bluuebunny/crossref_metadata_2025_split huggingface dataset:
Newtonian behavior of a styrene–butadiene–styrene block copolymer
Authors: Chung Chan I. , Gale John C. 
Published: April 2003

AbstractThe melt rheological behavior of an anionically polymerized styrene–butadiene–styrene (SBS) block copolymer sample (S: 7 × 103and B: 43 × 103) was studied using a Weissenberg rheogoniometer. Highly non‐Newtonian behavior, high viscosity and high elasticity, which are characteristics of ABA type block copolymers, were observed at 125°C, 140°C, and 150°C. The data at these temperatures superimposed well onto a master curve giving a constant flow activation energy. However, the data at 175°C indicated a marked change in the flow mechanism between 150°C and 175°C. At 175°C, the sample showed Newtonian behavior, negligible elasticity, and deviation from the master curve. These findings may be considered as an indication that the SBS block copolymer sample undergoes a structural change from a multiphase structure at low temperatures into a homogeneous structure at some temperature between 150°C and 175°C.
Influence of crystallization and annealing conditions on the morphology of bulk‐crystallized isotactic polystyrene
Authors: Overbergh N. , Berghmans H. , Reynaers H. 
Published: April 2003

AbstractThe influence of thermal history on the morphology of bulk‐crystallized isotactic polystyrene was investigated. Results from x‐ray diffraction (both wide‐ and small‐angle), DSC experiments, and electron microscope observations, were combined to define the influence of thermal history on the fold surface free energy σe. lamellar thickness, and crystallite perfection. The increase of the melting point with crystallization temperature is not only the consequence of an increase in lamellar thickness, but also of marked decrease of σe. Annealing above the crystallization temperature results in a fast reorganization to a more stable structure, as reflected in an increase in melting point. This reorganization, depending on the crystallization temperature, involves an increase in lamellar thickness, a decrease of σe, and eventually an increase in crystallite perfection.
Thermal expansion and compressibility in the chain direction of a polydiacetylene single crystal
Authors: Batchelder D. N. 
Published: April 2003

AbstractAn x‐ray back‐reflection rotating camera has been used to measure the lattice constant, thermal expansion, and compressibility in the polymer chain direction of a polydiacetylene, poly[bis(p‐toluene sulfonate) of 2,4‐hexadiyne 1,6‐diol]. The thermal expansion coefficient of the polymer chain is small and positive (0.9 ± 0.2 × 10−6 °K−) at 300°K, but negative below about 70°K. Application of 3.43 kbar hydrostatic pressure at 299°K changed the unit cell dimension in the polymer chain direction by less than 10 ppm.
Isothermal and nonisothermal dielectric relaxation studies on polycarbonate
Authors: Aoki Y. , Brittain J. O. 
Published: April 2003

AbstractDielectric relaxation measurements at very low frequency were carried out on polycarbonate. Two prominent peaks were resolved from the broad β‐relaxation peak with activation energies of 0.28 and 0.52 eV, respectively. Thermally stimulated discharge current was also studied and compared to the results obtained from the dielectric relaxation measurements.
Direct determination of interfacial energy between brittle and polymeric films
Authors: Chow T. S. , Liu C. A. , Penwell R. C. 
Published: April 2003

AbstractVery few analyses exist for determining the adhesion f thin brittle films in the micron range on low modulus polymeric substrates. A theoretical model and experimental means are developed to determine the adhesion for this situation using the concept of fracture mechanics and Griffith's energy criterion. An expression for the adhesion is derived in terms of the external loading, material constants, and thicknesses of the films.The model is compared with measurements of brittle films vacuum deposited onto polymeric substrates. Excellent agreement is obtained and interfacial energies are calculated. Since the moduli of thin films are very difficult to determine accurately, the effect of a variation in measurements of this material parameter on the adhesion is calculated. The effect of varying preparative conditions is also discussed.
Potentiometric titration of polyelectrolyte gels equilibrated with a solution of a strong polyelectrolyte: Influence of gel swelling
Authors: Merle Yves 
Published: April 2003

