bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐resolution NMR spectra and phase equilibria in poly(phenylacetylene)‐diluent mixtures
Authors: Sanford T. J. , Allendoerfer R. D. , Kang E. T. , Ehrlich P. 
Published: April 2003

AbstractThe C‐13 NMR spectra of partly crystalline poly(phenylacetylene) (PPA) in CDCl3 CCl4 are rather well resolved and the peaks can be matched with those of 1, 3,5‐triphenylbenzene. A different, less‐well‐resolved C‐13 spectrum is characteristic of a disordered PPA obtained by heating. We conclude that crystalline PPA has the chain conformation of a cis‐cis‐oid helix. This interpretation is consistent with the proton NMR spectra and is supported by the fluorescence spectra, which can display two bands, one concluded to be characteristic of the cis‐cis‐oid conformation, the other of chain conjugation in the disordered polymer. Phase equilibria of PPA in the presence of chloroform were determined and are represented as those of the quasiternary mixture cis‐cis‐oid helix, disordered polymer, and chloroform.
Negative thermal expansion of polymer crystals: Lattice model
Authors: Chen F. C. , Choy C. L. , Young K. 
Published: April 2003

AbstractThe lateral thermal motion of atoms in an inextensible polymer chain would cause a shortening along the chain direction. This effect could explain the observed negative thermal expansivity α along the chain direction of a polymer crystal. Using this idea, the expansivity α is calculated for a lattice of parallel linear chains. A value of −1.3 × 10−5 K is obtained for chains with a carbon backbone, in good agreement with data for polyethylene.
Phase transformation in mixtures of polystyrene and poly(vinyl methyl ether)
Authors: Davis D. D. , Kwei T. K. 
Published: April 2003

AbstractHomogeneous films comprised of mixtures of polystyrene and poly(vinyl methyl ether) can be obtained by evaporation from a ternary solution containing toluene as the solvent. Heterogeneous films result when the solvent is trichloroethylene. The possibility that a heterogeneous film cast from trichloroethylene can be transformed to a homogeneous one by physical means is a logical expectation when the polymer‐polymer interaction is favorable, though as yet no comprehensive report has appeared in the literature. We have accomplished the transformation by increasing the temperature. Optical microscopy and glass transition experiments were employed to observe the effects.
Small‐angle scattering studies of nafion membranes
Authors: Roche E. J. , Pineri M. , Duplessix R. , Levelut A. M. 
Published: April 2003

AbstractThe physical structure of Nafion membranes has been investigated by small‐angle neutron scattering (SANS) and small‐angle x‐ray scattering (SAXS). Samples in the acid form may exhibit two scattering peaks. The first, observed by SANS at an angle corresponding to a Bragg spacing of 180 Å, is shown to arise from structures in crystalline regions. A second peak at larger scattering angles is shown to arise from ion‐containing regions which may be swollen with water. Salt‐form samples made by soaking the acid form in an aqueous salt solution can also exhibit the same two scattering signals. But in amorphous salt‐form samples produced by quenching from the melt the first peak is absent. This permits a more accurate study of the second peak by SAXS, which shows that the second scattering component is present as a maximum over a wide range of water contents but is absent in a sample dried at 200°C. The position of the peak shifts to lower scattering angles (or larger spacings) at higher water contents. Possible structural models that might give rise to the maximum are discussed. A calculation of the SAX invariant is made and results are consistent with a phase separation of a large fraction of the water.
Comments on a paper by Axelson and Mandelkern concerning 13C NMR spectra of polymers
Authors: Boyer Raymond F. , Heeschen Jerry P. , Gillham John K. 
Published: April 2003

AbstractIt is shown that the 13C NMR spectral collapse temperatures Tc reported by Axelson and Mandelkern tend to give a constant ratio of Tc/Tg averaging 1.21 ± 0.05 and independent of Tg or of polymer structure. It is further shown that Tc is not a high‐frequency value for Tg because this would require Tc/Tg to decline with increasing Tg. Tc/Tg agrees in numerical value with Tu/Tg, where Tll is the liquid‐liquid transition lying above Tg. Direct comparison of Tc and Tu for four polymers PIB, PnBA, atactic PP, and isotactic PMMA shows very close agreement. The various results suggest, but do not prove, that Tc from 13C NMR spectroscopy may be a new, direct measure for Tll. A measured Tc of 233K for linear PE is compatible with a Tg near 195 K (233/195 = 1.19), whereas a Tg of 148 K gives the ratio 233/148 = 1.57, which is outside any value shown in tabulated form.
Crystallization of poly(α‐methyl‐α‐N‐propyl‐β‐propiolactones) prepared from homogeneous and heterogeneous initiators
Authors: Grenier Daniel , Leborgne Alain , Spassky Nicolas , Prud'homme Robert E. 
Published: April 2003

