bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal analyses of polymers. XIII. Crystalline character of the 70°c transition of poly(ethylene terephthalate)
Authors: Miller Gerald W. 
Published: April 2003

AbstractThe abrupt changes in the linear expansion and dilatometric measurements of poly‐(ethylene terephthalate) near 70°C indicate that the transition may be first order. DTA and DSC data show the normal heat capacity change at 70°C, while annealing for for 30 min. at 110°C induces further molecular order. Rapid quenching of PET after heating to 120°C yields an amorphous sample and measurement by depolarized light transmission as the sample is reheated shows rapid crystallization occurring near 80°C. With the occurrence of shrinkage near 68°C and apparent recrystallization at slow heating rates by depolarized light analyses, further support is added to the first‐order character of this phase transition. Isothermal annealing for short times at temperatures between 50°C and 80°C produces further increases in molecular order. Cyclic and linear PET oligomers do not contribute to the occurrence of the 70°C transition.
A method of calculating the activation energy spectra of polymers
Authors: Ikeda Susumu , Matsuda Kazuo 
Published: April 2003

AbstractContraction experiments were performed on hot‐stretched polystyrene during isothermal annealing and tempering. Activation energy spectra were obtained from the experimental data using the Primak theory. In the case of isothermal annealing the theory of Kimmel et al. with shift factors was used. There is an appreciable difference between this spectrum and that obtained from the tempering experiment by the original theory without shift factors. These two spectra should be the same according to the theory. In order to resolve the conflict, we have included a correlation between activation processes in the fundamental equation of the Primak theory. A new formula for calculating the activation energy spectra was obtained. For isothermal annealing, it can be written the same as that of Kimmel et al. The shift factor is also included in the formula for tempering. The activation energy spectra obtained by the new formula gives good agreement between the two methods.
Carbon‐13 nuclear magnetic resonance quantitative measurements of monomer sequence distributions in hydrogenated polybutadienes
Authors: Randall James C. 
Published: April 2003

AbstractThe 1,4–1,2 additions in three hydrogenated polybutadienes are described in terms of triads of monomer units, average sequence lengths, and branches per 1000 carbon atoms. A test for conformity with Markov statistical behavior shows that the measured triad distributions can be closely reproduced assuming a first‐order model. Transition probabilities from the statistical analysis can be used to calculate the relative concentration of any desired sequence. Steric factors during polymerization may lead to the first‐order bias in the monomer distribution.
The morphology of ultradrawn polyethylene. I. Nitric acid etching plus gel permeation chromatography
Authors: Weeks Norman E. , Mori Sadao , Porter Roger S. 
Published: April 2003

AbstractTransparent strands of high‐density polyethylene of unusually high c‐axis orientation have been produced by a solid‐state extrusion, involving pressure, temperature, and deformation, in an Instron capillary rheometer. Measured values for tensile modulus are higher than previously reported for any polyolefin. Previous modulus and electron microscopic data are consistent with a strand morphology comprised (≤20%) of of extended chain crystals. The remainder resembles an oriented fibrillar morphology such as found in highly drawn polyethylene. In the present study, fuming nitric acid etching of the ultraoriented strands, in combination with gel permeation chromatography (GPC), has provided incisive structural information. The strands exhibit ≥3X the resistance to acid degradation shown by conventionally drawn polyethylene. GPC molecular weight distributions (MWD) of etched samples show a single broad peak with a prominent high molecular weight tail. The crystal size, represented by the MWD, is in agreement with the crystal long period determined by small‐angle x‐ray scattering. The absence of multiple peaks in the etched MWD's is evidence of limited chain folding. The extended chain content, determined from the etched MWD's, is a strong function of strand formation temperature and is in agreement with the fraction of extended chains calculated from modulus measurements.
Elastic behavior of simple model networks
Authors: Smith K. J. , Gaylord R. J. 
Published: April 2003

