bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gelation‐crystallization in isotactic polystyrene solutions and its implications to crystal morphology, to the origin and structure of gels, and to the chemical homogeneity of polyolefins
Authors: Girolamo M. , Keller A. , Miyasaka K. , Overbergh N. 
Published: April 2003

AbstractAs part of a wider study on the crystallization of isotactic polystyrene solutions it was observed that at sufficient concentrations (> 3–5%) gelation sets in below a certain (very high) supercooling in competition with the usual single crystal formation which in itself produces turbid suspensions. It was established that gelation is a form of crystallization (mode A) which must be of fringed micellar type to provide the connectedness as opposed to the chain folded lamellae (mode B) which gives rise to discrete particles. The gel crystals (A) display sharp melt endotherms and produce distinct x‐ray diffraction patterns both of which, however, differ decisively from those provided by crystals B, a distinction which can be preserved even after removal of the solvent. The melting points of A are significantly lower than those of B and the x‐ray diffraction patterns of A are incompatible with the recognized structure of polystyrene (31 helix) possessed by B; they point to a broadly planar zig‐zag arrangement of the chain. This strongly suggests that we have blocks of chemically distinct sequences which could be syndiotactic or head‐to‐head tail‐to‐tail (presently with substantial support for the latter) which is responsible for the gel forming crystallization. However, so far the C13 nuclear magnetic resonance (NMR) results do not provide the evidence for these distinct species but explanations for our observations on any other basis seem to lead to unsuperable difficulties from other points of view. Consequently, the paper is left open ended with the possibilities discussed. Amongst these the existence of a very few but long, chemically distinct sequences seems most attractive. The wider implications of the facts as they stand for crystal morphology (fringed micelles versus lamellae), for the origin and structure of gels in general, for the crystallization of block copolymers and for issues relating to chemical homogeneity (tacticity, head‐to‐head tail‐to‐tail) are discussed and preliminary effects are quoted which indicate that these issues may also be relevant to the usual atactic polymers.
Mechanical loss processes in polysaccharides
Authors: Bradley S. A. , Carr S. H. 
Published: April 2003

AbstractDynamic mechanical properties of cellophane, amylose, and dextran have been obtained over the temperature range 100–520°K and frequency range 10−2 to 10+2 Hz on specimens containing various amounts of water. Four mechanical transitions have been characterized. At about 180°K, there is a γ transition that has been assigned to rotation of methylol groups; no comparable transition was found to exist in dextran. At about 240°K, there is a β transition that has been assigned to rotation of methylol–water complexes, but the β transition in dextran appears to be due to some other kind of motion. In cellophane at about 450°K there is an α2 transition which appears to have contributions from motion of chain segments in disordered regions. The α1 transition for cellophane occurs at temperatures too high to measure and may be due to segmental motions in chains within crystalline regions. Dextran and amylose were found to have at these same temperatures α loss processes that probably correspond to glass–rubber transitions in amorphous material. The changes in these mechanical loss mechanisms due to moisture uptake suggest that sorbed water associates with glucose repeat units in ways ranging from those which stiffen molecular structure to those which allow greater freedom for other types of motion to occur.
Solution behavior of styrene–ethylene oxide block copolymers
Authors: Nakamura Kanehiro , Endo Ryuichi , Takeda Masatami 
Published: April 2003

AbstractHydrophobic–hydrophilic water‐soluble block copolymers were prepared by “living” anionic polymerization. They consist of a polystyrene block and a polyethylene oxide block. From data on solution viscosity and high‐resolution NMR in water, the molecular dimensions of the two‐blocks copolymers are found similar to that of polyethylene glycols of the same molecular weight in the same solvent. These block copolymers exhibit microphase separation.
Ion binding in sulfonate‐containing polyelectrolytes
Authors: Tan J. S. , Marcus P. R. 
Published: April 2003

