bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermally stimulated current (TSC) study of the Tg and Tll transitions in anionic polystyrenes
Authors: Lacabanne Colette , Goyaud Patrice , Boyer Raymond F.
Published: April 2003

The thermally stimulated current (TSC) technique has been used to investigate three anionic polystyrenes of M̄n 17,000, 71,700, and 1.55 × 106, i.e., M < Mc, M > Mc, and M ≫ Mc, where Mc is the entanglement molecular weight. A current maximum near Tg designated TMg, has relaxation times which follow an Arrhenius equation. A second current maximum at T > Tg appears to be the Tll process and is designated TMll. Relaxation times for it follow a Vogel equation. TMg and TMll vary with molecular weight, increasing below Mc and leveling off above Mc at a temperature of about 170°C. Values of TMg and TMll are compared with values of Tg and Tll obtained from torsional braid analysis, which involves melt flow; and with differential‐scanning‐calorimetric values on fused films, where there is no transport of polymer. It is concluded from such cross‐comparisons that TSC, at least for polystyrene, is a quasistatic test which may involve microscopic viscosity. Macroscopic viscosity does not play a role. The ratio TMll/TMg is in the range 1.10–1.16, similar to Tll/Tg values by other methods. A few comments about Tll in atactic poly(methyl methacrylate) by the TSC method are given.
Drawing behavior of linear polyethylene. II. Effect of draw temperature and molecular weight on draw ratio and modulus
Authors: Capaccio G. , Crompton T. A. , Ward I. M.
Published: April 2003

The drawing behavior of linear polyethylene homopolymers with weight‐average molecular weights (M̄w) from 101,450 to ca. 3,500,000 has been studied over the temperature range 75°C to the melting point. In all cases 1‐cm gauge length samples were drawn in an Instron tensile testing machine at a constant cross‐head speed of 10 cm/min. With the exception of the lowest molecular weight polymer, it was found that increasing the draw temperature led to substantial increases in the maximum draw ratio which could be achieved, and that this increased monotonically with increasing draw temperature. Measurements of the Young's modulus of the drawn materials showed, however, that the unique relationship between modulus and draw ratio previously established for drawing at 75°C was not maintained to the highest draw temperatures. The highest draw temperature at which this relation held was found to be strongly molecular weight dependent, increasing from ca. 80 to ca. 125°C when M̄w increased from 101,450 to 800,000. In all cases conditions could be found for drawing samples to draw ratios of 20 or more with correspondingly large values of the Young's modulus.
Thermodynamic analysis of the plastic deformation of glassy poly(methyl methacrylate)
Authors: Haussy J. , Cavrot J. P. , Escaig B. , Lefebvre J. M.
Published: April 2003

A thermodynamic analysis of the thermally activated yielding of glassy atactic poly(methyl methacrylate) has been carried out. Samples were deformed in compression at a constant strain rate in the temperature range 150–330 K. Two different deformation modes are rate controlling below and above a critical temperature Tc of the order of 200 K. The low‐temperature mode is characterized by a purely exponential stress dependence of the strain‐rate, and thus defines a true stress‐activation volume. The higher‐temperature mode reveals a stress dependence of the strain rate in the form of a power law with a constant activation energy.
Morphological studies on polybutylene terephthalate
Authors: Stein R. S. , Misra A.
Published: April 2003

The morphology of poly(butylene terephthalate) (PBT) crystallized from the melt at various temperatures was studied by small‐angle light scattering, polarizing microscopy, and wide‐angle x‐ray diffraction. Spherulites with a maltese cross at 45° to the polars formed at lower temperatures while spherulites having an apparently higher melting point with a maltese cross along the polars (0°–90°) formed at higher temperatures. The spherulite size and crystallinity increased with increasing crystallization temperature. The Hv scattering patterns arising from the spherulites formed at lower temperature showed intensity maxima at azimuthal angles of 0° and 90°, while those obtained at higher temperatures showed the more common 45° intensity maxima. Microtomed samples from molded PBT bars showed spherulites with a 45° maltese cross which changed to a 0°–90° maltese cross upon heating just prior to melting. The skin‐core effect due to varying thermal histories in these molded bars was clearly observed. Solvent crystallized films contained positive 0°–90° spherulites. Some changes occurring upon uniaxial stretching of PBT films are also discussed.
Hydrodynamically induced formation of cellulose fibers. I. Observations on the formation of cellulose fibers from stirred solutions
Authors: Kalb B. , Manley R. St. John
Published: April 2003

Like synthetic polymers, a natural polymer such as cellulose may crystallize in fibrous form from stirred solutions. In the present work, it is demonstrated that cellulose fibers can be formed by precipitation from dimethyl sulfoxide/paraformaldehyde solutions by two methods that involve different mechanisms of fiber formation, viz., (A) precipitation of cellulose by addition of nonsolvent to the stirred cellulose solution, and (B) precipitation of cellulose by coagulation of droplets of cellulose solution in a stirred precipitant. Both processes yield fibers with properties depending on the stirring speed and the coagulant strength. The molecular orientation and tensile strength of the fibers produced by method A was low, but increased with the stirring speed, while some fibers formed by method B reached extremely high orientation, depending on the thickness of the fibers. The two mechanisms of fiber formation are discussed on the basis of the experimental observations.
Fourier transform infrared study of the gel form of isotactic polystyrene
Authors: Painter Paul C. , Kessler Richard E. , Snyder Randy W.
Published: April 2003