AbstractThe elastic behaviors of simple networks consisting of but a few chains have been calculated on the basis of the James and Guth theory of elasticity. The calculations show that the number of elastically effective chains in a network is less than the actual number of network chains, and that the total number of chain backbone links distribute themselves equally (approximately) among the effective chains. It is also demonstrated that a chain molecular weight distribution could be of consequence in non‐Gaussian elasticity. Extrapolation of the findings to a macroscopic network suggests that the number of effective chains is one half the number of network chains, and that each effective chain behaves as if it contained twice as many of backbone links as a network chain.
The crystallization of polymer–diluent mixtures
Authors: Fatou J. G. , Riande E. , Valdecasas R. Garcia 
Published: April 2003

AbstractA theory pertinent to the nucleation of polymer‐diluent systems for molecules of finite molecular weight has been developed. These results have been applied to the crystallization from polyethylene‐α‐chloronaphthalene mixtures using molecular weight fractions of polyethylene ranging from 4,000 to 250,000. This analysis is carried out over the composition range extending from pure polymer to a polymer fraction of 0.30. According to this theory, the interfacial basal free energy decreases as either the molecular weight or diluent concentration decreases.
High‐pressure phases in polymers. II. Spherulitic growth morphology in cis‐polyisoprene
Authors: Edwards B. C. , Phillips P. J. 
Published: April 2003

AbstractThe morphological details of the nucleation and growth of spherulites in cis‐polyisoprene at elevated pressures are discussed on the basis of transmission electron microscopy of films stained in situ by osmium tetroxide and cold‐stage electron diffraction of unstained films. The crystalline structure is unchanged but growth habits are modified. Spherulites begin, as in crystallization at atmospheric pressure, with a single lamella. The formation of a spherulite proceeds primarily through “spawning” and is unaffected by the imposition of pressure. Lamellae tend to propagate as plates or hedrites at supercoolings in excess of 50–60°C (e.g., 1 kbar at 0°C) unlike at atmospheric pressure where only ribbonlike lamellae are observed. Propagation is invariably as sheafs since nucleation of lamellae which grow perpendicular to the primary lamella is suppressed. The nucleation density varies considerably with pressure, a maximum being observed in the pressure plane at constant temperature (e.g., 0.70 kbar at 0°C). It is difficult to resolve clearly the morphological details in the diffusion controlled region because of fine texture. Although much more difficult to achieve experimentally, the effects of pre‐orienting the melt are similar to those occurring at atmospheric pressure.
Diluent effects on molecular motions and glass transition in polymers. I. Polystyrene–toluene
Authors: Adachi Keiichiro , Fujihara Ichiro , Ishida Yoichi 
Published: April 2003

AbstractThe effects of diluent on molecular motions and glass transition in the polystyrene–toluene system was studied by means of dielectric, thermal, and NMR measurements. Three dielectric relaxations were observed between 80 and 400°K. On the basis of NMR measurements on solutions in toluene and in deuterated toluene, relaxation processes were assigned to segmental motions of polystyrene, rotations of toluene, and the local motions of polystyrene and toluene in order of appearance from the high‐temperature side. The concentration dependence of the relaxation strength and of the activation energy for the primary relaxation (that at the highest temperature) show a step increment at about 50% by weight. The activation plots for the primary process were expressed by the Vogel–Tamman equation. With this equation, the temperatures at which the mean dielectric relaxation time becomes 100 sec is determined. This agrees well with the glass‐transition temperature Tg and hence Tg in concentrated solution is expressed by

in terms of the parameters A, B, and T0 of the Vogel–Tamman equation. The values of A and B are, respectively, about 12 and 0.65 and independent of the concentration. The physical meaning of these parameters is discussed.
Optical studies of the crystallization of trans 1,4‐polybutadiene in stretched networks
Authors: Akana Y. , Stein R. S. 
Published: April 2003

AbstractThe stress‐induced crystallization of trans 1,4‐polybutadiene was studied by observing changes in birefringence, stress, x‐ray diffraction, and low angle light scattering during the course of crystallization. From these data, the degree of crystallinity was determined as a function of time, temperature, and elongation. Data were fitted to the Avrami equation, leading to an exponent of the order of unity. Light‐scattering patterns suggested the simultaneous existence of two stretched forms: a rod‐like structure oriented preferentially parallel to the stretching direction and a deformed spherulitelike growth with its greatest extension perpendicular to the stretching direction.
Association of the reaction products in the ozone degradation of polyethylene and its relevance to the study of the fold surface structure
Authors: Patel G. N. , Keller A. 
Published: April 2003

