bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoluminescence from photoexcited polyethylene terephthalate
Authors: Takai Yoshiaki , Mori Koji , Mizutani Teruyoshi , Ieda Masayuki
Published: April 2003

Thermoluminescence from polyethylene terephthalate (PET) has been investigated. A correlation was found between thermoluminescence (TL) and thermally stimulated current (TSC). The apparent activation energy was estimated at 0.23–0.50 eV for both TSC and TL from −170 to 0°C. This activation energy presumably indicates the trap depth, which is decreased by molecular motions, since both TSC and TL are quenched efficiently with visible light, but not with infrared light of energy of the magnitude of thermal activation energy. The spectrum of TL glow curves agrees with the photoluminescence spectrum at −185°C, which is composed of an excimer and a monomer fluorescence and also a structured phosphorescence at wavelengths longer than 400 nm.
Fourier transform infrared analysis of the stereoregularity of atactic polystyrene
Authors: Jasse B. , Koenig J. L.
Published: April 2003

Fourier transform infrared spectroscopy provides a sensitive method allowing one to detect easily changes in the syndiotactic sequence content in polystyrene. The method is based on analysis of the 540‐cm−1 absorption band, which is conformationally sensitive. Results in the solid state and solution are presented. A shift of 2.5 cm−1 of the 540‐cm−1 band towards the high‐frequency side is observed between the solid state and solution.
A model for the adsorption of poly(γ‐benzyl‐L‐glutamate) from solution onto alkali‐halide substrates
Authors: Balik C. M. , Hopfinger A. J.
Published: April 2003

The isothermal adsorption of high‐and low‐molecular‐weight poly(γ‐benzyl‐L‐glutamate) (PBLG) onto (100) alkali‐halide surfaces has been studied with the intent of developing a model for the adsorption process. Data from both the solution and adsorbed phases were correlated in this study. The α‐helical conformation was maintained in solution and on the substrate for all molecular weights investigated. Fourier‐transform infrared spectroscopy proved to be a sensitive technique for conformational analysis of adsorbed PBLG films as thin as 200 Å. High‐molecular‐weight PBLG was adsorbed as an interwoven fibrous mat, homogeneously covering the entire substrate surface. This morphology was independent of the substrate. Adsorption of low‐molecular‐weight PBLG took on a lamellar morphology, often exhibiting epitaxial orientation in the substrate 〈100〉 directions. Quasielastic laser light scattering studies showed that low‐molecular‐weight PBLG had a much higher degree of aggregation in nonpolar solvents than did high‐molecular‐weight PBLG. The proposed adsorption model is essentially a modification of one suggested by Silberberg. It involves segmental adsorption of aggregates, as opposed to single macromolecules of PBLG. The unadsorbed segments of the aggregates form a concentrated interfacial region directly above the substrate. Further interaction and association of PBLG may occur in this region, thus reducing the epitaxial ordering influence of the substrate. Consequently, polymers which do not interact strongly in the concentrated interfacial region, such as polyethylene, are expected to be adsorbed epitaxially, as has been reported.
The thickness of adsorbed polymer layers at a liquid–solid interface as a function of bulk concentration
Authors: Priel Z. , Silberberg A.
Published: April 2003

With a glass apparatus which is capable of measuring the thickness of adsorbed polymer layers with as accuracy of 0.5 nm, determinations on adsorbed polystyrene layers in contact with extremely dilute solutions (ca. 10−7 g/ml) in toluene were performed. Thermodynamic equilibrium was proved to exist between the adsorbed polymer layer and bulk solution. The thicknesses found suggest that a fluid mechanical effect is operative, as has recently been calculated. It was shown that in the very dilute region the thickness of the adsorbed layer is initially a linearly increasing function of concentration, and that regions of (very low) concentrations exist over which a first plateau arises, where the layer is as thin as might be expected from isolated, adsorbed coil analysis. A second much higher plateau arises at concentrations in excess of 10−5 g/ml, which is the plateau usually described.
CO2 sorption in poly(ethylene terephthalate) above and below the glass transition
Authors: Koros W. J. , Paul D. R.
Published: April 2003

High‐pressure CO2 sorption data in semicrystalline poly(ethylene terephthalate) (PET) are presented for temperatures ranging from 25 to 115°C. The results are described by Henry's law above the glass‐transition temperature of PET, while a dual‐mode sorption model comprised of a Henry's law and a Langmuir isotherm applies in the glassy state. The disappearance of the Langmuir capacity of the polymer above Tg presumably results from the elimination of regions of localized lower density which are frozen into the glass upon quenching from the rubbery state. Exposure of PET to a high CO2 pressure produced a systematic variation in the apparent sorption equilibria. Correlation of the Langmuir capacity of PET with the dilatometric parameters of the polymer provides a useful framework for understanding the origin of the Langmuir sorption mode and for interpreting annealing and conditioning effects in glassy polymers.
Thermally stimulated current from extended‐chain crystals of polyethylene
Authors: Hashimoto Toshimasa , Sakai Tetsuya , Miyata Seizo
Published: April 2003

