bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between crystallization of the PDMS block and morphology of poly(butadiene‐b‐dimethylsiloxane)
Authors: Li Weidong , Huang Baotong
Published: April 2003

Studies using transmission electron microscopy, differential scanning calorimetry, and X‐ray diffraction showed correlations between the crystallization behavior of the polydimethylsiloxane (PDMS) block and the morphology of the block copolymer poly(butadiene‐b‐dimethylsiloxane) (PB‐PDMS). When the PDMS component existed as spheres dispersed in a PB matrix, the crystallization rate of the PDMS block was lower than when the PDMS phase existed in rod or cylinder form.
Small‐angle scattering of polarized light. IV. Isotropic to birefringent transition for spheres
Authors: Peuvrel E. , Siegert D. , Navard P. , Meeten G. H.
Published: April 2003

The Rayleigh‐Gans‐Debye approximation is used to investigate the small‐angle, cross‐polarized light scattering by a sphere of radius a, birefringence Δμ and relative index μ. If θmax is the polar scattering angle of the intensity maxima, the quantity Ûmax = 4πa/λ × sin (θmax/2) behaves in two different ways according to the signs of Δμ and μ − 1. When Δμ > 0, μ > 1 or Δμ < 0, μ < 1, then Ûmax varies from 2.8 to 4.1 as Δμ increases from zero. If Δμ < 0, μ > 1 or Δμ > 0, μ < 1, then Ûmax goes from 2.8 to about 6, thereafter decreasing to 4.1. Another interesting result is that the value of Ûmax for a highly briefringent sphere is 4.1 only for large diameters. It decreases to 4.0 when the diameter decreases.
CO2 permeability and amorphous fractional free‐volume in uniaxially drawn HDPE
Authors: Sha Hongjian , Harrison Ian R.
Published: April 2003

The CO2 permeability of uniaxially drawn high‐density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free volume of the amorphous component in the drawn polymers was made on the basis of experimental data. The dramatic variations in permeability resulting from drawing were shown to be the consequence of changes of fractional free volume in the amorphous phase of the drawn polymer. Good correlation exists between measured solubility and diffusion coefficients of drawn samples and the estimated fractional free volume; this correlation agrees with the existing free volume theory for diffusion in polymers.
The temperature window of minimum flow resistance in melt flow of polyethylene. Further studies on the effect of strain rate and branching
Authors: Waddon A. J. , Keller A.
Published: April 2003

The existence of a narrow temperature window (150–153°C) of smooth extrudability coupled with a minimum in flow resistance (extrusion pressure) in high‐molecular weight polyethylene (>4 × 105 g mol−1) was the subject of a previous article where it was associated with strain‐induced formation of the mobile hexagonal mesophase. The new findings of this note show that this minimum in flow resistance only sets in above a critical strain rate; this is interpreted in terms of the requirement of a critical strain rate in order to stretch molecules to their fully extended configuration. Furthermore, this critical strain rate is shown to be higher for lower molecular weight materials, in agreement with a priori considerations. Additionally, the temperature at which the pressure minimum occurs in a polyethylene containing methyl branches shifts to a significantly lower value than that for the linear material. This is interpreted in terms of the CH3 groups raising the crystal free energy, thereby lowering the temperature at which the transition to the hexagonal phase occurs.
Frequency and molecular‐mass‐dependent nonexponential proton NMR relaxation in polymer melts
Authors: Hiller W. G. , Schneider H. , Fedotov V. D.
Published: April 2003

A theoretical treatment of the nonexponential relaxation behavior of the different proton nuclear magnetic resonance (NMR) relaxation processes in polymer melts is presented. Formulas are derived for a three‐component model given by two versions and a homogeneous distribution of correlation times. The theoretical results were tested with measurements of T1, T2e, and T2 as functions of frequency and molecular mass in linear fractionated polyethylene samples. While the T1 relaxation always yields exponential magnetization decays, the T2e and T2 measurements show biexponential relaxation behavior. From the calculations it was found that the correlation time of the local motion is independent of the molecular mass, whereas the correlation time of the slowest motional process increases with M2.8w for the three‐component model and with M2.2w for the distribution of correlation times, respectively. © 1992 John Wiley & Sons, Inc.
Fickian diffusion in glassy polymer‐solvent systems
Authors: Vrentas J. S. , Vrentas C. M.
Published: April 2003

A free‐volume theory is developed for the analysis of Fickian diffusion processes in glassy polymers. Equations are presented for the prediction of mutual diffusion coefficients in concentrated glassy polymer‐penetrant systems. The concentration dependence of the mutual diffusion coefficient is dependent on how much free volume the solvent contributes to the system and on how the addition of solvent affects the densification of the polymer matrix. © 1992 John Wiley & Sons, Inc.
The relation between the microphase separation transition and the glass transition in diblock copolymers
Authors: Stühn B.
Published: April 2003

The microphase separation transition (MST) has been studied for short chain diblock copolymers poly(styrene‐b‐isoprene) and poly(styrene‐b‐mma). A detailed analysis of small‐angle x‐ray scattering (SAXS) profiles in the homogeneous phase allows determination of the interaction parameter and the spinodal temperature Ts of the MST. Ts for the PS/PI diblocks is found to be lower than the glass transition temperature of their hard blocks. This results in a coupling of the MST and the glass transition. Using both structural (SAXS) and thermal differential scanning calorimetry (DSC) methods it is shown that an endothermal peak found in the DSC diagrams is related to the combined effect of the MST and the glass transition. © 1992 John Wiley & Sons, Inc.
Characterization of inhomogeneous polyacrylamide hydrogels
Authors: Cohen Y. , Ramon O. , Kopelman I. J. , Mizrahi S.
Published: April 2003