Infrared spectra of isotactic polystyrene gel films are observed to be significantly different from those of amorphous and crystalline polymer, indicating that the gel form is in a different conformation than the usual 31 helical crystal structure. Computer‐assisted subtraction indicates that approximately 35% of the chains participate in the gel component, effectively ruling out structural defects as the origin of the ordered gel component.
Raman spectroscopic studies of the solid‐state polymerization of diacetylenes. II. Thermal polymerization of 1,6‐di‐p‐methoxybenzene‐sulfonyloxy‐2,4‐hexadiyne
Authors: Bloor D. , Ando D. J. , Hubble C. L. , Williams R. L.
Published: April 2003

The Raman spectra of 1,6‐di‐p‐methoxybenzene‐sulfonyloxy‐2,4‐hexadiyne (MBS) have been recorded during thermal polymerization. The spectra are similar to those of the related p‐toluene‐sulfonyloxy monomer but indicate a higher strain in the initially formed MBS polymer chains. Despite this similarity, the polymerization kinetics for the two monomers are markedly different. The polymerization behavior of MBS shows that the polymer chain initiation and propagation are practically independent of lattice strain. Possible causes for this independence are discussed.
Microkinetics of crystallization in poly(ethylene terephthalate)
Authors: Palys L. H. , Phillips P. J.
Published: April 2003

The lamellar growth kinetics and lamellar thickness of poly(ethylene terephthalate) crystallized from the glassy state have been determined as a function of crystallization temperature. Values of end and side surface free energies have been estimated as well as the residual lamellar thickness. Analyses carried out using secondary nucleation approaches indicate that the width of a critical nucleus is comparable to the effective substrate length for multiple nucleation in this and other slowly crystallizing polymers at high supercoolings. A “universal” critical value of T/T2ΔT below which the strip completion process ceases was found to exist. All crystallization must, therefore, occur through the deposition of critical nuclei. Models are proposed for this process which appear to be consistent with both neutron scattering and infrared experiments on quenched polyethylenes. Comparison of crystallization rates, expressed as “jump” rates, with relaxation frequencies suggest that in order for crystallization to occur at any given temperature the relaxation frequency must be at least two decades faster than the crystal “jump” rate.
Photoconductivity of poly(vinyl alcohol) films containing Cu2+ complexes
Authors: Sumita Osao , Fukuda Atsuo , Kuze Eiichi
Published: April 2003

Photoconductivity has been measured in well‐dried poly(vinyl alcohol) (PVAl) films containing Cu2+ complexes prepared by treatment with Cu(NO3)2, CuSO4, CuCl2, and CuBr2. When the ratio [Cu2+]/[MU] ([MU] denoting the concentration of PVAl monomer residues) is greater than 0.015, illumination at the charge‐transfer (UV) band produces a strong photocurrent in PVAl‐CuCl2 and PVAl‐CuBr2, but not in PVAl‐Cu(NO3)2 or PVAl‐CuSO4. Optical absorption spectra suggest that two halide ions enter the first coordination sphere in the cis configuration. The temperature dependence of ESR indicates the existence of antiferromagnetic superexchange interaction via intervening halide ions. Hence, there exists a network structure of the PVAl‐CuCl2 or PVAl‐CuBr2 complex. The dependence of the photocurrent on the polarity of the illuminated electrode shows that the majority of carriers are holes. Holes in the network structure produced by charge transfer from halogen to Cu2+ ions are concluded to be responsible for the photoconduction.
Rheo‐optical studies on the deformation mechanism of semicrystalline polymers. X. Orientation retardation spectrum of polyethylene
Authors: Kyu Thein , Suehiro Shoji , Nomura Shunji , Kawai Hiromichi
Published: April 2003

In order to explore the correlation between rheo‐optical and mechanical dispersions, orientation and lattice‐deformation retardation spectra are introduced in the phenomenological treatment of the stress‐orientation coefficient and crystal lattice compliance functions in dynamic x‐ray diffraction. A similar complementary treatment of the stress‐optical retardation spectrum is also carried out for the dynamic birefringence. To determine the mechanical and rheo‐optical retardation spectra, a deconvolution method based on the Fourier transform is developed. By this method, the mechanical and rheo‐optical retardation spectra of a low‐density polyethylene are computed from the imaginary components of the corresponding experimental functions; and subsequently, the real and imaginary components of the original functions are recalculated numerically from their respective retardation spectra and compared with the observed ones. The similarity of the normalized mechanical and rheo‐optical retardation spectra demonstrates that the α mechanical dispersion is related to orientation retardation of the crystal grains at their boundaries. Furthermore, separation of crystalline and amorphous contributions to the stress‐optical retardation spectrum is made on the basis of the two‐phase hypothesis for polyethylene. The amorphous contribution to the stress‐optical retardation spectrum is further resolved into two components corresponding to the α and β mechanical dispersions under the assumption that the resolved component for the α dispersion is symmetric in shape.
Phosphorescence studies of relaxation effects in bulk polymers. II. Emission depolarization study of relaxation mechanisms in poly(methyl methacrylate)
Authors: Rutherford Henry , Soutar Ian
Published: April 2003