AbstractHalf‐crystallization times t½, enthalpies of fusion ΔH, melting temperatures Tf glass transition temperatures Tg x‐ray patterns, and morphologies were obtained for nine samples of poly(α‐methyl‐α‐n‐propyl‐β‐propiolactones) prepared from different homogeneous or heterogeneous initiators. The bulk of the results indicates that all samples can be classified into two categories: Polymers A having t½≏, 100 min, ΔH ≏ 26 J/g, T ≏ 376 K, Tg ≏ 275 K, and Polymers B having t½ ≏ 10 min, ΔH ≃ 14.5 J/g T ≏ 425 K and Tg ≏ 271 K. Polymers A were prepared with homogeneous initiators while polymers B were polymerized with heterogeneous intiators. The difference in crystallization behavior between polymers A and polymers B is certainly due to a difference in microstructure, brought about by the initiators, which has been qualitatively observed by NMR.
Small‐angle light scattering by random assemblies of incomplete spherulites. Systems with partial degree of volume filling
Authors: Tabar R. J. , Wasiak A. , Hong S. D. , Yuasa T. , Stein R. S. 
Published: April 2003

AbstractA theory is presented to account for the effect of the impingement of growing spherulites on theirHvsmall‐angle light scattering patterns. The theory is developed on the basis of results of computer‐simulated two‐dimensional spherulite growth and calculated scattered intensities. The impingement produces a lowering of the intensity of the scattering maximum and the diminishing of the overall sharpness of the scattering peak. The extent of these effects increases with area fraction of spherulites. A procedure is suggested for determining correction factors that may be applied to intensity data obtained during the course of spherulite crystallization. An interpretation is made of the type of average spherulite size determined from the scattering angle of maximum intensity.
Component analysis of proton NMR spectra of linear polyethylene in the α‐transition temperature range and phase distribution
Authors: Horii Fumitaka , Kitamaru Ryozo 
Published: April 2003

AbstractBroad‐line 1H NMR spectra of linear polyethylene at temperatures in the α‐transition range can be analyzed in terms of contributions from the crystalline and noncrystalline components provided molecular motion in the crystalline region is adequately considered. The spectrum of solid n‐C32H66 or n‐C44H90 prior to melting is used to take account of the contribution of the crystalline region of the polymer to molecular motions. The temperature dependence of the component distribution in the polymer is briefly discussed for a wide range of temperatures, together with previously reported results at low temperatures. The noncrystalline component is in a rigid glassy state at very low temperatures but with rising temperature it transforms to a mobile glassy state with restricted molecular motion, and transforms partially to the rubbery state at high temperature. The crystalline component remains rigid at low temperature, but some molecular motion is associated with it at higher temperatures in the α‐transition range.
Stress relaxation of polybutadiene at large deformation. Measurements of stress and birefringence in shear and elongation
Authors: Kimura Shinichi , Osaki Kunihiro , Kurata Michio 
Published: April 2003

AbstractThe rheological behavior of an uncrosslinked polybutadiene on sudden application of finite strain was examined. The shear stress σ, two components of birefringence, and the extinction angle were measured in shear (magnitude of shear γ ≤ 3.5) and tensile stress and the birefringence were measured in uniaxial elongation (elongation ratio λ ≤ 3.8). Measurements were performed at 30°C with a tensile tester equipped with appropriate sample holders. The stress‐optical coefficient was 3.01 × 10−9Pa−1. The first and second normal‐stress differences v1 and v2 were separately evaluated with the use of stress‐optical law. The Lodge—Meissner relation v1 = γσ held good. The ratio v2/v1 was independent of time and varied from about −0.3 to −0.2 with increasing γ in the range of measurements. Each of the stress components was factored into a function of strain and one of time, and the latter was common to all the stress components. Simple formulas were proposed to represent stress components in step deformations.
Microwave properties of low‐density polyacetylene
Authors: Feldblum A. , Park Y. W. , Heeger A. J. , MacDiarmid A. G. , Wnek G. , Karasz F. , Chien J. C. W. 
Published: April 2003