AbstractAn association of reaction products was observed in the course of GPC analysis of ozone treated chain‐folded single crystals of polyethylene which, however, could be eliminated by washing with water. This recognition proved to be important for quantitative studies of the fold surface relying on oxidative fold cutting and should be of interest for studies of oxidative degradation phenomena for their own sake. With the association products appropriately removed, the random fold cutting mechanism could be more closely verified than was possible before. Anhydride linkages are suspected as the source of the association.
Low‐frequency dynamic mechanical behavior of lightly crosslinked 1,5‐trans‐polypentenamer in the rubberlike region
Authors: Hrouz J. , Janáček J. 
Published: April 2003

AbstractThe low‐frequency (10−3 to 5 × 10−1 Hz) dynamic mechanical properties were obtained over the temperature range of 25 to 96°C for 1,5‐trans‐polypentenamer networks prepared in the presence of 0,0.01, 0.02, 0.04, 0.1, 0.2, and 0.4% dicumyl peroxide. For comparison, similar properties of 1,4‐polybutadiene crosslinked with 0.02% dicumyl peroxide were also measured. Superimposed curves for the components of the dynamic compliance, Jp′ and Jp″, reduced to 25°C were obtained and the retardation spectra L were calculated over a range of four logarithmic decades deep in the rubberlike region. It was found that networks containing 0.04 and 0.1% DCP have a small loss maximum Jp″ in the reduced frequency region log ωaT between −2 and 0 which can be assigned to relaxations of untrapped entanglements. The values of (Jp′ − 1/ωη) for very lightly crosslinked polypentenamer networks approached equilibrium very slowly compared to 1,4‐polybutadiene crosslinked to the same degree, which suggests the participation of very long retardation times of this polymer which is also probably reflected in the comparatively high values of C2 of the Mooney–Rivlin equation.
Light scattering investigation of interaction between polymers in dilute solution
Authors: Kratochvíl Pavel , Vorlíček Jiří , Straková Dagmar , Tuzar Zdeněk 
Published: April 2003

AbstractParameters characterizing the interaction of nonidentical polymer molecules in dilute solutions of mixtures of two polymers have been defined on the basis of Stockmayer's theory of light scattering in multicomponent systems. Various procedures for evaluation of the interaction parameters from experimental data have been compared. Specific features of the investigation of such interactions are demonstrated with the scattering behavior of the system polystyrene‐poly‐(methyl methacrylate)‐dioxane.
The energetics of kinks in polyethylene
Authors: Boyd Richard H. 
Published: April 2003

AbstractThe energetics of kinks in polyethylene have been investigated by means of conformational energy calculations on crystalline arrays of C14H30, C18H38, and C22H46. All of the parameters required for assessment of relaxation effects by site theory were calculated including the static defect energies, barriers to defect reorientation, and site strains. Up to two deformable coordination shells in the surrounding lattice were included. In the energy minimization calculations, all molecular internal degrees of freedom were allowed to participate. The effects of chain mismatch along the C axis at large distances from the defect were calculated from a continuum theory. The static defect energy is calculated to be 6.6 kcal/mole for C14H30, and the barrier for reorientation of right‐handed to left‐handed kinks is 10 kcal/mole. The barrier to “unkinking” to the nondefect state is 2 kcal/mole. The strain induced by the defect is largely a shear in the {0 0 1} plane in the 〈1 1 0〉 direction. It is concluded that although the barrier to reorientation is consistent with kink reorientation contributing to the γ process the predicted intensity rules out any but a very weak contribution to the total process.
Heterogeneous nucleation of crystallization of high polymers from the melt. III. Nucleation kinetics and interfacial energies
Authors: Chatterjee A. M. , Price F. P. , Newman S. 
Published: April 2003