Phosphorescence depolarization measurements, under steady state polarized excitation, have been used to examine the relaxation behavior of bulk poly(methyl methacrylate) (PMMA). Poly(methyl methacrylate) bearing phosphorescent labels has been synthesized by copolymerization of small quantities of acenaphthylene (I), 1‐vinylnaphthalene (II), 2‐vinylnaphthalene (III), 1‐naphthyl methacrylate (IV), and 2‐naphthyl methacrylate (V), respectively, with methyl methacrylate. In no case was depolarization of emission due to probe rotation apparent below the onset of the β‐relaxation of the polymer. Rotation of label V was characterized by an activation energy of 94 kJ mole−1 in excellent agreement with that of the β relaxation measured by conventional relaxation techniques. This result clearly implicates ester motion in the β relaxation. No motion of label I, which cannot move independently of the polymer backbone, was evident in the vicinity of the β relaxation. Above 378 K the activation energy for rotational relaxation of label I of 460 kJ mole−1 is in excellent agreement with published data for the α transition in PMMA. This result is in accord with the general assumption that backbone segmental motion is involved in the α relaxation. However, backbone motion of lesser temperature dependence (Ea = 115 kJ mole−1) is apparent from depolarization behavior of probe I between 343 and 378 K. Label II shows three regions of relaxation behavior. In the temperature range above the β transition motion of the label independent of the polymer is evident (Ea = 44 kJ mole−1). At temperatures in excess of 343 K this motion becomes cooperative with that of the backbone yielding activation energies comparable to those obtained in system I. Label III, while exhibiting depolarization characteristics similar to those of label II in the vicinity of the β relaxation, emitted insufficient intensity to permit estimation of an energy of activation for the motion. The phosphorescence of label IV was completely depolarized over the entire temperature range studied. While phosphorescence intensity and lifetime data may be used to detect the existence of polymeric transitions, the photophysical behavior of the naphthalene species studied is independent of the attachment to the polymer and does not primarily yield information regarding the polymer relaxations.
Thermal and dynamic mechanical relaxation behavior of stereoregular poly(2‐hydroxyethyl methacrylate)
Authors: Russell Geoffrey A. , Hiltner P. Anne , Gregonis Donald E. , de Visser A. C. , Andrade Joseph D.
Published: April 2003

Thermal, dynamic mechanical, and dielectric relaxation techniques were used to determine the relaxation behavior of isotactic and syndiotactic poly(2‐hydroxyethyl methacrylate) (pHEMA). Activation energies Ea were determined for the dielectric γ relaxation and compared with those of poly(2‐methoxyethyl methacrylate) (pMEMA) to determine the influence of hydrogen bonding on side‐chain relaxation processes. No difference in Ea was observed between syndiotactic pHEMA and atactic (predominantly syndiotactic) pMEMA. Isotactic pHEMA, however, had Ea + 1 kcal/mole higher than that of syndiotactic pHEMA. This was attributed to improved side‐chain packing in the isotactic polymer.
Phase transitions in mesophase macromolecules. I. Novel behavior in the vitrification of poly(ethylene terephthalate‐co‐p‐oxybenzoate)
Authors: Menczel Jozsef , Wunderlich Bernhard
Published: April 2003

A 40:60 mole ratio poly(ethylene terephthalate‐co‐p‐oxybenzoate) was studied by dynamic scanning calorimetry. Vitrification occurred in two steps, which could be linked by optical microscopy to a two‐phase structure. For the lower glass transition, hysteresis was absent on heating and cooling through the transition temperature. Since all prior studied glasses show such hysteresis, this may be linked to the mesophase structure and raises the question whether mesophases always display such glass‐transition behavior.
Kinetic studies of structure formation during anionic adiabatic polymerization of ε‐caprolactam
Authors: Frunze T. M. , Shleifman R. B. , Belavtseva E. M. , Genin Ya. V. , Volkova T. V. , Kotel'nikov V. A. , Radchenko L. G. , Davtyan S. P. , Kuraschev V. V. , Tsvankin D. Ya.
Published: April 2003

The kinetics of crystallization and structure formation of polycaproamide (PCA) during anionic adiabatic polymerization of ε‐caprolactam was studied. The adiabatic crystallization was shown to comprise three successive stages. In the first stage PCA forms dendritelike structures, the space between which is filled with the monomer. In the second stage rather rapid crystallization proceeds to give large loose spherulites. The dendritic structures serve as nuclei for development of spherulites. In the third stage slow secondary crystallization occurs. It is accomplished by crystallization of the residual amorphous substance located both in the dendritic nucleus and throughout the volume of the spherulites. This process is followed by the partial disappearance of the dendritic nuclei and by thickening of lamellae, which results in a substantial densification of initial structures and appearance of fine spherulites. As a result, a fine spherulitic structure with 50% crystallinity is formed.
Spherulite morphology in liquid crystals of polybenzylglutamates. Optical rotatory power and effect of magnetic field
Authors: Patel Dahyabhai L. , Dupré Donald B.
Published: April 2003