Thermally stimulated current (TSC) has been observed in extended‐chain crystals of polyethylene above room temperature. The TSC spectra exhibit two current peaks of opposite polarity. The peaks were separated into separate components by curve fitting. The position of the negative peak, which appears at 123°C, is independent of charging conditions. The positive current increases after γ irradiation or aging of the samples.
Elastic modulus of the crystalline phase of poly(cis 1,4‐isoprene)
Authors: Avitabile G. , Napolitano R. , Riva F.
Published: April 2003

The crystalline elastic modulus of poly(cis 1,4‐isoprene) has been measured by x rays and calculated by molecular mechanics. The experimental modulus is E = (2.3 ± 0.3) × 109N m−2. The calculated modulus is E = (8.8 ± 0.1) × 109N m−2 for chains in S+ cis S−T conformation and E = (6.1 ± 0.1) × 109N m−2 for chains in S+ cis S+T conformation. The modulus calculated for a statistical structure including both conformation is E = (6.7 ± 0.1) × 109N m−2. The experimental modulus is thought to be a lower limit because of partial crystallinity of the sample. The chief mechanism of deformation is rotation around single bonds adjacent to the double bond.
Molecular confirmation and crystal structure of the β form of poly(ethylene oxybenzoate)
Authors: Takahashi Yasuhiro , Kurumizawa Toshimitsu , Kusanagi Hiroshi , Tadokoro Hiroyuki
Published: April 2003

The crystal structure of the β form of poly(ethylene oxybenzoate) was analyzed by x‐ray diffraction. Four nearly extended molecular chains pass through a unit cell with parameters a = 8.19 Å, b = 11.07 Å, c (fiber axis) = 19.05 Å, β = 114.8°, and the space group P21/n‐C. The structural difference between the α and β forms is mainly due to the internal rotation angles for the virtual bond
magnified image
and the CH2CH2 bond. They are essentially in trans confirmation in the β form, while the α form contains cis
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and gauche (CH2CH2) conformations.
Hydrostatic extrusion of polyoxymethylene
Authors: Coates P. D. , Ward I. M.
Published: April 2003

The hydrostatic extrusion behavior of polyoxymethylene (POM) is described. Extrusions were performed at 164°C for a range of different molecular weight grades. Excellent unflawed lengths of extrudate were obtained with axial Young's moduli, measured at room temperature, reaching values as high as 24 GPa. The extrusion characteristics are discussed in terms of the very strong dependence of the flow stress of POM on strain and strain rate and pressure. In addition to measurements of Young's modulus over a wide temperature range, data for shear modulus and transvers modulus are also presented. A limited amount of other structural measurements is presented.
Mechanical and transport properties of drawn low‐density polyethylene
Authors: Araimo L. , De Candia F. , Vittoria V. , Peterlin A.
Published: April 2003

Quenched, quenched and annealed, and slowly cooled branched low‐density polyethylene films were drawn at 25, 40, and 60°. The true draw ratio λL of the volume element was obtained and used to characterize the dependence on plastic deformation of the density, drawing stress, and work of plastic deformation, and the sorption and diffusion of methylene chloride. The effects observed are similar but less drastic than on linear high‐density polyethylene. In particular, the transformation from the original lamellar to the final fibrous structure seems to be fastest for λL between 3 and 4. But the changes of vapor transport clearly indicate that the transformation is not yet complete even at the highest draw ratio λL = 6, just before the sample breaks. Annealing at 90°C of the drawn samples with free ends restores or even increases the transport properties beyond those of the undrawn sample without causing the fibrous structure to revert to the original lamellar structure.
Laser Raman scattering in uniaxially oriented atactic polystyrene
Authors: Jasse B. , Chao R. S. , Koenig J. L.
Published: April 2003

Raman polarization measurements of atactic polystyrene (APS) films were recorded after uniaxial stretching. Twelve different polarization directions were observed by varying the direction and polarization of the laser and scattered radiation. The polarization behavior of several vibration modes were shown clearly in the Raman spectra. On the basis of these polarization properties and previous vibrational studies of model compounds of polystyrene as well as of monosubstituted benzene derivatives, a reassignment of some of the vibrational modes of APS is made and discussed.
The structure and properties of oriented fibers of poly(pentamethylene terephthalate). II. Structural analysis of two different crystalline phases by x‐ray crystallography
Authors: Hall I. H. , Rammo N. N.
Published: April 2003