AbstractEmf measurements have been used to study the activity and the extent of sodium ion binding to several polyelectrolytes, poly(styrenesulfonate) (PSS), poly(2‐acrylamido‐2‐methylpropanesulfonate) (PAMS), poly(3‐methacryloyloxypropane‐1‐sulfonate) (PMOS), and copoly[(N‐t‐butylacrylamide)‐(2‐acrylamido‐2‐methylpropanesulfonate)] (NB–AMS) (mole ratio 3.8:1). The activity coefficient of sodium ion in Na‐PAMS and Na‐PMOS without added salt is found to be in the range from 0.1 to 0.3 and is insensitive to changes in polymer concentration. However, it increases with increasing concentration of the added salt.The extent of sodium ion binding at a given sodium ion concentration, as estimated from the activity data for some sodium and tetrabutylammonium (TBA) salts, decreases in the order Na‐PAMS ≈︁ Na‐PMOS > TBA–PAMS > TBA–(NB–AMS). This indicates that a significant portion of the binding is attributed to the binding of TBA+ ions. Also compared are the results of ion binding in Na‐PAMS and Na‐PSS as a function of ionic strength. At low ionic strength (<1.0M), the order of binding strength is Na‐PAMS > Na‐PSS, while the order is reversed at high ionic strength (>1.0M). This finding is in good agreement with data obtained by dilatometry and viscometry.
Structural studies of single spherulites and partially spherulitic films of poly(methyl‐D‐glutamate)
Authors: Wilkes Garth L. , Mohadger Youseph , Holaday William 
Published: April 2003

AbstractIsolated spherulites of poly(methyl D‐glutamate) (PMDG) were nucleated in bromoform. The morphology of these spherulites was investigated by SEM and photographic small‐angle light scattering (SALS). From the SALS patterns, the development and growth of the spherulites could be noted. Films of PMDG cast from bromoform solution were found to be partially spherulitic. The mechanical properties of these films, prepared by different procedures, were compared with the general behavior of PMDG films cast from chloroform, the latter of which does not contain spherulitic texture.
The mechanical properties and structure of poly(m‐methylene terephthalate) fibers
Authors: Ward I. M. , Wilding M. A. , Brody H. 
Published: April 2003

AbstractA study has been carried out of the differences in mechanical properties of oriented fibers of poly(ethylene terephthalate) (2GT), poly(trimethylene terephthalate) (3GT), and poly(tetramethylene terephthalate) (4GT). The properties studied include the tensile stress–strain behavior, the recovery from strain, shrinkage at 100°C and the glass‐transition temperatures. The stress–strain curves of the three materials differ markedly. 2GT shows a monotonic increase in stress with increasing strain up to failure, which occurs at ∼20% strain, and the oriented fibers possess a comparatively high initial modulus. 3GT shows a much lower initial modulus and there is an inflection in the stress–strain curve at about 5% strain. The stress–strain curve of 4GT shows a number of distinct features. Although the initial modulus of 4GT is similar to that of 3GT, the stress–strain curve shows a pronounced plateau in the region between 4% and 12% strain. At higher strains the stresses rise rapidly before failure. These features of the stress–strain curves in the three polymers can be related to previous studies where the x‐ray diffraction spectrum and the Raman spectrum have been examined for fibers under stress. The ranking of both the recovery and shrinkage behavior of these materials is in the order 3GT > 4GT > 2GT. These results can also be understood in terms of the results of the previous structural studies, and it is concluded that the molecular conformations in both the crystalline and noncrystalline regions play a key role in determining the mechanical behavior.
Investigation of poly(trans‐1,4‐butadiene) crystals using the spin‐probe method
Authors: Nagamura T. , Woodward A. E. 
Published: April 2003