The stepwise growth and emergence of spherulitic structures as isolated entities from lyotropic solutions of polybenzylglutamate liquid crystals is described. Spherulites that form ringed internal structures indicative of a cholesteric organization of macromolecules have large optical rotatory powers. The sense of the rotation is solvent dependent. The morphology of the spherulite is distorted in the presence of a magnetic field. The pitch of the cumulative twist of “onion‐shell” molecular layers was measured as a function of field strength and found to follow the theoretical form shown previously to hold for continuous‐phase polypeptide liquid crystals.
Piezoelectric relaxation in poly(γ‐methyl‐L‐glutamate) at high temperature
Authors: Furukawa Takeo , Ogiwara Kiyoshi , Fukada Eiichi
Published: April 2003

Piezoelectric relaxation has been studied on elongated poly(γ‐methyl‐L‐glutamate) films with the α‐helical molecular conformation. Relaxation processes are observed near 0 and 100°C. Each process has a dual character composed of relaxational and retardational frequency dependences. The low‐temperature process is ascribed to thermal motion of side chains. The high‐temperature process, discussed in relation to the dielectric relaxation, is attributed to the ionic dc conduction connected with the two‐phase structure of crystalline regions and the electrode polarization.
Internal field of polymer crystals: Polarizability tensor of the methylene group from the birefringence of paraffin crystal
Authors: Pietralla M.
Published: April 2003

Using the concept of a point dipole lattice, it is shown that the internal field of induced dipoles can be calculated for crystals comprised of simple chain molecules. The only structure which must be taken into account accurately is that of the chain molecule itself. From the calculations, reliable values of the polarizability tensor of the CH2 unit are deduced from the birefringence of the paraffin crystal. In addition, it is shown that birefringence measurements provide a method for demonstrating the consistency of polarizability data so that no detailed structural information is needed. For the CH2 unit, it is found by both methods that α∥ − α⟂ = − 0.63 with respect to the chain direction [the units of polarizability α are 10−24 cm3 (cgs)]. The most probable anisotropies for the bond polarizabilities are α − α = 0.30, α − α = − 0.62.
Vibrational spectroscopic studies on modifications of poly(trans‐alkenylene)s. I. The orthorhombic modification of poly(trans‐pentenylene) and poly(trans‐heptenylene)
Authors: Holland‐Moritz K. , Van Werden K.
Published: April 2003

Experimental results of vibrational spectroscopic studies on the orthorhombic modification of poly(trans‐pentenylene) and poly(trans‐heptenylene) are discussed on the basis of a normal coordinate analysis for an isolated chain model.
Structure of native and regenerated cellulose as revealed by proton NMR analysis
Authors: Hirai Asako , Horii Fumitaka , Kitamaru Ryozo
Published: April 2003

Differences in fiber structure between cotton and cuprammonium rayon are studied by a refined broad‐line proton NMR analysis of samples swollen with deuterated dimethyl sulfoxide, which has no effect on the spectra but enhances differences in molecular mobility between crystalline and noncrystalline regions. The spectra obtained are decomposed into four components: broad, medium, narrow, and extremely narrow. These components are identified as contributions, respectively, from crystalline and rigid noncrystalline (frozen glassy) material, a noncrystalline glassy component exhibiting local segmental motion, a noncrystalline rubbery component exhibiting liquidlike molecular motion, and protons included in DMSO‐d6 as an impurity. The mass fraction of the narrow component in cotton was about 0.01, whereas it was as high as 0.18 in cuprammonium rayon. It is concluded that even in the swollen state, native cellulose is devoid of a liquidlike mobile component, but regenerated cellulose contains a considerable amount of a noncrystalline component involving liquidlike segmental motion of molecules.
Thermal conductivity and heat capacity of liquid and glassy poly(vinyl acetate) under pressure
Authors: Sandberg O. , Bäckström G.
Published: April 2003

The dependence of thermal conductivity λ and heat capacity per unit volume pcp on temperature and pressure for poly(vinyl acetate) has been measured by a transient hot‐wire probe technique. The measurements were made under pressures up to 0.5 GPa over a temperature range of 270–470 K. The temperature coefficient of thermal conductivity (∂ lnλ/∂T)p was found to increase with pressure for both the liquid and the glassy state. The change in heat capacity per unit volume in the region of the glass‐transition temperature was found to decrease with increasing pressure. The Ehrenfest relation does not explain the variation of the pressure coefficient of the glass‐transition temperature.
Tear strength and tensile strength of model filled elastomers
Authors: Dreyfuss P. , Gent A. N. , Williams J. R.
Published: April 2003

Measurements have been made of the tear strength, tensile strength, and energy dissipated during stretching for model filled elastomers consisting of polybutadiene with glass beads incorporated. The glass beads were pretreated with various silanes, some of which could, in principle, form covalent bonds with the polybutadiene matrix during free‐radical crosslinking of the latter and some of which could not. The tear strength of the elastomer was increased by the addition of glass beads, by about 25% for the largest beads, having a mean diameter of 150μm. This effect is attributed to increased roughness of the tear path. The breaking elongation in tension was reduced by the addition of glass beads but the breaking stress was only seriously reduced for the least‐well‐adhering beads. The stored strain energy density at break was reduced in all cases. This is attributed to large glass beads acting as fracture nuclei in tension. Calculated sizes of a Griffith crack, 150–300 μm, are consistent with this hypothesis. Strain energy dissipated due to dewetting was found to be in the range 4–13% of the input energy, depending upon the degree of interfacial adhesion, in addition to about 10% dissipated in the unfilled material. The maximum value observed is in reasonable agreement with theoretical predictions.
Study of the thermal effects in the necking of polymers with the use of an infrared camera
Authors: Maher J. W. , Haward R. N. , Hay J. N.
Published: April 2003

