bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gelation and crystallization of poly(ethylene terephthalate‐co‐isophthalate)
Authors: Berghmans H. , Govaerts F. , Overbergh N. 
Published: April 2003

AbstractGelation of solutions of poly(ethylene terephthalate‐co‐isophthalate) depends on chain structure, solvent, temperature, and concentration. Wide‐angle x‐ray scattering and differential scanning calorimeter experiments reveal the crystalline nature of the gel. The crystalline crosslinks, with a fringed micellar structure, are composed of terephthalate units. Orientation of the dried gels reveals the presence of crystallites with their largest dimension parallel or perpendicular to the chain axis. At high enough concentration of crystallizing units in the chain, folded‐chain lamellar structures are also formed. Compared with the fringed micellar crystallization, the induction time for this crystallization is short. Melting of the folded‐chain structures is very similar to the melting of pure poly(ethylene terephthalate). Because of the crystalline nature of this gelation, copolymers with only a small difference in composition can be fractionated according to the difference in micro‐structure.
Viscosities of dilute polymer solutions in nematic liquids
Authors: Brochard F. 
Published: April 2003

AbstractA nematic fluid is characterized by five friction coefficients. When dilute polymer coils are added to the fluid, all these coefficients are modified. Three Miesowicz viscosities (measured under an aligning magnetic field) and two coupling coefficients between orientation and flow are discussed. In our calculation, elastic dumbbells are used to model the flexible polymer chains. The results are written in terms of two size parameters R∥ and R⊥ and two chain friction coefficients λ∥ and λ⊥ (the label ∥ refers to a direction parallel to the nematic axis). This could be compared to other experiments (such as translational diffusion) which measure λ∥ and ⊥ directly. They may give useful estimates of coil conformation in nematic solvents.
Thermodynamics of swollen, partially crystallized pseudoeutectoid copolymers of ethylene
Authors: Kilian H.‐G. , Maier E. 
Published: April 2003

AbstractSwelling phenomena within partially crystallized linear copolymers of ethylene with randomly distributed noncrystallizable co‐units can be described by the thermodynamics of deformed cluster networks, the formulation of which is based on an earlier description of the melting of pseudoeutectoid copolymers.
Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. III. Quantitative surface analysis by x‐ray photoelectron spectroscopy
Authors: Yamamoto Fumio , Yamakawa Shinzo 
Published: April 2003

AbstractX‐ray photoelectron spectroscopy (ESCA) has been used for quantitative surface analysis of surface grafts prepared by mutual irradiation of polyethylene (PE) in methyl acrylate (MA) vapor with γ rays and high‐energy electrons. The binding‐energy shift between the C1s electrons in the ester group of poly(methyl acrylate) (PMA) and in PE is large enough (ca. 3.6 eV) to distinguish the PMA and PE components. The C1s peak‐area ratio of ester carbon to other carbons is related quantitatively to graft composition by constructing a calibration curve for a given instrument and excitation source, with a series of homogeneous grafts of known composition used as the calibration standards. Using the calibration curve and the measured peak ratio, the surface composition of the surface grafts is determined. The relations between surface compositions according to ESCA and attenuated total reflection (ATR) infrared spectroscopy and between adhesive bond strength and ESCA composition are discussed. In the electron‐induced grafts, the grafted surface reaches maximum adhesive bondability with attainment of 100 mole % MA in the surface detected by ESCA; i.e., with formation of a homopolymer layer. The ESCA composition can be used as an indicator of the presence of the homopolymer layer or as a criterion for predicting adhesive bond strength.
Ultrahigh modulus polyethylene. II. Effect of drawing temperature on void formation and modulus
Authors: Jarecki Leszek , Meier Dale J. 
Published: April 2003

