bluuebunny/crossref_metadata_2025 huggingface dataset:
Preferential solvation in polymer cosolvent systems: Polystyrene + cyclohexane + ethanol and poly(vinyl‐2‐pyridine) + nitromethane + carbon tetrachloride
Authors: Viras Fotini , Viras Kyriakos
Published: April 2003

Two cosolvent systems are studied by light scattering and viscosity measurements. The cosolvency mechanism is discussed in relation to the preferential adsorption, solubility parameter, and excess free energy of mixing of the two liquid components. The cosolvency effects are attributed to a “true” and an “apparent” cosolvency.
Pressure dependence of the dielectric properties and phase transitions of polyvinylidene fluoride (PVDF) and a copolymer with trifluoroethylene
Authors: Samara George A.
Published: April 2003

The frequency, temperature, and hydrostatic pressure dependences of the dielectric properties, molecular relaxations, and phase transitions in PVDF and a copolymer with a 30 mol% trifluoroethylene were investigated. The β‐relaxation peak temperature Tβ and the melting temperature Tm of both polymers, and the ferroelectric transition temperature Tc of the copolymer, are strong increasing functions of pressure. The magnitudes of the pressure derivatives of Tβ, Tc, and Tm increase in the order of the “transition” temperatures, i.e., Tβ(P) < Tc(P) < Tm(P). These results can be qualitatively understood in terms of the nature of the molecular motion and/or reorientation processes involved. The results on the copolymer suggest that pressure should induce a ferroelectric‐paraelectric transition in PVDF below Tm, but such a transition was not observed over the limited pressure range of the present experiments. The relaxational dynamic (not static) nature of the melting process in these materials is indicated by the observed dependence of Tm on probe frequency. The frequency (or rate) and strong pressure dependences of Tm of PVDF provide a rational explanation for why it is possible to use this polymer as a piezoelectric shock‐wave gauge to relatively high shock pressures and the accompanying high temperatures.
Rate‐dependent nonlinear constitutive equation of polypropylene
Authors: Kitagawa Masayoshi , Mori Tatsuya , Matsutani Tomohiko
Published: April 2003

In order to investigate the viscoelastic‐plastic properties of polymer solids and construct a constitutive equation for them, torsional tests were performed on polypropylene (PP) hollow cylinders. Testing was conducted under constant strain rate, abrupt change of strain rate, stress relaxation, creep, and cyclic loading conditions. The experimental data were compared with the numerical results derived from an overstress model. It is shown that the overstress theory explains the viscoelastic‐plastic properties of PP well, provided that the current strain is not below the maximum previous strain.
14CO2 and CO2 Transport in polycarbonate: Measurement of the time lag and permeability
Authors: Alger Montgomery M. , Ward William J. , Stanley Thomas J.
Published: April 2003

Transport of CO2 across polycarbonate films has been studied using a diffusion cell technique employing a radioactively labelled tracer (14CO2). Because the 14CO2 driving force could be established independently of the unlabelled CO2 driving force, several classes of experiments not possible with conventional techniques were performed. These different classes of experiments showed measurably different time lags. Formally, these experiments all are limiting cases of the more general mixed‐gas permeation problem; however, simplifying assumptions in the dual sorption theory are possible because the tracer concentration approaches zero and because the two species in this special mixed‐gas problem exhibit the same dual sorption parameters. These simplifications allow derivation of analytical expressions for the time lag for both the unlabelled and labelled gas species. The experimental measurements are in good agreement with the dual sorption model formulated for the mixed‐gas tracer diffusion problem.
Fit of a nonreptative model of polymer melt dynamics to experimental melt diffusion constant measurements
Authors: Yeates Alan T. , Skolnick Jeffrey , Yaris Robert
Published: April 2003

A model of polymer melt diffusion recently proposed by Skolnick, Yaris, and Kolinski and which does not invoke reptation as the dominant mechanism of polymer melt motion is used to fit polymer self‐diffusion constant data measured by Antonietti, Fölsch, and Sillescu for a homopolymeric melt as well as for a probe in a larger molecular weight matrix. The quality of fit of the data indicates that reptation theory cannot be verified by simple comparison to diffusion constant measurements.
Solution behavior of sulfonate ionomer interpolymer complexes
Authors: Lundberg R. D. , Phillips R. R. , Peiffer D. G.
Published: April 2003

The interaction of metal sulfonate ionomers with polymers containing low levels of amines has been investigated in solution. For example, zinc sulfo EPDM and a styrene/vinyl pyridine copolymer form such complexes over broad concentration ranges. The resultant solutions offer enhanced viscosities at dilute polymer concentrations. At high polymer levels solutions based on these complexes are lower in viscosity than the ionomer alone. These interpolymer complexes have been shown to exhibit an improved property/rheology balance in bulk systems. In solution, polymer complexes provide control of hydrocarbon solution viscosity not available with conventional polymers. Reduced viscosity‐concentration studies suggest that these polymer complexes are a result of the amine‐containing polymer interacting with intramolecular‐associated ionomer coils, which at higher concentrations form a pseudonetwork.
Rotational diffusivity of rodlike molecules in amorphous polymeric matrices
Authors: Hill Davide A. , Soane David S.
Published: April 2003

