bluuebunny/crossref_metadata_2025 huggingface dataset:
A model for dynamic relaxations in amorphous polymers. I. Conceptual framework, formal implementation of simplest version, and application to poly(ester carbonates)
Authors: Bicerano Jozef
Published: April 2003

A new model for the dynamic relaxations occurring below the glass transition temperature in amorphous polymers is introduced. This model combines ideas from theoretical solidstate physics, thermodynamics, and statistical mechanics. Formal analogies are made between the dynamic relaxations and phase transitions. The concepts of percolation theory are briefly discussed. The molecular level motions which might be giving rise to each dynamic relaxation are incorporated within this framework. The simplest version of the model is then formally implemented within the context of bisphenol‐A polycarbonate (BPAPC) and its poly (ester carbonates) (PEC). The following results are calculated: (1) Characteristic temperatures (Tc) for BPAPC, similar to γ1, and γ2 relaxation temperatures observed by dynamic mechanical spectroscopy (DMS) at commonly used measurement frequencies. (2) Tc for the β2 relaxation in tetrabromo‐BPAPC much higher than the Tc in BPAPC. (3) A slow and monotonic increase in both the intensity and the Tcof the γ2 relaxation with an increasing fraction of terephthalate comonomer in PEC copolymers. It is hoped that this model, which is admittedly tentative at this time, will be useful as a working hypothesis. The next paper of this series will provide extensions and generalizations of the model, and its application to the poly (alkyl methacrylates).
Solution behavior of random copolymers of styrene with sodium‐2‐acrylamido‐2‐methylpropane sulfonate
Authors: Wang Zhulun , Wang Jian , Chu Benjamin , Peiffer Dennis G.
Published: April 2003

The nonaqueous solution behavior of random copolymers of styrene (ST) with sodium‐2‐acrylamido‐2‐methylpropane sulfonate (Na‐AMPS) [poly(ST‐Na‐AMPS)] has been investigated using the transient electric birefringence (TEB) technique. The copolymers with varying high sulfonate contents (about 30–70 mol%), bridging the gap between conventional ionomers and classical polyelectrolytes, were dissolved in the solvent methylformamide (MFA) with a high permittivity ϵ of ca. 190. The solutions showed a negative birefringence at electric field strength E of the order of kV/cm. A typical Kerr effect was observed at low polymer concentrations C of ca. 10−3g/mL and electric field strengths of the order of kV/cm. However, the detailed, TEB studies demonstrated different behavior at two concentration regimes in dilute solution. At a low concentration regime (e.g., C ≤ 1 × 10−3g/mL for the copolymer with a 66.7 mol % sulfonate content) where the reduced viscosity exhibited a pronounced polyelectrolyte effect, the birefringence signal pattern showed a maximum before reaching a steady value. Additionally, during the rise at an applied electric field strength beyond a threshold value, it was observed that the nonexponential field‐free decay was slower than the single exponential field‐induced rise. The observed anomalous behavior was similar to those of a polyelectrolyte [sodium poly (styrene sulfonate)] in aqueous solution and might be attributed to the perturbation of the molecular shape by the applied electric field. At the higher concentration regime (e.g., C ≥ 4 × 10−3g/mL for the same copolymer with a 66.7 mol % sulfonate content) where the polyelectrolyte effects started to diminish as indicated by the viscosity study, the birefringence shape showed no variation with an increased electric field strength and the field‐free decay turned out to be faster than the single exponential rise. The dissociation of ionic aggregates was tentatively interpreted to be responsible for this observation. It seems that by simply varying the polymer concentration, poly (ST‐Na‐AMPS) could behave either as a polyelectrolyte or as an ionomer in a single polar organic solvent.
Cryodilation of thermoplastic PEBA elastomers
Authors: Okoroafor E. , Rault J.
Published: April 2003

PEBA block copolymers, poly(ether‐block‐amide), containing low concentrations of polyamide are thermoplastic elastomers. These materials, when strained at room temperature and then relaxed, exhibit dilation during cooling to low temperatures (ca.–10°C). This effect, of the order of 5–15%, depending on the concentration of the different blocks, is due to oriented crystallization of the soft polyether segments.
Dynamic mechanical analysis of RIM nylon‐6
Authors: Ning Xin , Ishida Hatsuo
Published: April 2003

The β relaxation process was shown to occur at different temperatures and exhibit a different activation energy for dry and wet samples prepared by reaction injection molding (RIM) of Nylon‐6. By employing a low operating frequency and controlled low moisture levels, it became possible to distinguish the two β relaxation processes, β1 and β2, in one sample by dynamic mechanical spectroscopy. It was shown that while β1 was associated with moisture in the sample, β2 was related to a structural mechanism independent of moisture. The effect of moisture content on the chain‐chain association (α relaxation process) and chain‐water association (β1, relaxation process) in nylon‐6 was assessed. The annealing mechanism of RIM Nylon‐6 at 85°C was probed by both dynamic mechanical spectroscopy and x‐ray diffraction.
The glass transition temperature of nonstoichiometric epoxy–amine networks
Authors: Vallo C. I. , Frontini P. M. , Williams R. J. J.
Published: April 2003