AbstractThe spin‐probe technique has been employed to study the nature of the surface regions of poly(trans‐1,4‐butadiene) crystals grown from dilute heptane and toluene solutions. The narrowing of the ESR spectrum of the nitroxide radical probe added to the PTBD crystals and the activation energy for the rotational motion of the probes were found to very with the crystallization solvent and annealing temperature; in every case heptane‐grown crystals showed a higher line narrowing temperature and activation energy than toluene grown crystals. Annealing at 80°C raised the narrowing temperature and the activation energy for crystal preparations from both solvents used, but annealing at high temperatures, near to but below the melting point, lowered both parameters again. These results support earlier assertions, based on infrared spectra, surface epoxidation, differential scanning calorimetry, broad‐line nuclear magnetic resonance, and dynamic mechanical results concerning the nature and location of the amorphous regions in PTBD crystals.
Effect of concentration of the crosslinking agent and diluent during polymerization on the viscoelastic spectra of poly(2‐hydroxyethyl methacrylate) networks
Authors: Ilavský M. , Hasa J. , Vojta V. , Janáček J. 
Published: April 2003

AbstractThe effect of concentration of the crosslinking agent (ethylene dimethacrylate) and diluent (water) during the crosslinking copolymerization on the shape and position of retardation spectra in the dry state has been investigated for poly(2‐hydroxyethyl methacrylate) networks. With increasing water content during network formation, the maxima of the retardation spectra, Lm, increase and the position of the spectra is shifted toward shorter retardation times, τ. The results are in quantitative agreement with the modified Rouse–Mooney (R–M) molecular theory and suggest the influence of deformation due to the diluent during network formation on the viscoelastic behavior. With increasing content of the crosslinking agent, the retardation spectra are shifted toward longer times. At a constant reference temperature T0 = 115°C the retardation time, τm, at the maxima of the spectra increases with increasing content of effective chains in the network, νe. However, after a correction for the effect of the monomeric frictional coefficient, ξ, τm/ξ decreases with increasing ve at a rate which agrees quantitatively with the R–M theory. The slope of the retardation spectra in the main transition region and the value of their maxima decrease with increasing ve; a comparison of these dependences with theory leads to the most probable distribution of submolecules in the chains. The contribution of long retardation times to the equilibrium compliance, Je, of the systems under investigation was estimated; it was shown that the application of the Thirion–Chasset extrapolation method for the determination of Je of loose networks requires a certain type of dependence of the retardation or relaxation spectra on τ.
High‐pressure phases in polymers. IV. Skeletal growth in cis‐polyisoprene
Authors: Edwards B. C. , Phillips P. J. 
Published: April 2003

AbstractThe crystallization of cis‐polyisoprene even at moderately elevated pressures results in the formation of a single‐crystal species which develops through skeletal growth. The nature of these crystals, which are produced at relatively low supercooling, is described. They occur concurrently with spherulites but exhibit a much higher growth rate. In common with single crystals grown from solution the size and shape of the species is a function of the supercooling.
On the structure of glassy polymers. III. Small‐angle x‐ray scattering from amorphous polyethylene terephthalate
Authors: Renninger A. L. , Uhlmann D. R. 
Published: April 2003

AbstractThe small‐angle x‐ray scattering (SAXS) from glassy polyethylene terephthalate has been measured using a Bonse–Hart system. The data cover the angular range (2θ) between 20 sec and 2 deg. After correcting for absorption, background, and beam divergence, the data have been placed on an absolute basis by comparison with the scattering from a standard silica suspension. The corrected absolute intensity decreases strongly with increasing angle over the range between 20 sec and 15 min, decreases more gradually in the range between 15 min and 45 min, and reaches a nearly constant asymptotic value over the range between 45 min and 2 deg. The magnitude of the scattering in the constant range, about 0.4 (electrons)2 Å−3, is very close to the value predicted by the thermodynamic fluctuation theory for fluids applied at the glass‐transition temperature [0.34 (electrons)2 Å−3]. The increase in intensity at angles smaller than about 45 min cannot be described by structures on the scale and volume fraction of the nodules reported in amorphous PET (50–100 Å), but can be well represented by small concentrations of heterogeneities, ranging in size from 100 to 2000 Angstroms, superimposed on the thermal density fluctuations frozen‐in at the glass transition. The bulk structure of this material seems well described as a random amorphous solid, containing simple thermal fluctuations and a small concentration (<1 vol‐%) of heterogeneities covering a range of sizes. The heterogeneities in the small end of the range may well be crystallites which formed on cooling.
Thermal shrinkage of oriented semicrystalline poly(ethylene terephthalate)
Authors: Bhatt G. M. , Bell J. P. 
Published: April 2003

