003

AbstractA method is given for the analysis of long‐chain branching in polymers by using combined GPC and intrinsic viscosity measurements. A computer program was written to evaluate branching indices by a tabular, iterative method. The method was applied to the evaluation of long‐chain branching in low‐density polyethylene.
Liquid‐induced reversible long‐spacing changes in polyethylene single crystals and their implications for the fold‐surface problem
Authors: Udagawa Y. , Keller A. 
Published: April 2003

AbstractThe long spacing of single‐crystal mats of polyethylene was found to increase reversibly on addition of liquids which normally act as swelling agents. The magnitude of the increase follows the sequence of the solvent power which these liquid exhibit at higher temperatures. The increase in long spacing depends to a minor extent on crystallization conditions, such as concentration and crystallization temperature, but increases very markedly with the molecular weight of the polymer. Heat treatment reduces the amount of swelling, even in the range of low treatment temperatures which do not produce a foldlength increase, implying a reorganization of the fold surface. It is inferred that there is a layer along the fold surface which expands by swelling which in turn implies a disordered amorphous component. Nevertheless, such disordered material need not be an intrinsic consequence of chain folding, as its amount can be reduced to insignificant proportions, e.g., by taking molecules which are short but still fold. Thus both, the presence of amorphous disorder and the nonunique nature of such a disorder along the surface is demonstrated. Further implications for the fold‐surface problem are discussed.
Fox‐Flory constant K obtained by viscometric measurements for poly(ethyl methacrylate) and poly(methyl methacrylate) systems
Authors: Vasudevan Padma , Santappa M. 
Published: April 2003

AbstractPoly(ethyl methacrylate) and poly(methyl methacrylate) prepared by benzoyl peroxide‐catalyzed polymerization were fractionated. The Fox‐Flory constant K was determined for these polymers by viscometry in several good and bad solvents. Application of some empirical methods for evaluation of K are also briefly discussed in relation to our results.
Some probability relations in multicomponent copolymers
Authors: Pyun Chong Wha 
Published: April 2003

AbstractIt was previously shown that for a stationary random copolymer of A, B, and C, we have in general p(AB) + p(AC) = p(BA) + p(CA), etc., in place of p(AB) = p(BA) which is valid for a stationary binary copolymer. Here, p(AB) for example, is the probability that a randomly picked pair of consecutive comonomers in the polymer consists of an A followed by a B. For a stationary ternary copolymer produced by a first‐order Markovian addition mechanism, we show that PABPBCPCA/PACPCBPBA = k, where k is a constant characteristic of a particular set of three monomers but independent of its composition. Here, PAB is the conditional probability of finding a monomer of B given that its immediate predecessor is an A. We further show that if the individual rate constants of the monomer additions involved take a special form such as used in the Alfrey‐Price Q–e scheme, then we have k = 1 irrespective of the kinds of monomers, and in addition we have p(AB) = p(BA), p(AC) = p(CA), etc. Thus, although these latter results were previously proposed by Ham as an alternative basis to supplant the Q–e scheme, they may rather be regarded as mathematical consequences of special assumptions adopted for the form of the individual rate constants. For a stationary random copolymer of four components A, B, C, and D, we have p(AB) + p(AC) + p(AD) = p(BA) + p(CA) + p(DA), etc., in general. For a first‐order Markovian four‐component copolymer, we show that there are seven different combinations of the conditional probabilities that are constants (k1, k2,…, k1) independent of the monomer composition. Again, if we assume the same special form for the rate constants involved, we find that all the seven constants k1, k2, …, k7 reduce to unity and p(XY) = p(YX) for X,Y, = A, B, C, D.
Effects of a static electric field upon dielectric properties of poly(vinylidene fluoride) and poly(vinyl fluoride)
Authors: Osaki Shigeyoshi , Uemura Shinsaku , Ishida Yōichi 
Published: April 2003