In this note, scaling laws for rotational diffusivity of dilute monodisperse rigid‐rod molecules (guest rods) in semidilute amorphous polymer solutions (host molecules) are derived. The coillike matrix molecules are modeled as a collection of flexibly connected rigid subunits. This allows an analogy with the Doi‐Edwards theory for monodisperse rigid rods in semidilute solutions to be used in the analysis. Very strong dependencies are predicted for the rotational diffusivity of the rods on host polymer volume fraction and rod length. In semidilute polymer solutions the coils dramatically hinder the rotational freedom of the rods for r2 ≫ ψp−1, r being the rod aspect ratio and ψp the polymer volume fraction.
Birefringence of polyethylene melt in transient elongational flow at constant strain rate
Authors: Koyama K. , Ishizuka O.
Published: April 2003

Simultaneous birefringence and elongational viscosity measurements were carried out on molten commercial grade, low‐density polyethylenes during simple elongational flow at constant strain rate and constant temperature. The birefringence increased with time during constant strain rate elongation. The increase in birefringence was a linear function of elongational stress throughout whole elongation, but the elongational viscosity increased in two stages. The increase in elongational viscosity can be divided into linear viscoelastic and nonlnear viscoelastic regions. The linear region appeared at small strain and the nonlinear region appeared at strain greater than 0.7. The elongational viscosity in the nonlinear region increased much more rapidly than that in the linear region. The Gaussian approximation, which is commonly used in molecular models, could be used for the transient elongational flow. A constant stress‐optical coefficient C = 1.3 × 10−10 cm2/dyn was obtained for all the elongational experiments, independent of strain rate (0.002‐0.2s−1). The stress‐optical coefficients were weakly dependent on temperature, as predicted by the theory of rubber elasticity.
The physical properties of bisphenol‐a‐based epoxy resins during and after curing. II. Creep behavior above and below the glass transition temperature
Authors: Plazek D. J. , Choy I. C.
Published: April 2003

The creep behavior of a series of fully cured epoxy resins with different crosslink densities was determined from the glassy compliance level to the equilibrium compliance Je at temperatures above Tg and at the glassy level below Tg during spontaneous densification at four aging temperatures, 4,4‐diamino diphenyl sulfone DDS was used to crosslink the epoxy resins. The shear creep compliance curves J(t) obtained with materials at equilibrium densities near and above Tg were compared at their respective Tgs. Tgs from 101 to 205°C were observed for the epoxies which were based on the diglycidyl ether of bisphenol A. Creep rates were found to be the same at short times, and equilibrium compliances Je were close to the predictions of the kinetic theory of rubberlike elasticity. Time scale shift factors determined during physical aging were reduced to Tg. At compliances below 2 × 10−10 cm2/dyn, Andrade creep, where J(t) is a linear function of the cube root of creep time, was observed. The time to reach an equilibrium volume at Tg was found to be longer for the epoxy resin with lower crosslink densities. The increase of density during curing is illustrated for the epoxy resin with the highest crosslink density.
The deformation behavior of polyethersulfone and polycarbonate
Authors: Plummer C. J. G. , Donald A. M.
Published: April 2003

In thin films of polyethersulfone and polycarbonate it is shown that crazing becomes increasingly likely to occur as the temperature is raised. The transition temperature depends on strain rate and molecular weight. Three regimes of behavior can be identified. In both the low‐temperature (shear deformation) and high‐temperature (crazing) regimes the strain to craze is independent of molecular weight. However, in the intermediate crazing regime chain length is important, indicating the importance of disentanglement over this temperature range. It is thought that at the highest temperatures disentanglement is still occurring, but the rate‐determining step is now general plastic flow into the craze fibrils.
Spectroscopic study of a model composite: Compressive behavior of the reinforcement fiber and the buildup of thermal residual stress
Authors: Fan C. F. , Hsu S. L.
Published: April 2003

The compressive behavior of polydiacetylene (PDA) single‐crystal fiber and the buildup of thermal residual stress in PDA/epoxy model composite systems have been studied by Raman‐mechanical spectroscopy. The compressive failure of the PDA fiber has been directly observed when the macroscopic compressive stress, applied during a bending experiment, exceeds a critical value. Fiber failure in model composites caused by thermal residual stress can also be observed by Raman measurements as well as optical microscopy. In fact, the most clear indication of fiber failure was the observation of kink bands formed. The thermal residual stress buildup which resulted from significant temperature changes in this model composite have also been studied. Contrary to most accepted views, our analysis showed the adhesion between the reinforcement fiber to the epoxy matrix to be strong.
Annealing of polymers in the solid‐melt region. I. A new approach to estimate the equilibrium melting temperature of polymer crystals
Authors: Khanna Yash P. , Kumar Rakesh
Published: April 2003

An annealing scheme for semicrystalline polymers is presented whereby a polymer is annealed in its solid‐melt region, leading to crystals approaching the equilibrium crystals in terms of melting temperature. The annealing data is mathematically treated to estimate the equilibrium melting temperature (T0m) of polymer crystals. As is the case with any extrapolation procedure, there are minor shortcomings with our approach, but these are far outweighed by the advantages; the latter are exemplified by a comparison with the widely used Hoffman‐Weeks method for estimating (T0m). The validity of our annealing scheme for the estimation of (T0m) is demonstrated by analysis of well‐studied polymers such as nylon 6, polyethylene terephthalate (PET), polyethylene (PE), polypivalolactone (PPL), and polytetrafluoroethylene (PTFE); other polymers studied include polyether ether ketone (PEEK) and nylon 4,6.
Direct observation of taut tie molecules in high‐strength polyethylene fibers by Raman spectroscopy
Authors: Prasad Keshav , Grubb David T.
Published: April 2003

