bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiothermoluminescence study of low‐temperature transitions in polyethylene
Authors: Zlatkevich L. Y. , Crabb N. T.
Published: April 2003

Molecular relaxation in a series of polyethylene samples has been investigated by radiothermo‐luminescence. Polyethylene structure is discussed in terms of different modes of molecular mobility in different structural regions. Each of the low temperature transitions is assigned to a certain structure region and structural unit(s). The influence of different polyethylene molecular parameters and processing conditions on its structure and mechanical properties is also considered.
SAXS determination of the amorphous surface layer thickness of polymer single crystals
Authors: Varnell W. D. , Harrison I. R. , Kozmiski S. J.
Published: April 2003

Polyethylene single crystals were grown from 0.1% solutions in xylene at 80 and 87°C. Oriented mats were made from each preparation and the small‐angle x‐ray scattering (SAXS) profiles obtained. Following treatment of the raw data for main‐beam position and width, background scatter, and the Lorentz factor, five Bragg reflections were resolved. A one‐dimensional lattice was used as a model for the oriented mats of single crystals. This model contains three parameters. An additional parameter Gx was also introduced to demonstrate the general effect of a broadening factor on the model. The effect of each parameter on the calculated diffraction pattern was examined. From this examination it was found that by assuming that the broadening functions are zero we can determine directly from the number of observable peaks the maximum possible thickness of the amorphous surface. Further, we find that the thickness of the amorphous layer must be less than the maximum value calculated if Gx is assigned values greater than zero. A “best‐fit” diffraction pattern was generated in order to estimate how much smaller the surface thickness can be such that one can still resolve five diffraction maxima. The range of amorphous surface thicknesses found from the calculated diffraction profile is 12–20 Å. This is in good agreement with complementary studies performed on the same crystal preparations.
Studies of polylactone/poly(vinyl chloride), polylactone/poly(vinyl fluoride), and polylactone/poly(vinylidene fluoride) blends
Authors: Aubin Madeleine , Prud'homme Robert E.
Published: April 2003

It is shown that polyvalerolactone/poly(vinyl chloride) (PVL/PVC) blends are miscible over all compositions since a single glass transition temperatureTgis observed, intermediate between those of pure PVL and pure PVC. Melting points, enthalpies of fusion and morphologies of PVL/PVC blends are also reported. It is also shown that polyvalerolactone, poly(α‐methyl‐α‐n‐propyl‐β‐propiolactone), poly(α‐methyl‐α‐ethyl‐β‐propiolactone), and poly(caprolactone) are immiscible with poly(vinyl fluoride) and poly(vinylidene fluoride), despite the fact that all these polylactones are miscible with PVC. Differences in electronegativity, in atomic radius, and in molar attraction between the fluoride and the chlorine atoms are probably responsible for this difference in behavior.
Direct observation of phase transitions of polyethylene under high pressure by a PSPC x‐ray system
Authors: Maeda Yoji , Kanetsuna Hisaaki , Nagata Kiyofumi , Matsushige Kazumi , Takemura Tetuo
Published: April 2003

A position‐sensitive proportional counter (PSPC) x‐ray measuring system is employed to observe directly phase transition processes of polyethylene at high temperature and high pressure. X‐ray diffraction measurements reveal important new experimental data. First, an irreversible crystal transition from the hexagonal to the orthorhombic structures occurs in the critical region where the hexagonal structure begins to appear at a pressure of 350 MPa. That is, the (100) hexagonal reflection is observed only on cooling at 350 MPa. At pressures above about 400 MPa, however, the hexagonal phase is stable and the phase transitions melt ↔ hexagonal ↔ orthorhombic occur reversibly. Second, during cooling at pressures above 400 MPa, the (100) hexagonal reflection can be observed at temperatures below the hexagonal ↔ orthorhombic transition temperature. This behavior suggests that all the crystal morphologies of polyethylene, from “highly‐extended‐chain” crystals to crystals with a low melting point, are formed by the transitions melt → hexagonal → orthorhombic. Third, in heating at elevated pressures above 500 MPa, a shoulder in the peak intensity versus temperature plot for the (100) hexagonal reflection is observed at a higher temperature than the large maximum which occurs immediately after the crystal transition. This behavior indicates melting in two stages of hexagonal structures with different thermal stabilities, and the shoulder at higher temperature may be due to the fusion of the hexagonal phase annealed either below or above the transition point.
Dielectric relaxation and glass transition temperature of copolymers
Authors: Yagihara Shin , Mashimo Satoru
Published: April 2003

Dielectric relaxation measurements were made on methyl methacrylate—styrene and methyl methacrylate–p‐chlorostyrene copolymers at temperatures higher than the glass transition temperatureTg. It was found that the temperature dependence of the relaxation time can be described satisfactorily by an expression derived recently for chain motion in amorphous polymers. The temperatureTgobtained from the expression agrees well with that determined by differential thermal analysis.
A site‐model theory of nonlinear viscoelasticity
Authors: White J. R.
Published: April 2003

The two‐site model theory is reexamined taking into account changes in site population, and the differential equation describing deformation behavior is solved without utilizing an approximation normally employed. The result is a nonlinear solution with the many of the characteristics found experimentally with polymeric materials.
Phase behavior of some polyamic acid plus ether systems
Authors: Orwoll Robert A. , St. Clair Terry L. , Dobbs Kerwin D.
Published: April 2003