Glass transition temperatures (Tg) of nonstoichiometric epoxy‐amine networks based on the diglycidylether of bisphenol A (DGEBA), are analyzed in terms of the network structure. In most cases reasonable predictions of Tg can be made using an empirical equation reported by L. E. Nielsen together with the experimental Tg value of the stoichiometric network and statistical calculations of the concentration of elastic chains. It is stated that in these rigid networks the concentration of elastic chains is the main structural factor associated to the variations of Tg with stoichiometry. For flexible networks based on the diglycidylether of butanediol (DGEBD), the effect of elastic chains on the Tg value is much less significant.
Oscillatory measurement of linear viscoelasticity: Dynamic moduli revisited
Authors: Conde Luis , Rubio Miguel A. , Fairén Victor , Riande Evaristo
Published: April 2003

The current technique for the measurement of linear viscoelastic dynamic moduli is reconsidered. The transfer function analysis reveals the existence of nonlinear components in the response of the sample in a wide range of excitation frequencies around the reasonances of the measuring system. This analysis permits the disclosure of the components of the response which behave in accordance to linear viscoelastic theory and separates the undesirable nonlinear components. This results in partial corrections of the anomalous behavior of the calculated dynamic moduli through the standard technique.
Mapping the phase diagram of an aromatic polyamide blend using infrared spectroscopy
Authors: Bhagwagar Dorab E. , Painter Paul C. , Coleman Michael M. , Krizan Timothy D.
Published: April 2003

The results of an infrared study of poly (meta‐phenylene adipamide)‐poly (ethylene oxide) blends are reported. This is the first time, to the authors' knowledge, that infrared spectroscopy has been used to experimentally map the phase diagram of a polymer blend. The results are compared with theoretical phase diagrams calculated from a recently described association model.
A study of crystalline transitions in a thermoplastic polyimide
Authors: Gautreaux C. R. , Pratt J. R. , St. Clair T. L.
Published: April 2003

A new polyimide derived from 4,4′‐isophthaloyldiphthalic anhydride (IDPA) and 1,3‐bis(4‐aminophenoxy‐4′‐benzoyl)benzene (1,3‐BABB) having semicrystalline behavior was prepared at NASA Langley Research Center in 1987. The crystalline transitions of this thermoplastic polyimide have been studied. The differential scanning calorimetry (DSC) pattern of partially imidized film exhibited two distinct crystalline melt endotherms. For this study each crystalline phase was isolated and enhanced by controlled thermal treatment. A film containing approximately 50% of both phases and an amorphous film were also prepared. Evaluations of these films were performed by DSC, wide‐angle x‐ray scattering (WAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Three distinct crystalline morphologies; ellipsoid, cubic, and needlelike embedded in an amorphous matrix were observed as a function of various cure conditions by SEM.
A 13C NMR study of the effect of γ‐irradiation on the chain dynamics of poly(ethylene oxide)
Authors: Schilling Frederic C. , Tonelli Alan E. , Cholli Ashok L.
Published: April 2003

A comparison of solid‐state 13C nuclear magnetic resonance (NMR) spectra of virgin and vacuum γ‐irradiated poly (ethylene oxide) (PEO) evidences marked differences. The unirradiated PEO shows a well‐resolved amorphous resonance and a weak, broad envelope of crystalline resonances, while the irradiated PEO presents well‐resolved resonances for both the crystalline and amorphous carbons. Upon recrystallization from the melt both PEO samples yield solid‐state 13C NMR spectra that are closely similar to that of the virgin, unheated sample. Observation of both melt‐recrystallized samples at −60°C yields similar spectra with well‐resolved crystalline resonances. Crosslinking is the predominant chemical change occurring during the γ‐irradiation of PEO under vacuum and produces a change in the motional character of the crystalline phase. This change is not the result of a reduction in crystallinity as evidenced by differential scanning calorimetry (DSC) observations. The most probable explanation is that the crosslinks are concentrated at the surface of the crystalline lamellae with a resultant change in the low frequency molecular motions of the crystalline chains. This motional change shifts the T1pH such that the crystalline carbon nuclei can now be cross‐polarized at room temperature and the resonance linewidth is reduced. Following melting and recrystallization the motional characteristics of the irradiated PEO are nearly identical to those of the unirradiated sample, probably as a result of a redistribution of the crosslinks throughout the amorphous phase during recrystallization.
Crystallization and melting of cold‐crystallized poly(phenylene sulfide)
Authors: Chung Jerry Sengshiu , Cebe Peggy
Published: April 2003