The Raman spectra of four gel‐spun high‐strength polyethylene fibers were recorded as a function of stress, with detailed study of the 1063 cm−1 band. The change in the peak position of this band was linear at low stresses, but there was little change at high stresses. The center of mass of the band moved linearly with stress until fracture, and the shift per unit stress was almost the same for all the fibers studied at 4.0 ± 0.5 cm−1/GPa. The line shape is symmetric at low stresses, and the full width at half maximum increases with stress. When plastic deformation begins the band develops a broad low intensity tail extending to 1000 cm−1. This corresponds to stresses of up to 15 GPa, and the tail contains up to 18% of the band intensity when the maximum stress is applied. Equivalent wide‐angle x‐ray studies showed no such tail, so the highly stressed material is not crystalline, although it must be in the all‐trans form to contribute to the Raman peak. Such load‐bearing extended‐chain‐disordered material is described as taut tie molecules. The amount is much larger than that usually derived from mechanical modelling, it is essentially all the amorphous material if the DSC crystallinity of 85% is correct. It is thought to be interfibrillar, stressed when fibrils slide past each other in creep. On unloading the fiber, the band became more symmetrical again but did not always return to its initial position at zero stress. The peak moved to a wave number greater than its initial value on unloading and then over time relaxed to its original value. Thus tensile stresses in the disordered material, balanced by compression in the crystals, are slow to relax. Lower molecular weight fibers (Mn = 8 × 105) had small anelastic effects, probably because they relaxed within the time of the experiment.
Strain‐induced crystallization of swollen, crosslinked polyethylene
Authors: McHugh A. J. , Yung W. S.
Published: April 2003

The kinetics of strain‐induced crystallization of swollen polyethylene networks have been measured using dynamometry coupled with optical birefringence. Fibers were prepared by gel‐spinning ultrahigh‐molecular‐weight polyethylene followed by crosslinking in dicumyl peroxide and swelling in xylene. Retractive force on crystallization was monitored at various temperatures and draw ratios. Fiber visualization was achieved using optical illumination coupled with video recording and digital analysis of the in situ transformation. Avrami plots of the transformation data showed good linear fits for low draw ratios in the range α < 1.2 and moderate undercoolings (60 < Tc < 70°C). Time exponents of unity were found, indicating a one‐dimensional, heterogeneous growth mechanism whose temperature dependence could be described by a formalism similar to that recently used for flow‐induced growth.
Electron spin resonance and optical spectroscopic studies of the conducting polymer precursor: Poly(3,4‐diisopropylidene cyclobutene)
Authors: Kim Soon Sam , Cebe Peggy , Swager Timothy M.
Published: April 2003

The doping process in a recently developed conducting polymer precursor, poly(3,4‐diisopropylidene cyclobutene) (PDPCB)1 was studied by electron spin resonance and optical spectroscopy. Thin films of PDPCB were exposed to several oxidants, I2, AsF5, or a combination of AsF5 and AsCl3 or AsF3, and monitored in situ by ESR. At the initial stages of doping, the films developed broad ESR spectra with Gaussian line shape. Except in the case of doping with I2, resolved hyperfine structures from cation radicals were observed. As the doping progressed, the ESR spectra gradually transformed to narrower line widths with a Lorentzian component. The Lorentzian component can be attributed to charge carrier species developed in the film through doping. The results of optical spectroscopy (UV‐visible) are incorporated to elucidate the effect of doping on electronic transitions of the doped PDPCB.
Paracrystalline structure of poly(paraphenylene vinylene)
Authors: Granier Thierry , Thomas Edwin L. , Karasz Frank E.
Published: April 2003

The previous description1 of highly oriented films of poly(p‐phenylene vinylene) is augmented by close packing energy calculations and quantitative analysis of layer line intensity profiles observed via electron diffraction. The chain axial translational disorder is of the paracrystalline type: partial registration of chains occurs within the (100) layers while the layers themselves are randomly shifted from one another along the chain direction.
Network fraction and molecular motions in polymer composites: An NMR relaxation and self‐diffusion study
Authors: von Meerwall E. , Stone T.
Published: April 2003

We have used NMR T2 relaxation and pulsed‐gradient spin‐echo diffusion techniques to study properties of Arco R45M hydroxyl‐terminated polybutadiene, either unfilled or containing 65 wt.% filler particles (SiO2, NaCl, Al) and cured with isophorone diisocyanate (IPDI), as functions of IPDI content. A short T2 relaxation component arises from the network (gel) whose amount is greatest (up to 92%) near NCO/OH stoichiometry. Gel fraction and stoichiometry concentration both are affected slightly by filler surface reactivity but principally by filler particle size. The diffusion rate of the nonnetwork (sol) molecules has a range of 1–2 orders of magnitude. This range is narrowest near stoichiometry for the smallest filler (SiO2), i.e., the situation in which the sol molecules are least mobile. Branching theory and the hypothesis of a layer of reduced mobility in a wide vicinity of the filler particles provides semiquantitative explanations of these observations.
Polycaprolactone‐based block copolymers. II. Morphology and crystallization of copolymers of styrene or butadiene and ε‐caprolactone
Authors: Heuschen J. , Jérôme R. , Teyssié Ph.
Published: April 2003