The physical and structural properties of acrylamide gels have been characterized by osmotic deswelling, mechanical compression, and x‐ray scattering. These properties vary considerably with the concentration of the crosslinking agent bisacrylamide, at fixed total monomers concentration (10% wt/wt water). In particular, changes in the properties appear more prominent at a crosslinking level of about 5‐6% (wt bisacrylamide/wt monomers). The compression modulus of as‐prepared and swollen gels passes through a maximum at this level of crosslinking. The swelling pressure curves can be separated into osmotic and elastic contributions of the gel network. The elastic part exhibits similar behavior to the compression modulus. The scaling of the osmotic part with the gel concentration varies with the degree of crosslinking, changing from 2.33 to 3.09. This indicates that the solvent power of water decreases with increasing crosslinking level, towards Φ conditions. The scattering patterns from the gels have been analyzed as arising from additive contributions from a homogeneous gel matrix, and embedded heterogeneities having a higher crosslinking density. These heterogeneities become much more prominent at the same level of crosslinking about 5‐6%. Hysteresis observed in the sorption/desorption behavior of polyacrylamide gel suggests that further irreversible structural changes may occur at water activities lower than probed by osmotic deswelling. © 1992 John Wiley & Sons, Inc.
Fermi resonance in the infrared spectra of Nylon‐11
Authors: Fina Leslie J. , Yu Hsin Her
Published: April 2003

Nylon‐11 is prepared by casting from the solvents trifluoroacetic acid and m‐cresol and by melt‐crystallization. Room‐temperature infrared spectra are compared in terms of possible crystal structures. The spectra are examined for the presence of Fermi resonance which occurs between the N‐H stretching fundamental mode and the overtone and combination modes of the amide I and II vibrations. An analysis of peak frequencies and intensities is used to provide support for the assignment of the amide II overtone and the amide I + II combination modes. A newly observed peak in the spectra is assigned to the amide I overtone. Symmetry considerations are discussed which predict the resonance of the overtone and combination modes with the N‐H stretching fundamental. © 1992 John Wiley & Sons, Inc.
Chain scission in polystyrene by impact fracture
Authors: Yang Arnold C.‐M. , Lee C. K. , Ferline Susan L.
Published: April 2003

The number of chain scissions ns per unit fracture area by impact in high‐molecular weight polystyrene is determined to be approximately 3.3 × 1014/cm2 at room temperature. This is almost 20 times larger than would be expected if chain scissions took place only at, or very close to, fracture surfaces. This result was obtained by measuring the molecular weight decrease and the total fracture area of the impact fragments by using size exclusion chromatography and statistical particle size measurements, respectively. The large ns strongly indicates that significant chain breakage occurs during crazing before the propagation of cracks. An average craze thickness before breakdown under impact is estimated from ns to be around 2 μm. In a diluted polymer, ns is found to be significantly lower than the extrapolated value, assuming a linear dilution of entangled chain crossings at the fracture surface. This low chain scission density, however, can be explained by taking into account the reduction of craze breakdown strain in the diluted polymers. Finally, the broken chain ends of polystyrene appear to be stable under ambient conditions. © 1992 John Wiley & Sons, Inc.
A computer simulation of trapping electrophoresis
Authors: Slater Gary W. , Villeneuve Christine
Published: April 2003

The gel electrophoretic migration of streptavidin‐DNA complexes is severely altered by the phenomenon known as “trapping electrophoresis.” We present a first computer simulation study of this process. Our simulations use the very efficient biased reptation algorithm. The steady state is characterized by a large increase in band broadening and interband separation. However, we also find that for a narrow range of molecular sizes, the separation power of gel electrophoresis is greatly increased. We discuss the implications of our findings for the possible improvement of DNA sequencing technologies. © 1992 John Wiley & Sons, Inc.
Aggregation in conducting copolymer solutions
Authors: Dai Liming , White John W.
Published: April 2003

The structure of polyacetylene–polyisoprene block copolymer solutions prepared by a modified anionic to Zeigler‐Natta method is reprted. Small‐angle x‐ray scattering results are consistent with formation of wormlike micelles, which arise mainly from interactions between the polyacetylene blocks of the copolymer in solution at room temperature. Aggrgation of the wormlike micelle can be described in terms of fractal geometry. I2‐doping produces marked changes in the optical spectrum of the acetylenic block and the small‐angle scattering indicates a change in polymer aggregation to a lamellar form. It is concluded that micellar structure is the natural morphology for solutions and gels of conducting polyacetylene–polyisoprene copolymers and that this persists into the solid state. Thus, conduction mechanisms for these polymers may bear re‐examination using micelles as the structural basis. © 1993 John Wiley & Sons, Inc.
Diffusion of nonionic azo dyes in nylon‐6
Authors: Shibusawa Takao
Published: April 2003