In this study, we report the melting behavior of poly(phenylene sulfide), PPS, which has been cold‐crystallized from the rubbery amorphous state. We find that the crystallization kinetics are faster for cold‐crystallized PPS than for melt‐crystallized material, due to formation during quenching of a short‐range ordered, but noncrystalline, structure. We observe that the endothermic response of cold‐crystallized PPS at a large undercooling consists of a low temperature endotherm, followed by an exothermic region, and by the main higher melting endotherm. The lower melting peak temperature of cold‐crystallized PPS increases as the crystallization temperature increases, but the main upper melting peak temperature remains almost the same. The size of the exothermic region is strongly related to the degree of undercooling, and must be taken into account in order properly to determine the degree of crystallinity of the material prior to the scan. When the crystallization time is varied, we see a systematic decrease in the size of the main endotherm, and an increase in size of the lower melting endotherm. This suggests that a portion of the main endothermic response is due to reorganization during the scan. Annealing will not only increase the degree of crystallinity but also improve the crystal perfection; therefore the ability of an annealed sample to reorganize decreases as the annealing time increases. However, an additional third melting peak is seen when a cold‐crystallized sample is annealed at high temperature for a sufficiently long residence time. The existence of the third melting peak suggests that more than one kind of distribution of crystal perfection may occur when PPS has been cold‐crystallized and subsequently annealed.
The absorption coefficient spectrum of poly(methyl methacrylate) in the soft X‐ray region
Authors: Yates B. W. , Shinozaki D. M. , Kumar Ashok , Meath William J.
Published: April 2003

The total photoabsorption cross section for poly(methyl methacrylate) (PMMA) is measured experimentally, using synchrotron radiation, over the photon energy range 40 < E < 1000 eV. The experiments utilize nominally monochromatic radiation from a grazing incidence grating monochromator (the “Grasshopper” at the Canadian Synchrotron Radiation Facility) on the storage ring “Aladdin” at the University of Wisconsin. The raw experimental data are corrected for the spectral contamination of the incident radiation from the monochromator by utilizing a calculated photoabsorption spectrum for PMMA. The calculations are carried out using the “mixture” rule and reliable dipole oscillator strength distributions for smaller molecules related to PMMA.
Relative molecular weight distributions of cis‐polybenzoxazole/polyphosphoric acid rodlike liquid crystalline polymer solutions from dilute solution rheometry
Authors: Shaffer Edward O. , Carriere Craig J. , Bubeck Robert A.
Published: April 2003

The molecular weight for a dilute solution of cis‐polybenzoxazole (PBO) in polyphosphoric acid (PPA) was determined by fitting the rheological data with a semiempirical polydisperse hybrid theory. The hybrid theory models a semiflexible rigid rod as an elastic cylinder. The cylinder has both a rotational relaxation spectrum given by an ideal rigid rod and an internal bending relaxation spectrum spaced in accord with the relaxation time spectra of a flexible coil with fully developed hydrodynamic interactions. The model was fitted to rheological data collected for a 0.05 weight percent solution with intrinsic velocity (one‐point determination) of 320 ± 10 cc/g. The model predicts a number‐average molecular weight near 12800 ± 400 g/mol with a polydispersity index of 2.5 ± 0.1. By using the Yamakawa‐Yoshizaki equation the intrinsic viscosity is calculated for the model molecular weight distribution as 310 cc/g.
Properties of sulfonated poly(butylene terephthalate)
Authors: Gorda K. R. , Peiffer D. G.
Published: April 2003

The synthesis, morphology, and mechanical properties of sulfonated poly(butylene terephthalate) (PBT) and its unsulfonated analogs were studied. The morphology of these copolymers crystallized from the melt were examined by a combination of wide‐angle x‐ray scattering (WAXS), polarized light microscopy, and small‐angle light scattering (SALS). Stress‐strain measurements are correlated with the morphological results. Spherulitic morphology, with a maltese cross at 45°C with respect to the crossed polars, is formed at low sulfonate levels (≤ 5.0 mol %). At a higher ion content, the maltese cross rotates 45° to form a cross pattern. At still higher sulfonate contents, typically 13 mol %, the light scattering pattern disappears completely. Microscopic and WAXS examination of these functionalized PBT copolymers confirms that the crystallinity level decreases with increasing ion content and is eliminated completely at the higher sulfonation level. The spherulite radius, however, remains invariant until the highest functionalization level. On the contrary, the morphology and properties of the unsulfonated isophthalate copolymer analogs remain relatively constant over the entire composition range examined. In several compositions clearly inferior properties are noted compared with the ion‐containing copolymers.
Conductivity and dielectric properties of the monomer and polymer of the bis(p‐toluene sulfonate) of 2,4‐hexadiyne‐1,6‐diol
Authors: Pingsheng He , Chune Li , Jianbang Peng
Published: April 2003