Three series of amorphous semicrystalline poly(styrene‐b‐ε‐caprolactone)s have been synthesized with polystyrene blocks of 6000 (series A), 40000 (series B), and 70000 (series C) molecular weight, respectively. In these materials, the polymer miscibility evolves from a situation where a diffuse interphase involves the major part of the volume of the copolymer (series A) to a sharp phase separation as observed for copolymers with the longest PS block (series C). The crystallization of PCL blocks is mainly governed by the phase morphology. In copolymers of series A, the crystallization rate of PCL blocks is slowed down the more as the miscibility with PS increases, and ultimately the degree of crystallinity Xc decreases significantly. When phase separation is sharp, Xc changes dramatically at the phase inversion and decreases when PS forms the continuous phase. At the inversion Xc depends on the mean size of the PCL microdomains as compared with the thickness of the crystalline lamellae. The periodicity of the phase morphology as observed by TEM is influenced by the solvent used in casting films, whereas monolamellar monocrystals can be obtained by a self‐seeding technique.
The morphology of the spherulitic surface in polyethylene
Authors: Lustiger A. , Lotz B. , Duff T. S.
Published: April 2003

Studies of lamellar shapes and profiles in linear polyethylene have often been implemented by microscopic examination of appropriately etched random slices through spherulitic specimens. However, since a spherulite crystallized from a bulk specimen is a three‐dimensional assembly of radially oriented lamellae with a twisting orientation (except for very high Tcs), it may be difficult to draw appropriate conclusions from a random slice. A technique has been developed that allows one to prepare spherulitic surfaces such that their distance relative to the geometric center can be well characterized. A computer‐based graphical representation is also presented which suggests that the projection of lamellae on such surfaces is adequately represented by a radially oriented assembly of helicoidally twisted lamellae. Based on the agreement between the experimental results and the computer model, it is suggested that the C and S shapes previously observed by other researchers are not necessarily intrinsic to the lamellar profile but may arise due to geometrical effects as the lameliae project onto a surface at various angles. From these results it is also evident that in ringed spherulites lamellae undergo continuous twisting rather than successive misalignment of essentially untwisted segments.
A generalized, topologically consistent, dual‐mode transport model for glassy polymer‐gas systems
Authors: Petropoulos J. H.
Published: April 2003

A dual‐mode transport treatment for glassy polymer‐gas systems is presented in which due account is taken of random‐walk topology. This permits elimination of the restrictive homogeneous random‐walk condition, which must hold if the existing simple dual‐mode transport model is to be considered rigorous. The results obtained from the new treatment indicate that the aforesaid simple model requires only minimal modification, as far as transport in the solution (Henry's law) mode is concerned. The simple model description of adsorption (Langmuir) mode transport, on the other hand, is shown to be subject to minor or major limitations and qualifications, according to whether the mobility of adsorbed molecules is, respectively, comparable to/lower than, or substantially higher than, that required by the homogeneous random‐walk condition. The present treatment permits reasonable semiquantitative interpretation, within the context of current dual‐mode sorption theory, of the transport behavior typically observed experimentally. The results indicate that experimental adsorption mode diffusion coefficients, as currently calculated, cannot be considered to be quantitatively meaningful.
Structure‐property relationships of copolyamides. I. Thermal properties and crystallization
Authors: Jo Won Ho , Baik Doo Hyun
Published: April 2003

Six nylon salts [hexamethylenediammonium adipate (6.6), hexamethylenediammonium terephthalate (6.T), hexamethylenediammonium isophthalate (6.I), p‐xylylenediammonium adipate (PXD.6), m‐xylylenediammonium adipate (MXD.6), and m‐xylylenediammonium isophthalate (MXD.I)] were copolymerized with ε‐caprolactam. The resulting random copolyamides showed different modes of crystallization as confirmed by the melting temperature depression and the decrease in the isothermal crystallization rate. By selective hydrolysis it was found that the differences in Tm depression and isothermal crystallization rate were due to partial inclusion of comonomers in the crystal lattice. The effect of comonomer structure on the crystallization rate is also discussed.
A study of solvent diffusion in thin polyimide films using laser interferometry
Authors: Tong H. M. , Saenger K. L. , Durning C. J.
Published: April 2003