Polyamic acids, prepared by reacting 3,3′,4,4′‐benzophenone tetracarboxylic acid dianhydride with 3,3′‐diaminobenzophenone and with 4,4′‐diaminobenzophenone, were dissolved in tetrahydrofuran and in bis(2‐methoxyethyl) ether at concentrations up to 40 wt %. Reversible phase separation was observed when these systems were heated. Evidence cited indicates that all observed phases are isotropic, notwithstanding the fact that a number of aromatic polyamides are mesogenic.
Phase equilibrium study of the ternary system composed of two monodisperse polystyrenes and cyclohexane
Authors: Hashizume J. , Teramoto A. , Fujita H.
Published: April 2003

Mixtures of two “monodisperse” samples of polystyrene (M1 = 4.53 × 104, M2 = 10.3 × 104; Mw/Mn < 1.01) in cyclohexane were allowed to separate into two phases at different polymer concentrations and temperatures. The compositions in the two phases were measured by gel permeation chromatography, and used to determine isothermal binodals. From the binodal data the critical temperature and concentration were estimated as functions of the composition of the polymer mixture, and the separation factor σ for each polymer component was calculated. In contrast with typical results in the literature, σ was almost independent of molecular weight of the polymer. It is shown by deriving a general expression for σ that theoretical prediction of σ requires accurate knowledge about the Flory–Huggins interaction parameter as a function of the concentrations of individual polymer components.
Spectroscopic study of rigid‐rod polymers. I. Structures of model compounds
Authors: Venkatesh G. M. , Shen D. Y. , Hsu S. L.
Published: April 2003

Poly(p‐phenylene benzbisoxazole) and poly(p‐phenylene benzbisthiazole) belong to the class of extended‐chain, rigid‐rod polymers possessing high modulus, high strength, and good thermal and oxidative resistance. Fibers and films of these polymers are processed from anisotropic solutions in strong acids such as methane sulfonic acid or polyphosphoric acid. The electronic absorption and vibrational spectra of the model compounds have been investigated in order to characterize the structures in the solid state and in nonprotonic solvents. The dramatic intensity differences in the spectra obtained have been interpreted by variations in the dihedral angle between the plane of the phenyl group and the plane of the central heterocyclic ring which affect the resonance configuration between the two rings.
Production and properties of fibers spun from nylon 6/lithium chloride mixtures
Authors: Richardson A. , Ward I. M.
Published: April 2003

The possibility of producing high‐modulus nylon 6 fibers by incorporation of lithium chloride (LiCl) in the polymer prior to spinning and drawing has been examined. Samples containing 2% and 4% LiCl (w/w) together with an unsalted control were studied. Particular attention was given to optimizing the spinning process by varying the melt temperature and the draw‐down. The spun fibers were subsequently drawn in a tensile testing machine at 135°C, preliminary studies having established that this was desirable for the production of high‐modulus material. The influence of annealing after drawing was also examined. Drawn fiber moduli in the range 8–9 GPa were obtained, compared with ca. 5–6 GPa for unsalted material. Limited structural studies (birefringence and wide‐angle x‐ray diffraction) suggest that the enhancement of modulus is due to an increase in the stiffening effect of extended molecules in the noncrystalline regions. Dynamic mechanical measurements show that there is reduced chain mobility in the disordered regions of the polymer, suggesting strong polymer‐ion interactions. The salt can be readily removed by washing the fibers in boiling water, with significant reduction in moduli. This militates against commercial application of the salted fibers.
Fourier‐transform infrared study of the reversible interaction of water and a crosslinked epoxy matrix
Authors: Antoon M. K. , Koenig J. L. , Serafini T.
Published: April 2003

Fourier‐transform infrared spectroscopy is utilized to characterize the interaction of a crosslinked epoxy matrix with sorbed water vapor. The perturbations of the epoxy vibrational spectrum are evidence for weak H bonding between water molecules and polar groups in the resin. The epoxy‐water interactions are reversible.
Effect of interfacial bonding on the strength of adhesion of elastomers. I. Self‐adhesion
Authors: Chang R.‐J. , Gent A. N.
Published: April 2003

Two partially gelled (crosslinked) layers of elastomer were pressed into intimate contact and the gelation reaction was then taken to completion. By varying the extent of initial gelation, the degree of chemical interlinking was varied from zero, when two fully reacted sheets were pressed together, up to a level characteristic of the final density of molecular linking within each layer, when they were brought together before any reaction had occurred. The strength of adhesion between the layers was measured under threshold conditions, i.e., at low rates of peel, at high temperatures, and, in some instances, with the layers swollen with a compatible liquid. Linear relations were obtained between the threshold work of detachment per unit of interfacial area and the amount of chemical interlinking, deduced from the kinetics of molecular linking within each layer. At any degree of interlinking, ranging from zero to the fully interlinked state, the work of detachment was lower for networks composed of shorter molecular chains, in accordance with the Lake–Thomas theory for the threshold strength of elastomer networks. By extrapolation to the fully interlinked state, the strength of adhesion corresponding to cohesive rupture was inferred. These values agreed with measured tear strength for polybutadiene gelled by a free‐radical process. For a sulfur crosslinking system, and for both free‐radical and sulfur crosslinking of poly(ethylene‐co‐propylene), the threshold tear strength of the elastomer was found to be much higher than the extrapolated value from adhesion measurements. This discrepancy is ascribed to roughness of the tear plane in relatively strong elastomers, in contrast to the smooth separation of flat adhering layers. Adhesion of fully crosslinked sheets was generally low, 1–2 J/m2. Higher values, 5–25 J/m2, were found with sulfur crosslinking systems, especially those yielding a high proportion of polysulfidic crosslinks. Interlinking via polysulfide crosslink interchange reactions is suggested in these cases.
Effect of interfacial bonding on the strength of adhesion of elastomers. II. Dissimilar adherends
Authors: Chang R.‐J. , Gent A. N.
Published: April 2003