AbstractThe maximum degree of molecular orientation and deformation obtained by ultradrawing of high‐density polyethylene in air is limited by formation of internal voids (both longitudinal separation of fibrils and perpendicular cracking), and thus values of Young's moduli which are achievable by ultradrawing techniques are also limited to values much below the theoretical limit for fully extended chains. Temperature has a significant effect on the critical draw ratios at which intensive void formation begins, and also on the draw ratio at which failure occurs during the ultradrawing. The temperature effect is observed only for high‐density polyethylene having a wide molecular‐weight distribution, and which can be drawn at higher temperatures (30–40°C below its melting point), e.g., Dow Chemical polyethylene LP51.1. As a result of ultradrawing at higher temperatures, transparent, ultrahigh modulus samples having draw ratios of order of 40 have been obtained. The higher drawing temperatures significantly reduce fibril separation, and perpendicular cracking is shifted toward higher draw ratios. Hence, with LP51.1 the highest Young's moduli (65–70 GPa) have been exhibited by the samples which were ultradrawn at 100–105°C.
Molecular organization of the coupling agent interphase of fiber‐glass reinforced plastics
Authors: Ishida Hatsuo , Koenig Jack L. 
Published: April 2003

AbstractThe structure of the silane coupling agent interphase of fiber‐glass reinforced plastics has been studied by Fourier transform infrared and laser Raman spectroscopy. It is found that there is a degree of order in the molecular organization of the coupling agent interphase for the vinyl and cyclohexyl functional silane coupling agents. When a cyclohexyl functional silane is used, crystalline layers of silanetriol on the glass fibers are observed. The extent of order is determined by the structure of the adsorbed species, which is influenced by the structure of the silane in the treating solution. Two factors introducing disorder in the interphase are the magnitude of aggregation of the silanes in solution and irregularities in the topology of the glass surface.
Transitions and the relaxation spectrograph: Poly(oxymethylene)
Authors: Blumberg Avrom A. , Niemira Edwin R. 
Published: April 2003

AbstractIn place of directly assaying the relative rebound height of a ball from a polymeric sample, the passage time of the ball between fixed points is used in a much more precise version of the poor man's relaxation spectrograph. Poly(oxymethylene) has a sharp transition at — 74.8°C which progressively becomes broader and moves to — 39.0°C as the polymer is pretreated at 70°C and exposed to 330 nm light for times up to 1038 ksec. A second transition, broad and shallow, is seen in the range 104 to 124°C and is unaffected by the pretreatment. This is attended by a slight decrease in density, proportional to the time held at 70°C, at the rate of −3.54 × 10−9 g/cm3 sec.
Dynamic mechanical properties of polymers filled with agglomerated particles
Authors: Nielsen Lawrence E. 
Published: April 2003

AbstractThe filler particles in most filled polymers are not perfectly dispersed but are more or less agglomerated. The degree of agglomeration and the strength of the agglomerates, which can be modified by surface treatments, have a very great effect on the dynamic mechanical properties. Filler agglomerates which are wetted by the polymer matrix produce higher elastic moduli than similar agglomerates which are not wetted. The relative damping in most filled polymers is very temperature‐dependent. A qualitative explanation is given for this temperature dependence. The degree of agglomeration and the strength of the agglomerates are important factors in determining the damping.
Equation of state of semicrystalline and crystalline polymers
Authors: Jain R. K. , Simha Robert 
Published: April 2003

AbstractThe equation of state of a semicrystalline system can be expressed in terms of the corresponding functions for the crystal and the melt, extrapolated into the solid region. This relation may be employed to obtain crystal data by means of information on the semicrystalline material or vice versa. We consider four polymers, namely, polyethylene (LPE), isotactic polypropylene (PP), polyethylene glycol (PEG), and poly(tetrahydrofuran) (PTHF). For LPE, the combination of melt and crystal theories predicts satisfactorily the volume of the semicrystalline polymer at atmospheric and elevated pressures. Good agreement between theory and experiment obtains for PEG and PTHF equilibrium melts. In addition to a PP sample measured and discussed by Zoller, a second PP polymer by Leute et al. is considered. From the corresponding semicrystalline data, the equation of state of the crystal is then derived. The PVT results for the three crystalline polymers obtained in this indirect manner are in satisfactory agreement with the predictions of crystal theory. For purposes of comparison, a polymer melt with a low melting point, viz., cis‐1,4‐polybutadiene, is also discussed in terms of theory. A consideration of the scaling parameters and derived quantities for both crystal and melt had resulted in certain correlations encompassing LPE, PVF2, and PClF3. These cannot be generalized to the systems considered here, particularly in the crystalline state. PEG stands out in respect to several characteristic quantities in both states, whereas PP can be more nearly grouped with the previous three polymers. The theoretical equation of state for the polymer crystal does not satisfy a principle of corresponding states. However, practically useful and accurate interpolation formulas for the theoretical expressions, polynomials at atmospheric pressure, and Tait equations for the compression ratios are derived. Over certain ranges of reduced temperature and pressure, the theoretical isotherms can be approximated by master curves for the four polymers. At atmospheric pressure, such representations are limited.
Polymer solidification as a dissipative process
Authors: Lindenmeyer Paul H. 
Published: April 2003