Using laser interferometry, we have determined in situ the thickness increase with time of thin supported polyimide films (4–8 μm in initial thickness) immersed in n‐methyl‐2‐pyrrolidone (NMP) as a function of NMP temperature (22–120°C). Similar experiments were also performed in dimethyl sulfoxide (DMSO) at 22°C with polyimide films of 4.1 μm in thickness. For NMP, the equilibrium fractional thickness increase (about 20%) is independent of initial polyimide thickness and temperature. The time scale for reaching equilibrium sharply decreases with temperature from 2–3 days at 22°C to 30–60 min at 120°C. Compared with NMP, the rate of DMSO sorption is considerably faster, reaching equilibrium swelling of about 28% in about 5 h at 22°C. To describe the transport process, we applied a phenomenological model proposed by Astarita and Sarti1 but reformulated in polymer fixed frame to enable straightforward comparison with the thickness data. Our analysis indicated that the transport of NMP is best described as anomalous, that is, intermediate between diffusion controlled and case II transport. The effective diffusion coefficient Deff and the front velocity U0 at 22°C were found to be 3–6 × 10−12 cm2/s and 8 × 10−9 cm/s, respectively. Our front velocity is in good accord with the value of 6 × 10−9 cm/s obtained for a similar polyimide based on gravimetric measurements.2 Both Deff and U0 show an activation energy of ∼56 kJ/mol. For DMSO, however, the transport is clearly case II. The front velocity at 22°C was found to be about 6 × 10−8 cm/s, which is about four times that obtained by Rutherford back‐scattering spectrometry.3
An indirect GPC calibration method for the low‐molecular‐weight region
Authors: Tsitsilianis C. , Mitsiani G. , Dondos A.
Published: April 2003

A new gel permeation chromatography indirect calibration method is proposed for a polymer for which samples of known molecular weight and narrow molecular weight distribution are not available. This method is based on conversion of an experimentally obtained calibration curve for another polymer (polymer standard) through the universal calibration concept but using a new intrinsic viscosity‐molecular weight relation. This indirect calibration curve is proposed especially for the low‐molecular‐weight region, where the method based on the Mark‐Houwink‐Sakurada equation gives erroneous results.
Molecular design of multicomponent polymer systems. XIV. Control of the mechanical properties of polyethylene–polystyrene blends by block copolymers
Authors: Fayt R. , Jérôme R. , Teyssié Ph.
Published: April 2003

The present investigation deals with the tensile mechanical properties of the melt‐blended polyethylene/polystyrene pair as controlled by poly(hydrogenated butadiene‐b‐styrene) copolymers. It is clearly demonstrated that moderate amounts of these copolymers (2–10%) significantly increase both the ultimate strength and elongation at break of blends of polystyrene with various types of polyethylene (low‐density, high‐density, linear low‐density, and hydrogenated polybutadiene) and synergistic effects may result. The mechanical performance is strikingly dependent on the molecular characteristics of the copolymers. Over a broad range of molecular weights (60,000–270,000), diblocks are more effective than graft, triblock, or star‐shaped copolymers. It is also demonstrated that using polymeric emulsifiers under usual processing conditions in the melt state is powerful technique for preparing valuable polymer alloys.
Network structure and mechanical properties of allophanate‐cured polyurethane rubber
Authors: Oikawa Hidetoshi , Nagai Tsuyoshi , Murakami Kenkichi
Published: April 2003

An allophanate‐cured polyurethane (PU) has been prepared. The relationship between trifunctional network structure and mechanical properties is discussed. Mooney‐Rivlin constants C1 and C2 are determined from stress‐strain isotherms. C2 is approximately constant. The average value of structure factor A3 in the limit at large deformation is 0.432, in fair agreement with the theoretical prediction of 1/3. The structure factor A′3 of all PU samples becomes roughly unity in the limit at small deformation. The experimental results are interpreted by the recent Flory theory (a fluctuation‐constraint model of junctions). The κ parameter decreases with increasing crosslink density; the ξ parameter is small and approaches zero. Increasing crosslink density tends to cause phantom deformation for extended PU networks. However, the absolute value of the reduced stress in the limit at large deformation (or for the equivalent phantom network) [f] is believed to be overestimated for PU networks with high crosslink density. The origin of this behavior is discussed in detail.
Chemorheology of allophanate‐cured polyurethane rubber
Authors: Nagai Tsuyoshi , Oikawa Hidetoshi , Murakami Kenkichi
Published: April 2003

Chemical stress relaxation (CSR) of allophanate‐cured polyurethane (PU) was measured under two kinds of degradation conditions: (1) degradation in butylamine (BuNH2)/dimethyl sulfoxide solution; (2) degradation at high temperature in nitrogen. The allophanate groups of the crosslink sites in PU networks are selectively cleaved by BuNH2, and CSR is not influenced by the crosslink density within experimental error. This suggests the validity of Tobolosky's method for distinguishing between random scission along network chains and the cleavage of crosslinks from the dependence of CSR on crosslink densities. In addition, CSR of PU samples degraded at high temperature in nitrogen was also found to be independent of the crosslink density. It follows that thermal degradation of PU networks occurs by the cleavage of crosslink sites in the same manner. CSR is compared with the relative degree of thermal degradation of PU sample, determined by‐the amine‐decomposition method and the swelling method. Consequently, the total (or residual) crosslink density of degraded PU networks corresponds essentially to the intermittent CSR.
Rheological studies of thermotropic liquid crystal copolyesters: P‐hydroxybenzoic acid / 2‐hydroxy‐6‐naphthoic acid
Authors: Yang D.‐K. , Krigbaum W. R.
Published: April 2003