The electrical conductivity of single crystals of the bis(p‐toluene sulfonate) of 2,4‐hexadiyne‐1,6‐diol (TS) and its polymer (PTS) was measured in a temperature range 77–373 K (to 353 K for TS), dielectric properties were measured from 123 to 283 K. Anomalies of the conductivity and the real part of the complex dielectric permittivity of TS and PTS along the molecular stacking direction at the temperature corresponding to the low‐temperature phase transitions were observed. The dependence of phase transitions on the polymerization conversion of the monomer TS was examined. The phase diagram of the TS‐PTS mixed system was constructed.
Generalized composite degradation kinetics for polymeric systems under isothermal and nonisothermal conditions
Authors: Nam Jae‐Do , Seferis James C.
Published: April 2003

A composite degradation methodology is extended to the conversion‐dependence function in order to explain the importance of multiple reaction mechanisms which might be considered to be involved in degradation processes. Based on two elementary reaction mechanisms, a specific form of the model equation is derived, which is capable of describing various types of degradation behavior showing sigmoidal rate as well as deceleratory rate. The conversion‐dependence function is derived to be independent of the Arrhenius‐type reaction constant or temperature, and thus the kinetic parameters are determined by analytic methods that have been developed for isothermal and dynamic‐heating experiments without any modification or additional assumptions. The developed model equation is tested by predicting the isothermal master curve of polyether‐ether‐ketone (PEEK), which is used as a model system in this study. The activation energies of the model system are analyzed using comparable methods for isothermal and dynamic experiments, which compare favorably in terms of the activation energy as a function of conversion. The resulting model equation, based on the kinetic parameters determined by isothermal experiments, can accurately predict both isothermal and dynamic‐heating thermogravimetry utilizing the same constants and identical reaction mechanisms without additional assumption.
Positron annihilation in irradiated and unirradiated polyethylenes
Authors: Suzuki T. , Oki Y. , Numajiri M. , Miura T. , Kondo K. , Ito Y.
Published: April 2003

Positron lifetimes were measured for four kinds of polyethylene samples and were resolved into four components. The temperature dependence of the two longlived components was examined in detail. In agreement with other results, the longest lived component could be reasonably assigned to ortho‐positronium located in amorphous regions. This component was shown to be sensitive to the defects in high‐density polyethylene introducted in the course of its production. Both the intensity and the lifetime of the second longest lived component were structure insensitive, i.e., they did not change even on passing through the melting point. This component has been tentatively assigned to a positronium compound state. The effect of gamma‐ray irradiation was also examined. Although the intensity (I4) of the longest lived component was reduced by the irradiation, correlation between I4 and the free radical concentration was poor, and the reduction in I4 caused by the irradiation is considered to be due to structure change and not to chemical reasons.
Influence of concentration on the activation energy for diffusion in polymer‐solvent systems
Authors: Zielinski John M. , Duda J. L.
Published: April 2003

The self‐diffusion of benzene, toluene, and ethylbenzene in polystyrene have been analyzed using the Vrentas/Duda free‐volume diffusion model. Diffusion coefficient predictions suggest an exponential concentration dependence of the activation energy required to overcome attractive forces, E. Without the use of any diffusion data approximating E as zero over the entire concentration range yields self‐diffusion coefficient predictions which are in good agreement with experimental data. © 1992 John Wiley & Sons, Inc.
Brillouin scattering study of a polymer hydrogel
Authors: Vanderwal J. , Sidebottom D. , Walton D. , Johari G. P.
Published: April 2003

Brillouin light‐scattering measurements of H2O imbibed in hydrogels of poly(2‐hydroxyethyl methacrylate) of two cross‐linking densities have been made at 294 K. Increase in the amount of water imbibed in 19‐30 Å size pores of the cross‐linked network causes the velocity of sound to decrease monotonically from a value, which differs for the two pure polymers, to a limiting value for pure water. The absorption coefficient reaches a maximum at about 30% water content and then decreases toward that for pure water. The velocity and absorption coefficient of both pure polymer and hydrogel containing 32% water were measured from 110 to 300 K. The former decreases and the latter increases with increasing temperature, and both show a change in the slope at about 160 K for the hydrogel, which agrees with the calorimetric glass transition temperature of the hydrogel. The effect of the water on the velocity and absorption coefficient of the polymer increases with temperature. © 1992 John Wiley & Sons, Inc.
Surface‐enhanced Raman scattering study of polymer on metals. III. Chemisorbed polybenzimidazole and its corrosion‐inhibiting properties at high temperature
Authors: Xue Gi , Dong Jian , Wu Peiyi
Published: April 2003