Diffusion of 2,4‐dinitroaniline and three nonionic azo dyes in Nylon‐6 film was studied by analysis of the concentration‐distance curves (profiles) of penetrants in the polymer. Actual diffusivities D(c) of penetrants in polymer, diffusion coefficients as a function of the concentration Cf of penetrant in polymer, were calculated from the profile. It was found that D(c) is almost constant or decreases gradually with decreasing Cf in the range of high‐medium Cf but decreases appreciably with decreasing Cf at low Cf. The change in D(c) with Cf was explained in terms of the dual‐mode sorption‐diffusion model. The penetrants diffuse in the polymer as two distinct species, i.e., a dissolved species and an adsorbed species. The former is the penetrant taken up by the polymer by a partition mechanism (dissolved species) and the latter is that taken up by Langmuir sorption (adsorbed species). The actual diffusivity DP(c) of the dissolved species decreases with decreasing Cf. While the actual diffusivity DL(c) of the adsorbed species normally increases gradually with decreasing Cf. DP(c) is usually larger than DL(c). © 1993 John Wiley & Sons, Inc.
Polymer crystallization and reorganization during heating: Simulation with the sadler/gilmer model
Authors: Goldbeck‐Wood G.
Published: April 2003

Polymer crystallization and melting under nonisothermal conditions are investigated by means of an extended version of the two‐dimensional Sadler / Gilmer pinning model. In particular, the case of a constant heating rate is simulated. Lamellar thickening and eventual melting are studied for a range of heating rates and initial temperatures. An approach to equilibrium (i.e. infinite thickness at Tom) by slowing down the heating rate is found to be more than exponentially suppressed. Similarities with heating experiments on polyethylene and PEEK are demonstrated. © 1993 John Wiley & Sons, Inc.
Elastic modulus and atomic displacements of skeleton and side groups in stretching of a polymer chain
Authors: Enomoto Satoru , Chuman Hiroshi , Kurihara Azusa
Published: April 2003

We propose a new method of calculating elastic modulus and atomic displacements of a stretched polymer chain. We use a stretched Cartesian coordinate system and a stretched B matrix defined by the Cartesian displacement components of the bonds to express the potential energy matrix Fx for stretching. The method is used to calculate elastic moduli of planar‐zigzag‐chain vinyl polymers and helical‐chain isotactic polypropylene and the atomic displacements of their skeleton and side groups. The skeletal displacements of planar‐zigzag‐chain polymers are about ten times larger than those of the side groups and reverse displacements of the two adjacent skeletal units occur in the direction perpendicular to the stretching direction along the fiber axis. In the case of isotactic polypropylene, the methyl group has more effect than the torsional change around the CC bond on the skeletal deformation. © 1993 John Wiley & Sons, Inc.
Synthesis and electrical conductivity of poly(1,4‐phenylenevinylene‐co‐2‐nitro‐1,4‐phenylenevinylene)
Authors: Jin Jung‐Il , Yu Sang‐Hyeun , Shim Hong‐Ku
Published: April 2003

A series of PPV copolymers containing 2‐nitro‐1,4‐phenylenevinylene (NO2‐PV) units were prepared via the water‐soluble precursor route. They were obtained in film form and were doped with I2 and FeCl3. Doping increased the electrical conductivities to maximum values of about 3×10−2 and 3×10−1 s cm−1, respectively, for the two dopants. Conductivity depended strongly on the composition of the copolymers; it reached a maximum value at ca. 1–2 mol % of NO2‐PV units in the copolymers and then dropped rapidly with further increase in NO2‐PV content. Electronic effects of the substituent and morphological changes induced by copolymerization appear to interplay intricately, resulting in the occurrence of a maximum conducting composition. © 1993 John Wiley & Sons, Inc.
Transition regions and surface melting in partially crystalline polyethylene: A raman spectroscopic study
Authors: Mutter R. , Stille W. , Strobl G.
Published: April 2003

Structures of semi crystalline high‐molecular weight polyethylene and their changes with temperature were studied by analysis of Raman spectra. Decomposition of spectra into contributions of an orthorhombic crystalline phase, a meltlike phase, and two kinds of transition regions yields the respective mass fractions. The results of temperature dependent measurements is indicative of a largely reversible surface melting process, the transition regions being located at the crystal surfaces. As‐polymerized samples show a large fraction of the intermediate phase. Annealing leads to a reduction of this phase. © 1993 John Wiley & Sons, Inc.
Morphology and properties of polycaprolactone‐poly(dimethyl siloxane)‐polycaprolactone triblock copolymers
Authors: Lovinger Andrew J. , Han B. J. , Padden Frank J. , Mirau Peter A.
Published: April 2003

The molecular structure, crystallization, solid‐state morphology, thermal properties, and phase behavior of two copolymers consisting of a poly(dimethylsiloxane) (PDMS) mid‐block coupled to polycaprolactone (PCL) end‐blocks were investigated. Both copolymers (which differ only in the molecular lengths of the PCL end‐blocks) were found to be lamellar systems, whose core consists of PCL chains having the same crystal structure as PCL homopolymer, and whose amorphous interlayers contain the PDMS blocks and the PCL noncrystalline segments. From x‐ray and electron‐microscopy results, it is expected that the PCL blocks may be folded once in the longer copolymer and not at all in the shorter. As a result of their differing PCL lengths, the former crystallizes as regular PCL spherulites (at a growth rate reduced with respect to PCL homopolymer), whereas the latter yields only defective, immature axialites of low overall crystallinity. Electron diffraction showed that these spherulites grow preferentially along b crystallographic axis and that the PCL crystalline stems are arranged perpendicularly to their lamellae. © 1993 John Wiley & Sons, Inc.
Unusual pressure‐induced phase behavior in crystalline poly‐4‐methyl‐pentene‐1
Authors: Rastogi S. , Newman M. , Keller A.
Published: April 2003

