bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic mechanical and dielectric relaxations of polystyrene below the glass temperature
Authors: Yano Okimichi , Wada Yasaku 
Published: April 2003

AbstractDynamic mechanical and dielectric properties of various kinds of polystyrene, including bulk‐polymerized, monodisperse, isotactic, and thermally degraded samples, have been measured below the glass temperature to 4°K. Five relaxation processes are found, designated β, γ, γ′, δ, and ε in order of descending temperature. The β peak (350°K at 10 kHz) is attributed to the local oscillation mode of backbone chains and the γ′ peak (180°K at 10 kHz) to rotation of phenyl groups. The δ peak (100°K at 10 kHz) is observed only in dielectric properties of the bulk‐polymerized sample and is assigned to weak polar bonds, such as oxygen bonds in the chain. The δ peak (55°K at 10 kHz) which is prominent in dynamic mechanical properties is interpreted in terms of lattice defects due to a syndiotactic diad inserted between isotactic sequences in a chain or vice versa. The ε peak (ca. 25°K at 10 kHz) is first reported in the present work, but the mechanism involved is not yet clear.
Investigation of cooperative kinetics on reactions of functional groups on polymer chains
Authors: Goldstein B. N. , Goryunov A. N. , Gotlib Yu. Ya. , Elyashevich A. M. , Zubova T. P. , Koltzov A. I. , Nemirovskii V. D. , Skorokhodov S. S. 
Published: April 2003

AbstractThe kinetics of aminolysis of 1,2;3,4‐meso‐erythritol dicarbonate and 1,2;3,4;5,6‐mannitol, sorbitol, and dulcitol tricarbonates by n‐butylamine in dimethylformamide solution was investigated. The dicarbonate and tricarbonates are considered respectively as models of dyads and triads in the poly(vinylene carbonate) chain. The theoretical kinetic curves for the dimer and the trimers were calculated by solution of kinetic equations and close agreement with experiment was obtained. A version of the Monte‐Carlo method was developed to provide a model for the reaction process by a computer calculation including the neighboring group effect in enhancing reactivity. The theoretical curve for a trimer coincides with the experimental one. These results confirm the accelerating influence of the unreacted neighboring groups. For the polymeric chain the experimental and calculated curves deviate for conversions beyond 10%. This indicates an additional polymer effect, which is as yet unexplained.
Fractionation during crystallization
Authors: Sadler D. M. 
Published: April 2003

AbstractExtensive gel‐permeation chromatography (GPC) results are presented which reveal in much more detail than hitherto the effects of fractionation during the crystallization of polyethylene from solution. It is suggested how these results may be used to assess the affects of fractionation on the production of single crystals. In addition the results are compared with the fractionation which would be expected assuming the crystals to be in equilibrium with the solution. It was found that the results can be explained very well on this basis. A discussion of this rather unexpected result is included.
Formation of spherulites in polyamides. V. “odd‐odd” polyamides
Authors: Magill J. H. 
Published: April 2003

AbstractThe crystallization of a series of “odd‐odd” polyamides has been examined for a variety of fusion conditions and crystallization temperatures. Diverse kinds of spherulites and other crystalline structures have been formed in these nylon polymers by direct crystallization from the melt and by melt‐seeding techniques. The structures formed in this way have been characterized primarily with the aid of optical microscopy. In this series of polymers, characteristic textural features yield a fairly unified pattern of crystallization behavior. Crystalline aggregates are formed near the respective melting points of these polymers. In very thin sections (ca. 0.1μ), plateletlike crystals of high crystallinity exhibit optical and diffraction behavior characteristic of single crystals.
Adsorption of polymers at the solution–solid interface. V. Styrene–methyl methacrylate copolymers on carbon
Authors: Hopkins A. , Howard G. J. 
Published: April 2003