AbstractA weak acid gel (carboxylmethyldextran) was titrated with sodium hydroxide while equilibrated with a solution sodium poly(vinyl sulfate), a salt of a strong acid polyelectrolyte.It was found that the quantity

in which V/V0 is the volume of gel relative to its volume in acid form in pure water, is independent of the concentration Cp of the polyelectrolyte solution and of the relative volume of gel.The relation

where α is the degree of ionization, pK′ is the apparent pK of the gel, γ is the activity coefficient of the counterion in the gel phase, and v is the number of ionizable groups, is found to be constant for all values of Cp and for 0.1 < α < 0.9. These results can be extended to highly crosslinked ionexchange resins.
Influence of γ‐irradiation in the molten state on the dynamic mechanical β relaxation and on the thermally stimulated depolarization currents of polyethylene
Authors: Pineri M. , Berticat P. , Marchal E. 
Published: April 2003

AbstractDynamic mechanical and thermally stimulated depolarization current data have been obtained on polyethylene, γ‐irradiated in the molten state, as a function of irradiation dose. The β peak which appears in mechanical experiments has been attributed to motions of the chain backbone. The branches, like the crosslinks coming from γ‐irradiation, are fixed tie points for the chains.
Persistence vectors and higher moment tensors of polyoxyalkanes
Authors: Abe Akihiro , Kennedy J. W. , Flory P. J. 
Published: April 2003

AbstractStatistical mechanical averages of vectors and tensors characterizing the spatial configurations of polyoxymethylene (POM) and polyoxyethylene (POE) chains, i.e., the chain vector r connecting the ends of the chain and the tensors formed from this vector, are evaluated in internal reference frames attached to the first two bonds of each chain as functions of its length. Convergences of the persistence vectors a ≡ 〈r〉 with chain length to their limits a∞ are delineated. For POE, the orientation of a∞ with respect to the X1 axes (the direction of the first bond) depends markedly on the choice of the initial bond and hence also on the internal frame of reference. Cartesian tensors up to fourth rank formed from the displacement vector ρ = r − a are evaluated for n = 4–1922 bonds for POM and n = 3–300 bonds for POE. The second moment tensor 〈ρρT〉 calculated for POM is nearly cylindrically symmetric about the axis perpendicular to the plane of the first two bonds. Corresponding symmetry is absent in POE. Correlation with the freely jointed chain is investigated for the components of the tensors of fourth rank formed from the reduced vector
\documentclass{article}\pagestyle{empty}\begin{document} $\tilde \rho = \left\langle {\rho \rho ^{\rm T} } \right\rangle ^{ - 1/2} \rho $\end{document}. Use of the equivalent chain model for this purpose is validated for POE but not for POM, even at n = 2000 bonds. At the limit 1/n = 0, the parameter m, representing the number of bonds of the real chain equivalent to one of the model, is estimated to be ca. 31 for POM. For POE a value of m = 10.3 ± 1.3 holds for n > 20 for all components. Results are compared with those calculated previously for polymethylene, poly(dimethylsiloxane) and polypeptides. The fact that values of m derived by analysis of moments are larger than those obtained in the usual manner by fitting the model chain to 〈r2〉0 and rmax for the real chain demonstrates the inadequacy of artificial models for the representation of the real chain.
Structure–chain length correlations in poly(N‐vinylcarbazole)
Authors: Griffiths C. H. , Van Laeken A. 
Published: April 2003

AbstractNarrow molecular weight distribution samples of PVK have been prepared over the molecular weight (Mn) range of 3.7 × 103 to 2.7 × 106. No evidence of influence of the synthetic procedure on polymer tacticity has been observed. The glass‐transition temperature Tg was linearly dependent on 1/Mn (Tg∞ = 227°C) as predicted by the Fox‐Flory chain‐end free‐volume model but no measurable change in free volume was detected. Crystallizability decreased with Mn and was zero in fractions below Mn = 46,000. This behavior coincides with that predicted by the nucleation theory outlined by Hoffman.21 This indicates that the chain‐end free energy controls the stability of PVK folded‐chain nuclei. The critical molecular weight for nucleation at 305°C was found to be some where in the range Mn = 1 ± 0.5 × 105. No change in the structure of the folded‐chain lamellae with Mn was observed but evidence was obtained to support adjacent reentry of chains and a resulting localized crystal distortion.
The determination of the molecular weight distribution of amylose by gel permeation chromatography
Authors: Van Dijk J. A. P. P. , Henkens W. C. M. , Smit J. A. M. 
Published: April 2003