Two elastomer layers, differing either in initial degree of crosslinking or in chemical reactivity, were bonded together by a free‐radical crosslinking process. The elastomers employed were polybutadiene (BR) and an ethylene‐propylene copolymer (EPR) differing in the efficiency of crosslinking by dicumyl peroxide by a factor of about 20. When a fully crosslinked sheet of either elastomer was pressed into contact with a partially crosslinked sheet of the same elastomer and the crosslinking then taken to completion, the strength of adhesion under threshold conditions was found to be qualitatively in accord with the predictions of a simple theoretical treatment for the degree of interlinking in terms of the corresponding homogeneous crosslinking reaction. Whereas the theory suggests that the effective degree of interlinking will be one‐half of that generated in a homogeneous system, the experimental results were in accord with a figure of about 70%. When a layer of one elastomer was bonded to a layer of the other in a similar way, the strength of adhesion was found to be relatively high when the initial fully crosslinked layer was BR and relatively low when it was EPR. These results were also in qualitative agreement with theoretical predictions for the degree of chemical interlinking developed between layers differing in chemical reactivity. Thus a general correlation appears to hold between the threshold strength of adhesion and the amount of interlinking.
Instabilities of the deformation process in cold drawing of poly(ethylene terephthalate) and other polymers
Authors: Pakula T. , Fischer E. W.
Published: April 2003

The relationship between drawing rate and drawing stress was studied for amorphous poly(ethylene terephthalate) (PET) under various experimental conditions. Three types of expriments were performed: simple drawing with necking at constant rate, drawing through a conical die, and drawing at constant stress. Under constant stress conditions a transition between two stable regimes of drawing can be observed. The transition occurs at a critical stress σc at which the rate of neck propagation changes by some orders of magnitude. Such a transition was found both below and above the glass transition of PET. With constant drawing rates instabilities of neck propagation were observed under certain experimental conditions. Such self‐oscillations, described by other authors, are not due to heat effects as has been proposed, but are related to the existence of the critical stres σc.

Stress‐induced transitions in deformation behavior as in PET were observed for polypropylene and nylon 6 but not for polycarbonate. The results obtained by various methods including morphological studies do not support the assumption that the instabilities are caused by thermal effects due to the dissipation of deformation energy. Rather, a model is proposed which is based on the existence of a “spinodal transition” from the isotropic into the highly oriented state.
Accordion‐type laser‐Raman scattering by drawn linear polyethylene
Authors: Peterlin Anton , Snyder Robert G.
Published: April 2003

One can reproduce the observed accordion‐type laser‐Raman (ALR) scattering of highly drawn linear polyethylene if one assums that any gauche defect in the crystal lattice which interrupts the all‐trans conformation sequence of the molecular chain completely decouples the accordion‐type longitudinal oscillations of the two sections on both sides of the defect. Each oscillates independently of the rest. The length of the section, smaller than the full length of the straight chain between the crystal surfaces, determines the frequency of the ALR absorption. One such defect per five chain stems of the ideal crystal yields a straight‐length distribution which agrees sufficiently well with that derived from the ALR spectrum. Small‐angle x‐ray scattering very generally registers the resulting decrease of the electron density of the crystalline component without yielding more detailed information about the location and frequency of such gauche defects.
Stress relaxation and dynamic viscoelastic properties of end‐linked poly(dimethyl siloxane) networks containing unattached poly(dimethyl siloxane)
Authors: Granick Steve , Pedersen Sven , Nelb Gary W. , Ferry John D. , Macosko Christopher W.
Published: April 2003