When a polymer specimen yields under tension by the process of cold‐drawing, heat is generated in the necking region. This beating effect has been studied in polycarbonate, polyethylene, polypropylene, and PVC with the use of a thermovision system which produces a real time thermal image of the necking specimen. In this way it was possible to observe the temperature distribution over the surface of the neck and to show that at least 85% of the mechanical work done on the specimen during necking was converted into heat. A semiempirical equation relating the maximum temperature to the drawing rate has been derived.
Structural evolution of an ABA poly(styrene‐b‐isoprene) block copolymer with temperature
Authors: Widmaier J. M. , Meyer G. C.
Published: April 2003

The structural evolution with temperature of an anionically synthesized ABA poly(styrene‐b‐isoprene) (SIS) lamellar block copolymer (total molecular weight 45,000; isoprene content 38% by weight) was studied by melt‐rheological measurements, electron microscopy, and x‐ray and light diffraction. Above 225°C, the dynamic viscosity was found to be independent of frequency up to a critical frequency. The variation of the elastic modulus confirmed the occurence of a transition between 215 and 225°C. For the temperature range considered, all results superimposed well on a two‐branch master curve. It was concluded that above 225°C, our SIS behaves like a Newtonian material, whereas for lower temperatures and/or higher frequencies classical non‐Newtonian behavior is found. The melt‐rheological properties were explained by microscopy and diffraction investigations, which allowed us to follow morphological changes as the temperature was raised. It was found that the two‐phase lamellar structure is progressively destroyed, and the transition temperature of 225°C corresponds to the temperature above which complete mixing occurs.
Light scattering in multicomponent solutions—A general equation
Authors: Procházka Ondřej , Kratochvíl Pavel
Published: April 2003

A general equation for light scattering in multicomponent solutions is derived and applied to some important systems. The equation is compared with one published earlier by Casassa and Eisenberg [Adv. Protein Chem., 19, 287 (1964)], and the difference between them is explained.
Star‐shaped block copolymers. III. Surface and interfacial properties
Authors: Huynh‐Ba‐Gia  , Jérôme R. , Teyssié Ph.
Published: April 2003

Surface and interfacial activities of A(B)2 star‐shaped block copolymers, where B is a polyoxirane block and A a polydiene or polyvinyl block, have been measured at 20°C. The surface tension of organic solvents is only slightly lowered by these copolymers, whereas a significant surface activity is noted in water. Interfacial tensions are dependent on both the nature of the organic solvent (aliphatic or aromatic hydrocarbons) and the molecular parameters of the copolymers; 50% polyoxirane seems to be the composition of maximum surface activity. The role played by the molecular architecture [A‐B or A(B)2] of the copolymers is demonstrated. The same limiting interfacial tension is obtained on increasing the concentration of diblock [A‐B] or star‐shaped block [A(B)2] copolymer. The limiting value is, however, attained at significantly lower concentration with the star‐shaped copolymers. Their ability to fill the interface is accordingly higher.
Light scattering from polymer films having optically anisotropic rodlike texture. III. Inter‐rod interference
Authors: Hashimoto Takeji , Ebisu Satoshi , Kawai Hiromichi
Published: April 2003

Effects of interparticle interference on depolarized light scattering from polymer films having nonspherulitic (rodlike, disklike, or fibrous) crystalline superstructures are explored, both theoretically and experimentally. Discrepancies between the observed “rodlike scattering” and the predicted scattering based on “single‐rod” theory are pointed out and accounted for in terms of various types of aggregation models for polymeric solids and solutions.
Orientation distribution functions for uniaxially oriented polymers
Authors: Bower D. I.
Published: April 2003

Most methods of studying molecular orientation in polymers can give only limited information about the distribution of molecular orientations, and this is particularly true of methods for studying the noncrystalline material. It is shown, however, that if the mean values P2 and P4 of the second‐order and fourth‐order Legendre polynomials in cosθ can be determined for the chains in a uniaxially oriented polymer, where ‐ is the angle between the chain axis and the drawing or extrusion direction, some qualitative statements about the form of the distribution can be made with complete certainty for some, but not all, sets of values of P2 and P4. It is shown in addition, that if the distribution is fairly smooth a good estimate of its general form can also be obtained, and that a knowledge of P6 and higher‐order means will not improve this estimate appreciably unless they are known with great accuracy.
Formation and characterization of polydiacetylene monolayer fibers
Authors: Day David R. , Lando Jerome B.
Published: April 2003

Monolayers of certain surface‐active diacetylene compounds were polymerized at the gas—water interface and collapsed to self‐supporting fibers. The monolayer fibers were found to have an unusual morphology in that while the polymeric backbones have a random orientation, the hydrocarbon side chains are all perpendicular to the fiber axis. The fiber d spacings determined from x‐ray diffraction agree well with electron diffraction data from unperturbed polymeric monolayers. Tensile tests of the monolayer fibers indicate average strength and high modulus.
Negative thermal expansion in oriented crystalline polymers
Authors: Choy C. L. , Chen F. C. , Young K.
Published: April 2003