Oriented fibers of poly(pentamethylene terephthalate) will crystallize in one of two phases. In one phase (designated α), which is preferred in the unstressed fiber at room temperature, the chain is contracted from its chemical repeat length. In the other (designated β), induced by tension, it is nearly fully extended. The structural analysis of both forms is described. The unit cells of both phases are triclinic. The parameters of the α phase are a = 4.7 Å, b = 5.8 Å, c = 24.7 Å, α = 112°, β = 94°, γ = 105°. For the β phase they are a = 5.0 Å, b = 5.8 Å, c = 28.2 Å, α = 126°, β = 74°, γ = 120°. The methylene sequence is all trans in the β phase but, surprisingly, in the α phase, three of its bonds are near the eclipsed conformation. The other surprising feature is the departure from planarity of one of the terephthaloyl residues in the β phase. These, and other features of the structures are compared with those of other chemically similar materials, both monomeric and polymeric.
Structure of glassy polymers. V. Small‐angle x‐ray scattering from polystyrene
Authors: Renninger A. L. , Uhlmann D. R.
Published: April 2003

Small‐angle x‐ray scattering (SAXS) from glassy atactic polystyrene has been measured using a Bonse–Hart system. After correcting for absorption, background, and beam divergence, the scattering has been placed on an absolute basis using a standard silica suspension as a reference.The desmeared absolute intensity decreases strongly with increasing scattering angle over the range between 20 sec and 20 min. At larger angles, the intensity decreases much more slowly with increasing angle and approaches the value expected for density fluctuations frozen‐in at the glass transition. The angular variation of intensity is well described by the scattering from heterogeneities of various sizes and concentrations superimposed on the scattering from thermal density fluctuations. These heterogeneities range in radius from 10 to 4000 Å. The present SAXS results on glassy polystyrene seem inconsistent with the presence of nodular features as representative of the bulk polymer.
Chain mobility of some terephthalic acid polyesters in solution. A 13C spin‐relaxation study
Authors: Komoroski Richard A.
Published: April 2003

Carbon‐13 spin‐lattice relaxation times (T1), nuclear Overhauser enhancements (NOE), and resonance linewidths (Δp) have been measured for a series of terephthalic acid polyesters containing ethyl, butyl, hexyl, and isopropyl groups between neighboring terephthalate units. The relaxation parameters of all carbons in the terephthalate groups are independent of the length of the separating alkyl chain. Reduced NOE's are seen for all carbons. The data are interpreted in terms of a log X2distribution of correlation times of constant width, but variable average mobility. The average mobility in the alkyl chain increases with increasing distance from the terephthalate group in a given polymer. For a given position in the chain. mobility increases with increasing chain length. This behavior is consistent with the presence of independently reorienting, highly solvated terephthalate groups.
The heat of fusion of polymer crystals: Polyethylene crystals in suspension
Authors: Harrison I. R. , Runt J. , Stanislow L. J. , Bell D. A.
Published: April 2003

Recent experiments have supported the view that polyethylene (PE) single crystals kept in suspension, in a variety of liquids, have different physical properties compared with the same crystals after drying. The present work was undertaken in an attempt to directly measure one of the basic properties of crystals in suspension, namely their percent crystallinity (X). Differential scanning calorimetry was chosen as the primary tool for this investigation. A method has been developed to determine the weight of PE in a suspension of crystals in a nonsolvent. Thus, a determination of X can be made. For suspension crystals, X was found to be at least 88.5%, some 6% larger than that for the corresponding dried or freeze‐dried material. Implications with regard to the fold‐surface structure are discussed. Differences in degree of crystallinity as a function of drying procedure have also been observed.
Far‐infrared studies of ion clustering in ionomers
Authors: Rouse George B. , Risen William M. , Tsatsas Andreas T. , Eisenberg Adi
Published: April 2003

The far‐infrared spectra of polystyrene methacrylic acid/(PSMA) ionomers have been investigated as a function of cation and ion‐site concentration to obtain spectroscopic evidence of domain formation. A far‐infrared band, due to the vibration of a higher‐order cluster, is found at 170 cm−1in Na+‐form PSMA. This band, which is observed in addition to the known cation‐motion bands, is assigned to the vibrations of aggregates involving many cations and anionic sites close together, and the results are discussed in light of ion aggregation models.
Glassy polymer solutions: Morphology of in situ crystallized additives
Authors: Narkis M. , Siegmann A. , Puterman M. , Dibenedetto A. T.
Published: April 2003