Stress relaxation in uniaxial extension and dynamic shear moduli G′ and G″ have been studied in networks of vinyl‐terminated poly(dimethyl siloxane) (PDMS) of five different molecular weights (Mn from 1800 to 29,200) crosslinked with cis‐dichlorobis (diethyl sulfide) platinum (II) and containing 10 and 15 wt % of two samples of high‐molecular‐weight unattached linear hydroxyl‐terminated PDMS (Mw 700,000 and 950,000). The Mw/Mn ratio of both the network prepolymers and the unattached linear species was approximately 2. In stress relaxation the stretch ratio was 1.25 or less and the shear relaxation modulus was calculated from the neo‐Hookean stress‐strain relation. In the dynamic measurements, the strain amplitude was 15% or less; after conversion to the timedependent shear relaxation modulus G(t) the two sets of measurements were combined and the contribution of the unattached species G1(t) was calculated by difference. After multiplication by (1 − v)−1G/Ge, where v2 is the volume fraction of network, G is the plateau modulus of the uncrosslinked polymer, and Ge is the equilibrium modulus of the network containing unattached molecules, G1(t) was compared with G11(t), the relaxation modulus was essentially the same in both environments. The relaxation was slower in the networks than in the uncrosslinked polymer by 1 to 2 orders of magnitude, and it increased gradually with increasing Ge, which is a measure of total to pological obstacles represented by crosslinks plus trapped entanglements. A similar but less striking difference between relaxation in a network and in the homologous environment of a linear polymer was previously observed in end‐linked polybutadiene networks and the butadiene phase of a styrene‐butadiene‐styrene block copolymer. It appears that, in these systems where the topology of the obstacles is fixed, the reptation is severely restricted or else alternative modes of configurational rearrangement which contribute to relaxation in the uncrosslinked polymer are suppressed.
Hypersonic relaxation in polybutadiene and polyisoprene
Authors: Jarry J.‐P. , Patterson G. D.
Published: April 2003

Brillouin scattering is used to study hypersonic relaxation in 1,2‐polybutadiene and cis‐polyisoprene. The temperature of maximum loss was determined to be 125°C for a frequency of 5.0 GHz for polybutadiene and 100°C at a frequency of 5.9 GHz for polyisoprene. Hypersonic loss maxima are examined for many polymers and general conclusions are reached concerning the factors that can be used to predict the temperature of maximum loss.
Crystalline stoichiometric adducts of polyamides with phosphoric acid
Authors: Aharoni Shaul M.
Published: April 2003

It is shown the crystalline stoichiometric adducts of phosphoric acid with polyamides such as nylon 6 and poly‐p‐benzamide, and probably nylon 66, nylon 69, nylon 11, and nylon 12, can be prepared. These adducts are characterized by their unique wide‐angle x‐ray diffraction patterns and by rather low melting or decomposition temperatures. The thermal behavior and infrared data, indicate that interactions between the acid and the polymeric amide residues are weak.
Orientation and morphology of high‐density polyethylene film produced by the tubular blowing method and its relationship to process conditions
Authors: Choi Kyung‐Ju , Spruiell Joseph E. , White James L.
Published: April 2003

The orientation and crystallinity of a series of high‐density polyethylene (HDPE) tubular films is characterized using wide‐angle x‐ray scattering pole‐figure analysis and birefringence. The films ranged from uniaxial to equal biaxial. The data were used to compute biaxial orientation factors which were then plotted on an orientation‐factor triangle diagram. It was shown, within the range of conditions studied, that both the crystalline biaxial orientation factors were unique functions of the stresses exerted on the bubble at the freeze line. Both correlations are the same as those developed by Dees and Spruiell for melt‐spun HDPE fibers. SAXS measurements on the films suggest lamellar structures in both uniaxial and biaxial films.
Effect of glass filler size on the tensile properties and tear strength of polybutadiene
Authors: Eckstein Y. , Dreyfuss P.
Published: April 2003

An experimental study of the tensile properties, tear strength, hysteresis, and swelling ratio of model composite elastomeric compounds consisting of polybutadiene filled with glass beads has been carried out as a function of the size of the beads. The diameter of the beads ranged from 25 to 1000 μm and the volume fractions examined were 0.16, 0.092, and 0.048. Mechanical properties of the filled elastomers were functions of the loading (separation distance), the particle size (surface area/volume), and the elastomer‐filler systems studied.
Miscibility of polycaprolactone/chlorinated polyethylene blends
Authors: Bélorgey Georges , Prud'Homme Robert E.
Published: April 2003

Blends of polycaprolactone (PCL) with chlorinated polyethylenes (PECls) having chlorine contents of 25, 30, 36, 42, and 48% by weight were prepared and studied by differential scanning calorimetry and small‐angle light scattering (SALS). It was found that blends made with PECls containing 30% or more chlorine are completely miscible with PCL (a single glass transition temperature Tg is found) while the PCL/PECl(25) blends are immiscible. PCL crystallizes in the miscible blends at any composition and it has an enthalpy of fusion which decreases only slightly with PECl content. Blends in the PECl composition interval of 0–80% are spherulitic, as shown by SALS, but a rodlike morphology is found at the 85% composition and dispersed crystals are observed at higher compositions. It is suggested that the k parameter of the Gordon‐Taylor equation can be taken as a measure of the strength of the specific interaction between PCL and PECl. Low values of k (0.26 and 0.35) are found for PCL/PECl blends but a higher value of k (0.51) has been reported for PCL/poly(vinyl chloride) (PVC) blends, indicating a stronger interaction in the latter mixtures. In agreement with these findings poly(α‐methyl‐α‐n‐propyl‐β‐propiolactone) and poly(valerolactone) are not miscible with PECl, whereas they were previously shown to be miscible with PVC.
Dynamic bulk and shear relaxation in glassy polymers. I. Experimental techniques and results on PMMA
Authors: Yee A. F. , Takemori M. T.
Published: April 2003