Chemisorption of polybenzimidazole on silver and copper etched with nitric acid has been observed by surface‐enhanced Raman scattering (SERS). The polymer is found to react chemically with silver, forming a complexed film on the surface. The SERS spectra show that polybenzimidazole film inhibits oxidation of the metal at high temperature, unlike chemisorbed benzimidazole, benzotriazole, and poly(4‐vinyl pyridine). © 1992 John Wiley & Sons, Inc.
Kinetics of orientation of a side‐chain liquid–crystal polymer as measured by a high‐temperature SQUID‐magnetometer
Authors: Fuhrmann K. , Dries Th. , Fischer E. W. , Ballauff M.
Published: April 2003

A superconducting quantum interference device (SQUID) magnetometer suitable for measurements of the magnetic susceptibility up to 600 K has been used to follow the kinetics of realignment in the nematic phase of a side‐chain liquid–crystal polymer. Experiments are performed using monodomain and polydomain samples. Results obtained in monodomain samples are in quantitative agreement with the prediction of the continuum theory up to an angle of approximately 60°. Experiments conducted at higher starting angles give clear indication of backflow effects. Data obtained from experiments on polydomain samples have been compared with model calculations using the data on the monodomain samples. This comparison leads to the conclusion that in this case backflow effects play an important role, too. All results show that SQUID magnetometry allows monitoring of the kinetics of realignment with highest precision. © 1992 John Wiley & Sons, Inc.
The dependence of slow crack growth in a polyethylene copolymer on test temperature and morphology
Authors: Lu X. , Mcghie A. , Brown N.
Published: April 2003

The slow crack growth resistance was measured in an ethylene‐octene copolymer as a function of the morphological changes produced by varying the thermal history. Morphology was varied by annealing the quenched state at temperatures between 86°C and the melting point. The slow crack growth behavior was measured by the lifetime of a notched tensile specimen under a constant load. In general, the lifetime exhibited a maximum at a critical value of the annealing temperature. This critical annealing temperature decreased with a decrease in the temperature at which the lifetime was measured. The former result is understandable in terms of the increase in crystal strength as the annealing temperature is increased and the decrease in the number of tie molecules when more material is melted as the annealing temperature increases. The latter result depends on the relationship between crystal size and the effect of testing temperature. Differential scanning calorimetry data played a key part in analyzing the results. © 1992 John Wiley & Sons, Inc.
Activation parameters associated with the β relaxation of poly(cyclohexyl acrylate)
Authors: Díaz‐Calleja Ricardo , Riande Evaristo , Román Julio San
Published: April 2003

The interpretation of the mechanical and dielectric β relaxations of poly(cyclohexyl acrylate) by the coupling scheme suggests that the dielectric relaxation process is more complex than the mechanical one, contrary to what occurs in the glass–rubber relaxation. The distribution of activation energies for the dielectric process, obtained from isochronal and isothermal loss curves, increases with temperature and frequencies. The determination of the distribution of the activation‐free energy indicates a distribution of the activation entropy for both the mechanical and dielectric β process, suggesting that a distribution of preexponential factors in the Arrhenius equation also exists. © 1992 John Wiley & Sons, Inc.
The effect of lattice compressibility on the thermodynamics of gas sorption in polymers
Authors: Barbari T. A. , Conforti R. M.
Published: April 2003

A compressible lattice model with holes, the glassy polymer lattice sorption model (GPLSM), was used to model the sorption of carbon dioxide, methane, and ethylene in glassy polycarbonate and carbon dioxide in glassy tetramethyl polycarbonate. For glassy polymers, an incompressible lattice model, such as the Flory–Huggins theory, requires concentration‐dependent and physically unrealistic values for the lattice site volumes in order to satisfy lattice incompressibility. Rather than forcing lattice incompressibility, GPLSM was used and reasonable parameter values were obtained. The effect of conditioning on gas sorption in glassy polymers was analyzed quantitatively with GPLSM. The Henry's law constant decreases significantly upon gas conditioning, reflecting changes in the polymer matrix at infinite dilution. Treating the Henry's law constant as a hypothetical vapor pressure at infinite dilution, gas molecules in the conditioned polymer are less “volatile” than those in the unconditioned polymer. Flory–Huggins theory was used to model the sorption of carbon dioxide, methane, and ethylene in silicone rubber. Above the glass transition temperature, the criterion of lattice incompressibility for Flory‐Huggins theory was satisfied with physically realistic and constant values for the lattice site volumes. © 1992 John Wiley & Sons, Inc.
Direct imaging of smectic B phase of poly(p‐xylylene)
Authors: Zhang Weiping , Thomas Edwin L.
Published: April 2003