Measurements on the thermal expansivity α∥ and α⟂ (along and normal to the draw direction, respectively) have been carried out for a series of oriented polymers with widely different crystallinities (0.36–0.81) and draw ratios (1–20) and over large temperature ranges covering the major amorphous transitions in each case. While α⟂ increases with temperature, α∥ tends to decrease sharply above the transition temperature. For highly crystalline polymers, α∥ decreases to values typical of polymer crystals (−1 × 10−5 K−1) and this can be attributed to the constraining effect of the crystalline bridges connecting the crystalline blocks. However, for polymers of lower crystallinity, α∥ may become an order of magnitude more negative and this remarkable phenomenon is attributed to the rubber–elastic contraction of taut tie‐moleucles. Since taut tie‐molecules and bridges have drastically different effects on α∥ at high temperatures, this allows a rough determination of their relative fractions.
Conformational properties of polar polymers. II. Poly(vinylidene chloride)
Authors: Boyd Richard H. , Kesner Laya
Published: April 2003

A recently developed polarization model for representing polar bond effects in conformational energy calculations is applied to poly(vinylidene chloride) (PVDC). The geometries and conformational energies of a number of conformers of 2,2,4,4,6,6‐hexachloroheptane were calculated. The geometries were found to be similar to the hydrocarbon analog polyisobutylene (PIB) in that steric crowding results in the usual T, G, G′ states being split into + or − distortions of the torsional angles away from the traditional values. Only distortions of the same sign occur in the same pair of bonds interior to CCl2 groups. Distortions of G states towards eclipsed were found to be much more stable than those away. The interior skeletal valence angle is also distorted to an unusually large value, ca. 121°. The calculated dipole moments were used to infer a group moment for CCl2 of 1.56 D. The calculated conformational energies were fitted by linear combinations of interaction parameters representing the stabilities of G+, G− bonds (relative to T+, T−) and the interactions between bonds across intervening CCl2 groups. These parameters were used in statistical mechanical calculations of the characteristic and dipole‐moment ratios. In order to make comparison with experiment, the dipole‐moment/repeat unit of a 90% (by weight) PVDC copolymer with PVC was measured and found to be 1.42 ± 0.05 D. From this, the dipole‐moment ratio for PVDC homopolymer is inferred to be ca. 0.8. The characteristic and dipole‐moment ratios calculated from the interaction parameter set were somewhat too high but adjustment of the gauche energies downward brings the calculated ratios into agreement with experiment. The same statistical model along with energy parameters previously calculated also gives agreement with experiment for the characteristic ratio of PIB. The calculated geometries are in agreement with the conformation in the crystal being (T+G′+T−G−).
Concentration dependence of the distribution coefficient for macromolecules in porous media
Authors: Anderson John L. , Brannon Judeth H.
Published: April 2003

Partitioning of macromolecules between pore and bulk solutions directly affects both equilibrium and transport processes such as exclusion chromatography and movement of solutes through porous media. Because of interactions between macromolecules and the pore wall, the variation of the macromolecule activity with concentration is different inside the pore than in bulk solution. This difference causes a concentration dependence of the distribution coefficient, as reported in experiments involving exclusion chromatography. In order to explain this effect, we develop a model for a concentration‐dependent distribution which explicitly accounts for a coupling between pore–macromolecule and macromolecule–macromolecule interactions. Predictions using this model are reported for the case of rigid spherical macromolecules in both cylindrical and slit pores, including both steric (hard sphere–hard wall) and long‐range (screened electrostatic) interactions. An important result is the existence of a general correlation between the first order concentration effect and measurable properties of the macromolecule and porous medium.
Relaxation of shear and normal stresses in step‐shear deformation of a polystyrene solution. Comparison with the predictions of the Doi–Edwards theory
Authors: Osaki Kunihiro , Kimura Shinichi , Kurata Michio
Published: April 2003

The shear stress σ, two components of birefringence, and extinction angle were measured for a concentrated polystyrene solution in step‐shear deformation of magnitude of shear 0.3 ≤ γ ≤ 4.0. The stress‐optical coefficient did not depend on either γ or time. The first and the second normal‐stress differences v1 and v2 were evaluated with the use of the stress‐optical law. Over a certain range of long times, σ could be factored as σ = γh(γ)G(t) and the quantity h(γ) agreed with the prediction of the Doi–Edwards theory based on the de Gennes tube model of entangled polymer chains. At short times the effect of γ on σ/γ was smaller than at long times. The relaxation spectrum became approximately independent of γ at the short‐time end of the rubbery plateau region. The ratios v1/σ and v2/v1 were independent of time and were in quantitative agreement with those predicted by the Doi–Edwards theory: v1/σ was equal to γ, v2/v1 was negative, and |v2/v1| decreased with increasing γ.
Network models of concentrated polymer solutions derived from the yamamoto network theory
Authors: Fuller G. G. , Leal L. G.
Published: April 2003

Several choices of the functions describing the creation and destruction processes of entanglement junctions in the Yamamoto network theory of concentrated polymer solutions have been examined. These choices are simple functions of the extension of the network segments bridging the entanglement points and it is demonstrated that the moments of the distribution function describing the network conformation can be solved for analytically. This has been done for a wide range of two‐dimensional flows, both for the steady state and transient start‐up and relaxation problems. The macroscopic stress tensor and flow birefringence are calculated and a variety of nonlinear effects are predicted and discussed.
Ordering phenomena in thin polystyrene films
Authors: Cohen Y. , Reich S.
Published: April 2003