In this paper the authors describe in detail the experimental techniques for the simultaneous measurement of the dynamic Young's modulus and the dynamic Poisson's ratio, from which the dynamic bulk and shear moduli can be calculated. Experimental results are presented on the effects of temperature, frequency, and tensile strain on these properties of poly(methyl methacrylate) (PMMA). The temperature and frequency effects indicate that the β relaxation in PMMA is not a purely internal motion but is coupled to the bulk.
Comparison between neutron and quasielastic light scattering by polyacrylamide gels
Authors: Geissler E. , Hecht A. M. , Duplessix R.
Published: April 2003

The authors describe small‐angle neutron scattering measurements of the screening length ζ in polyacrylamide‐water gels. Although these are inhomogeneous systems, the screening length is clearly observable and is in good numerical agreement with the relation E = 3kT/4πζ3, where E is the longitudinal elastic modulus of the gel obtained from measurements of the intensity of qu‐asielastically scattered light. Static light scattering observations reveal a larger‐scale (ca. 30 nm) superstructure in the gel.
Influence of the conformation of polyethylene on wide‐angle neutron scattering patterns
Authors: Stamm M.
Published: April 2003

Wide‐angle neutron scattering investigations of mixtures of deuterated and nondeuterated chains are well suited to detect sequences of regular adjacent reentry folding of a polymer chain in particular crystallographic directions. It is shown that the diffuse neutron scattering intensity is peaked at large scattering angles for (100) and (010) folding, whereas (110) folding is difficult to detect. Detailed calculations indicate that the position, intensity, and half‐width of the diffuse peak depend strongly on the mode of folding as well as on the number of adjacent stems. By a comparison with experimental data adjacent reentry folding in (100) and (010) crystallographic planes with more than five adjacent stems can be excluded. The implications for other folding models containing regular folded chain sequences are discussed.
Mechanical and transport properties of drawn crosslinked low‐density polyethylene
Authors: DeCandia F. , Russo R. , Vittoria V. , Peterlin A.
Published: April 2003

The values of drawing dependence of the density ρ, axial elastic modulus E, and maximum draw ratio λ of crosslinked low‐density polyethylene (CLPE) rather similar to those obtained with un‐crosslinked branched material of similarly low density. Very much the same applies to the equilibrium concentration of sorbed methylene chloride in the amorphous component and the zero‐concentration diffusion coefficient D0. The exponential concentration coefficient γD, however, even at the maximum draw ratio, shows no indication of the rapid increase so characteristic of the completed transformation from the lamellar to the fibrous structure. On the basis of this finding, one can understand the small deviations in the dependence of the mechanical properties between the crosslinked and uncrosslinked branched material. The segments between the crosslinks, much shorter than the free molecules, favor the formation of the interfibrillar tie molecules that limit the drawability of the sample. But since they cannot be extended to the same length as the free molecules, they contribute less to the total fraction of tie molecules per amorphous layer and hence yield a smaller axial elastic modulus.
Fractionation in mixtures of polyethylene oxide fractions during crystallization
Authors: Prud'Homme Robert E.
Published: April 2003

Two narrow‐molecular‐weight‐fraction polyethylene oxides were mixed and studied by differential scanning calorimetry (DSC), small‐angle x‐ray scattering (SAXR), microscopy, and small‐angle light scattering (SALS). DSC measurements indicate the presence of two melting points at each composition, leading to a eutectic diagram with a eutectic point located close to the axis of the constituent with the lower molecular weight. The depression in melting point of the higher‐molecular‐weight component allows the calculation of a thermodynamic interaction parameter of −0.09 between the two fractions, indicating that they are miscible in the melt despite the fractionation process occurring during crystallization. Two SAXR long periods are also observed at each composition, indicating phase separation during crystallization. These two phases are included into large spherulites, the structure of which depends mainly upon the crystallization characteristics of the higher‐molecular‐weight component. The other component must then crystallize between the spherulite lamellae. Finally, small spherulites of the order of the micron are observed from the SALS patterns inside the large spherulites (of the order of one millimeter as seen by microscopy). The two polyethylene oxide fractions give rise to different size SALS spherulites and both types of spherulites are present in the mixtures.
The energetics of the epitaxial deposition of polyethylene onto the basal plane (0001) of graphite
Authors: Baukema P. R. , Hopfinger A. J.
Published: April 2003

Polymer‐substrate interaction energetics have been determined in order to describe the epitaxial deposition of polyethylene into graphite. The potential energy was calculated using van der Waal's interactions. A closed‐form representation of the potential was derived for a substrate which was considered infinite in planar area. Inspection of the relative polymer‐substrate energies for various positions above the substrate indicate a planar‐zigzag polyethylene chain segment deposits with its backbone parallel to the substrate. The chain axis preferentially orients in the (1120) directions of the graphite surface layer. Specifically, deposition occurs along the lines which intersect the nearest‐neighbor midpoints of the CC bonds in the surface layer.
Oscillatory shear flow of polymeric systems
Authors: Isayev A. I. , Hieber C. A.
Published: April 2003

On the basis of the Leonov viscoelastic constitutive equation, oscillatory shear flow of elastic fluids in the linear and nonlinear regimes has been considered. The Fourier components and associated phase angles of the shear and normal components of the elastic strain tensor have been found as functions of frequency and deformation amplitude in the range usually employed in experiment, and are presented in a form convenient for further rheological applications. In the linear case, the results correspond to many known theories. In the nonlinear case, the theoretical results have been compared with experiments, on different polymeric systems, with very good agreement being obtained for the shear stress in polymeric solutions but only qualitative agreement for the shear stress and first normal‐stress difference in polymer melts.
Structure‐property behavior of films containing disk spherulites: A model study
Authors: Mohajer Y. , Wilkes G. L.
Published: April 2003