In the present work the phenomenon of in situ crystallization of low molecular weight organic compounds from an amorphous polymer was studied. Phase diagrams of tetrachloroxylene and tetrachlorobenzene with polystyrene showing softening, precipitation, and dissolution have been constructed. Three modes of crystallization, namely, needlelike, dendritic, and tiny crystalline particles have been observed depending on cooling rate. Hot stage optical microscopy and electron microscopy have been used to study crystallization, dissolution, and morphology. Softening temperature was determined by the vicat method. Shearing of samples undergoing crystallization has produced oriented samples.
The heating rate dependence of polymer melting points
Authors: Harrison I. R. , Runt J.
Published: April 2003

The melting points (Tm) of small quantities (ca. 0.1 mg) of polyethylene (PE) single crystals in the dried state and in suspension were determined as a function of heating rate. Melting points were also obtained for large amounts (ca. 3 mg) of dried‐down crystals. It has been reported previously that PE crystals of high molecular weight possess a single melting point and this Tm decreases with increasing heating rate. However, all samples in our study show multiple melting behavior. Moreover, suspension samples show little or no variation in the various peak temperatures with heating rate. There is some dependence of Tm on heating rate for small dry samples but the change in Tm is not nearly as great as previously reported. These small changes can be the result of the relatively poor resolution of small dry samples compared to suspension. Differences between the behavior reported here and those of other authors can be explained on the basis of the relative contributions to the various melting endotherms.
Mechanical relaxations in episulfide network polymers
Authors: Charlesworth John M.
Published: April 2003

A variety of condensation network polymers have been prepared by the reaction between amine, episulfide, and epoxide monomers. The mechanical relaxations occurring in these systems have been examined using a torsion pendulum and the role of hydrogen bonding in the mechanism of the β relaxation is shown to be insignificant. The chemical reaction between amine and episulfide groups has been investigated by IR spectroscopy and is shown to parallel the reaction between amine and epoxide groups. However, steric and electronic factors are suggested to decrease the extent of reaction when aromatic amines are involved. In the case of networks prepared from blends of episulfide and epoxide monomers, measurements of the gel time, together with the mechanical behavior around the glass transition, indicate that either interpenetrating or two‐phase networks are formed. This is postulated to be a consequence of the high reactivity of the episulfide ring compared to the epoxide ring. The blending of small amounts of episulfide monomer with the epoxide monomer prior to curing may provide an effective method for lowering gel times without reducing the crosslink density and its dependent physical properties.
The elastic potential function of slightly compressible rubberlike materials
Authors: Peng S. T. J.
Published: April 2003

In order to obtain an analytical expression for the stored energy function W of slightly compressible rubberlike materials, two recent results are used to obtain a unified expression

where Γi are a new set of invariants, and H(Γ1,Γ2) is the shear part of the stored energy function which is now assumed to be a separate symmetric function of the modified stretch ratio, λ = λi/I, i.e.,

Various analytical forms of h(λ) are proposed. Also, a straightforward transformation technique is formulated such that one can easily relate the stress‐strain relation in terms of modified stretch ratio λ to the new invariants Γi. Thus, by a combination of the above equations and the transformation technique, one may readily determine the elastic strain energy function of slightly compressible materials from careful measurements of the volume change in multiaxial deformations.
Deformation and structure of doubly oriented polyethylene
Authors: Cowking A. , Munro F.
Published: April 2003

Doubly oriented low‐density polyethylene with parallel lamellae was compressed along the initial draw direction (i.e., at right angles to the lamellar surfaces) at 20°C. Wide‐ and low‐angle x‐ray diffraction were used to determine the changes in the molecular orientation and in the texture. During the compression, specimens previously annealed at or near 102°C were found to undergo changes in length, in long spacing, and in molecular orientation which were consistent with an (001) chain slip mechanism. In specimens annealed at higher temperatures x‐ray diffraction indicated that during compression some series component of the long spacing was compressed by a much smaller amount than the remainder of the long spacing, which deformed by chain slip; in these cases it was found that the macroscopic strain along the compression axis (εy) was greater than the strain in the long spacing along that axis (εd). It is suggested that the missing strain which makes εy greater than εd is due to partial melting and the consequent development of amorphous regions between the stacks of lamellae.
Electric field dependence of lower critical phase separation behavior in polymer–polymer mixtures
Authors: Reich S. , Gordon J. M.
Published: April 2003

The electric field dependence of the cloud point temperature of a poly(vinyl methyl ether)–polystyrene mixture has been experimentally measured in a laser light scattering experiment. It is found that the cloud point temperature is depressed linearly with the square of the applied electric field. A thermodynamic derivation of the electric field dependence of the spinodal temperature for polymer–polymer mixtures is also presented. A large disagreement between the experimental and theoretical findings is noted and possible explanations for this discrepancy are discussed.
Molecular motion in poly(L‐histidine) in the solid state
Authors: Oshima Ryuichi , Kumanotani Ju
Published: April 2003