AbstractThe adsorption of a series of block and random styrene–methyl methacrylate copolymers on an animal charcoal and on Graphon has been studied. On charcoal, adsorption decreases with increase of molecular weight because of the inability of larger coils to penetrate into the adsorbent. An analysis is presented which requires that coils undergo considerable distortion on adsorption in pores. The adsorption of random copolymers on Graphon is also in reverse order of molecular weight; this effect may be due to particle bridging leading to the formation of interparticle “pores.” The relative affinity of the styrene and methyl methacrylate residues is different on charcoal and Graphon, respectively; on both surfaces, however, relatively few of the more active residues are required for adsorption. Block and random copolymers are adsorbed to different extents which depend on the nature of the adsorbent surface.
Adsorption kinetics in the polyethylenimine–cellulose fiber system
Authors: Kindler William A. , Swanson John W. 
Published: April 2003

AbstractThe rate of adsorption of fractionated polyethylenimine (PEI) from water onto regenerated cellulose fibers was studied as a function of the polymer diffusion coefficient. Differences in polymer molecular weight, salt concentration, and pH were employed to vary the diffusion coefficient which was measured independently by a free‐diffusion technique. The sorption rate was measured at the same conditions and found to increase with decreasing molecular weight, increasing polymer concentration, decreasing salt concentration, and increasing pH. A simplified rate equation based on diffusion control with Langmuirian adsorption in stirred solution was developed by utilizing the concept of a Nernst diffusional film. The equation was successful in predicting the relationship between adsorption rate and diffusion coefficient for most cases studied. It was found, however, that a very large barrier to mass transfer retards the adsorption rate. For the system studied it was concluded that this barrier is a result of diffusion into and subsequent adsorption onto the internal porous structure of the cellulose.
Electron microscopy of drawn polypropylene
Authors: Sakaoku K. , Peterlin A. 
Published: April 2003

AbstractExtremely thin polypropylene films formed by evaporation of dilute solutions floating on water, thin films deposited on Mylar or on carbon‐coated Mylar, and bulk samples were deformed; after etching with aqua regia or chromic acid, the surfaces were studied by electron microscopy of surface replicas. At small draw ratio, microfibrils with lateral dimensions of about 200 Å, originating in micronecks at crack boundaries of the original crystal lamellae, were obtained in isolated areas exhibiting maximum local strain separated by large regions of much less deformed material. With increasing draw ratio the necked regions grow, the old structure gradually being reduced to smaller and smaller islands until it disappears completely. The inhomogeneity of strain in adjacent bundles of microfibrils creates a great many longitudinal voids with more or less disoriented microfibrils bridging the gaps. The regular arrangement of crystalline blocks of rather uniform length and width can be occasionally seen on surface replicas of drawn samples, and much better on dark‐field electron micrographs of drawn and annealed thin membranes. In the latter case the blocks are very uniform and have similar dimensions along and perpendicular to the axis of the microfibril. The evidence from the electron micrographs, together with previous small‐angle x‐ray scattering data, supports Peterlin's molecular model for plastic deformation of crystalline polymers.
Molecular morphology of cellulose
Authors: St. John Manley R. 
Published: April 2003

AbstractNative celluloses of various biological origins, as well as regenerated celluloses were examined by electron microscopy after suitable dispersion. In all cases the specimens were found to be composed of a common filamentary unit which is rectangular in cross section and has the approximate dimensions 35 × 20 Å. It is suggested that these are the basic morphological units of cellulose; they are therefore called protofibrils. For protofibrils of regenerated cellulose it is shown that: (1) the molecular contour length greatly exceeds the protofibril length, (2) the mass of the protofibril corresponds to that of a single molecule, and (3) the protofibril length increases with molecular weight. Additionally, high resolution electron micrographs of native and regenerated protofibrils show an apparent axial texture with a periodicity of about 40 Å. From these observations and the knowledge that the molecular chain axis is aligned parallel to the protofibril axis, a model of the protofibril is deduced. The model consists of a ribbon which is pleated on itself so as to form a planar zigzag structure of rectangular cross section. This supersedes a previously proposed model of circular cross section. The structure is composed of a single folded, chain, arranged so that the short extended segments between the folds are parallel to the protofibril axis. The protofibril is thus regarded as the morphological expression of the cellulose molecule. Microfibrils and protofibrils often exhibit kinks, the angle between the kinked portions being 120°. This phenomenon is satisfactorily explained by the protofibril model and in fact provides good support for it. Finally, various properties of cellulose are considered in relation to the model. By contrast with the earlier crystalline–amorphous concepts of cellulose fine structure, it is suggested that protofibrils are completely crystalline structures, and that the properties of cellulose may be understood by considering processes that occur at the level of the protofibril as a unit.
Diffusive and hydraulic permeabilities of water in water‐swollen polymer membranes
Authors: Yasuda H. , Lamaze C. E. , Peterlin A. 
Published: April 2003