We report some highly unusual phase behavior, of general implication for condensed matter, on the polymer poly(4‐methyl‐pentene‐1) (P4MP1) induced by changes in pressure and temperature, as observed in situ by x‐ray diffraction. Upon increasing pressure beyond a threhold, the polymer, crystalline under ambient conditions, loses its crystalline order isothermally, passing through a continuously varying sequence of mesomorphic states, the process being reversible. This behavior is observed in two widely separated temperature regions, suggesting, for the first time in a single component system, the possibility of reentrant liquid‐crystal and amorphous phases. At the upper temperature region (ca. 250°C) there is a consecutive increase and decrease of melting point with pressure. In the lower temperature region (room temperature) the pressure converts the crystal into an amorphous‐like glass obviating the need for going through the melt first, and this in a reversible manner. The latter pressure‐induced disordered phase converts into crystal on raising the temperature, and reverts to the glassy, disordered phase on lowering the temperature. Some aspects of this behavior have been found quite recently in water‐ice and silica but the process of “melting on cooling” has no precedent in any known system. Other unexpected findings include a new pressure‐induced modification of P4MP1 with a one‐way only entry with temperature, but full reversibility with pressure leading to a triple point in the PT phase diagram. The above highly uncommon results are putting several prevailing preconceptions to test which are being scrutinized. In the course of it some early expectations on general phase behavior, allowing among others for reentrant phases in one component systems, are being invoked as potentially appropriate for certain polymeric systems, if not for condensed matter in general. © 1993 John Wiley & Sons, Inc.
Langmuir‐Blodgett films of polymethacrylates with side chains containing functionalized aromatic schiff's bases
Authors: Takahashi T. , Miller P. , Chen Y. M. , Samuelson L. , Galotti D. , Mandal B. K. , Kumar J. , Tripathy S. K.
Published: April 2003

Langmuir‐Blodgett (LB) film formation has been investigated for polymers in which non‐linear optical (NLO) moieties are attached to the side chain of a polymethacrylate (PMA) backbone. Polymer monolayers were successfully transferred onto hydrophilic glass substrates using a moving‐wall type LB trough. The LB films were characterized by pressure‐area isotherms, polarized ultraviolet visible spectra, ellipsometry, and second harmonic generation measurements. The characterization shows that NLO moieties in the side chain are inclined at a shallow angle to the plane of the substrate. The second‐order nonlinear optical coefficient and molecular hyperpolarizability were also calculated. © 1993 John Wiley & Sons, Inc.
Improvement to the lattice‐fluid prediction of gas solubilities in polymer liquids
Authors: Rodgers Patrick A. , Sanchez Isaac C.
Published: April 2003

Previously we have shown that the Lattice Fluid (LF) model can quantitatively predict, without adjustable parameters, gas solubilities for hydrocarbon and chlorinated hydrocarbon vapors in nonpolar polymers. For polar polymers, the model can also predict, with reasonable success, the solubilities of polar and aromatic vapors. However, the solubilities in polar/nonpolar combinations of gas and polymer are systematically overestimated. These are cases in which the geometric mean approximation for the interaction parameter is not expected to be valid. This paper demonstrates that with the addition of a simple empirical correlation for the interaction parameter based on Hansen's three‐dimensional solubility parameters, the LF model is then able to quantitatively predict solubilities in all types of gas/polymer systems (excluding strongly self‐associating systems, such as alcohols). No adjustable parameters are used; only the pure component equation‐of‐state and solubility parameters are required. © 1993 John Wiley & Sons, Inc.
Configuration‐Dependent properties of the poly(dimethylsilmethylene) chain in the third‐order interaction approximation
Authors: Wu Xiaoyi , Jin Jinsheng , Zhang Linxi , Xu Jianmin
Published: April 2003

On the basis of rotational isomeric state theory, first‐order, second‐order, and third‐order conformation energies Eσ, Eω and Eφi respecively, are calculated for poly(dimethylsilmethylene) (CH2—Si(CH3)2)x using the Lennard–Jones potential function. With the third‐order interaction included, the characteristic ratios and temperature coefficients 〈R2〉0 and 〈μ2〉0 are obtained:

These results are in satisfactory agreement with the experimental data previously reported. © 1993 John Wiley & Sons, Inc.
Liquid–liquid transition in polymers and glass‐forming liquids
Authors: Murthy S. S. N.
Published: April 2003

It is shown that many simple glass‐forming liquids exhibit a phenomenon known in the area of polymer science as the liquid–liquid transition. The phenomenon manifests itself as a third‐order transition in the equilibrium liquid‐specific heat data around approximately 1.2 Tg and also as a bifurcation of the liquid relaxation into primary and secondry processes. It is stressed that the above phenomenon is due to a smooth changeover of the liquid from one dynamic regime to the other and hence is not due to any real phase transition. It is suggested that a liquid cluster kind of picture for the supercooled liquid regime, is capable of explaining the above phenomenon and is consistent with observation made on polymers and monomeric liquids. © 1993 John Wiley & Sons, Inc.
Interconversion between mechanical and dielectric relaxations for poly(cyclohexyl acrylate)
Authors: Díaz‐Calleja Ricardo , Riande Evaristo , Román Julio San
Published: April 2003

Storage E′ and loss E″ relaxation moduli are reported as functions of frequency for poly(cyclohexyl acrylate) (PCA) at several temperatures. The possibility that these results, in conjunction with the dipolar correlation coefficient, can be used to predict the frequency dependence of the real ε and loss ε″ and the components of the complex dielectric permittivity ε* of PCA is studied. A relation between ε* and the complex relaxation modulus E* is obtained by assuming that the lag of the rotating dipoles in the electric field is caused by both dielectric and mechanical friction. The values of ε* obtained from mechanical results by means of this expression are very close to those obtained from other relations based on the assumption that the lag of the dipoles is caused exclusively by mechanical friction. © 1993 John Wiley & Sons, Inc.
Broadening of the glass transition in blends of poly(aryl ether ketones) and a poly(ether imide) as studied by thermally stimulated currents
Authors: Sauer Bryan B. , Hsiao Benjamin S.
Published: April 2003