Thin films of a polyester of lactic and glycolic acid were prepared to give controlled amounts of disk spherulites. The spherulite contents ranged from zero to 100% and were accurately measured. The stress‐strain properties of the films were then determined at 60°C, i.e., about 20°C above the glass transition temperature Tg. The mechanical behavior varied quite systematically with spherulite content and displayed little dependence on spherulite size. It was found that much of the mechanical data could be reasonably well described by a simple composite model. In addition, the yield strain as well as the strain to break could be principally coupled to the deformation of only the amorphous phase. SEM and optical microscopy studies supported the above conclusion, also demonstrating that the isolated spherulites adhered well to the amorphous matrix and behaved as stress concentrators in the system when the deformation temperature was above Tg.
Spectroscopic study of rigid‐rod polymers. II. Protonation effect
Authors: Shen D. Y. , Venkatesh G. M. , Burchell D. J. , Shu P. H. C. , Hsu S. L.
Published: April 2003

The protonation of a heterocyclic rigid‐rod polymer poly(p‐phenylene benzbisthiazole) and its model compound has been studied by UV‐visible and Raman spectroscopy. Because of the two nitrogens on the heterocyclic ring, spectroscopic features of unprotonated, half‐protonated, and fully protonated structures have been identified. For the fully protonated molecule, there is also an increase in conjugation between the phenyl ring and the heterocyclic ring.
Small‐angle neutron scattering from two‐phase polymeric systems
Authors: Koberstein Jeffrey T.
Published: April 2003

A small‐angle neutron scattering method is presented for the determination of single‐chain scattering functions in heterogeneous two‐phase polymeric materials such as incompatible polymer blends and microphase‐separated diblock copolymers. Development of the method makes use of both the discrete and continuum approaches to scattering theory. In this fashion it is shown that extraction of the single‐chain scattering function requires only two experimental observations, regardless of the compressibility of the system. These experiments consist of small‐angle neutron scattering profiles from two samples: an unlabeled two‐phase material and a similar two‐phase material in which a portion of the molecules in one phase have been replaced by molecules which are contrast labeled by isotopic deuterium substitution. Anticipated difficulties associated with actual application of the procedure and requirements of the necessary experimental samples are discussed.
Möussbauer spectroscopy of nafion polymer membranes exchanged with Fe2+, Fe3+, and Eu3+
Authors: Rodmacq B. , Pineri M. , Coey J. M. D. , Meagher A.
Published: April 2003

Mössbauer spectra of “Nafion” perfluoronated acid membranes exchanged with iron or europium have been studied as a function of ion concentration, water content, temperature, and applied magnetic field in order to characterize the ionic phase in these materials. In every sample, the recoil‐free fraction falls to zero at a temperature which decreases from 280 to 220 K with increasing water content. The sudden fall in recoil‐free fraction corresponds to a glass transition in the ionic phase rather than its melting point. In Fe2+ Nafion, the spectrum is independent of water content above 6 wt%, and is typical of fully hydrated, isolated Fe2+(H2O)6 species. The isomer shift, quadrupole splitting, and linewidth all change continuously below 6 wt % water, indicating a range of environments for the iron. For Fe3+ Nafion, ions in several distinct environments can be identified on the basis of their magnetic properties. Isolated Fe3+ species (Fe–Fe distances greater than 12 Å) showing paramagnetic hyperfine structure in their 4.2‐K spectra predominate in slightly neutralized samples, and in those with high water content. The proportion of dimers, whose quadrupole splitting is about 1.7 mm/s, increases with increasing iron content or decreasing water content. A third component of the spectra has a quadrupole splitting of 0.4 mm/s. It is associated with paramagnetic iron having other iron ions in the neighborhood, and also with iron ions located in the interior of small groups or chains formed from dimers. There is no iron belonging to magnetically ordered clusters involving hundreds of ferric ions of the type found in some other ionomers. All the exchanged ions belong to the ionic phase, and none are associated with the polymer backbone.
An analysis of the β transition of linear and branched polyethylenes by carbon‐13 NMR
Authors: Dechter J. J. , Axelson D. E. , Dekmezian A. , Glotin M. , Mandelkern L.
Published: April 2003

Carbon‐13 nuclear magnetic resonance relaxation parameters have been obtained as a function of temperature for a set of branched polyethylenes whose β transition temperatures were determined independently. Resolvable spectra could be obtained at temperatures either corresponding to or very close to the temperature of the β transition. Together with results for other systems, these observations preclude the indentification of the β transition with the glass temperature. From the measured spin relaxation times and nuclear Overhauser enhancements average correlation times were calculated as a function of temperature. The average correlation times were calculated as a function of temperature. The average correlation time is on the order of 10−8−10−9 s at the β transition. These results argue strongly against it being assigned to the glass temperature.
The use of chemical contrast in the SEM analysis of polymer blends
Authors: Hobbs S. Y. , Watkins V. H.
Published: April 2003