AbstractThe diffusive permeability of water P, which relates to diffusive flux of water under a concentration gradient of water (measured by diffusion of tritiated water), and the hydraulic permeability of water K, which relates to the water flux under a hydraulic pressure gradient are defined. For the case of diffusive transport one has P = KRT/ν1, where ν1 is the molar volume of water. The relationship between P and K was investigated as a function of hydration H, i.e., the volume fraction of water in swollen polymer membranes. The following characteristic features of water permeability are revealed. (a) In the lowhydration region (H < 0.2), water permeates by diffusion even under an applied hydraulic pressure gradient and KRT/ν1 = P. (b) In the higher hydration region KRT/ν1 is greater than P, and the ratio ω = KRT/ν1P increases nearly exponentially with decrease of (1‐H)/H. Water in this region moves partly by bulk flow under an applied hydraulic pressure gradient but moves only by diffusion in the absence of a pressure gradient. (c) The dependence of log P on (1‐H)/H is nearly linear in regions of both high and low hydration but the slopes are different. The transition occurs in about the same H range where the discrepancy between P and KRT/ν1 becomes significant. Excellent agreement was found between the experimental data for P as a function of H and the theoretical prediction based on the free‐volume concept of diffusive transport in hydrated homogeneous membranes.
Glass transition temperatures of some linear polymers containing phenyl side groups
Authors: Pizzirani Giovanna , Magagnini Pierluigi , Giusti Paolo 
Published: April 2003

AbstractThe glass transition temperatures of a number of poly(vinyl phenyl ketones), poly‐(vinyl benzoates), and poly(phenyl acrylates) have been measured by a refractometric method. The effects exerted on Tg by the nature and position of the ring substituents and by the different groups binding the pendant phenyl rings to the polyvinyl chain are discussed. The importance of knowledge of the side‐group motions in the glassy state for the interpretation of glass temperature data is emphasized.
Viscoelastic properties of linear polymers in the high‐elastic state
Authors: Vinogradov G. V. , Dzyura E. A. , Malkin A. Ya. , Grechanovskiǐ V. A. 
Published: April 2003

AbstractThe relation between molecular weight, chain rigidity and the length of the high‐elasticity plateau is determined from frequency and temperature dependences of the storage modulus for polybutadienes and polystyrenes with Mw/Mn ⩽ 1.1. Use is made of the concept of equivalence of high‐elastic states characterized by equal lengths of high‐elastic plateaus for linear polymers. The high‐elastic states of the linear polymers studied are equivalent if the polymer chains have equal numbers of dynamic segments and if the reference temperature is T0 = 1.22Tg, where Tg is the glass transition temperature. The viscoelastic properties of the polymers in the high‐elastic state are determined unambiguously by Tg and the molecular weight of the dynamic segment. The quantitative relation between thermomechanical characteristics obtained by measuring deformation versus temperature under a constant time regime and dependence of storage modulus versus frequency under isothermal conditions is discussed.
Study of low‐frequency motions of extended chains in polyethylene by Neutron inelastic scattering
Authors: Berghmans H. , Safford G. J. , Leung P. S. 
Published: April 2003