Ordering of polystyrene (PS) molecules in thin films collapsed from toluene solutions onto a glass substrate by dip coating is studied in relation to the polymer molecular weight and its distribution. The degree of ordering of chain elements is deduced from measurements of film birefringence, between the normal and parallel directions to the film surface, as a function of film thickness. A technique has been developed for measuring this birefringence by monitoring the intensity of laser light passing through the film, as a function of the angle of incidence. Films of monodisperse low‐molecular‐weight PS exhibit high ordering very close to the substrate, but this ordering decays within 1 μm from the glass surface. Films of monodisperse high‐molecular‐weight PS, on the other hand, exhibit a much smaller, but very long‐range degree of order. In a blend of PS of these two molecular weights, as well as in a polydisperse sample, these effects appear in tandem. The long‐range ordering effect, evident in the 100,000 molecular weight polystyrene films, is much smaller in magnitude in lower‐molecular‐weight films, reflecting probably the importance of chain entanglements.
Carbon‐13 NMR linewidths of polyethylenes and related polymers
Authors: Dechter J. J. , Komoroski R. A. , Axelson D. E. , Mandelkern L.
Published: April 2003

The carbon‐13 NMR linewidth (proton decoupled) of linear and branched polyethylenes crystallized so as to yield different supermolecular structures, as well as a polyethylene oxide sample, have been studied in detail. The purpose has been to assess the different molecular contributions to the linewidth in the completely amorphous polymer as well as in the amorphous regions of the semicrystalline state. These studies on a number of different structures were complemented by both proton‐decoupled and dipolar‐decoupled magic‐angle spinning experiments on a particular sample, as well as frequency dependence studies. It is found that the abnormally broad resonance lines previously reported for the molten polymer can be significantly reduced by adopting appropriate methods of sample preparation and magnetic‐field homogenization at each temperature. Relatively narrow lines result which can be interpreted in a conventional manner. In the semicrystalline state, the resonance lines are relatively broad and are shown to be morphology dependent. Specific contributions and their temperature dependence are discussed.
Metal‐containing coordination polymers. XI. Crystallization and melting behavior of a semicrystalline polyester and its Mg (II) complexes
Authors: Székely‐Pécsi Zs. , Vancsó‐Szmercsányi I. , Cser F. , Varga J. , Belina K.
Published: April 2003

The effect of metal ion content and thermal history on the crystallization and melting behavior of a semicrystalline low‐molecular‐weight poly(butylene adipate) and its Mg complexes was studied by wide‐angle x‐ray diffractometry and differential scanning calorimetry. Both the polyester and the metal‐containing derivatives are dimorphous, and a β to α transformation takes place as the annealing temperature is increased. The dependence of the degree of crystallinity on the thermal history is more pronounced at higher Mg contents because of the effect of metal ions on the rate of crystallization. Melting of specimens with nonequilibrium structure is accompanied by simultaneous recrystallization processes such as perfection of crystallites and transformation of the crystal forms. The rates of these processes decrease with increasing metal content. The crystallizability is also reduced in the presence of Mg. Above the stoichiometrically equivalent Mg content, an abrupt change in the percentage of crystallinity accompanied by a considerable alteration in the microstructure of the crystalline phase occurs.
Apparatus for infrared measurement of sorption/desorption in strained polymeric films
Authors: Phillips J. C. , Peterlin A. , Waters Paul F.
Published: April 2003

A new apparatus has been developed for optical measurement of sorption/desorption in transparent polymer films at a given strain or stress. The technique utilizes a chosen infrared absorption frequency of the diffusing vapor in a spectral region where the film has negligible absorption. From the time dependence of the IR absorption at this frequency the sorption/desorption behavior of the film may be determined at any strain or stress. The simultaneous measurement of mechanical relaxation as a function of the amount of sorbed vapor is also possible. The results presented here show the applicability of the apparatus for determining the transport and mechanical properties of a low‐density polyethylene film in ethyl acetate vapor at 30°C.
Study of the molecular conformation of an aromatic polyamide–hydrazide by intrinsic viscosity
Authors: Bianchi E. , Ciferri A. , Preston J. , Krigbaum W. R.
Published: April 2003

The persistence length of poly(terephthaloyl p‐amino benzhydrazide) (X‐500) in dimethyl sulfoxide (DMSO) has been determined from intrinsic viscosities measured for several whole‐polymer samples. An approximate correction is applied for excluded volume effects, and these corrected values are fitted using the viscosity treatments of Yamakawa and Fujii and of Eizner and Ptitsyn. Both give for the persistence length of X‐500 values in the range 30–35 Å. Revised treatment of our previous light scattering data for the same polymer yields 49 Å for the persistence length. Thus the chain extension of X‐500 falls between those of para‐linked polyamides and those of typical freely coiling macromolecules. Phase diagram studies indicate the solubility of X‐500 in DMSO decreases with rising temperature, and can be increased by the addition of LiCl. No anisotropic phase is found in DMSO at the highest volume fraction of polymer, v2 = 0.19, which can be obtained with 4 g/dl LiCl. The critical concentration of X‐500 needed for the appearance of the anisotropic phase depends upon solvent since Morgan reported an anisotropic phase for this polymer in 100% H2SO4 when v2 ≈ 0.13.
Ultradrawing of high‐molecular‐weight polyethylene cast from solution. II. Influence of initial polymer concentration
Authors: Smith Paul , Lemstra Piet J. , Booij Henk C.
Published: April 2003