Blends of poly(aryl ether ketones) (PAEKs) and an amorphous poly(ether imide) (PEI) were used as model systems to study the broadening of the glass transition due to crystallization and the resulting depletion of PAEK from the amorphous phase. Two different PAEKs were studied, which are completely miscible with PEI in the amorphous state; poly(aryl ether ether ketone) (PEEK) and a slower crystallizing poly(aryl ether ketone ketone)(PEKK). Relatively rapid crystallization conditions were chosen in order to trap a significant fraction of PEI between the PAEK crystal lamellae or between bundles of lamellae. The broad glass transitions are apparently a result of the nonuniform nature of this process. The breadth of the glass transition was quantified by thermally stimulated currents (TSC) applied in the thermal sampling (TS) mode. The results compared favorably with DSC data. The magnitude of the apparent activation energy obtained by the TS method allows one to assign the relaxations as cooperative (glass transition‐like) or non‐cooperative and to define the limits of the glass transition with a higher degree of precision than other techniques. Cooperative relaxations can be resolved with this technique, even if they are only a small fraction of the overall relaxing species at a given temperature. In some cases the glass transition region was found to broaden to ca. 60°C after crystallization. © 1993 John Wiley & Sons, Inc.
Permeation and sorption in polynorbornenes with organosilicon substituents
Authors: Bondar V. I. , Kukharskii Yu. M. , Yampol'skii Yu. P. , Finkelshtein E. Sh. , Makovetskii K. L.
Published: April 2003

Gas sorption properties, permeability coefficients, and diffusion coefficients of a series of norbornene polymers are presented. Introduction of the Si(CH3)3 group into the polynorbornene (PNB) backbone chain results in significant increases in glass transition temperature, permeability, and diffusion coefficient for a number of gases (H2, O2, N2, CO2, CH4, C2H6). The transport properties and sorption isotherms for poly(5‐trimethylsilyl norbornene) (PTMSNB) are very similar to those for poly(vinyltrimethyl silane) (PVTMS), which contains the same side‐chain group but differs from PTMSNB by the structure of its main chain. For another silicon‐containing polymer poly[5‐(1,1,3,3‐tetramethyl‐1,3‐disilabutyl) norbornene] (PDSNB) having a bulkier side‐chain group, the glass‐transition temperature is decreased in comparison with that of PNB, presumably owing to self‐plasticization. Both silicon‐containing norbornene polymers (PTMSNB and PDSNB) have permeability coefficients for “rapid” gases like H2 or CO2 of about 102 Barrer. The high values of the Langmuir sorption capacity C′H for PTMSNB and PVTMS, as well as the high diffusivity and mobility of spin probes in these polymers, were attributed to a large free volume related to the bulky Si(CH3)3 groups attached directly to the main chain. © 1993 John Wiley & Sons, Inc.
Ar atom emission as a probe of craze formation and craze growth in polystyrene
Authors: Dickinson J. T. , Jensen L. C. , Langford S. C. , Dion R. P.
Published: April 2003

A report of measurements of Ar emission during the loading of polystyrene and high impact polystyrene in vacuum is presented. Argon was introduced into the material prior to the experiment by storing the samples in an Ar atmosphere. The development of crazes during loading was monitored by videotaped visual observations and scattered light measurements. Increased Ar emission is observed at the onset of crazing, provided that the crazes intersect the surface. The strength of the Ar signal depends upon the extent of crazing; especially intense signals are observed from samples which display significant crazing prior to fracture. High‐impact polystyrene shows intense emissions at yield which soon decay due to the depletion of Ar from the near surface material. The emission intensity rises again prior to fracture, when surface crazes become connected to crazes in the bulk. Thus the emission of volatile species during deformation reflects the growth of crazes intersecting the surface, as well as changes in the “connectivity” of the craze network. © 1993 John Wiley & Sons, Inc.
Dipole moment and dielectric relaxation of poly(dimethylsilazane) oligomers
Authors: Salom Catalina , Riande Evaristo , Hernändez‐Fuentes Irmina , Dïaz‐Calleja Ricardo
Published: April 2003

The polarity of polysilazane chains is studied using as models hexamethyldisilazane (HMDSZ) and an oligomer of amine‐terminated poly(1,1‐dimethylsilazane) (PDMSZ). Solvent effects and the contribution of the atomic polarization to the dipole moment of both PDMSZ and HMDSZ are discussed. A qualitative interpretation of the dipole moment of the oligomer suggests that gauche states about the skeletal bonds may be disfavored with respect to the alternative trans states. The dielectric spectrum of PDMSZ presents a glass‐rubber relaxation followed by two weak secondary absorptions. The experimental results show that the relaxation strength Δε of PDMSZ is lower than that corresponding to poly(1,1‐dimethylsiloxane) (PDMS). The analysis of the glass‐rubber relaxation by using the coupling scheme suggests that strong intermolecular interactions occur in the chains that presumably arise from hydrogen bonding interactions between amine groups. © 1993 John Wiley & Sons, Inc.
Compatibility and crystallization in poly(ethylene oxide)‐poly(methyl methacrylate) semi‐interpenetrating polymer network
Authors: Ahn Sung‐Hee , An J. H. , Lee D. S. , Kim S. C.
Published: April 2003