AbstractThe low‐frequency skeletal and intermolecular modes (below 900 cm−1) have been studied for a sample of “as‐polymerized” Ziegler‐Natta polyethylene for which extended‐chain conformations have been proposed. These results have been compared with data from a sample of stirred‐solution‐crystallized polyethylene and with previous measurements for highly crystalline samples of folded‐chain polyethylene. Measurements were also made of the temperature dependence of these modes for the as‐polymerized material and of the polarization dependence of these modes for an oriented sample of solution‐stirred polyethylene. In the neutron spectra and the corresponding derived frequency distributions, the observed major “singular” frequencies for both the skeletal and intermolecular modes are in reasonable accord with those previously observed for folded‐chain samples of high crystallinity and in Raman measurements. In addition, these frequencies agree with those predicted by theory for the singular frequencies corresponding to the phase‐frequency relationships for the skeletal and intermolecular modes of an infinitely extended chain in a crystal. However, in the spectra of the extended‐chain materials, these singular frequencies, in general, appear sharpened and enhanced in intensity relative to those for previously reported results on folded‐chain polyethylenes; consequently, assignment of their characteristic frequencies is easier. In addition, evidence is presented to show that, for the extended‐chain materials, these frequencies broaden less rapidly with increasing temperature, and the corresponding average vibrational amplitudes are smaller than those observed for highly crystalline samples of folded‐chain material. It is suggested that in these materials the reduction of the number of chain folds and the increased intramolecular ordering give rise to increased thermal stability of the configurations with regard to segmental rotation and to decreased vibrational amplitudes relative to folded‐chain materials. When the aspolymerized materials is preheated above the normal melting point for polyethylene, the neutron spectra revert to those more characteristic of the folded‐chain materials, indicating that a relaxation of chain extensions has occurred. However, on the basis of these results, on quantitative estimates of the characteristic relaxation time can be presented. Additional frequencies, besides those predicted by theory for the skeletal and intermolecular modes and those associated with either multiphonon contributions or the presence of chain folds, are observed. The origin of these frequencies remains unclear but may warrant further theoretical consideration.
Crystal deformation during the growth of kink bands in oriented polyethylene
Authors: Robertson Richard E. 
Published: April 2003

AbstractWhen oriented polyethylene is sheared at an angle to the orientation axis, kink bands often develop and grow, with a resulting change of the crystalline orientation. Beside the crystalline reorientation, the following changes within the kink bands have been observed with wide‐angle x‐rays: (a) partial transformation to a monoclinic from the normal orthorhombic unit cell; (b) partial alignment of the orthorhombic b axes; (c) rotation of the orthorhombic c axes of a fraction of the crystals around the kinks by an extra 40 to 60° beyond that of the fibrils; and (d) misalignment of the orthorhombic (hk0) planes by a few degrees. These results are suggested to arise, at least in part, from crystal flattening and from crystal twinning or pseudotwinning on planes intersecting the molecular axes.
Halogenation of polyethylene. I. Bromination of single crystals
Authors: Harrison Ian R. , Baer Eric 
Published: April 2003

AbstractIt has been demonstrated that the fold surfaces of polymers can be specific towards chemical attack, if the reaction is mild and nondestructive of the fold. Bromination of suspensions of single crystals of polyethylene in carbon tetrachloride has been shown to be such a system. This chemical modification of a fold surface is a powerful means of extending the applications of the physical methods available. Several methods were used, among them DTA, DSC, infrared spectroscopy and small‐angle x‐ray diffraction. Experimental results from these methods lead to the following conclusions. (a) Bromination takes place preferentially at the folds and is consistent with a regular adjacent reentry fold model. (b) Annealing of these brominated crystals demonstrates the major role played by the crystal surface in this process. (c) The preparation and properties of a novel copolymer system has been demonstrated. It is felt that this copolymer system may prove a useful addition to those systems presently available.
Transport properties of methylene chloride in drawn polyethylene as a function of the draw ratio
Authors: Williams J. L. , Peterlin A. 
Published: April 2003