Molecular motions in poly(L‐histidine) (PLH) and its hydrochloride in the solid state have been studied by NMR and dielectric measurements. Four relaxation processes, β,γ,δ, and ε, are observed for PLH. The δ relaxation is assigned to rotation of an imidazole ring about the CβCγ bond, since the observed activation energy of 2.7 kcal/mole agrees with the calculated energy barrier for rotation of the central imidazole ring about CβCγ in an imidazole trimer model and the experimentally determined dielectric relaxation strength is consistent with the theoretically estimated value based on the two‐state transition theory. The γ relaxation was attributed to the restricted rotational motion about CαCβ. The β relaxation is related to motion of water molecules bound by PLH. The ε relaxation is assigned to the wagging mode of imidazole groups in the defect region as observed for polymers containing pendent aromatic rings. No relaxation is observed in the hydrochloride of PLH due to the increased interaction between imidazolium cations as side groups. This is confirmed by the comparison of dipole moments of protonated and deprotonated imidazoles estimated by molecular‐orbital calculations.
Diffusion‐controlled formation of porous structures in ternary polymer systems
Authors: Cohen Claude , Tanny G. B. , Prager Stephen
Published: April 2003

We propose a theory for the appearance of two‐phase structures during the formation of polymer membranes from a casting solution immersed in a coagulant bath. Our model is based on diffusion induced phase separation at the spinodal in the ternary nonsolvent‐solvent‐polymer system. A simplified treatment of the interdiffusion process by the diffusion layer method permits the formulation of criteria for the formation of two‐phase structures in the course of the solvent‐coagulant exchange. Our criteria are expressed in terms of the composition dependence of the chemical potentials in the stable and metastable region of the ternary phase diagram. Comparison with experimental results shows qualitative similarities with theoretical predictions.
Phase transitions in cellulose solutions. The kinetics of precipitation of cellulose from diluted cadoxen solutions
Authors: Theil Michael H. , Caviness Elton T.
Published: April 2003

Solutions of cellulose (degree of polymerization: 296 ± 16) in tris(ethylenediamine)cadmium(II)hydroxide‐ethylenediamine‐water (cadoxen), 1.015% (weight per volume) were diluted 1:1.5 with water. The ensuing isothermal precipitations were followed dilatometrically at temperatures ranging from 27.50 to 48.45°C. The precipitation data were characterized by a positive temperature coefficient. They generally conformed to a one‐dimensional nucleation rate law; the Avrami exponents were close to unity. Alternatively, they fit a first‐order reaction rate expression with respect to cellulose concentration. The low crystallinity of the precipitated cellulose leads to the interpretation of the kinetics in terms of the dissociation of a cellulose‐cadoxen complex, rather than phase separation, as the rate‐determining step. The nucleation rate law suggests a one‐dimensional nonrandom cooperative chemical process, while the first‐order rate law suggests a random process.
Physical properties and structure of silk. VI. Conformational changes in silk fibroin induced by immersion in water at 2 to 130°c
Authors: Magoshi Jun , Mizuide Michio , Magoshi Yoshiko , Takahashi Kazuo , Kubo Mieko , Nakamura Shigeo
Published: April 2003

Silk fibroin films in the random‐coil and β‐form conformations were immersed in water at temperatures from 2 to 130°C, and conformational changes were followed by x‐ray diffraction, infrared spectroscopy and differential scanning calorimetry. On treatment with water below 60°C, the random‐coil conformation is converted to the α form and above 70°C to mixtures of the α and β conformations. The β‐form content increases as the immersion temperature is raised. The β form is not affected by immersion in water in the temperature range studied.
Effect of the solvent upon the diffusion coefficient of polydisperse polystyrene and styrene‐acrylonitrile copolymer in dilute solution
Authors: Raju Krishnam , Blanks Robert F.
Published: April 2003

A laser homodyne spectrometer was used to obtain translational diffusion coefficients for dilute polystyrene and styrene‐acrylonitrile copolymer solutions at room temperature. Data were obtained in the concentration range from 0.01 to 2.0 g polymer per 100 cm3 solution for polystyrene in benzene and in decalin; and for copolymer in dimethyl formamide, in methyl ethyl ketone, and in benzene. The samples were polydisperse polystyrenes of weight average molecular weights between 80,000 and 350,000 and polydisperse copolymers of weight average molecular weights between 200,000 and 800,000. The SAN copolymers were random copolymer samples containing 24% by weight acrylonitrile. For each of the systems investigated the concentration dependence of the diffusion coefficient was linear over the concentration range studied, and was expressed as D(c) = D0(1+kDc). Values of D0 could be explained with a modified Kirkwood‐Riseman expression. Values of the parameter kD obtained from the slopes could be interpreted using the two‐parameter theory approach as suggested by Vrentas and Duda. The value of kD is positive for high‐molecular‐weight polymers and negative for low‐molecular‐weight polymers. For a particular polymer, the molecular weight at which kD changes sign is greater for poor solvents than for good solvents. Observed values of D0 were 1 × 10−7 to 7 × 10−7 cm2/sec.
Effect of free volume fluctuations on polymer relaxation in the glassy state. II. Calculated results
Authors: Robertson Richard E.
Published: April 2003