Single crystals of poly(p‐xylylene) were grown in dilute α‐methylnaphthalene solution and studied by bright‐field and high‐resolution electron microscopy (HREM). The crystallization process was discussed in terms of the dependence of crystal form on crystallization conditions. A 0.15 nm resolution was achieved from high‐resolution images of a frozen liquid crystalline phase. High‐temperature electron diffraction patterns confirmed the existence of the liquid‐crystalline phase in agreement with previous work of Lieser. The HREM images show the molecular packing in the smectic B phase. © 1992 John Wiley & Sons, Inc.
Energy‐consuming micromechanisms in the fracture of glassy polymers. I. Chain scission in polystyrene
Authors: Mohammadi N. , Yoo J. N. , Klein A. , Sperling L. H.
Published: April 2003

The number of chain scissions per unit area that occur during the fracture of partially annealed latex films from Mn ≃ 180,000 g/mol polystyrene particles of about 275 Å radius were measured and correlated to annealing times. A curve with four regimes was found. At short annealing times the curve is nearly flat, in what is called the chain pull‐out regime. In the second regime, the number of chains broken per unit area increases with a 0.8 power of annealing time as entanglement of the diffusing polymer chains increases in neighboring host particles. This is in good agreement with Wool's theory which predicts a 0.75 power dependence. Then, after reaching a peak, the number of scissions decreases in the third regime, indicating a change in fracture mechanism. The number of chain scissions increases again in the fourth regime, as final healing of the film interface takes place. Fracture surface analysis reveals a rough surface for short annealing times and a smooth surface for longer annealing times. The number of polymer chain scissions per unit area of fracture surface showed no dependence on initial molecular weights for t ≫ τr where t and τr are annealing and relaxation times, respectively. The number of chain bridges crossing a unit area of interface was suggested as the basic molecular property. © 1992 John Wiley & Sons, Inc.
Chain orientation and anisotropies in optical and dielectric properties in thin films of stiff polyimides
Authors: Boese D. , Lee H. , Yoon D. Y. , Swalen J. D. , Rabolt J. F.
Published: April 2003

Thin films of poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by optical waveguide, ultraviolet‐visible (UV‐VIS), infrared (IR), and dielectric spectroscopies. The polyimide films exhibit an extraordinarily large anisotropy in the refractive indices with the in‐plane index n∥ = 1.806 and the out‐of‐plane index n⊥ = 1.589 at 1064 nm wavelength. No discernible effect of the film thickness on this optical anisotropy is found between films of ca. 2.1 and ca. 7.8 μm thickness. This large birefringence is attributed to the preferential orientation of the biphenyltetracarboximide moieties with their planes parallel to the film surface, coupled with the strong preference of BPDA‐PDA chains to align along the film plane. The frequency dispersion of the in‐plane refractive index n∥ is consistent with the results calculated by the Lorentz–Lorenz equation from the UV‐visible spectrum exhibiting several absorption bands in the 170–500 nm region. The contribution from the IR absorption in the range 7000–400 cm,−1 computed by the Spitzer‐Kleinmann dispersion relations from the measured spectra, adds ca. 0.046 to the in‐plane refractive index n∥. Tilt‐angle–dependent polarized IR results indicate nearly the same increase for the out‐of‐plane index n⊥. Application of the Maxwell relation then leads to the out‐of‐plane dielectric constant ε⊥ ≃ 2.7 at 1.2 × 1013 Hz, as compared with the measured value of ca. 3.0 at 106 Hz. Assuming this small difference to remain the same for the in‐plane dielectric constants ε∥, we obtain a very large anisotropy in the dielectric properties of these polyimide films with the estimated in‐plane dielectric constant ε∥ ≃ 3.4 at 1.2 × 1013 Hz, and ε∥ ≃ 3.7 at 106 Hz. © 1992 John Wiley & Sons, Inc.
High‐Pressure phase behavior of mixtures of poly(ethylene‐co‐methyl acrylate) with low‐molecular weight hydrocarbons
Authors: Hasch Bruce M. , Meilchen Melchior A. , Lee Sang‐Ho , McHugh Mark A.
Published: April 2003

Cloud‐point data to 180°C and 2,800 bar are presented for three poly(ethylene‐co‐methyl acrylate) copolymers [10, 31, and 41 mol % methyl acrylate (MA)] and for polyethylene in ethylene, ethane, propylene, and propane. At low concentrations of MA in the backbone of the copolymer, the saturated hydrocarbons are better solvents for the copolymer than their olefinic analogs because polarizability drives the phase behavior. For the higher MA‐content copolymers, which have more polar repeat units, the unsaturated hydrocarbons are better solvents owing to favorable quadrupolar interactions between the solvent and the polymer segments. The cloud‐point curves of the high MA‐content copolymers in the unsaturated hydrocarbons are shifted to very high temperatures to overcome strong acrylate‐acrylate interactions in the polymer. In fact, the 41 mol % MA copolymer cannot be dissolved in propane at temperatures to 180°C and pressures to 2,800 bar even though the copolymer is predominantly ethylene, while the same copolymer dissolves in propylene at 40°C and at pressures as low as 1,400 bar. Although the Sanchez‐Lacombe equation of state is used to model the cloud‐point curves, two temperature‐dependent mixture parameters are needed for a good fit of the data. © 1992 John Wiley & Sons, Inc.
Structure factor for starburst dendrimers
Authors: Hammouda Boualem
Published: April 2003