AbstractDielectric measurements on poly(vinylidene fluoride) at higher temperatures result in anomalously large values of ε′ and ε″ at lower frequencies. When a static field is applied, a drastic decrease of ε′ and ε″ occurs. The effects of a static field can be summarized as follows: (1) the field effect upon ε′and ε″ is more significant at lower frequencies; (2) with increasing field strength, the rate of decrease of ε′and ε″ with time becomes greater and the ultimate values are smaller; (3) when the field is removed, ε′and ε″ recover but the ultimate recovery is incomplete; (4) the field effect depends strongly on temperature. Such behavior seems to be attributable to the displacement of ionic impurities and to their electrolysis. These results provided a method to remove the contribution of ionic impurities to ε′and ε″ and to measure the relaxation process due only to dipoles of a polymer. The application of this method revealed the dielectric high temperature absorption which had been masked by the ionic conduction in poly(vinyl fluoride).
Measurement of the stress‐relaxation modulus in the primary transition region
Authors: Kelchner R. E. , Aklonis J. J. 
Published: April 2003

AbstractDifficulties have been encountered in experimentally measuring the stress‐relaxation modulus for systems with steep slopes in the primary transition region. The usually applied “factor‐of‐ten” rule is shown to apply in these cases as well as in cases where the relaxation is slower; with the steep slope, however, the rule offers little help, since the decay in the modulus is so fast that stresses are usually very small at times when direct modulus calculations may be made. A technique is suggested which allows calculation of the modulus in this difficult region. A slow constant strain‐rate deformation is followed by a constant strain period. Modulus values for times during the constant strain rate period are calculated using well known relationships. Long‐time values are calculated from the definition of the modulus (the factor‐of‐ten rule being employed) and a recursion relation is developed which is used for modulus calculations during the constant strain period at relatively short times where effects of strain rate are important. Starting values for the recursion relation are long‐time moduli which can be calculated directly.
Kinetic study of dissolution of poly(vinyl chloride) in cyclohexanone
Authors: Lapc̆ík Lubomír , Valko Ladislav 
Published: April 2003

AbstractThe kinetics of dissolution of five fractions of commercial poly(vinyl chloride) in cyclohexanone was studied at temperatures from 20 to 70°C. Good agreement was observed between the experimental results and equations expressing the dependence of the induction periods and the rates of dissolution on temperature and molecular weight. It was found that the apparent activation energy for the swelling process lies in the range 9–14 kcal/mole and the apparent activation energy for the dissolution diffusion process in the range 8–12 kcal/mole. The apparent dependence of activation energies on number‐average molecular weight indicates that the chain ends are more important in determining the dissolution rate than the centers of the polymer chains.
Thermodynamic and conformational properties of polystyrene. III. Dilute solution studies on branched polymers
Authors: Berry G. C. 
Published: April 2003

AbstractLight‐scattering and viscometric measurements on dilute solutions of five branched polystyrene polymers are reported. The data include studies in decalin as a function of temperature, including the theta temperature, and in toluene. The results for the radius of gyration and the second virial coefficient are not in accord with the two parameter random‐flight model. Possible causes of this descrepancy are considered. It is shown that the intrinsic viscosity of branched chains is not uniquely determined by the radius of gyration.
Optical anisotropy of polymer chains and Markov processes. I. Polyethylene
Authors: Lemaire Bernard , Fourche Georges 
Published: April 2003

AbstractA study of the average molecular optical anisotropy 〈γ2〉 of tetrahedral lattice polyethylene chains of any length has been carried out by using Markov processes. The results of this treatment include simplified models of polymer chains, as well as more elaborate models, which are in current use.
Structural phenomena in polymers arising at low temperatures and by the action of high forces
Authors: Kargin V. A. , Andrianova G. P. , Tsarevskaya I. Yu. , Goldanskii V. I. , Yampolskii P. A. 
Published: April 2003

AbstractNew structural phenomena which can be produced in polymers at low temperatures or by the action of high forces are described and discussed. Experimental evidence supports the argument that the deformation of polymers can develop not only as a result of conformational changes of the macromolecules proper but also by transformation of more complex structural formations. The consequence of this phenomenon is the possibility of large deformations far below the glass‐transition temperature in a crystalline polymer with well‐developed supermolecular structure. This type of deformation takes place without molecular orientation. Another phenomenon discussed is the sharp change of supermolecular structure in crystalline polymers caused by the action of a shock wave. These effects ought to be connected with an energetic rather than entropic deformation mechanism because the transformations occur at a supermolecular level. Thus, there can be two extreme types of deformation processes: the well‐known conformation changes that occur at a molecular level, and the deformation of supermolecular structures. Examples of the pure form of the latter type of mechanism obtained under extreme conditions are given.
Low‐temperature mechanical relaxations in polymers containing aromatic groups
Authors: Chung C. I. , Sauer J. A. 
Published: April 2003