A novel method for investigating the morphology of multiphase polymers is discussed. In this procedure, inherent differences in secondary and backscattered electron emission from the various components rather than topographical variations are used to produce image contrast. The combined use of various selective stains and energy‐dispersive x‐ray analysis to accentuate and positively identify individual phases is discussed. The effects of coating thickness and type and changes in accelerating voltage on image quality are also described.
A laser light‐scattering study of the structure of agarose gels
Authors: Key P. Y. , Sellen D. B.
Published: April 2003

Diffusion coefficients of dextran fractions within agarose gels surrounded by dextran solution have been measured by laser light scattering using the autocorrelation method. Plots were made of the diffusion coefficient relative to that in dilute solution, D/D0, against the logarithm of hydrodynamic diameter logd for each concentration of agarose, and superimposed by displacing horizontally to produce a unified plot. In this way it was shown that D/D0 is a function of Cbd, where C is agarose concentration, with b = 1/3 and 1/2 for the cases in which the dextrans were mixed in before gelation and allowed to diffuse in afterwards, respectively, the plots being the same for a reference concentration of 0.7%. A value of b = 1/2 is that which would be expected if the molecular weight per unit length of the gel fibers were independent of concentration, and a value of 25 kg mol−1 nm−1 is calculated. Mobile concentrations of dextran within the gels relative to those in the surrounding solutions were found by determining the scattered intensity associated with the diffusing dextran molecules from the zero‐time value of the autocorrelation function. All results and calculations are discussed in terms of current theories, and compared with earlier work on calcium alginate gels for which a molecular weight per unit length of gel fiber of 0.59 kg mol−1 nm−1 was calculated. The nature of the spectral broadening of the light scattered from agarose gels in the absence of dextran is described.
Mechanical relaxation mechanism of epoxide resins cured with aliphatic diamines
Authors: Ochi Mitsukazu , Okazaki Masatoshi , Shimbo Masaki
Published: April 2003

The mechanism of low‐temperature relaxations in bisphenol‐A‐type epoxide resins cured with aliphatic diamines, with aliphatic diamines in the presence of salicylic acid as an accelerator, and with tertiary amines was investigated to compare the dynamic mechanical properties and the chemical structure of these networks. Mechanical relaxations are observed at about −140 and −60°C. The former relaxation is denoted the γ relaxation and the latter the β relaxation. The β relaxation of the cured epoxide resins containing hydroxyether groups is a sum of contributions from the relaxation of these groups and of other parts of the network structure. A new relaxation due only to the motion of the hydroxyether group can be estimated from the difference of tanδ curves between the aminecrosslinked and ether‐crosslinked systems. The γ relaxation is attributed to the motion of a polymethylene sequence consisting of at least four carbon atoms.
The temperature dependence of the viscoelastic softening and terminal dispersions of linear amorphous polymers
Authors: Plazek Donald J.
Published: April 2003

Thermorheological simplicity is shown to hold for poly(vinyl acetate) in the temperature range extending from Tg + 25°C to Tg + 80°C. Between Tg and Tg + 25°C the softening (glass to rubberlike) viscoelastic dispersion exhibits time‐scale shift factors aT different from those of the terminal (rubberlike to steady‐state) dispersion. The aT values calculated from zero‐shear viscosities coincide with those from the terminal dispersion in the temperature range 60–154°C (Tg ≅ 35°C). The aT shifts obtained from the response in the terminal dispersion can be fitted to the Williams, Landel, and Ferry equation over the entire temperature range 42–154°C. The aT obtained from the softening dispersion is shown to exhibit a different functionality. An empirical modification of the Doolittle equation yields a very flexible relation which can be fitted to some aTs which cannot be represented by the usual Doolittle free‐volume expression.
An expression for local composition in polymer‐solution thermodynamics
Authors: Canovas A. A. , Rubio R. G. , Renuncio J. A. R.
Published: April 2003

An expression for local composition which describes nonrandom interactions between unlike molecules in polymer solutions is proposed. This expression makes the nonrandom model compatible with the one‐fluid hypothesis and satisfies the limits of randomness when experimental conditions evolve in such a way. Data on several binary systems are studied using this model which represents simultaneously activity and heat‐of‐mixing data.
Moderately concentrated solutions of polystyrene. I. Viscosity as a function of concentration, temperature, and molecular weight
Authors: Hager B. L. , Berry G. C.
Published: April 2003

Data on the viscosity η of moderately concentrated solutions of polystyrene are reported. Several solvents were investigated, including cyclopentane solutions over a temperature span between θU = 19.5°C and θL = 154.5°C. The data were analyzed in terms of a relation giving η as a function of αφM, where αφ is the expansion factor for the chain dimensions in a solution with volume fraction φ of polymer with molecular weight M. It is shown that values of αφ so determined decrease as ∂ lnαφ/∂ lnφ = (1 − 2μ)/6μ for φ greater than φ* = 0.2M/s3 for moderately concentrated solutions, where s is the root‐mean‐square radius of gyration and μ = ∂ ln[η]/∂ lnM with [η] the intrinsic viscosity.
Simulation of reversible polycondensations with monomer having reactivity different from that of higher homologs
Authors: Gupta Santosh K. , Agarwalla N. L. , Rajora P. , Kumar Anil
Published: April 2003