Advances in polymer synthesis have made possible the polymerization of “starburst dendrimer” gels which are grown from a central initiator core through controlled branching reactions with a constant multiplication of the number of monomeric blocks from one generation to the next. The structure factor for such dendrimers is calculated using Gaussian monomer‐monomer interactions. The results are somewhat lengthy but analytical forms are obtained. © 1992 John Wiley & Sons, Inc.
Monte Carlo calculations of hole size distributions: Simulation of positron annihilation spectroscopy
Authors: Vleeshouwers S. , Kluin J.‐E. , Mcgervey J. D. , Jamieson A. M. , Simha R.
Published: April 2003

Consequences are explored of a hole size distribution in an amorphous polymer for the ortho‐positronium (o‐Ps) lifetime (τ3) and intensity (I3), determined by positron annihilation lifetime spectroscopy. The disordered lattice model, with a vacancy fraction h as a central quantity, is used to represent the equation‐of‐state behavior of the polymer. By means of Monte Carlo simulations, we obtain the cluster size distribution as a function of h and hence temperature. The predicted average cluster size and the cluster concentration are compared to τ3 and I3 data, respectively, for bisphenol‐a polycarbonate. Furthermore, the influence of an o‐Ps lifetime distribution on the experimental mean τ3 is investigated. By mimicking the computational methods used in experimental analysis, agreement between experiment and theory in respect to τ3 and to I3 in the melt ensues. In the glass, however, the experimental I3 becomes increasingly smaller with decreasing temperature than is computed. These deviations may result from a distortion of the equilibrium free volume. © 1992 John Wiley & Sons, Inc.
Regular, adjacent reentry folding in single crystals of a liquid crystal polymer crystallized from the nematic state
Authors: Lin D. , Dean D. , Geil P. H.
Published: April 2003

Folded chain single crystals 35 Å thick have been grown from the liquid crystal state of an aromatic‐aliphatic azomethine ether polymer (AZMEP‐n) having a 10‐carbon flexible segment (n = 10). Electron diffraction has permitted refinement of the triclinic unit cell. The molecular axes lie at an ca. 65° angle to the lamella normal and fold every third chemical repeat distance. For AZMEP‐1 and ‐8 extended chain lamellae are formed; for AZMEP‐7 both folded and extended chain lamellae are found. The observations of folded chain lamallae are in agreement with prior suggestions from our laboratory of chain folding in the liquid crystalline state in thin films. © 1992 John Wiley & Sons, Inc.
The application of simultaneous chemiluminescence and thermal analysis for studying the glass transition and oxidative stability of poly(N‐vinyl‐2‐pyrrolidone)
Authors: Scheirs J. , Bigger S. W. , Then E. T. H. , Billingham N. C.
Published: April 2003

A computer‐controlled chemiluminescence (CL) instrument incorporating a differential scanning calorimeter was used to simultaneously acquire photochemical and enthalpic data for poly(N‐vinyl‐2‐pyrrolidone) (PVP). Samples were subjected to a linear temperature ramp under nitrogen and their luminescence response recorded. The resultant dynamic CL peak is attributable to the decomposition of hydroperoxide groups and the subsequent mutual termination of secondary polymer peroxyl radicals. It is shown that dynamic CL can be used to characterize the level of oxidation in PVP, which in commercial samples, may be partly related to the level of residual polymerization inititor and to the drying process. The temperature at which maximum CL emission occurs correlates with the glass transition temperature (Tg) of the polymer and increases with increasing molecular weight. A marked increase in the Tg of PVP occurs after it is aged in air for 24 h at 120°C. This is due to the loss of adsorbed moisture from the polymer which was confirmed by thermogravimetric analysis. Oxidation profiles of PVP were obtained by plotting the integrated CL peak area as a function of aging time. The profiles are compared with data obtained from isothermal CL and viscosity measurements. Gas perturbation experiments suggest that when drying PVP under nitrogen at elevated temperatures significant populations of longlived macroalkyl radicals are formed which can peroxidize the polymer on exposure to air. © 1993 John Wiley & Sons, Inc.
Oxygen permeability of surfactant/polymer composite films with multibilayer and inverted hexagonal structure
Authors: Taguchi Kazuhiro , Yano Shoichiro , Hiratani Kazuhisa , Minoura Norihiko
Published: April 2003