AbstractThe shrinkage of commercial oriented poly(ethylene terephthalate) filaments was studied within the framework of the kinetic theory of rubberlike elasticity. Previous workers had found that the shrinkage and optical behavior of amorphous polymers could be satisfactorily explained in terms of this theory. Such an analysis is now applied to semicrystalline samples of moderate and high draw ratios (from 2× to 6×).It was found in this work that the thermal shrinkage force behavior as well as the optical anisotropy as a function of stretch can be explained in terms of the theory of rubberlike elasticity, if the following reasonable assumption is made: the average number of statistical segments per network chain in the noncrosslinked sample increases as a function of the draw ratio. A possible mechanism for such behavior is the relaxation of some of the chain entaglements due to the strain imposed externally on the fiber.
Morphology and modulus–temperature behavior of semicrystalline poly(ethylene terephthalate) (PET)
Authors: Groeninckx G. , Berghmans H. , Smets G. 
Published: April 2003

AbstractThe influence of the thermal history on the morphology and mechanical behavior of PET was studied. The degree of crystallinity (density measurements) and the morphological structure (electron microscopy and small‐angle x‐ray diffraction) depend on the crystallization temperature. The viscoelastic parameters obtained from the modulus–temperature curves are mainly determined by the morphology of the samples. The glass‐transition temperature, Ti, is a function of the crystallinity and the crystallization temperature. It is maximum for a crystallinity between 0.34 and 0.39 for a sample crystallized isothermally between 120 and 150°C. This dependence on crystallization conditions is ascribed to the conformation of the amorphous chain segments between the crystalline lamellae as well as the concentration and the molecular weight of the polymer material rejected during isothermal crystallization. Both factors are supposed to be temperature‐dependent.The value of the rubbery modulus is a function of both the volume concentration of the crystalline lamellae and the structure of the interlamellar amorphous regions (chain folds, tie molecules, chain ends, and segregated low molecular weight material). Annealing above the crystallization temperature of isothermally crystallized samples has a marked influence on their morphology and mechanical behavior. The morphological structure and the viscoelastic properties of annealed PET samples are completely different from those obtained with samples isothermally crystallized at the same temperature.
Morphological mechanics of springy polymers
Authors: Wool Richard P. 
Published: April 2003

AbstractThe mechanics of “springy” or “hard elastic” row‐crystallized polymers were investigated. It was found that their unique tensile and physical properties could be explained by adhesive fracture mechanics and simple beam deflection. The deformed lamellae had an apparent negligible modulus of flexural rigidity. An adhesive failure model was designed which duplicated all the tensile characteristics of springy polymers, including constant lateral contraction, critical stress, peel stress, rehealing, energetic elasticity, and cyclic strain behavior. The ideal relative density change as a function of strain was found to be the same for all springy polymers. Dynamic infrared analysis showed that the molecular orientation decreased during the deformation of springy polypropylene films. The latter is due to the deflection of lamellae. Rehealing was accompanied by a time‐dependent reversal of orientation. The enthalpic elasticity is derived from the strain energy of the lamellar network.
Light scattering by helical fiber structures: Experimental models
Authors: Visconti S. , Hien N. V. , Borch J. , Marchessault R. H. 
Published: April 2003