AbstractIn the melt crystallization of isotactic polypropylene, poly(ethylene oxide) and poly(butene‐1) in contact with substrates, the existence of a fixed number of nucleating sites on the substrate surfaces has been established. When these sites become active successively (the transient in the number of nuclei is long) during crystallization, pseudohomogeneous nucleation on the substrate occurs. Nucleation rates for poly(butene‐1) and poly(ethylene oxide) on substrates and in bulk have been measured. These data can be used for comparing the nucleating ability of substrates. Estimates of the variation of bulk nucleation rates from one volume element to another as well as for repeated crystallization within a given volume element have been included. Finally, the temperature coefficients of heterogeneous nucleation rates have been combined with the temperature coefficient of spherulitic growth rate of poly(butene‐1), to yield values of the interfacial energy parameters appearing in the theory of heterogeneous nucleation. The quantitative characterization of the nucleating ability of substrates by this method is an improvement over the mere use of nucleation densities or nucleation rates.
The optical interference pattern in a polystyrene craze layer
Authors: Doyle M. J. 
Published: April 2003

AbstractIn the interference pattern seen in monochromatic light reflected from a craze layer in polystyrene, the bright fringes are of alternating intensity. The phenomenon is explained in terms of a four‐beam interference. Apart from the two reflections from the outer surfaces of the craze layer others arise from a thin layer of approximately constant thickness within the craze layer at its median plane. The phenomenon provides independent evidence to support the electron microscopic observations of the microstructure of crazes in polystyrene.
Dynamics of macromolecular chains. III. Time‐dependent fluorescence polarization studies of local motions of polystyrene in solution
Authors: Valeur Bernard , Monnerie Lucien 
Published: April 2003

AbstractFluorescence anisotropy decay experiments are described for polystyrene in various ethylacetate‐tripropionin mixtures. Decay curve trends agree with the proposed theoretical autocorrelation function. Study of the effects of viscosity shows that the mean relaxation time varies according to a nonlinear law for low viscosities and that the relaxation time θ, reflecting the effects of the possible departures from the motions permitted by an ideal tetrahedral lattice, obeys a law of the type: θ = α + bη. Furthermore, the effects of the direction of the fluorophore transition moment are examined.
Dynamics of macromolecular chains. IV. Quenching and fluorescence polarization studies of polystyrene in solution
Authors: Valeur Bernard , Monnerie Lucien 
Published: April 2003

AbstractCombined measurements of quenching and fluorescence polarization corroborate the results previously obtained by the polarized fluorescence anisotropy decay technique and, more especially, confirm the form of the proposed orientation autocorrelation function. The use of this method to determine the mean relaxation time of the relaxation time distribution is also explained.
Structural studies of polyesters. VIII. Molecular and crystal structure of polydiketene
Authors: Yokouchi Mitsuru , Chatani Yozo , Tadokoro Hiroyuki 
Published: April 2003

AbstractThe molecular and crystal structures of polydiketene were studied by infrared spectroscopy and x‐ray diffraction. It was confirmed from the infrared spectra that diketene molecules in the crystal polymerize by ring opening upon γ‐ray irradiation. The unit cell of the product as polymerized is orthorhombic,P22121‐D23, witha= 5.43 Å,b= 8.94 Å, andc(fiber axis) = 7.75 Å. Two molecules pass through the unit cellmagnified imageThe molecule has a conformation shown by the Fischer projection for a lefthanded (2/1) helix; The internal rotation angle around the O—C bond is nearlygauche(−84°), unlike other polyesters. On the basis of x‐ray analysis, several molecular conformation models were selected by utilizing calculations of intramolecular interaction energies.
Effect of fungal degradation on mechanical properties of cellophane
Authors: Bradley S. A. , Carr S. H. 
Published: April 2003

AbstractChanges in dynamic mechanical properties of cellophane films due either to fungal attack or to hydrochloric acid hydrolysis have been measured. It appears that damage caused by cellulase enzymes that are released from a fungal overgrowth is localized in noncrystalline regions. These effects include a substantial reduction in elastic modulus, a reduction in temperature at which relaxation processes involving chain segmental mobility occur, and a broadening of loss tangent peaks due to segmental mobility and to rotations of methylol groups. Comparing results obtained from cellulase hydrolysis with those obtained from acid hydrolysis, it is clear that enryme attack proceeds by a characteristic and selective process. Implications regarding the embrittlement often seen to accompany biodegradation are discussed.
Brillouin scattering from polymer films
Authors: Patterson G. D. 
Published: April 2003