AbstractThe universal calibration for gel permeation chromatography (GPC) has been applied to amylose and dextrans. The molecular weight distribution of amylose has been measured starting from known data on dextrans. The agreement found between the molecular weight averages resulting from GPC and those obtained by other methods justifies the procedure followed. The GPC measurements were performed with dimethylsulfoxide as the elution solvent and deactivated silica gel (Porasil) as the column‐filling material.
The mechanical degradation of polystyrene
Authors: Grayson Michael A. , Wolf Clarence J. , Levy Ram L. , Miller Daniel B. 
Published: April 2003

AbstractThe catastrophic failure of a polymeric material is preceded by a number of complex, partially understood events occurring on the molecular level. These events range from the flow of ordered regions to the cleavage of primary bonds in the chain. In recent years, stress‐induced bond cleavage in polymers has received increased attention, many authors nothing the presence of free radicals and/or volatile products released upon fracture; a free‐radical decomposition mechanism involving up to 103 molecules per chain rupture also has been postulated. A special tensile stress–strain and shear apparatus was developed and located inside the ion‐source housing of a time‐of‐flight mass spectrometer to characterize the volatile products released during mechanical degradation of polystyrene. Volatile compounds evolved during stress and fracture of polystyrene were monitored either continuously or by z‐axis modulated oscilloscopic display. The polystyrene was purified by two methods: vacuum outgassing and fractional reprecipitation. Large amounts of styrene evolved from both the as‐received and outgassed samples; however, essentially none was observed from the reprecipitated samples. Previous reports on monomer evolution during mechanical stress of polystyrene may be the result of residual monomer and not mechanical degradation products. The product of the surface density of primary radicals and the chain length for unzipping is less than 3 × 1010 radicals/mm2 indicating a maximum radical concentration of approximately 1010 radicals/mm2.
The effects of combined pressure–temperature on mechanical behavior of polypropylene
Authors: Yoon H. N. , Pae K. D. , Sauer J. A. 
Published: April 2003

AbstractThe effects of combined pressure and temperature on the mechanical behavior of polypropylene have been studied. Tests were conducted in tension and compression superimposed on various hydrostatic pressures up to 7 kbar at temperatures of 20, 50, and 75°C. The experimental data have been analyzed in view of molecular and continuum approaches.It has been observed that the Young's modulus and the yield strength in both tension and compression increased significantly with increasing pressure at all temperatures studied. However, the rate of increase of the Young's modulus undergoes abrupt change about the glass‐transition pressure (Pg). The Pg is linearly dependent on the test temperature and the pressure coefficient of the Tg is estimated, from Pg versus temperature relations, to be about 18°C/kbar for the polypropylene samples of this study. Pressure dependence of the yield stress is described by a generalized Eyring theory incorporating pressure effects and two flow mechanisms, the α‐ and the β‐relaxation processes. The theory predicts a bilinear dependence of the yield stress of polypropylene on hydrostatic pressure as observed in the tests.The paper also described a method of healing stress whitening in polypropylene by a combination of shear stress and hydrostatic pressure.
Monte Carlo study of defect fluctuations and reptation in polymer melts
Authors: Kimmich R. , Doster W. 
Published: April 2003

AbstractDefect fluctuations in highly distorted polymer chains were simulated by Monte Carlo calculation. The NMR autocorrelation function was derived and described by the superposition of three exponential functions with time constants spread over two orders of magnitude. As a consequence of defect diffusion, longitudinal chain diffusion (reptation) can be expected in polymer melts. By simulating the mean‐square displacement of a segment, it was found that after sufficiently long times, compared with defect density correlation times, a linear relationship holds fairly well. As a rule of thumb, it can be stated that the linear Einstein equation is valid for times much greater than 103 mean step times in practical cases (chain length: several thousand segments, defect concentration: 10–20%), or, in other words, for mean‐square displacements greater than a few diffusion step lengths. A long‐time chain‐diffusion coefficient depending on the molecular weight and on the defect concentration could be derived. Effects on the low‐field NMR relaxation behavior are derived and discussed.
Carbon‐13 NMR spin‐lattice relaxation times of isotactic and syndiotactic sequences in amorphous polypropylene
Authors: Randall James C. 
Published: April 2003