AbstractThe sorption and diffusion constants of CH2Cl2 at room temperature in quenched polyethylene film drawn at 60°C to different draw ratios λ between 6 and 25 drop drastically between λ = 8 and λ = 9 and then remain nearly constant, dropping only slightly up to λ = 25. Also, the exponential dependence of diffusion constant on concentration of sorbent increases abruptly in the same draw interval and then remains constant at the higher draw ratios. The data may be explained well by a composite madel: a low‐permeability fiber structure embedded in a high‐permeability spherulitic matrix. As the draw ratio is increased, the initially spherulitic film is gradually transformed into the fiber structure with the transformation being completed between λ = 8 and λ = 9. During subsequent drawing to λ = 25 the mutual arrangement of microfibrils, the basic elements of the fiber structure, changes by longitudinal sliding. However, their transport properties remain nearly constant. The diffusion constant drops a little as a consequence of the increased fraction of tie molecules which reduces the number of unperturbed sorption sites.
Crystal structure of methyl acrylate
Authors: Brown Allan , Gillbro Tomas , Nilsson Bo 
Published: April 2003

AbstractMethyl acrylate, CH2CHCOOCH3, has been crystallized, and x‐ray data have been collected at −120°C. The crystals are orthorhombic, space group Pnma, with four molecules in the unit cell. The structure has been determined by using symbolic addition procedures, and refined to a final residual R factor of 0.10. The molecule is planar, and the intramolecular bond distances and angles are in good agreement with values obtained for the liquid monomer by electron diffraction techniques. Considerations of crystal geometry indicate that the packing hardly permits dimerization or polymerization of the molecules in regions of crystal perfection.
Transitions and relaxations in aromatic polymers
Authors: Wrasidlo Wolfgang 
Published: April 2003

AbstractTransition and relaxation phenomena in 26 structurally related polyquinoxalines and other aromatic polymers were studied over a temperature range from 70 to 770°K by means of calorimetric, dilatometric, dynamic mechanical, and dielectric techniques. Differential thermal analysis and x‐ray data showed these polymers to be essentially amorphous. The lack of crystallinity is attributed to geometric isomerism, resulting in conformational as well as configurational disorder. Calorimetric measurements gave discontinuities in heat capacities ranging from 12 to 54 cal/°C per mole of repeat‐unit structures and provided unambiguous assignments of glass transition temperatures of these polymers. Depending upon structure, Tg varied from 489 to 668°K. Thermal expansion curves of annealed bulk polymer samples between 70 and 770°K exhibited only one discontinuity over the entire temperature range, namely at Tg, thus indicating the absence of any motion leading to transitions in the solid state of these polymers. Viscoelastic properties were obtained by means of torsional braid analysis and a longitudinal vibrational apparatus. In a typical case, the dynamic mechanical relaxation spectrum contained three loss maxima. A peak of low amplitude occurring at 483°K was attributed to impurity effects, resulting from endgroups and species of low molecular weight. The second and only major relaxation process occurred at 579°K, in the glass transition interval. A third, weak loss peak of unknown origin was found in the liquid state at 683°K. On the other hand, the dielectric loss curves of various polymers exhibited only one broad and strong absorption maximum at temperatures 30 to 100°K higher (depending upon a particular polymer) than equivalent major mechanical loss peaks. These differences are interpreted from a mechanistic point of view. Major mechanical relaxations occurring in the glass transition interval of these polymers are proposed to result from translational motions.
Polymerization of monolayers. VI. Influence of the nature of the exchangeable ion on the tacticity of insertion poly(methyl methacrylate)
Authors: Blumstein Alexandre , Parikh Kirit K. , Malhotra Shadi L. , Blumstein Rita 
Published: April 2003

AbstractThe influence of the nature of exchangeable cations on the tacticity of poly(methyl methacrylate) (PMMA) prepared from montmorillonite–MMA adsorption complexes was investigated. The strength of ion‐dipole interactions was estimated either by the value of the electrostatic interaction potential or by the value of the carbonyl‐stretching frequency shift. It was shown that Pi, the percentage of isotactic triads in the polymer, increases with increasing strength of the ion‐dipole interactions, while the persistence ratio and the mean length of closed isotactic (or syndiotactic) sequences remain essentially unchanged regardless of the nature of the cation. It was shown that values of Pi may vary from 0.15 for weakly interacting ions to 0.5 for strongly interacting ones, reaching at the upper limit the value calculated from the model proposed in a previous paper, thus confirming its validity.