AbstractBecause their conformational entropy is a nonlinear function of size, polymer molecules can only solidify under conditions far from equilibrium with the formation of dissipative structures. A dissipative structure is nonhomogeneous, it evolves with time from an initially space‐dependent fluctuation, and has a characteristic size that depends upon the initial perturbation and the conditions that apply during its entire history. The glass transition is envisioned as the formation of the ultimate dissipative structure where all of the latent heat of crystallization is dissipated within the structure. The mechanism of glass formation can be described as the spinodal decomposition of a homogeneous liquid into two interpenetrating networks of high‐ and low‐energy solids with a characteristic distance and a gradient of density and/or composition extending through both high‐ and low‐energy regions.
Isobaric thermal behavior of glasses during uniform cooling and heating: Dependence of the characteristic temperatures on the relative contributions of temperature and structure to the rate of recovery. II. A one‐parameter model approach
Authors: Kovacs A. J. , Hutchinson J. M. 
Published: April 2003

AbstractIsobaric variations of the characteristic temperatures Tg and Tmax, obtained on uniform cooling and heating of glasses, are investigated in terms of their dependence on the relevant experimental variables, using a single retardation time model. The corresponding partial derivatives of Tg and Tmax are derived as functions of the partition parameter x (ranging between zero and unity), which determines the relative contributions of temperature and structure to the retardation time. It is shown that the variation of Tg with the cooling rate is independent of x. In contrast, Tmax critically depends on x, and its value as well as those of its three partial derivatives are linear functions of x−1. The variations of Tmax are analyzed in terms of a set of reduced variables, leading to simple reduction rules between any two of the experimental variables when the third is kept invariant. The reduction rules are further substantiated by investigating the behavior of glasses in two‐step thermal cycles, which result in a unique set of inter‐relationships between any pair of the partial derivatives of Tmax, whatever the value of x. The results are discussed in terms of their relevance to the behavior of real glasses.
Ratios of average molecular weights and molecular weight distributions in polymers
Authors: Pyun C. W. 
Published: April 2003

AbstractIf Mmin and Mmax are lower and upper bounds, respectively, to the molecular weights of different molecular weight species contained in a polymer, the weight‐average to number‐average molecular weight ratio Mw/Mn cannot exceed (1 + Mmax/Mmin)2/(4Mmax/Mmin). The ratio attains this maximum possible value if the masses of the two species with molecular weights Mmin and Mmax are equal and the masses of all the other species are negligibly small, corresponding to maximum spread in the molecular weight distribution within the specified bounds. Also for a given value of Mw/Mn = α, the Mmax cannot be smaller than [2α − 1 + 2α1/2(α − 1)1/2]Mmin. The minimum possible value of Mmax/Mmin consistent with α given is obtained in the case of maximum spread described above. If only one species is predominant, then both Mw/Mn and Mmax/Mmin approach unity, as is well known. Similar relations hold for the ratios of higher‐order average molecular weights for which the role of the mass fractions is replaced by higher‐order distribution functions.
Chain conformations of block copolymers
Authors: Kurata Michio , Kimura Tsunehisa 
Published: April 2003

AbstractAn analytical theory of block copolymer conformations is developed for systematically studying the effects of the chain length, chain architecture, and segment interactions. The main results obtained for AB diblock and ABA triblock chains are as follows: (i) In the absence of AA and BB interactions, both diblock and triblock chains collapse to a dense form if the AB interaction is attractive. In the collapsed coil form, the mean‐square end‐to‐end distance 〈R2〉 is proportional to the square root of the number of segments n1/2. (ii) The diblock chain has a dumbbell form if AA and BB interactions are attractive and AB interaction repulsive, but the triblock chain collapses. In the dumbbell form, 〈R2〉 is proportional to n.
Longitudinal acoustic mode in polymers. V. Nature of perturbing forces in n‐paraffins and polymers
Authors: Chang Chih , Krimm S. 
Published: April 2003