AbstractSpin‐lattice relaxation times (T1) for methyl, methylene, and methine carbons in an amorphous polypropylene have been measured as a function of temperature from 46 to 138°C. The carbons from isotactic sequences characteristically exhibited the longest T1's of those observed. The T1 differences increased with temperature with the largest difference occuring for methine carbons where a 32% difference was observed. Activation energies were determined for the motional processes affecting T1's for isotactic and syndiotactic sequences with essentially no dependence upon configuration noted.
Nonlinear viscoelasticity of polystyrene solutions. III. Stress development at the start of steady shear flow and an experimental check of some constitutive models
Authors: Osaki Kunihiro , Ohta Shinichi , Fukuda Mitsutoshi , Kurata Michio 
Published: April 2003

AbstractThe development of the shear stress at the start of shear flow at constant rate of shear κ was measured for polystyrene solutions in diethyl phthalate with a cone‐and‐plate rheometer. Ranges of molecular weight M and concentration c were 3.10 × 106−7.62 × 106 and 0.112−0.329 g/cm3, respectively. The shear stress as a function of time t exhibited a marked maximum at large κ when either M or c was relatively low. When M and c were high, the maximum was broad and low. In a few extreme cases no maximum was observed in the range of κ studied. The constitutive model of Bernstein, Kearsley, and Zapas could describe approximately the shear stresses at a sudden start and on cessation of steady shear flow with a memory function evaluated from the strain‐dependent relaxation modulus. The strain dependence of the memory function for solutions of low M or c was approximately expressed as exp{−α|s|} where α is a constant (ca. 0.37) and |s| is the absolute value of shear strain. When M and c were high, the strain dependence was found to be more diffuse and to require several terms if approximated by exponential functions of |s|. The Lodge model based on a strain‐rate dependent relaxation spectrum was not able to describe the strain‐dependent relaxation modulus as well as the interrelation between shear stresses at a sudden start and a cessation of steady shear flow.
Application of fourier transform infrared spectroscopy to the study of semicrystalline polymers: Poly(ethylene terephthalate)
Authors: D'esposito L. , Koenig J. L. 
Published: April 2003

AbstractAn infrared absorbance subtraction technique has been used to “isolate” bands in the composite spectrum of semicrystalline polymers according to their crystalline or amorphous character. Amorphous and crystalline spectra for annealed, melt‐quenched, and solution‐cast poly(ethylene terephthalate) have been separated. The spectra of the amorphous component show an increased intensity of bands associated with the trans configuration of oxygen about the CC bond when the polymer is annealed. This increased “trans” band intensity reflects the increased proportion of trans structures as a result of annealing. The amorphous trans bands are shifted approximately 1–3 cm−1 from their positions in the crystalline “trans” spectrum. The frequency shift of these bands can be attributed to the differences in chain interactions that exist in the amorphous phase and the crystalline lattice. We have also found that under identical anealing conditions the amorphous phase of the melt‐quenched polymer contains an increased intensity of conformational trans bands compared to the sample cast from solution.
Reduction of dielectric loss in radiation‐polymerized polyethylene
Authors: Nakagawa Koichi , Tsuru Shinji 
Published: April 2003

AbstractLow dielectric loss polyethylenes have been produced by γ‐radiation polymerization of oxygen‐free ethylene monomers. Dielectric measurements were made at 500 MHz and 20°C. The lowest dielectric loss tangent of the polyethylene was 3.3 × 10−5. Polar groups contributing to the dielectric loss have been found to be carbonyl groups, terminal vinyl groups, methyl groups, and hydroxyl groups contained in the polyethylene. The contribution of each group to the loss tangent has been calculated from a comparison of the variation of the loss tangent with the content of each group as determined by infrared analysis. It has been found that the reduction of the loss tangent is mainly due to the decrease in the concentrations of the carbonyl groups and the terminal vinyl groups and that the presence of a considerable amount of the hydroxyl groups prevents a further reduction of the loss in the polyethylenes. The results obtained from the analysis of the radiation‐polymerized polyethylenes were applied to commercially available polyethylenes.
Piezoelectric relaxation in poly(γ‐benzyl‐glutamate)
Authors: Furukawa Takeo , Fukada Eiichi 
Published: April 2003