The rheological behavior of the thermotropic liquid crystal copolyesters composed of p‐hydroxybenzoic acid and 2‐hydroxy‐6‐naphthoic acid (indicated as HBA/HNA) is investigated for three different compositions: 75:25, 58:42, 30:70 (in mol%). The inherent viscosities are 9.2, 5.1, and 7.8 dl/g, respectively. Yield stress is observed for all three samples. This indicates the existence of crystallites in the melt which may be related to the shear thinning viscosity at low shear stress. Melt fracture, and a die swell ratio which increases with shear rate, are also observed at higher temperatures and at low shear stress for the two copolyesters having compositions 75:25 and 30:70. We have also estimated for 30HBA/70HNA at 335°C the entrance pressure loss, Δpent, and ΔPent/δw, where δw is the shear stress at the capillary wall. The large value of ΔPent/δw suggest that HBA/HNA is a highly elastic polymeric material. It is found that both ΔPent and ΔPent/δw increase with shear rate. However, the high elasticity does not account for the disappearance of melt fracture and contraction of die swell at high shear stress. This abnormal phenomenon is ascribed to the formation of a network of crystallites caused by blocky regions in the copolymer.
Pressure‐jump volume‐relaxation studies of polystyrene in the glass transition region
Authors: Tribone J. J. , O'reilly J. M. , Greener J.
Published: April 2003

An apparatus has been constructed that permits the measurement of time‐dependent changes in pressure near the point of vitrification. The same instrument is used for measuring steady‐state PVT properties, which are necessary for a proper analysis of the dynamic measurements. The former experiments are referred to as pressure‐jump volume‐relaxation (PJVR) measurements and serve as a direct probe of the structural relaxation process that occurs in all glasses. Experiments have been performed on polystyrene from 110 to 150°C and up to 2 kbar using pressure steps of 500 bars. The qualitative observations are analogous to those obtained at atmospheric pressure by rapid changes in temperature, namely (1) nonlinearity, (2) asymmetry, and (3) memory effects associated with complicated temperature or pressure histories. Each of these effects is accounted for semiquantitatively by a phenomenological order‐parameter model that has been extended to include the effect of pressure. Deviations between theory and experiment increase as temperature and pressure increase, this being manifest mostly in a predicted recovery curve (expansion isobar) that recovers the equilibrium volume more quickly than the experimental data; the contraction isobars are in most cases predicted within experimental error. The adjustable parameters of the model are found to vary somewhat with pressure and temperature, apparently due to variations in δ and Δκ. The activation volume suggests that 10–20 monomer segments are involved in the recovery process, assuming that the activation volume itself represents only a fraction of the dynamic unit (as observed in molecular glasses).
Sorption and dilation in poly(ethyl methacrylate)–carbon dioxide system
Authors: Kamiya Yoshinori , Mizoguchi Keishin , Hirose Takuji , Naito Yasutoshi
Published: April 2003

Sorption and dilation in the system poly(ethyl methacrylate) (PEMA) and carbon dioxide are reported for pressures up to 50 atm over the temperature range 15–85°C. The sorption isotherms were obtained gravimetrically. The dilation accompanying sorption was measured directly with a cathetometer. At low temperatures the sorption and dilation isotherms were concave toward the pressure axis in the low‐pressure region and turned to convex with increasing pressure. As the experimental temperature approached and exceeded the glass transition temperature of 61°C, both isotherms became convex or linear over the whole range of pressure. Partial molar volumes of CO2 in PEMA were obtained from sorption and dilation data, which were described well by the extended dual‐mode sorption and dilation models developed recently. The temperature dependence of the dual‐mode parameters and the isothermal glass transition are discussed.
Nylon 6 structure in solid state as studied by high‐resolution 13C‐NMR spectroscopy
Authors: Kubo Kimihiro , Yamanobe Takeshi , Komoto Tadashi , Ando Isao , Shiibashi Toru
Published: April 2003

High resolution 13C‐NMR spectra of nylon 6 samples crystallized under various conditions and of a drawn sample were measured at room temperature by the cross polarization/magic angle spinning (CP/MAS) and pulse saturation transfer/magic angle spinning techniques. Additionally, 13C‐NMR spectra of the drawn sample were measured at temperatures from 20 to 100°C by the CP/MAS technique and at 20 and 100°C by the low‐power decoupling/magic angle spinning technique. The nylon 6 structure in the solid‐state is discussed on the basis of these results. The solid‐state 13C chemical shift data are used for reference in a study of conformation in solution.
Incremental vapor sorption in a phase‐segregated polyurethane elastomer
Authors: Schneider Nathan S. , Mee Caryn F. , Goydan Rosemary , Angelopoulos Anastasios P.
Published: April 2003

Incremental vapor sorption and desorption runs have been carried out with o‐dichlorobenzene (ODCB) a strongly swelling solvent, in 2, 6, and 10 mil polyether polyurethane films. Two‐stage sorption behavior occurs at intermediate and higher concentrations but is generally absent in the desorption runs. Analysis of the two‐stage curves, using the Berens‐Hopfenberg model of independent Fickian diffusion and first‐order relaxation processes, leads to apparent diffusion coefficients which increase with thickness and show a pronounced maximum with concentration, whereas the relaxation rate constant decreases with concentration. Correction for the pressure drift during the runs, due to the low vapor pressure of ODCB, reduces the thickness dependence. The negative concentration dependence of the relaxation rate constant is related to the distribution of microdomain stabilities. Calculated values of the self‐diffusion coefficient show that the maximum in the apparent diffusion constant with concentration can be accounted for largely, but not entirely, by the thermodynamic contributions. It is proposed that the additional factor is relaxation‐controlled swelling which arises from the strong coupling between the matrix and hard‐segment responses.
Numerical analysis of lamellar thickness distributions
Authors: Voigt‐Martin I. G. , Mandelkern L.
Published: April 2003