The relaxation following a change in temperature of amorphous polymers near the glass transition has been calculated. The calculation uses a chain model consisting of cis and trans backbone rotational states. The relaxation is assumed to proceed by localized conformational changes whose rates are controlled by the fractional free volume in small enough regions of the polymer that thermal fluctuations need to be considered. The relaxation is treated as a stochastic process, and an approximate solution is obtained for a finite set of relaxation environments. Using what is believed to be the most plausible set of parameters for polystyrene, relaxation curves are computed for the internal energy that are very similar to the curves obtained by Kovacs and others for the volumetric relaxation of poly(vinyl acetate) and polystyrene.
Creep deformation caused by crazing
Authors: Kitagawa M. , Kawagoe M.
Published: April 2003

Creep deformation caused by crazing is analyzed using an analog of dislocation dynamics. Results are compared with experiments on polycarbonate and poly(vinyl chloride) subjected to the action of kerosene as a crazing agent. Good agreement between the theory and experiment shows the value of the dislocation analog approach. The theoretical craze creep strain is found to be numerically approximated by the commonly used law similar to the Nutting equation, and may provide a physical foundation for this widely used equation formally derived from rate theory.
Dielectric relaxation in the odd‐numbered polyamides: Nylon 7‐7 and nylon 11
Authors: Yemni Tarik , Boyd Richard H.
Published: April 2003

Odd‐numbered polyamides have dipoles with components that point in the same direction in the planar zigzag conformation (rather than alternating as in the even‐numbered polyamides). An investigation of the dielectric properties of two odd nylons was undertaken here to see if dipole correlation resulting from this effect could be detected. It was found that the dielectric constant and relaxation strength associated with the α loss process (amorphous phase glass–rubber relaxation) when normalized for dipole concentration was indeed markedly higher in the odd nylons. The effect of uniaxial orientation induced by solid‐state extrusion on the isotropy of the dielectric properties was also studied. A previous study on nylon 6–10 found a reduction in relaxation strength of the α process in both the parallel and perpendicular directions but with the perpendicular direction being much stronger than the parallel. A similar result was found here for the odd polyamides. Thus the reduction in intensity appears to be due to effective reduction in the amount of amorphous material and not due to any change in dipole correlation induced by orientation. The anisotropy in relaxation strength can be explained by a composite material effect resulting from parallel stacking of crystal lamellas and interlamellar amorphous material and without invoking any anisotropy in the amorphous‐phase dielectric strength. Thus there is no reason to conclude that the amorphous phase undergoes orientation as a result of the crystal‐phase orientation.
A crystal transition in poly(γ‐n‐alkyl L‐glutamate)s
Authors: Sasaki Shintaro , Nakamura Takao , Uematsu Ichitaro
Published: April 2003

A thermally reversible crystal transition was found for γ‐helical poly(γ‐n‐alkyl L‐glutamate)s (alkyl = ethyl, propyl, butyl, and amyl). The transition temperature is higher than that of the side‐chain mechanical dispersion, and decreases from 115 to −5°C, as the alkyl groups become longer. The transition in poly(γ‐n‐propyl L‐glutamate) is clearly first order. The structures were analyzed by x‐ray diffraction at various temperatures. It is noteworthy that the pseudohexagonal form observed below the transition temperature is less ordered than the hexagonal form at higher temperatures. The mechanism of this transition is discussed.
Physical and mechanical properties of ultra‐oriented high‐density polyethylene fibers
Authors: Mead W. T. , Desper C. R. , Porter Roger S.
Published: April 2003