Reversible AB‐type polycondensations have been simulated in a batch reactor where the monomer reacts with itself or any higher oligomer with a rate constant R times that for higher mers. Similarly, the rate of reaction of the condensation product with an AB group at the end of a polymer chain has been assumed to be R' times that with an “internal” AB group. The variation of the number‐average chain length μn with time (until equilibrium is reached) has been obtained. μn is found to be lower and the polydispersity index higher in the presence of the reverse reactions. Where the equilibrium conversions are high enough, a split in the molecular‐weight distribution (MWD) curves is observed for even‐ and odd‐order homologs for R < 1, though this effect is considerably diminished as compared with that in similar irreversible polycondensations. It is also found that the most probable distribution does not adequately represent the MWD when the functional groups violate the equal‐reactivity hypothesis and number‐average chain lengths are relatively small.
Defects in polydiacetylene single crystals. II. Dislocations in pTS
Authors: Young R. J. , Petermann J.
Published: April 2003

The structure of single crystals of a substituted diacetylene polymer (pTS) has been investigated by using transmission electron microscopy. It has been found that edge dislocations with Burgers vector parallel to the chain direction are present at a density of up to 1013 m−2. It is suggested that the dislocations may be present first of all in the monomer crystals and become locked into the monomer structure during polymerization. It has been found that the dislocations have a tendency to line up in rows perpendicular to the chain direction and when the density of the dislocations in a row is sufficiently high a small−angle grain boundary can be formed. A possible structure for the dislocations on a molecular level is suggested and the effect of the presence of the dislocations upon the polymerization behavior, mechanical properties, and electric properties is discussed.
Magnetic effects and viscosity in the nematic phase of a polymer series
Authors: Hardouin F. , Achard M. F. , Gasparoux H. , Liebert L. , Strzelecki L.
Published: April 2003

Magnetic measurements were made on a series of polyesters in their nematic state and compared to their apparent viscosity at the same temperature. At similar molecular weights, the length of a flexible segment in the main‐chain polymer plays an important role in both the magnetic orientation effects and the apparent viscosity behavior. Moreover, on cooling from a perfectly oriented nematic sample, the alignment remains down to room temperature. In contrast with nematic monomers, these polymers behave like solids, even at the lowest velocity of a rotating magnetic field.
Birefringence of highly oriented fibers
Authors: Yang H. H. , Chouinard M. P. , Lingg W. J.
Published: April 2003

A spectrophotometric method was developed for measuring the birefringence of highly oriented synthetic fibers. This method surmounts the low birefringence limit of the standard quartz compensator method and the difficulties in interpretation of the photographic fringe method. A highly oriented aramid fiber gave birefringence values of 0.60–0.75 by this method, compared with 0.25 for polyester and 0.06 for nylon by other conventional methods. The operating principles and excellent results of this new method provide a basis for the extension of routine birefringence characterization to highly oriented fibers.
One‐dimensional order/disorder in a polydiacetylene
Authors: Patel G. N. , Khanna Y. P.
Published: April 2003

A polydiacetylene film, found to be amorphous by x‐ray diffraction, possesses some kind of order as suggested by differential scanning calorimetry (DSC). The order/disorder phenomenon which occurs upon heatingcooling is also accompanied by a green/yellow color transition. On the basis of analogies between crystallization and the order in this material, we have extended the application of the Avrami equation to determine the dimensionality of the order in the polymer. Kinetic analysis of the exothermic transition (disorder → order) by DSC suggests that the material has one‐dimensional order. The disruption and formation of this order, which accompany the color changes in this polydiacetylene, give rise to endothermic and exothermic transitions, respectively. Supporting evidence for the proposed one‐dimensional order/disorder concept is cited.
NMR studies of molecular mobility in uniaxially stretched oriented polymers
Authors: Egorov E. A. , Zhizhenkov V. V.
Published: April 2003

The effect of elasticlike uniaxial tension on molecular mobility in polymers have been studied over a wide temperature range using the broad‐line NMR technique. The studies were carried out on oriented semicrystalline samples of nylon 6, poly(ethylene terephthlate), polypropylene, polyethylene, polyoxymethylene, poly(vinyl alcohol), and polytetrafluorethylene. Above the low‐temperature transition the NMR spectra are reversibly transformed under tension. Increases in the second moments of the spectra are attributed to weaker molecular motion in stressed polymers. The only exception is polypropylene, in which the reverse, i.e., enhancement of molecular mobility, can be observed in a certain temperature range. In the spectra of polymers stretched above the glass transition temperature the narrow component decreases, thus indicating inhibition of micro‐Brownian motion, a phenomenon we call “mechanical vitrification.” Such mechanical vitrification is proved to result from reduction in the number of possible tie‐chain conformations in the non‐crystalline regions and not from closer packing of chains. In discussing the results we use the experimental data on the reduction of the number of gauche isomers under tension (on average, one transition of a gauche link to the trans state causes at least five methylene groups in the main chain to become immobile). The results of studies of molecular mobility in stretched polymers are used for more accurate definition of the mechanisms of molecular motion at different temperatures. A method for evaluation of the energy of intermolecular interactions which hinder small‐scale motion at low temperature is suggested.