AbstractMany polymers cannot be prepared as clear amorphous blocks suitable for classical light scattering studies. However, most linear polymers can be prepared as films which are somewhat transparent. With the advent of high contrast multipass interferometers, these films can now be studied by Brillouin scattering. This work demonstrates the wide range of polymeric materials that can now be studied by Brillouin spectroscopy.
Preparation and characterization of copolymers of chloroprene and methyl methacrylate
Authors: Khan A. A. , Brame E. G. 
Published: April 2003

AbstractThe preparation of chloroprene–methyl methacrylate copolymers in the presence of Lewis acids (Et1.5AlCl1.5) in hydrocarbon solvent and the effect of Lewis acids concentration on copolymer composition are described. 13C NMR spectra were obtained on these copolymers. In samples of high MMA content, tactic placements of MMA were observed as well as several different kinds of sequences for chloroprene and MMA. In samples of low MMA content, no tactic placements of MMA were found but several different kinds of chloroprene sequences were observed. From the analysis of the 13C NMR spectra of the different copolymers examined, it is apparent that all the various kinds of chloroprene sequences in these copolymers can be determined.
Polyethylene networks crosslinked in solution: Preparation, elastic behavior, and oriented crystallization. I. Crosslinking in solution
Authors: De Boer A. Posthuma , Pennings A. J. 
Published: April 2003

AbstractA study has been made of the crosslinking of linear polyethylene in solution. Networks containing a low number of trapped entanglements and elastically ineffective chain ends were prepared by crosslinking high molecular weight linear polyethylene in 1,2,4‐trichlorobenzene solutions with dicumyl peroxide at 120°C. No syneresis was observed during crosslinking except at high peroxide concentrations. The networks were characterized by swelling measurements, infrared spectroscopy, and differential scanning calorimetry. The crosslinking efficiency, calculated from swelling, was found to be proportional to the square of the polymer volume fraction. The proportionality constant was 0.8, indicating close to unit efficiency for undiluted polymer.Chemical modification of the polyethylene chains by attachment of peroxide and solvent fragments was of the order of one foreign unit per elastically active network chain, depending on peroxide and polymer concentration. Sol–gel analysis indicated that no chain scission occurred. These results are shown to be consistent with a “cage” mechanism for crosslinking. The possible topological consequence of this mechanism, preferential crosslinking of entanglements, is discussed. The concentration of trapped entanglements was also found to be proportional to the square of the polymer volume fraction. The proportionality constant corresponds to a molecular weight between entanglements of 4000 for the undiluted polymer, which is close to the value of 4200 found for networks prepared from the undiluted polymer. Since the results obtained are based mainly on the use of the swelling equation, different aspects of the applicability of this equation for the evaluation of the crosslinking process are discussed. As regards the reference dimensions, which should be known for a quantitative application of the elastic theory, the results strongly support the use of the dimensions of the network chains after completion of crosslinking.
Generalized correlations for molecular weight and concentration dependence of zero‐shear viscosity of high polymer solutions
Authors: Zakin J. L. , Wu R. , Luh H. , Mayhan K. G. 
Published: April 2003

AbstractData are presented to show that two correlations of viscosity–concentration data are useful representations for data over wide ranges of molecular weight and up to at least moderately high concentrations for both good and fair solvents. Low molecular weight polymer solutions (below the critical entanglement molecular weight Mc) generally have higher viscosities than predicted by the correlations.One correlation is ηsp/c[η] versus k′[η], where ηsp is specific viscosity, c is polymer concentration, [η] is intrinsic viscosity, and k′ is the Huggins constant. A standard curve for good solvent systems has been defined up to k′[η]c ≈︁ 3. It can also be used for fair solvents up to k′[η]c ≈︁ 1.25· low estimates are obtained at higher values.A simpler and more useful correlation is ηR versus c[η], where ηR is relative viscosity. Fair solvent viscosities can be predicted from the good solvent curve up to c[η] ≈︁ 3, above which estimates are low. Poor solvent data can also be correlated as ηR versus c[η] for molecular weights below 1 to 2 × 105.