AbstractThe results of an initial study of the microwave properties of low‐density foamlike (CH)x are reported for intermediate dopant levels. The electrical conductivity and dielectric constant are obtained at microwave frequencies, and the results are analyzed in terms of effective medium theory. The possibility of utilizing the doped foamlike (CH)x as an efficient microwave absorber is discussed.
Conformation of linear polyethylene in 1‐chloronaphthalene: Light scattering characterization of polymers. IV
Authors: Suzuki Hidematsu , Muraoka Yoichiro , Inagaki Hiroshi 
Published: April 2003

AbstractLight scattering measurements were carried out on a linear polyethylene sample NBS 1475 in 1‐chloronaphthalene at 135 and 115°C to determine the weight‐average molecular weight, the second virial coefficient A2, and the z‐average mean‐square radius of gyration. By use of these results, the system is analyzed in terms of the interpenetration function Ψ for A2. Observed values of A2 are rather large but the excluded volume is nevertheless relatively small. Such behavior seem to be similar to that of semiflexible polymers. The characteristic ratio Cn,LS as determined by light scattering is found to be almost twice the literature value of 6.7, which was obtained from viscosity measurements. This discrepancy is explained by comparing the theoretical value of the Flory viscosity parameter Φ at the nondraining limit with values calculated from the light scattering results.
Irreversible effects of moisture on the epoxy matrix in glass‐reinforced composites
Authors: Antoon M. K. , Koenig J. L. 
Published: April 2003

AbstractThe irreversible effects of moisture exposure on anhydride‐crosslinked epoxy resin films are investigated by means of Fourier‐transform infrared spectra. Hydrolytic attack of water at the ester linkages is accelerated in alkaline media and is a mechanically activated process. Matrix hydrolysis is also enhanced in the presence of inorganic fillers.
Conformational properties of polar polymers. I. Poly(vinyl chloride)
Authors: Boyd Richard H. , Kesner Laya 
Published: April 2003

AbstractA recently developed method for including polar bonds in conformational energy calculations is applied to poly(vinyl chloride). Inductive effects on dipole moments and the effects of intervening atoms on electrostatic interaction energies are represented by polarizability centers in conjunction with bond centered dipoles. Solvation energies are estimated by means of a continuum dipole–quadrupole electrostatic model. Calculated energies of a number of conformations of meso and racemic 2,4‐dichloropentane and the iso, syndio, and hetero forms of 2,4,6‐trichloroheptane give satisfactory representations of isomer and conformer populations. Electrostatic effects are found to be quite important. However they appear to be effectively of sufficiently short range that the calculated conformer energies are found to be fit well by a linear combination of interaction parameters (consisting of gauche, skew chlorine, four‐bond CH2…CH2, CH2…Cl, and Cl…Cl interactions) conventional to vinyl polymers and a special four‐bond interaction that arises when the bond sequence ClCHCH2CHCl is (nearly) coplanar. These interaction parameters when assembled into statistical weight matrices lead to calculated values of both the characteristic ratio and the dipole moment ratio in satisfactory agreement with experiment. Least energy paths for transitions between the most stable conformations are also calculated.
Mixed‐crystal infrared studies of chain‐folding in polyethylene single crystals: Low‐temperature and molecular weight studies
Authors: Cheam T. C. , Krimm S. 
Published: April 2003

AbstractInfrared spectra of 40 PEH/1 PED mixed crystals have been obtained at low temperature as a function of the molecular weight of the PED. The band contour in the CD2 bending region was resolved into crystalline and noncrystalline components by a least‐squares fitting of Gaussian‐plus‐Lorentzian bands. The splittings of the crystalline component were analyzed in terms of the theory for finite chains of coupled oscillators, with the help of normal coordinate calculations for certain structures. Together with some results on n‐paraffin mixed crystals, our studies show that (i) the spectroscopic observations are associated with interactions of crystalline stems of a single molecule; (ii) the observed crystalline splittings are incompatible with an essentially “switchboard” model of chain folding; (iii) adjacent reentry folding predominates, with folding along single (110) and (200) planes occurring; and (iv) for high molecular weights of PED double (110) fold planes prevail. These results are seen to be consistent with the morphologies known to be associated with the conditions of crystallization.
Crystalline transitions in powders of nylon 66 crystallized from solution
Authors: Starkweather Howard W. , Jones Glover A. 
Published: April 2003