Differential scanning calorimetry together with dynamic mechanical analysis were employed to investigate the crystallinity and the miscibility in poly(ethylene oxide)/crosslinked poly(methyl methacrylate) semi‐IPN (interpenetrating polymer networks). The crystallinity of poly(ethylene oxide) in the semi‐IPN is found to depend on the crosslink density of PMMA as well as the overall content of PEO. Of special interest is that an increase in the crosslink density tends to increase the crystallinity contrary to our expectation, indicating crystallization and phase separation may proceed simultaneously during IPN formation. The investigation of glass transition behaviors with dynamic mechanical analysis suggests phase separation (i.e., there exist two amorphous phases: one PEO‐rich phase, the other a PMMA‐rich phase). © 1993 John Wiley & Sons, Inc.
On the solution characterization of an all‐aromatic liquid‐crystalline copolyester
Authors: Cinquina P. , Cam D. , Tampellini E. , Chapoy L. L.
Published: April 2003

Solution characterization of the thermotropic liquid–crystalline copolyester synthesized from terephthalic acid, phenyl hydroquinone, and (1‐phenylethyl) hydroquinone (2 : 1 : 1) has been performed. Viscometry, size exclusion chromatography, and light scattering have been carried out under the optimal conditions found for measurement: 85°C in a 50/50 mixture by weight of phenol/1,2,4‐trichlorobenzene. The absolute weight‐average molecular weight from light‐scattering measurements served for calibration of indirect methods of charac‐terization (e.g., the limiting viscosity number [η] is related to the molecular weight by [η] = 5.10 × 10−4 Mw0.72), and the molecular weight per unit chain length, \documentclass{article}\pagestyle{empty}\begin{document}$ \bar M_L * $\end{document}, from light scattering and size exclusion chromatography (SEC) is found to be 28 Å−1, consistent with theoretical expectations. The calculated persistence length q is 28 Å. Moreover, the meth‐odology of SEC characterization enables the kinetics of solid‐state postpolymerization of this liquid‐crystalline copolyester to be studied. © 1993 John Wiley & Sons, Inc.
Structure and compatibility of poly(vinyl alcohol)‐silk fibroin (PVA/SA) blend films
Authors: Tsukada Masuhiro , Freddi Giuliano , Crighton John S.
Published: April 2003

The structure and compatibility of poly(vinyl alcohol)‐silk fibroin (PVA/SF) blend films were analyzed by differential scanning calorimetry (DSC), thermomechanical (TMA) and thermogravimetric (TGA) analysis, x‐ray diffractometry, and scanning (SEM) and transmission (TEM) electron microscopy. DSC curves of PVA/SF blend films showed a major endothermic peak at 220°C, along with a peak at 280°C. These endotherms were assigned to the thermal decomposition of the ordered PVA elements and to the thermal degradation of silk fibroin, respectively. The PVA/SF blends behaved in a manner intermediate to the pure components, as suggested by both contraction expansion and sample weight retention properties recorded by TMA and TGA measurements. The IR absorption spectra of the blends were identified as purely a composite of the absorption bands characteristic of both PVA and SF pure polymers. The X‐ray diffraction patterns of PVA/SF blends showed overlapping spacing due to PVA and SF. A dispersed phase formed by spherical particles of 3–7 μm diameter was observed by SEM and TEM. All these findings suggest that PVA and SF are incompatible. © 1994 John Wiley & Sons, Inc.
Gel spinning of poly(vinyl alcohol) from dimethyl sulfoxide/water mixture
Authors: Cha Won‐Ill , Hyon Suong‐Hyu , Ikada Yoshito
Published: April 2003

Gel spinning of poly(vinyl alcohol) (PVA) was attempted from the PVA dope prepared from the mixture of dimethyl sulfoxide (DMSO) and water. The DMSO/H2O = 80/20 (w/w) mixture and methanol were found to be the best solvent for the spinning dope and the coagulant, respectively, to give PVA fiber with the highest drawability. PVA fiber with the highest strength and Young's modulus were obtained from the undrawn gel fibers when subjected to hot two‐stage drawing under conditions such as to produce maximum drawability. Furthermore, higher draw ratios of PVA fiber were attained at 6 wt % dope by lowering the coagulating temperature of methanol. In the present work, the highest tensile strength (2.8 GPa) and the highest Young's modulus (64 GPa) were realized, when the spinning dope was prepared from PVA with DP of 5,000 and the DMSO/H2O (80/20) mixed solvent to have the PVA concentration of 6 wt %, the coagulating temperature of methanol was −20°C, and the two‐stage drawing was carried out at 160 (first) and 200°C (second). The PVA fiber prepared under this gel spinning condition could be elongated to 45 times draw ratio. The very high drawability of PVA fibers obtained from the DMSO/H2O (80/20) mixture dope was ascribed to the ability of the DMSO/H2O mixture to promote gelation. © 1994 John Wiley & Sons, Inc.
The use of near infrared (NIR) spectroscopy to study specific interactions in polymer blends
Authors: Ghebremeskel Yacob , Fields Jeffrey , Garton Andrew
Published: April 2003

The purpose of this brief communication is to demonstrate how near infrared (NIR) spectroscopy can be used to study specific interactions is miscible polymer blends. We will first demonstrate, using model systems and blends of polycaprolactone (PCL) and phenoxy [poly(hydroxypropylether of bisphenol‐A)], that information obtained from the OH stretch overtone absorption in the NIR is consistent with the information obtained from the OH stretch fundamental in the mid‐IR region. We will then illustrate the advantages of NIR analysis of specific interaction with spectra obtained, over a range of temperatures, from thick (2 mm) films of blends of Nylon‐6 and the zinc salt of sulfonated polystyrene (ZnSPS). © 1994 John Wiley & Sons, Inc.
Design of anhydrous electrorheological (ER) suspensions based on I2‐doped poly(pyridinium salt)
Authors: Yu Wei‐Ching , Shaw Montgomery T. , Huang Xiao‐Yan , Harris Frank W.
Published: April 2003