A comparison of crystallite thickness distributions, as obtained from thin section electron microscopy, small‐angle x‐ray scattering, and low‐frequency Raman acoustical model (LAM), is discussed in detail. It is shown with the aid of a large number of examples that a reliable numerical estimate of crystal thicknesses and long spacings is a complex problem. The values that are obtained by the different experimental techniques depend not only on the crystallite morphology, such as curvature and lateral extension, but very specifically, and crucially, on the nature of the thickness distribution. A series of widely different types of size distributions have been developed by controlling the molecular weight and crystallization temperature. Studies of these distributions, by the aforementioned experimental techniques, have revealed the reasons when and why agreement or disagreement is obtained in the determination of the crystallite thickness distribution.
The equation of state and heat of fusion of poly(ether ether ketone)
Authors: Zoller Paul , Kehl Thomas A. , Starkweather Howard W. , Jones Glover A.
Published: April 2003

The pressure‐volume‐temperature properties of poly(ether ether ketone) (PEEK) were studied experimentally at temperatures of 400°C and pressures to 200 MPa. Specific volume data were fitted successfully to the empirical Tait equation for T < Tg and T > Tm and to the theoretical Simha‐Somcynsky equation of state for the melt. The pressure dependence of the glass‐transition temperature is about 0.57–0.59°C/MPa and that of the melting point 0.483°C/MPa. The pressure dependence of the melting point, the specific volume of the melt at Tm, and the specific volume of the crystal at Tm determined from x‐ray diffraction data at elevated temperatures were combined in the Clapeyron equation to calculate a heat of fusion of 161 ± 20 J/g for the PEEK crystal. This value is somewhat higher than the previously reported value of 130 J/g.
Viscoelastic properties of UHMW‐PE fibers in simple elongation
Authors: Leblans P. J. R. , Bastiaansen C. W. M. , Govaert L. E.
Published: April 2003

Stress relaxation after a simple elongational step strain, creep under a constant simple elongational stress, and stress build‐up under a constant Hencky strain rate have been measured for ultrahigh‐molecular‐weight polyethylene (UHMW‐PE) fibers. The data from the various experiments are consistent with the Boltzman superposition principle in the experimental region of small strains or short times. This leads to a simple constitutive equation in which temperature can be incorporated via time‐temperature superposition. The measured power‐law relaxation of the UHMW‐PE fiber leads to analytical expressions for the dynamic quantities in simple elongation.

The constitutive equation is the one‐dimensional equivalent of the gel equation derived for cross‐linking gels at the gel point. The similarity between the rheological behavior of fibers and cross‐linking gels at the transition point might lead to an enhanced understanding of the molecular processes occurring during deformation.
The initial stages of crystallization of polyethylene from the melt
Authors: Barham P. J. , Keller A.
Published: April 2003

Synchrotron x‐radiation has been used to follow the development of low‐angle diffraction in sharp fractions of polyethylene. The polymer is shown to crystallize in very thin lamellae which rapidly thicken in a single step to twice, three times, or four times the original thickness. This dramatic refolding is more pronounced at higher crystallization temperatures. After the sudden integral jumps in fold length, the thick lamellae continue to grow thicker logarithmically with time. The significance of these findings for the most basic issues of polymer crystallization and for the experimental methodology of its study is highlighted.
Light‐scattering study of polyelectrolyte complexes: Heparin with partially aminoacetalized poly(vinyl alcohol) in aqueous solution
Authors: Hara M. , Nakajima A.
Published: April 2003

The structure of soluble polyelectrolyte complexes composed of heparin (Hep) and partially aminoacetalized poly(vinyl alcohol) (PVAA) in aqueous solution was investigated by light scattering. The pH was fixed at 3.2 while the ionic strength and mixing ratio were varied. At high ionic strength (0.5), polyelectrolyte complexes were not formed owing to the screening effect of simple salts on polyion charges. At low ionic strength (0.005), polyelectrolyte complexes formed were stable and dispersed when either the polycation or the polyanion was in great excess, whereas the complexes became unstable and coagulated when the concentrations of polycation and polyanion approached each other. At intermediate ionic strength (0.1), when PVAA was in excess, complex formation was similar to that at low ionic strength (0.005); but with an excess of Hep, polyelectrolyte complexes with similar structure (i.e., roughly spherical with average diameters about 2,700 Å) were formed over a wide range of mixing ratio. This observation is of interest in connection with the physiological activity of Hep in vivo.
FTIR investigation of interactions in blends of PMMA with a styrene/acrylic acid copolymer and their analogs
Authors: Jo W. H. , Cruz C. A. , Paul D. R.
Published: April 2003