AbstractBinary mixtures of n‐paraffins have been examined by Raman spectroscopy in order to elucidate the nature of the perturbations on the chains. For a short‐chain species diluted in a longer‐chain species, the longitudinal acoustic mode frequency of the former decreases from its value in the pure state to that corresponding to a chain with free ends. This observation, as well as others, confirms our previous suggestions that longitudinal perturbing forces are responsible for increasing this frequency over its unperturbed value. These results also provide new insights into the structures present in solid solutions of n‐paraffins. They reemphasize the necessity of incorporating the effects of such perturbations in applications of the longitudinal acoustic mode to morphological studies of polymers.
Evaluation of the relaxation modules from the response to a constant rate of strain followed by a constant strain
Authors: Smith Thor L. 
Published: April 2003

AbstractThe stress response σ(t) to a constant rate of strain $ \dot \varepsilon $ ε during the period 0 < t ≤ t* and to the constant strain ε* $ ( = \dot \varepsilon t*) $ thereafter is considered in terms of the Boltzmann superposition principle. When t ≤ t*, the data directly give the constant‐rate modulus F (t) ≡ σ(t)/ε(t), which can be converted straightforwardly into the relaxation modulus E(t). Results from illustrative calculations show that a reduction in the relaxation rate effects a decrease in [σ(t*)/ε*]/E(t*) and also in the time at which [σ(t)/ε*]/E(t) becomes essentially unity. To evaluate E(t) at t > t*, F(t) is first obtained from σ(t) and F(t − t*) by using a derived equation similar to that presented by Meissner. Thereafter, F(t) is transformed into E(t). For illustration, E(t) for a rubbery solid is evaluated over some 2.5 decades of time from its response to a strain rate of 0.25 min−1 for 0.40 min and thereafter to the attained strain of 0.10 for 5.4 min.
Permeability of heterogeneous gels
Authors: Weiss N. , Van Vliet T. , Silberberg A. 
Published: April 2003

AbstractGels made by radical copolymerization of monofunctional and difunctional monomer units in the presence of swelling medium will tend to be heterogeneous. A case in point is acrylamide co‐polymerized with N,N′‐methylene bis‐acrylamide in water. Such gels can be assumed to be two‐phasic with both phases gels, but of different average concentration and average degree of cross‐linking. As Weiss and Silberberg have shown, permeability can be used to characterize the distribution in space. In this paper, their earlier model is expanded and improved by considering specifically the permeability of each of the two phases and taking into account that each of these phases separately must have come into swelling equilibrium with the swelling medium, water. It can be shown that only the length of the Kuhn statistical element remains as a free parameter in this model. Essentially the same value of this parameter, however, accurately accounts for the measured permeability. It is found that at an overall volume fraction of about 0.16, the two‐phase structure tends to disappear. For higher degrees of crosslinking, this occurs because the more dilute phase takes over the entire space; for more lightly crosslinked systems, the more concentrated phase takes over. The heterogeneity of the distribution lies in the nanometer range and reasonable agreement between the results obtainable from permeability and from viscoelasticity can be demonstrated. These results are consistent with the model for the polymerization process.
Effect of microroughness on rubber friction
Authors: Borch Jens 
Published: April 2003

AbstractFriction was measured and analyzed for rubber belts sliding against paper and polymer film surfaces of different roughness. As expected, increased paper smoothness created an increase in the friction coefficient. However, it was found that continuous rubber usage during testing also created an increase in friction coefficient for constant surface roughness of both paper and film. This was analyzed as due to an increase in N and C values for the load‐dependent friction coefficient, μ = CW−N where W is normal load and Nmax ≈ 0.33 (papers) or Nmax ≈ 0.6 (polymer films). Using adhesion friction theory, it was shown that friction data can be fitted with a unified equation: C = μ0c−N, where μ0 = μ N = 0 and c is a constant for the rubber and belt configuration tested.
Correlation between environmental stress cracking and liquid sorption for low‐swelling liquids
Authors: Shanahan M. E. R. , Schultz Jacques 
Published: April 2003