AbstractStudies have been made of the secondary relaxation processes in the solid state of a number of polymers containing aromatic groups in the polymer chain. The polymers investigated include one, polystyrene, with the aromatic group in side‐chain positions, and six high polymers in which phenylene rings lie in the main backbone chain. In polystyrene, wagging and torsional motions of the side chain phenyl rings give rise to a low‐temperature δ‐relaxation which is centered at 33°K (1.7 Hz) and which has an activation energy of about 2.3 kcal/mol. Most of the polymers with phenylene rings in the main chain exhibit a low‐temperature relaxation in the temperature region from 100°–200°K. This relaxation process is centered at 159°K (0.54 Hz) in poly‐p‐xylylene, at 162°K (0.67 Hz) in polysulfone, and at 165°K (1.24 Hz) in poly(diancarbonate). In poly(2,6‐dimethyl‐p‐phenylene oxide), two overlapping low‐temperature relaxations are found, one in the range 125–140°K and the other near 277°K (ca. 1 Hz). The low‐temperature secondary relaxation process in all of these polymers is believed to be associated with local reorientational motion of the phenylene, or substituted phenylene, rings or with combined motion of the phenylene rings and nearby chain units. For these low temperature relaxation processes, the activation energy is about 10 kcal/‐mole. The temperature location of the relaxation appears to depend on the specific units to which the phenylene rings are attached and on steric and polar effects caused by substituents on the ring. In the poly‐p‐xylylenes the relaxation is shifted to much higher temperatures by a single Cl substitution on the ring but remains at essentially the same temperature position when dichlorosubstitution is made. The effects of water on the magnitude and temperature location of the observed low temperature relaxations, as well as the implications of the study for other polymers containing aromatic groups in their backbone chains, are discussed.
Properties of ethylene–propylene–vinyl chloride graft copolymers. II. Viscoelasticity and composition of graft copolymer and composite
Authors: Bares J. , Pegoraro M. 
Published: April 2003

AbstractThe viscoelasticity and volume expansion of the raw polymerizate of ethylene–propylene copolymer with vinyl chloride grafts, and of the individual components has been studied. The raw polymerizate (composite) and the pure ethylene–propylene–vinyl chloride graft copolymer were found to consist of two phases. The pure graft copolymer has an ethylene–propylene matrix containing some fraction of poly(vinyl chloride) (PVC) grafts and a microphase with the remainder of the PVC grafts. The raw polymerizate consists of a PVC matrix plasticized with ethylene–propylene chains and a microphase of the ethylene–propylene copolymer. An attempt has been made to calculate the participation of components in microphases and the minimum dimension of the PVC microphase aggregates.
ESR single‐crystal study of radical and radical‐pair formation in some γ‐irradiated vinyl monomers
Authors: Gillbro T. , Kinell P.‐O. , Lund A. 
Published: April 2003

AbstractSingle crystals of methyl methacrylate (MMA), methyl acrylate (MA), and acrolein (A) have been prepared by a low‐temperature technique. After irradiation with γ‐rays at 77°K the paramagnetic species were identified by ESR spectroscopy. MMA gave a seven‐line single spectrum from radicals formed by hydrogen addition. The hyperfine coupling constants are slightly anisotropic with a mean value of 22 G. Radical pairs were observed as ΔMs = 1 and ΔMs = 2 transitions; the hyperfine coupling was 11 G. From the strongly anisotropic dipolar interaction, upper limits for the distances between the pair components were calculated to be 5.45 Å and 6.3 Å. MA gave a five‐line main spectrum with the same hyperfine coupling values and two radical pairs, one with a distance 5.9 Å between the components. In a there was also a strongly anisotropic interaction. The hyperfine coupling of the ΔMs = 2 transition was 9.8 G. The number of radical pairs compared to the total number of radicals increases only slightly with the radiation dose. This makes it likely that pair formation occurs in the spurs and blobs formed by the γ‐radiation. At an increased temperature the radical pairs disappeared; the spectrum of MMA changed to that characteristic of propagating polymer radicals.