Ultra‐oriented high‐density polyethylene fibers (HDPE) have been prepared by solid‐state extrusion over 60–140°C range using capillary draw ratios up to 52 and extrusion pressures of 0.12 to 0.49 GPa. The properties of the fibers have been assessed by birefringence, thermal expansivity, differential scanning calorimetry, x‐ray analysis, and mechanical testing. A maximum birefringence of 0.0637 ± 0.0015 was obtained, greater than the calculated value of 0.059 for the intrinsic birefringence of the orthorhombic crystal phase. The maximum modulus obtained was 70 GPa. The melting point, density, crystallinity, and negative thermal expansion coefficient parallel to the fiber axis all increase rapidly with draw ratio and at draw ratios of 20–30 attain limiting values comparable with those of a polyethylene single crystal. The properties of the fibers have been analyzed using the simple rule of mixtures, assuming a two‐phase model of crystalline and noncrystalline microstructure. The orientation of the noncrystalline phase with draw ratio was determined by birefringence and x‐ray measurements. Solid‐state extrusion of HDPE near the ambient melting point produced a c‐axis orientation of 0.996 and a noncrystalline orientation function of 0.36. Extrusion 50°C below the ambient melting point produced a decrease in crystallinity, c‐axis orientation, melting point, and birefringence, but the noncrystalline orientation increased at low draw ratios and was responsible for the increased thermal shrinkage of the fibers.
Linear polyethylene in a glassy phase: The value of the glass‐transition temperature
Authors: Cutler D. J. , Glotin M. , Hendra P. J. , Jobic H. , Moritz K. Holland , Cudby M. E. A. , Willis H. A.
Published: April 2003

Raman spectroscopy, x‐ray diffraction, and thermal analysis are used to investigate the structure of linear high‐density polyethylene rapidly quenched from the melt to cryogenic temperatures. All the results point to the production of a glassy phase which crystallizes when heated above 170 K.
Properties of cellulose acetate. III. Light scattering from concentrated solutions and films. Tensile creep and desalination studies on films
Authors: Goebel K. D. , Berry G. C. , Tanner D. W.
Published: April 2003

Light scattering from concentrated solutions of cellulose acetate in acetone is discussed in terms of exponential correlation functions for refractive‐index fluctuations. These are related to intermolecular aggregation. Light scattering, tensile creep and recovery, and hyperfiltration studies with films of cellulose acetate cast from acetone are discussed in terms of the state of aggregation in the films. It is concluded that intermolecular aggregates are probably small and imperfectly formed regions of microcrystallinity stable up to about 210°C, with the overall state one of near amorphous disorder.
Ultrasonic degradation of polycaproamide in 40% sulfuric acid solution
Authors: Szorek Ryszard
Published: April 2003

The influence of polymer‐polymer interactions and ultrasonic parameters on the ultrasonic degradation of polycaproamide in aqueous 40% H2SO4 was investigated. It was found that the rate data for the concentrations studied could be represented well by Ovenall's rate equation. However values of the rate constant chosen to fit Ovenall's equation tend to decrease with increasing concentration of polycaproamide from 0.5 to 2.0 g/100 cm3. With increasing ultrasonic power, the degradation rate increases, but it decreases as frequency is increased. This suggests that cavitation has a dominant role.
Extensions of the Avrami equation to various polymer crystallization models
Authors: Hay James N. , Przekop Zbigniew J.
Published: April 2003

Computer modelling studies of the progress of crystallization in polymer melts have been carried out initially on those systems analyzed by Avrami and then extended to include a number of complications which may be characteristic of real systems, in particular (a) mixed mechanism, (b) volume shrinkage, (c) variable crystalline density, and (d) nonrandom nucleation. It is concluded that the Avrami equation is a reasonable approximation to most of these systems except (c).
Longitudinal growth of polymer crystals from flowing solutions. VI. Melting behavior of continuous fibrillar polyethylene crystals
Authors: Pennings A. J. , Zwijnenburg A.
Published: April 2003

The melting behavior of continuous fibrillar crystals of high‐molecular‐weight polyethylene has been investigated. The macrofibers were grown from dilute solutions in xylene subjected to Couette flow in the temperature range between 103 and 118.5°C. The thermograms, as determined by differential scanning calorimetry, exhibit three melting endotherms with peak temperatures at 141, 150.5, and 159.5°C after extrapolation to zero scan speed. All peaks were found to be strongly superheatable. Reduction of fiber length, in particular by etching with fuming nitric acid, led to the disappearance of the melting peaks at 150.5 and 159.5°C. The remaining peak at 136°C appeared not to be superheatable. The heat of fusion of the fragmented fibers was 69.8 cal/g. Wide‐angle x‐ray diffractograms taken on a macrofiber while gradually heated at a rate of 0.35°C/min at constant length showed that the triclinic phase present in the fiber disappeared at 130°C and that the orthorhombic cell transformed into the hexagonal modification at 150°C. This hexagonal phase was still observable at 180°C. The retractive force developed on heating at constant length displays first a slight decrease followed by a maximum at 150°C. Beyond the latter temperature the stress decays abruptly corresponding to the temperature at which fracture of the fiber could be observed visually. From all these observations it is inferred that the first melting endotherm in the differential scanning calorimeter (DSC) thermograms arises from the melting of unconstrained fibrillar crystal regions which are able to shrink during fusion. Moreover, the melting of lamellar overgrowths on the elementary fibrils on shish‐kebab type may contribute to this endotherm. The second melting endotherm at about 150°C is associated with the transformation of the orthorhombic into the hexagonal lattice in constrained parts of the sample. This latter “rotator” phase allows slippage of the polymer chains past each other, giving rise to stress relaxation. The third endotherm arises from melting of this hexagonal phase and the heat take‐up connected with the formation of higher energy gauche states upon randomization of the chains in the melt. Almost smooth, fully constrained fibrillar crystals grown at high temperature absorb more than 15.5 cal/g during this process, indicating that the polymer chains in such fibers must be highly extended.
Infrared studies of the reversible stress‐induced crystal‐crystal phase transition of poly(tetramethylene terephthalate)
Authors: Stambaugh B. , Lando J. B. , Koenig J. L.
Published: April 2003