AbstractPowders of nylon 66 were crystallized from solution in methanol and in other solvents. These powders exhibit a latent heat of about 4.5 cal/g at the Brill transition near 200°C where the unit cell changes from a triclinic to a pseudohexagonal form. The dimensions of the hydrogen‐bonded sheets are almost unchanged up to 240°C, but the separation between the sheets increases with increasing temperature. Above 245°C, the interchain separation increases rapidly, and permits the powder to be extruded in an essentially plastic manner to form coherent extrudates. As the temperature of treatment is increased above 245°C, the latent heat of the Brill transition is reduced toward zero, the heat of fusion is reduced from about 30 cal/g to about 20 cal/g, and an endotherm at 261°C is replaced by one at 267°C.
Flow birefringence of concentrated polymer solutions in two‐dimensional flows
Authors: Fuller G. G. , Leal L. G. 
Published: April 2003

AbstractThe results of flow birefringence measurements are reported for polymer solutions of moderate concentration subjected to a wide range of two‐dimensional flows. These flows were generated in a four‐roll mill which enables one to systematically vary the ratio of the vorticity to the rate of strain in the flow while holding the velocity gradient constant. It is shown that steady‐state birefringence data collected over a wide range of flow types can be correlated against the eigenvalue of the velocity gradient tensor, in agreement with criterion for strong and weak flows from model calculations. Transient birefringence measurements in which purely extensional flows were started from rest are also reported. It was observed that the birefringence went through a pronounced overshoot in time for two different polymer/solvent systems. Flow induced increases in the solution turbidity were also observed and the increased turbidity remained constant over a period of many hours after extensional flows were arrested. The birefringence, on the other hand, decayed to zero almost immediately after the flows were stopped. These changes in the turbidity suggest that crystallization of the polymer was occurring. The qualitative results of experiments are compared to recent network model calculations using the theory of Yamamoto for concentrated polymer systems. It is found that this model can predict qualitatively many of the experimental observations if the function describing the breakage of polymer chain entanglements is allowed to depend on the conformation of the polymer segments bridging the entanglements. In particular, this dependency of the entanglement breakage on the conformation of the network segments leads to a predicted overshoot of birefringence when purely extensional flows are started from rest. It is also demonstrated through this model that birefringence data taken over a wide range of flow types can be used to estimate the degree to which the network deforms affinely with the flow field.
Annealing of polypropylene films crystallized from a highly extended melt
Authors: Schultz J. M. , Lin J. S. , Hendricks R. W. , Petermann J. , Gohil R. M. 
Published: April 2003

AbstractThin films of isotactic polypropylene were drawn from the melt at a very high rate of extension. Transmission electron micrographs of this material reveal fibrous crystals lying along the draw direction. The chain axis and fiber axis are identical. Dark field micrographs show a dark/light modulation along the fiber axis. Annealing at temperatures below 110°C produces no qualitative change in the electron microscope observations. Annealing between 110 and 150°C produces gradual dominance of lamellar crystals, oriented normal to the draw direction. Small‐angle x‐ray scattering (SAXS) data exhibit a strong streaking normal to the fiber axis, in broad agreement with the observed fibrosity. A Bragg peak along the draw directions shows that the modulation observed microscopically is a density modulation. The absence of second‐order maxima and the dependence of the SAXS peak on treatment temperature strongly suggest that the axial modulation is a spinodal decomposition of the material into crystalline and amorphous regions.
NMR spin–spin relaxation in solid and molten polyethylene structures
Authors: Kamel I. , Charlesby A. 
Published: April 2003