AbstractSamples of two helically wound monofilaments were used as experimental models to check the theoretical expression for light scattering from helixes. A method of estimating the pitch and tilt of the helixes was outlined and the results were compared with measurements from microscopy. The agreement was satisfactory. Layer line streaking and splitting was observed and explained in terms of irregularity of the helical parameters. Samples of several helically wound monofilaments were also prepared and their scattering patterns were compared with those from native and regenerated cellulosic fibers.
Acoustic emission of a crazing polymer
Authors: Grabec I. , Peterlin A. 
Published: April 2003

AbstractThe acoustic emission from a crazing polyvinyltoluene in a tensile and bending experiment is described. Acoustic emission appears as a series of bursts which most likely correspond to the initiation and growth of crazes. The emission intensity is characterised by acoustic activity (pulse rate) measured by the ring‐down technique. The average activity increases with strain. During repeated loading the acoustic activity shows a measurable intensity and significant rise only beyond the maximum strain of the former runs. This is equivalent to Kaiser's effect in metals. Acoustic emission during the creep experiment occurs in three characteristic periods. They are characterized as the relaxation, fatigue, and breakdown periods. Visual observations indicate that the relaxation period corresponds to the initiation, and the fatigue period to the growth of crazes. In the breakdown period a macroscopic crack develops and the sample fails.
Effect of partially immobilizing sorption on permeability and the diffusion time lag
Authors: Paul D. R. , Koros W. J. 
Published: April 2003

AbstractThe gas permeability and diffusion time lag may exhibit varying degrees of pressure dependence for glassy polymers. The sorption isotherm appears to consist of contributions from both Langmuir and Henry's law terms in such systems. This “dual sorption” theory advanced in the literature pictures gas held by the Langmuir mode as being completely immobilized. In the present paper, this model is extended to accommodate different degrees of partial immobilization of gas sorbed by this mode using two different formulations. One uses a transport expression based on concentration gradients while the other is based on chemical potential gradients. The predictions are that: (1) total immobilization results in a constant permeability with a time lag which strongly decreases with pressure; (2) no immobilization results in a constant time lag with a permeability which decreases strongly with pressure; and (3) incomplete immobilization results in both the permeability and time lag decreasing with pressure but neither as strongly as in the other limiting cases. The differences which may arise by the two formulations of the model are discussed.
The mechanical behavior of poly(methyl methacrylate) under pressure
Authors: Matsushige K. , Radcliffe S. V. , Baer E. 
Published: April 2003

AbstractTensile deformation of poly(methyl methacrylate) carried out under hydrostatic pressures up to 4 kbar has shown that the pressure‐transmitting fluid (silicone oil) strongly affects the mechanical properties of this polymer. Unsealed specimens fractured in a brittle manner at almost the same strain of 5% in the whole pressure range examined, while specimens sealed with Teflon tape and rubber showed a brittle to ductile transition at only 0.25 kbar. At this pressure, the craze initiation and shear band initiation stresses were found to become equal. The pressure dependence of the shear band initiation stress could be expressed well with a “nonlinear” pressure‐dependent von Mises criterion and the onset of the shear banding was proved to relate to the enthalpy energy density stored in the specimen. The combination of the nonlinear pressure‐dependent von Mises criterion and the enthaply energy density concept enabled us to predict the pressure dependence of Young's modulus.
Brillouin scattering from amorphous bisphenol‐A polycarbonate
Authors: Patterson G. D. 
Published: April 2003

AbstractBrillouin scattering has been studied from amorphous bisphenol‐A polycarbonate in the temperature interval 60–240°C. Both longitudinal and transverse Brillouin peaks are observed over the entire range. The behavior of both types of Brillouin splittings, Δωl and Δωt, in the region of the glass–rubber relaxation is typical of an amorphous polymer. Equilibrium values of Δωl and Δωt were obtained 20°C below the glass‐transition temperature Tg determined at cooling rates of 20°C/hr. Comparison of the present results with previous ultrasonic data reveals a considerable dispersion in the longitudinal phonon velocity below Tg. The origin of the large transverse Brillouin intensities is related to the structure of polycarbonate.