Fourier‐transform infrared (FTIR) spectroscopy was used to examine the interactions in miscible blends of a styrene (92%)/acrylic acid (8%) copolymer (SAA8) with poly(methyl methacrylate) (PMMA). From the residue or interaction spectra and shifts of carbonyl and carboxylic acid stretching bands, it is concluded that there is a significant specific interaction involving hydrogen bonding between the carbonyl groups of the PMMA and the carboxylic groups of the SAA8. Similar FTIR spectra of some low‐molecular‐weight liquid analogs for the various monomer units of these polymers do not indicate a comparable interaction. This explains why direct calorimetry with these compounds fails to model correctly the expected exothermic mixing of the blends. Furthermore, the role of the aromatic moiety in the SAA polymer appears to reduce the degree of self‐association of the carboxylic acid groups based on results for the model compounds. Coupled with molecular rigidity, the above mechanism makes the carboxylic acid units in SAA8 more available for interaction with the PMMA carbonyls.
Crystal structure of polysulfonamides
Authors: Sasaki S. , Takigawa S.
Published: April 2003

Structures of poly(alkylene‐1,3‐benzenedisulfonamide)s [HN(CH2)mNHO2SC6H4SO2]n (PMm: 2 ≤ m ≤ 6) were studied by x‐ray diffraction and infrared spectroscopy. The crystal structure of PB6 is monoclinic, space group C2/mC2h3, with a = 7.70 Å, b = 7.76 Å, c (molecular axis) = 14.1 Å, and β = 117°. Two mirror‐image molecules repeating with two monomeric units in an identity period 28.2 Å occupy the same lattice site with equal probability. The alkylene chains assume the planar zigzag conformation, which is the structure isomorphous with PB4. An intermolecular hydrogen bond is formed between each NH group and one of the two O = S groups of the corresponding SO2 unit. The c axis tends to tilt from the fiber axis by an inclination angle of about 3° around the b axis.
Isothermal crystallization of poly(vinylidene fluoride) in the presence of high static electric fields. II. Effect of crystallization temperature and electric field strength on the crystal phase content and morphology
Authors: Marand Hervé , Stein Richard S.
Published: April 2003

The melt crystallization of poly(vinylidene fluoride) in a static electric field was studied for different fields strengths and undercooling conditions. The γ‐phase nucleation process was examined directly by polarized optical microscopy and indirectly by small‐angle light scattering. The crystal phase content was assessed by differential scanning calorimetry. It is shown that the γ‐phase nucleation density and γ‐phase content increase with field strength and that the higher the crystallization temperature, the larger the effect of the field. These experimental results confirm the predictions of the model of nucleation in an electric field that we published previously. It is also noted that the degree of crystallinity and the perfection of crystal orientation along the γ‐phase spherulite radical direction decrease with field strength. The homogeneity of morphology resulting from the crystallization in the field is also examined by polarized optical microscopy on specimens microtomed across their thickness. When the crystallization is carried out under high field (E ≈ 0.1 MV/cm) and high temperature (T > 166°C) a nonuniform morphology results, characterized by a higher nucleation density at the positive electrode than at the negative electrode. Near the negative electrode very large disklike spherulites are seen to grow parallel to the substrate.
Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. IV. Computer modeling
Authors: Cheng Stephen Z. D. , Noid Donald W. , Wunderlich Bernhard
Published: April 2003

A crystal surface is modelled and Monte Carlo simulations are attempted to learn about conformations and motion of a macromolecule that could lead to crystallization. Chains with up to 200 mobile segments have been analyzed. The diffusion distance of a given chain segment increases with positioning closer to the chain end, and completion of crystallization accelerates with decreasing length of remaining amorphous chain ends and increasing temperature.
Rectangular and oblique layer packings of alkane chains and the eutectic solid formed by their interaction
Authors: Dorset Douglas L.
Published: April 2003

In the crystalline state, the paraffin, n‐hexatriacontane, and wax, octadecyl octadecanoate, both pack in either rectangular or oblique layers, have the same methylene subcell in either case and have similar molecular volumes. Despite these similarities, no cosolubility is found in the solid state for binary mixtures of the two compounds, because the favored layer packing for each material is different. Although a morphological description of the eutectic solid based on crystal form for the two compounds grown from the melt would lead to a “faceted‐faceted” nomenclature, implying noncooperative crystal growth, a closer inspection reveals that a one‐dimensional epitaxy is likely to exist across the major (001) faces of the two components. The solid is therefore a special example of a lamellar eutectic for which only two layers can coexist.
Electron spin resonance study of γ‐irradiated poly(acrylic acid)
Authors: Rao B. Sanjeeva , Murthy M. Ramakrishna
Published: April 2003

Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ‐irradiated in air at room temperature and recorded at room temperature and at liquid‐nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least‐squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10‐line spectra are assigned to the chain radicals CH3CHCH2 ∼ and/or ∼ CH2CHCH2 ∼. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the CαCβ bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption.
Dual‐mode sorption kinetics of gases in glassy polymers
Authors: Subramanian S. , Heydweiller J. C. , Stern S. A.
Published: April 2003

The transport of gases in many glassy polymers can be described satisfactorily by means of a “dual‐mode sorption” model. The transport behavior observed with a given gas/polymer system can be characterized by the model parameters, which are obtained from solubility measurements in conjunction with absorption/desorption or permeability measurements. The present study discusses the inverse problem, namely, the prediction of the absorption/desorption behavior of a gas in a glassy polymer from a specified set of dual‐mode sorption parameters. Satisfactory agreement is obtained between reported absorption rates of sulfur dioxide in glassy polycarbonate and of water vapor in Kapton®†

†Trademark of E. I. du Pont de Nemours & Co.

and the rates predicted by the dual‐mode sorption model. This study also confirms the consistency of the model.