AbstractThe NMR spin‐spin relaxation (T2) spectra of high‐density polyethylene (PE) has been investigated over a wide range of temperatures, both in the solid and molten states. Previous work in these laboratories has shown that the T2 relaxation spectrum of molten polyethylene differs from that of other polymers studied in that (a) it cannot be decomposed into two relaxation spectra (T2S and T2L) and (b) there is some evidence of a memory effect. This paper attempts to elucidate these observations, and compare them with the spin‐spin relaxation of polyethylene at lower temperatures. In the solid state, the T2 decay comprises both a Gaussian distribution for the crystalline region, and an exponential decay for the amorphous component. The effects of crystallization conditions and of temperature were determined. In the molten state the T2 decay is more complex, but can be resolved into three exponentials. The longest (T2L) component arises as expected from the most mobile, low molecular weight fraction. The T2S component is due to an entangled but mobile network, as in other polymers. In addition, a short relaxation component T2X is observed, which is influenced by previous crystallinity and the processing history of the material, and is ascribed to some vestigial degree of structure in the molten phase.
High‐resolution polymer separations in a four‐pass hairpin thermal field‐flow fractionation column
Authors: Giddings J. Calvin , Martin Michel , Myers Marcus N. 
Published: April 2003

AbstractA thin‐channel four‐pass hairpin thermal field‐flow fractionation (FFF) column is described, and the advantages of its unique dimensional characteristics are explained. The problem of isolating the performance of this and other separations columns from the ubiquitous polydispersity effects are discussed and treated theoretically. The discussion is extended to size exclusion chromatography, and it is shown that the 2 to 6 times lower selectivity of the latter compared to FFF leads to the requirement for 4 to 36 times more theoretical plates to encounter polydispersity effects and thereby obtain information on polymer molecular weight distribution. A fractogram of six narrow polystyrene samples obtained from the hairpin system is shown to imitate closely the fractograms obtained from two totally different thermal FFF columns, showing that polydispersity dominates and that molecular weight information is revealed for these samples with only a few hundred theoretical plates. Various experimental and theoretical attempts are made to isolate the polydispersity and column contributions to plate height, including cut‐and‐recycle experiments, the observation of plate height versus velocity curves, and the direct calculation of the contributing effects. The various methods are subject to moderate errors, but are in rough agreement. The plate height plots show that the polydispersity effect contributed 53% and 68% to the measured plate height for 51,000 and 160,000 molecular weight samples, respectively. The latter polymer is shown to emerge with ca. 1300 true column plates. It is suggested that much higher column efficiency will be observed in the future if higher retention levels can be experimentally realized.
Polymerization of p‐acryloyloxybenzoic acid
Authors: Menczel Jozsef , Walsh J. P. , Wunderlich Bernhard 
Published: April 2003

AbstractPolymerization of p‐acryloyloxybenzoic acid by heating on a hot stage was previously reported to lead to a lyotropic mesophase. Using optical microscopy, thermal analysis, and infrared analysis, it was shown that this mesophase involves oligomers of poly(p‐oxybenzoate) formed from the monomer by ester interchange through internal acidolysis.
Generalized Rouse–Zimm theory for polymer solutions
Authors: Hess W. , Jilge W. , Klein R. 
Published: April 2003

AbstractGeneralized Rouse–Zimm equations are derived using a local equilibrium ansatz for the segment distribution function. The relaxation frequencies depend on excluded‐volume effects and other interactions such as entanglement in semidilute solutions through exact static correlation functions. For the case of ring polymers general expressions are given for diffusion coefficients and mean‐square displacements. By use of the “blob” model, explicit results are presented for a dilute good‐solvent system.
Free‐volume estimates in heterogeneous polymer systems. I. Diffusion in crystalline ethylene–propylene copolymers
Authors: Kreituss A. , Frisch H. L. 
Published: April 2003

AbstractApparent thermodynamic diffusion coefficients were obtained from carbon tetrachloride, benzene, and n‐hexane sorption‐desorption kinetics in crystalline and amorphous ethylene‐propylene copolymers (with propylene content from 1 to 70 wt. %, and crystallinity from 0% to 77%), in high‐density and low‐density polyethylene, and in polypropylene. The dependence of the diffusion coefficient vs. concentration curves on crystallinity and propylene content in the copolymers is reported. The diffusion coefficient at zero penetrant concentration increases with decrease in crystallinity. The apparent diffusion activation energies in the temperature interval investigated (25 to 75°C) are independent of temperature and are constant for crystalline copolymers. A modified Fujita‐like free‐volume theory for diffusion in crystalline polymer systems is introduced, and the theoretical estimates of diffusion coefficients show satisfactory agreement with experiment.