AbstractThe piezoelectric d‐ and e‐constants, together with the elastic constant and the dielectric constant, were measured for oriented poly(γ‐benzyl‐glutamate) (PBG) films with various elongation ratios as a function of frequency and temperature, using an apparatus developed by us. The results are discussed in terms of a general theory of piezoelectricity for inhomogeneous systems, in particular for a disperse two‐phase system. The piezoelectricity of PBG film is proved to originate from the piezoelectric and optically active symmetry of PBG crystallities and their orientation distribution by three findings: (1) the d14 component of the piezoelectric matrix, which is the only component for a uniaxially or uniplanarly oriented system, is observed; (2) d14 > 0 for PBDG and d14 < 0 for PBLG; (3) d14 is proportional to the degree of orientation Fc of PBG crystallites, as determined by x‐ray diffraction. By extrapolating to perfect orientation, d14 is determined to be 5 × 10−8 cgs esu, if the side chains of PBG are rigid. The piezoelectric relaxation of PBG due to thermal motion of the side chains has a dual character: it is relaxational at lower frequencies and retardational at higher frequencies. On the assumption that the α‐helical main chains surrounded by the bulky side chains are responsible for the origin of the piezoelectricity, such relaxation phenomena are interpreted in terms of the relaxation of the local elastic field in the main chains. An equivalent model having the same frequency characteristics is proposed to include the higher order structure of the PBG film.
Comments on the optical properties of fully conjugated polymers: Analogy between polyenes and polydiacetylenes
Authors: Baughman R. H. , Chance R. R. 
Published: April 2003

AbstractThe similarity of the π‐electron backbones of the polyenes and the polydiacetylenes suggests an analogy between these two fully conjugated, linear polymers. The extent of the analogy is discussed through the examination of a series of model compounds: the polyenes and the polyenynes. The optical band gaps and the polarizabilities of polyenynes are compared to those of the polyenes and to the predictions of a modified free‐electron model. It is concluded that the chain‐dependent electronic properties of the polyenes may be extrapolated with some confidence to the polydiacetylenes.
Carbon‐13 nuclear magnetic resonance quantitative measurements of average sequence lengths of like stereochemical additions in polypropylene and polystyrene
Authors: Randall James C. 
Published: April 2003

AbstractSequence lengths of stereochemical additions in vinyl polymers are described in terms of the number average lengths of like configurational placements. Under these circumstances, a pure syndiotactic polymer has a number average sequence length of 1.0; a polymer with 50:50 meso, racemic additions has a number average sequence length of 2.0 and polymers with more meso than racemic additions have number average sequence lengths greater than 2. Amorphous and crystalline polypropylenes and an amorphous polystyrene are examined using 13C NMR as examples of the applicability of the average sequence length method. The results appear to be accurate for amorphous and semicrystalline polymers but limitations are present when this method is applied to highly stereoregular vinyl polymers containing predominantly isotactic sequences.
Birefringence and stress relaxation in polyisobutylene
Authors: Berglund Charles A. , Taylor Carl R. 
Published: April 2003

AbstractRelaxation of birefringence and stress in simple extension has been studied for polyisobutylene at ‐26.0°C and 25.0°C for extension ratios ranging from about 1.2 to 2.0. The dependence of both the stress and birefringence on the extension ratio, for a given time, is well described by equations of the Mooney–Rivlin form. The Mooney–Rivlin treatment of the birefringence experiments was found to reinforce but not add to information available from the stress‐relaxation experiments alone. At 25.0°C, the stress‐optical coefficient is found to be stress dependent. Possible explanations of this behavior are discussed. An experiment is also reported in which the birefringence is observed under zero stress immediately after cutting a strained sample. The zero stress birefringence is believed to be due to regions of stress‐induced crystallization taking a finite time to melt after the stress is removed.