Ultradrawing of films of high‐molecular‐weight polyethylene (M̄w = 1.5 × 106) produced by gelation crystallization from solution is discussed. The influence of the initial polymer volume fraction (ϕ) on the maximum draw ratio (λmax) of the dried films is examined in the temperature region from 90–130°C. The results can be described very well by the relation λmax = λ ϕ−1/2 where λ is the (temperature‐dependent) maximum draw ratio of the melt‐crystallized film. An attempt is made to discuss the marked influence of the initial polymer volume fraction on λmax in terms of the deformation of a network with entanglements acting as semipermanent crosslinks.
Electrostatic fiber spinning from polymer melts. I. Experimental observations on fiber formation and properties
Authors: Larrondo L. , St. John Manley R.
Published: April 2003

It is demonstrated that continuous filaments of rapidly crystallizing polymers, such as polyethylene and polypropylene, can be spun from the melt using an electric field as the only driving force. The molten polymer is fed into a metallic capillary forming a hemispherical drop at the end of the orifice. An electrical field is applied between the capillary and a conducting plate held perpendicular to the axis of the orifice. Above a critical field intensity a fine continuous jet of molten polymer is drawn; rapid crystallization ensues and a continuous fiber is formed. For fibers spun in an uncontrolled thermal environment, corresponding to ambient air temperature, and at electric field intensities of 6 and 7 kV cm−1, the properties are typically those of unoriented or slightly oriented polyolefin fibers, such as would be obtained in a conventional fiber spinning process.
Electrostatic fiber spinning from polymer melts. III. Electrostatic deformation of a pendant drop of polymer melt
Authors: Larrondo L. , St. John Manley R.
Published: April 2003

It has been previously shown that fine jets can be drawn from polymer melts with the aid of an electric field. In an effort to understand the mechanism of jet formation, preliminary experiments have been carried out on the deformation of pendant drops of molten polymers(nylon 12 and polyethylene) subjected to an electric field. The drop deformation was measured as a function of field intensity and frequency, and the results were interpreted in terms of a theory due to Torza et al. It is shown that there is qualitative agreement between the theory and experimental observations. This permits the identification of the parameters influencing the drop deformation and leads to a qualitative picture of the mechanism of deformation.
Negative thermal expansivity of polymer crystals: Planar zig‐zag chain model
Authors: Chen F. C. , Choy C. L. , Wong S. P. , Young K.
Published: April 2003

The thermal expansivity of polymer crystals in the direction parallel to the chain axis α∥ is studied in a planar zig‐zag chain model. Using values of force constants for polyethylene, it was found that α∥ = −1.3 × 10−5 K−1, in good agreement with experimental results. Torsional modes are found to contribute slightly more than half α∥. The expansivity is independent of the mass of the atomic groups on the chain and only weakly dependent on the interchain van der Waals interaction.
Empirical relation for diffusion of gases in hydrocarbon polymers: Interpretation in terms of fractional free volume
Authors: Peterlin A. , McCrackin F. L.
Published: April 2003

An empirical relationship between the diffusion coefficients of gases in three polyethylenes and their diffusion coefficient in natural rubber is given. The diffusion coefficients are given within a relative error of 4.7%. This relationship is interpreted according to the fractional free volume theory. The ratios of the fractional free volumes in the polyethylenes to the fractional free volume in natural rubber are derived.
Small‐angle neutron scattering by two‐component particles: Application to block copolymers
Authors: Ionescu L. , Picot C. , Duval M. , Duplessix R. , Benoit H. , Cotton J. P.
Published: April 2003

General equations for small‐angle neutron scattering are derived for block copolymers in dilute solution. The effects of excluded volume and polydispersity are examined. The applicability of the method of variable contrast to such systems is discussed.
Strain birefringence in ethylene‐propylene copolymers
Authors: Llorente M. A. , Mark J. E.
Published: April 2003

A series of polymeric networks were prepared by the γ‐radiation crosslinking of two ethylene‐propylene copolymers containing 62 and 69 mol % ethylene units. The elastomeric materials thus obtained were studied in elongation, both swollen and unswollen, over the temperature range −30 to 95°C. The experiments involved measurements of both the elastic force and birefringence, using primarily changes in temperature at constant length (rather than changes in length at constant temperature). There is evidence for crystallization in these networks, as manifested by marked decreases in force and increases in birefringence at relatively low elongations and at temperatures as high as 70°C. As expected, the birefringence and related quantities were found to be more sensitive to crystallization than the force, with the stress‐optical coefficient showing the greatest sensitivity. The results obtained in the elongation‐temperature regions presumably free from effects of network crystallization were used to calculate values of the temperature coefficient of the unperturbed dimensions of the chains, and values of the optical‐configuration parameter. Both are widely used to characterize (spatial) configurations of chain molecules. Values of the former quantity are in very good agreement with those predicted some years ago using a rotational isomeric state model for ethylene‐propylene chains of various chemical and stereochemical compositions. The extension of these theoretical calculations to include the stress‐optical coefficient should provide further information on crystallization in ethylene‐propylene elastomers and the configurational characteristics of these copolymeric chains.