A rigid‐rod aromatic poly(pyridinium salt) was synthesized and doped with iodine (I2) for making anhydrous electrorheological (ER) fluids. The I2‐doped particles were further processed into ones having insulating skins. Dielectric properties and current densities of the suspensions containing these particles were studied to elucidate the roles of conductivity of the dispersed phase in the ER suspension. © 1994 John Wiley & Sons, Inc.
Crystallinity of fully aromatic thermotropic polyesters of 3,3'‐bis(phenyl)‐4,4'‐biphenol and 1,1'‐binaphthyl‐4,4'‐diol
Authors: Bhowmik Pradip K. , Beaucage Gregory , Bhattacharya Subrata K. , Lenz Robert W.
Published: April 2003

The degree of crystallinity of as‐made fully aromatic, thermotropic polyesters was determined for two different series of polymers, each of which contained a symmetric monomer having either pendant phenyl groups or fused aromatic rings by the WAXD technique. All of the homopolymers had a high degree of crystallinity in spite of bulky substituents attached to the mesogenic moiety. Surprisingly, the homopolymer of 2,6‐naphthalenedicarboxylic acid with each of the monomers had a higher degree of crystallinity and Tm than those of the homopolymer of terephthalic acid with each of the respective monomers. As expected, on copolymerization with 30 mol % of either 4‐hydroxybenzoic acid or 6‐hydroxy‐2‐naphthoic acid, all of the resulting copolymers had a much lower degree of crystallinity and Tm/Tf values compared to those of the respective homopolymers in each series. © 1994 John Wiley & Sons, Inc.
Molecular modeling of polymers. 10. Characterization of conformational transitions of poly(acrylic acid) and poly(methacrylic acid) using dyad structures
Authors: Ravi M. , Hopfinger A. J.
Published: April 2003

The conformational profiles of nearest side‐chain neighbors, methylene‐dyad structures, of poly(acrylic acid), PAA, and poly(methacrylic acid), PMA, were determined as a function of tacticity, extent of ionization, and presence of counterion. The dominant backbone conformer states are quite similar for both isotactic and syndiotactic diads in a common charge state. Thus, the overall dimensional properties of isotactic syndiotactic and atactic chains of PAA or PMA, based upon dyad interactions, are predicted to be alike for a given charge state. Significant deviations from precise t, g+, and g− states are found for the dyad minimum energy conformations. The rod‐to‐coil and coil‐to‐rod transitions observed in PAA and PMA, respectively, as a function of increasing counterion concentration can be explained, to a large extent, by the conformational profiles of the corresponding dyad model structures. © 1994 John Wiley & Sons, Inc.
Relaxation behavior, intramolecular interactions, and local motions on monosubstituted esters of poly(itaconic acid)
Authors: Díaz‐Calleja Ricardo , Saiz Enrique , Riande Evaristo , Gargallo Ligia , Radic Deodato
Published: April 2003

The mechanical relaxation spectrum of poly(monocyclohexylmethylene itaconate) (PMCMI) exhibits two well‐developed absorptions in the glassy state that in increasing temperature order are named γ and β absorptions. Owing to the restricted conformational versatility of the backbone, the polymer presents a weak glass‐rubber relaxation whose intensity is significantly lower than that of the γ absorption. Comparison of the mechanical spectrum of this polymer with that of poly(dicyclohexylmethylene itaconate) (PDCMI) allows the conclusion that the β relaxation is produced by motions in which the COOCH2C6H11 side groups are involved. The location of the mechanical γ peak suggests that this absorption is produced by flipping conformational transitions in the cyclohexyl residue. Three dielectric absorptions are observed in the glassy state of PMCMI which in increasing temperature order are called δ, γ, and β relaxations. Both the location and the activation energy of the dielectric and mechanical β absorptions suggest that both relaxations are caused by the same molecular motions. Dipolar interactions in the liquid and glassy state are calculated and the results compared with those experimentally evaluated. © 1994 John Wiley & Sons, Inc.
Double ferroelectric‐to‐paraelectric transition in 70/30 vinylidene fluoride‐trifluoro ethylene copolymer as revealed by dielectric spectroscopy
Authors: Ezquerra T. A. , Kremer F. , Baltá‐Calleja F. J. , Lopez Cabarcos E.
Published: April 2003

The variation of dielectric properties with temperature in the 1 kHz to 1 GHz frequency range for the 70/30 copolymer of vinylidene fluoride with trifluoroethylene has been associated to two processes: the β relaxation process associated with the glass transition of the amorphous phase and the ferroelectric‐to‐paraelectric crystal transition. The β process follows a Vogel‐Fülcher behavior exhibiting an anomaly in the vicinity of the crystal transition. Analysis of the ferroelectric‐to‐paraelectric Curie transition reveals the existence of a double relaxation maximum in the dielectric losses. Results have been interpreted in terms of the Havriliak‐Negami relaxation function. The variation of the relaxation strength and of the broadening parameter has been investigated as a function of temperature. The obtained results are discussed in terms of a two‐step phase transformation mechanism for the Curie transition: a first transition from the low temperature “all‐trans” ferroelectric phase to a more defective phase; a second transition from the latter phase to the final paraelectric structure. © 1994 John Wiley & Sons, Inc.
Interfacial bonding, energy dissipation, and adhesion
Authors: Gent A. N. , Lai S.‐M.
Published: April 2003