AbstractThe environmental stress cracking (ESC) of polyethylene has been studied under conditions of dynamic equilibrium with the liquid for low‐swelling liquids. Even among active ESC agents, there is a clear relative order of efficiency. It has been shown that the liquid becomes less efficient with increasing equilibrium swelling. This fact has been attributed to local plasticization of the crack front leading, in turn, to a reduction in the high‐stress concentrations associated with a wedge‐shaped crack. Some semiquantitative ideas are proposed in an attempt to explain the relation between ESC efficiency and volume/volume sorption.
Molecular motion and spin relaxation in polydiethylsiloxane
Authors: Burnett L. J. , Durrett M. G. 
Published: April 2003

AbstractQuantitative comparison of previously published NMR spin‐relaxation data for polydiethylsiloxane with theoretical predictions for a variety of motional processes allowed both the nature and time scale of molecular motions to be identified. At the lowest temperatures, methyl reorientation produced a T1 minimum and was found to proceed with an activation energy of 2.4 kcal/mole in both amorphous and crystalline phases. Reorientation of the ethyl groups in the amorphous phase was observed at a higher temperature with an activation energy of 9.3 kcal/mole. Relaxation in the melting region was influenced by flexing and stretching of the helical polymer chain. The maximum angular displacement of the chain was estimated to be 24°, with an activation energy for this process of 2.6 kcal/mole.
Crystallization of alkyl‐aromatic polyimides (polyalkanimides)
Authors: Korshak V. V. , Babchinitser T. M. , Kazaryan L. G. , Vasilyev V. A. , Genin Ya. V. , Azriel A. Ye. , Vygodsky Ya. S. , Churochkina N. A. , Vinogradova S. V. , Tsvankin D. Ya. 
Published: April 2003

AbstractPolyalkane imides based on 3,3′,4,4′‐diphenyloxidetetracarboxylic, pyromellitic and 1,4,5,8‐naphthalenetetracaboxylic acids, and aliphatic diamines containing 4, 6, 8, 10, or 12 methylene groups have been studied. Relations governing the effect of structure on solubility, heat resistance, density, and crystallizability have been established. Conformation analysis has been carried out and models of the macromolecules have been constructed. The morphology of the crystalline polymers has been studied. For the polymers of the given class, crystallization capability is shown to be associated with the conformational flexibility of the macromolecular unit determining a given acid moiety by the number of methylene groups in the diamine unit.
Displacement measurements using double‐exposure speckle photography of small‐angle scattered light
Authors: Holoubek J. , Sedláček B. 
Published: April 2003

AbstractDouble‐exposure speckle patterns created by scattered light were used to study tensile deformation of isotactic polypropylene film. The method makes possible a quantitative investigation of the deformation process (relative magnitude and orientation of the displacement vector, Poisson's ratio μ) by means of a simple optical analysis of stepwise deformations covering the desired range. The displacement vector and Poisson's ratio have been determined with an accuuracy of ± 5% in the range of small deformations (up to 18% relative deformation); and the role of stress relaxation has been examined. Limitations of the method, such as the range of measurable displacements, effect of prestressing, and stability of the system, etc., are discussed. Among advantages of the method are comparative simplicity and accuracy, and the possibility of its application to other systems studied by the small‐angle light scattering method.
Effect of casting conditions on polymorphism of nylon‐12
Authors: Ishikawa Toshihiko , Nagai Susumu , Kasai Nobutami 
Published: April 2003

AbstractPolymorphism in nylon‐12 film, which appears on casting from a phenol‐ethanol solution, has been investigated by x‐ray diffraction and infrared absorption. The casting temperature was varied from 30 to 130°C and the ambient atmospheric pressure from 50 to 760 Torr. Casting at 30°C gives only the α form, while casting above 90°C yields only the γ form. At intermediate temperatures, both α and γ forms are obtained, with the γ content increasing as the casting temperature and/or the rate of evaporation of solvent are increased. The ethanol component of the casting solvent appears to act only as a melting‐point depressant for phenol. In contrast, nylon‐6 film cast from the same solvent system between 30 and 160°C gives only the α form. It is proposed that the difference in polymorphism of nylons‐12 and ‐6 is caused by differences in molecular flexibility due to the length of the methylene chain.