The reversible stress‐induced crystal‐crystal phase transition of poly(tetramethylene terephthalate) (PTMT) has been studied using infrared spectroscopy. Two spectral regions were used to study this transition: the 900–1000 cm−1 methylene rocking region and the 1300–1550 cm−1 methylene bending region. The bands at 917 and 1456 cm−1 are assigned to the ∝ phase. The bands at 935 and 1388 cm−1 have components from the α phase and the β phase. Dynamic stretching experiments performed above and below the glass‐transition temperature indicated different mechanisms of the phase transition.
Effects of polymer solutions on colloid stability
Authors: Joanny J. F. , Leibler L. , De Gennes P. G.
Published: April 2003

Some theoretical properties of a semidilute polymer solution (in a good solvent) near a repulsive wall (no adsorption) are discussed. (i) Near a single wall, the existence of a depletion layer (where the concentration is strongly reduced) with thickness equal to the correlation length ξ(c) is predicted. Scaling laws are obtained for the concentration cs at the first layer as a function of the bulk concentration c, and for the concentration profile c(z) at distance z from the wall. (ii) When two parallel walls are separated by a slab of polymer solution (thickness d), there is an attractive interaction between the plates. The range of the attraction is ca. 3ξ(c) and can be varied by suitable choice of concentration. It may lead to destabilization of certain colloidal systems.
Isobaric volume and enthalpy recovery of glasses. II. A transparent multiparameter theory
Authors: Kovacs A. J. , Aklonis J. J. , Hutchinson J. M. , Ramos A. R.
Published: April 2003

A multiordering parameter model for glass‐transition phenomena has been developed on the basis of nonequilibrium thermodynamics. In this treatment the state of the glass is determined by the values of N ordering parameters in addition to T and P; the departure from equilibrium is partitioned among the various ordering parameters, each of which is associated with a unique retardation time. These times are assumed to depend on T, P, and on the instantaneous state of the system characterized by its overall departure from equilibrium, giving rise to the well‐known nonlinear effects observed in volume and enthalpy recovery. The contribution of each ordering parameter to the departure and the associated retardation times define the fundamental distribution function (the structural retardation spectrum) of the system or, equivalently, its fundamental material response function. These, together with a few experimentally measurable material constants, completely define the recovery behavior of the system when subjected to any thermal treatment. The behavior of the model is explored for various classes of thermal histories of increasing complexity, in order to simulate real experimental situations. The relevant calculations are based on a discrete retardation spectrum, extending over four time decades, and on reasonable values of the relevant material constants in order to imitate the behavior of polymer glasses. The model clearly separates the contribution of the retardation spectrum from the temperature‐structure dependence of the retardation times which controls its shifts along the experimental time scale. This is achieved by using the natural time scale of the system which eliminates all the nonlinear effects, thus reducing the response function to the Boltzmann superposition equation, similar to that encountered in the linear viscoelasticity. As a consequence, the system obeys a rate (time) ‐temperature reduction rule which provides for generalization within each class of thermal treatment. Thus the model establishes a rational basis for comparing theory with experiment, and also various kinds of experiments between themselves. The analysis further predicts interesting features, some of which have often been overlooked. Among these are the impossibility of extraction of the spectrum (or response function) from experiments involving cooling from high temperatures at finite rate; and the appearance of two peaks in the expansion coefficient, or heat capacity, during the heating stage of three‐step thermal cycles starting at high temperatures. Finally, the theory also provides a rationale for interpreting the time dependence of mechanical or other structure‐sensitive properties of glasses as well as for predicting their long‐range behavior.
Gelation and crystallization of poly(ethylene terephthalate‐co‐isophthalate)
Authors: Berghmans H. , Govaerts F. , Overbergh N.
Published: April 2003

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

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

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

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

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