Thin sheets of several elastomers have been adhered together by CC or SS interfacial bonds and peeled apart at various rates and temperatures. For CC bonding, values of the work G required per unit area to separate the sheets could be superposed to form a master curve versus peel rate using Williams‐Landel‐Ferry (WLF) temperature shift factors. Threshold values Go at low rates and high temperatures ranged from virtually zero for nonbonded sheets up to the tear strength of the sheet itself, 50‐80 J/m2, for fully interlinked sheets, in proportion to the density of interfacial bonds. The strength thus appears to be the sum of two terms: Go and a viscoelastic loss function which itself is approximately proportional to Go. By comparing the dependence of G upon rate of peel with the dependence of dynamic shear modulus μ′ upon oscillation frequency, an effective length of the fracture zone was deduced. It was extremely small in all cases, only about 1 Å. With sulfur interlinks, values of G were larger at all peel rates and varied more with temperature than predicted by the WLF relation. This is attributed to a concomitant decrease in SS bond strength with temperature, and an increase in energy dissipation as the weaker sulfur bonds fail. © 1994 John Wiley & Sons, Inc.
Thermal and structural analysis and crystallization behavior of new poly(ether‐alkyl) oxadiazoles
Authors: Pace E. Di , Fichera A. M. , Laurienzo P. , Malinconico M. , Martuscelli E. , Perenze N. , Volpe M. G.
Published: April 2003

A new series of poly(ether‐alkyl)oxadiazoles of general formula:

with m = 3, 4, and 5 has been obtained from the corresponding polyhydrazides through thermal cyclization reaction. The polymers were characterized by infrared spectroscopy, differential scanning calorimetry, wide‐angle x‐ray analysis, and optical microscopy. The polymers were crystalline, with a crystalline texture and structural parameters strongly dependent on the value of m. The Tm's and Tg's value decreased with increasing number of CH2. © 1994 John Wiley & Sons, Inc.
Study of PVB aggregation process by electron microscopy
Authors: Zhang Yanfei , Sun Hongjian , Shen Jiarui
Published: April 2003

The structure of aggregates formed from poly(vinyl butyral) (PVB) in tetrahydrofuran (THF) was studied by transmission electron microscopy (TEM). We have found that the primary associated particles are nearly spherical and, as the association advances, the particles lengthen. Eventually aggregates branch to form a three‐dimensional network. The bulk PVB was investigated by scanning electron microscopy (SEM). We have found that the bulk PVB grains are aggregates of the particles the shape and dimension of which are similar to those of the primary associated particles formed in PVB solution. © 1994 John Wiley & Sons. Inc.
Electron spin resonance study of γ‐irradiated poly(methacrylic acid)
Authors: Rao B. Sanjeeva , Hasan Mohd. Fasiul , Reddy N. Subbarami , Reddy Y. Sudarsana
Published: April 2003

Low temperature relaxations in poly(methacrylic acid) (PMAA) have been studied by electron spin resonance (ESR) spectroscopy. The observed 8 line ESR spectra of irradiated PMAA in the temperature range 77‐300K (LNT‐RT) is attributed to the free radicals of the type ∼ CH2CHCH3. Assignment of ESR spectra to free radicals has been made on the basis of magnetic parameters employed to simulate ESR spectra at different temperatures. Further, ESR spectra below LNT have been simulated, using the set of parameters employed to simulate the experimental spectrum at LNT. Magnetic parameters of the ESR spectra at LNT and below LNT indicate γ‐ and δ‐relaxations of PMMA chains. © 1994 John Wiley & Sons, Inc.
Analysis of structure and properties of poly(ethylene terephthalate) fibers
Authors: Fu Yigang , Annis Brian , Boller Andreas , Jin Yimin , Wunderlich Bernhard
Published: April 2003

The structure of four semicrystalline poly(ethylene terephthalate) fibers were analyzed with full‐pattern (two‐dimensional Rietveld) x‐ray diffraction refinement, small‐angle x‐ray scattering, and thermal mechanical analysis, and compared to some of their known mechanical properties. The classical two‐phase model of crystal and amorphous phases were unable to correlate structure and properties. We found that there must be a third phase, an oriented, intermediate phase, located mainly between the fibrils. About 1/3 of the intensity of fiber diffraction of the analyzed samples was contributed from such intermediate phase. For some fiber properties the intermediate phase plays a similar role as proposed for “taut tie molecules.” A simple model for the description of structure‐insensitive properties of PET fibers was developed, based on this quantitaitve separation into three phases. The oriented intermediate phase changes the definition and calculation of the basic parameters of the fiber structure, such as crystallinity and orientation. Based on small‐angle x‐ray evidence, the crystallites are assumed to be separated by layers of largely amorphous material, both surrounded by the intermediate phase. The initial modulus of the fiber is determined mainly by the amount and orientation of the intermediate phase which has a maximum modulus of about 500 g/d on full orientation instead of the earlier predicted 150 g/d for fully oriented semicrystalline fibers. Based on the relationship between tenactity and average orientation function, the maximum tenacity for PET fibers of a structure like the ones analyzed may reach 20–45 g/d instead of earlier predictions of 10 g/d. The additional information needed to understand the structure‐sensitive property of shrinkage is discussed. Presently easily accessible parameters have no quantitative predictive capabilities. © 1994 John Wiley & Sons, Inc.