The permeability of oxygen through horizontally oriented multibilayer films of polyion complexes prepared from quaternary ammonium‐type surfactants [CH3(CH2)n‐1]2N+(CH3)2Br−(n = 14, 16, 18), and poly(p‐styrenesulfonate) or poly[2‐(acrylamido)‐2‐methyl‐1‐propanesulfonate], was measured in water using an oxygen electrode. The permeability depended mainly on the phase of the multibilayers. Thus, it increased abruptly (about 10‐fold) near each phase transition temperature because of the fluidity enhancement of the multibilayer. Inverted hexagonal type nonbilayer films prepared from the polyion complexes and cholesterol had greater permeability (2–20‐fold) than the multibilayer films in both phases. The large permeability of the nonbilayer films was attributed to the lack of a barrier such as the bilayer and lower crystallinity of the films. It was associated neither with an increase in thermal movement of the lipid surfactant molecules nor with an increase in the water content of the films by the addition of cholesterol. © 1993 John Wiley & Sons, Inc.
Capillary and slit‐die flow of two liquid‐crystalline polymers. The effect of pressure on viscosity
Authors: Izu Pilar , Muñoz María Eugenia , Peña Juan J. , Santamaría Anton
Published: April 2003

Viscosity measurements on two commercial thermotropic liquid crystalline polymers (LCPs) (a copolyester and a polyesteramide) were performed using both capillary and slit die methods. The results are in agreement with those presented in the literature for the same LCPs, when the measurements are carried out with a L/D = 30 die; these results are affected more by Bagley corrections for the polyesteramide than for the copolyester. For both LCPs, viscosities measured in the slit die are lower than those obtained by capillary rheometry. Nevertheless, the difference is much bigger in the case of the polyesteramide, for which a reduction by a factor of 3 is observed. This is not due to the preshear or thermal history, since the same piston‐barrel system and thermal treatment were applied in both types of measurements. Depending on the polymer sample and temperature, concave and convex curvatures were observed in the pressure profiles during the slit flow. From these curvatures, the pressure coefficient α of viscosity was evaluated. However, in the case of the polyesteramide the convex curvature leads to a negative coefficient (the viscosity decreases with pressure, instead of increasing). This result may be explained by envisaging a change in the structure of the melt along the slit length. © 1993 John Wiley & Sons, Inc.
Protonation of leucoemeraldine in the solid state and in solution
Authors: Neoh K. G. , Kang E. T. , Tan K. L.
Published: April 2003

The protonation of leucoemeraldine in power form and in N‐methylpyrrolidinone (NMP) solution by HCIO4 and HBF4 has been studied by x‐ray photoelectron spectroscopy (XPS), infrared (IR), and ultraviolet (UV)‐visible absorption spectroscopy. In powder form, less than 25% of the amine nitrogens can be protonated in the absence of oxygen. The effects of oxygen on the degree of protonation and the distribution of amine and imine units upon deprotonation of the salt are investigated. The degree of protonation in leuccemeraldine can be increased to about 50% with 3 M HCIO4, similar to that achievable with emeraldine base in powder form. In NMP solution, leucoemeraldine is easily oxidized by dissolved oxygen. Protonation of both leucoemeraldine and emeraldine base in NMP solutions results in metastable species which gradually undergo deprotonation. The resulting products are affected by the O2 content of the solutions. © 1993 John Wiley & Sons, Inc.
Gas transport in polybutadiene treated with aqueous bromine
Authors: Rein D. H. , Baddour R. F. , Cohen R. E.
Published: April 2003

Diffusion, solubility, and permebility coefficients were measured for He, Co2, Ar, and CH4 in polybutadiene (PB) and in polybutadiene reacted in the solid state to various extents with aqueous bromine. Analysis of the sorption curves and X‐ray emission spectra showed that the bromination created a heterogeneous membrane with an outer brominated skin and an unreacted core. At relatively low extent of bromination, the diffusion and permeability coefficients for CO2, Ar, and CH4 decreased by two orders of magnitude, while the transport coefficients for He were virtually unchanged. The permeability coefficients for CO2, Ar, and CH4 became immeasurably small after about 3% bromination. The ideal separation factor for gas pairs with different molecular size increased with bromination, suggesting applications in gas separation processes. © 1993 John Wiley & Sons, Inc.
Cosolvency effects on copolymer solutions at high pressure
Authors: Hasch Bruce M. , Meilchen Melchior A. , Lee Sang‐Ho , Mchugh Mark A.
Published: April 2003

Cloud‐point data to 180°C and 2800 bar are presented for polyethylene, poly(methyl acrylate), and two poly(ethylene‐co‐methyl acrylate) copolymers (10 and 31 mol % methyl acrylate) in propane and chlorodifluoromethane with two cosolvents, acetone and ethanol. The addition of small amounts of either cosolvent to the copolymer–solvent mixtures shifts the cloud‐point curve to lower pressures and temperatures, as both cosolvents provide favorable polar interactions with the acrylate group in the backbone of the copolymer. Ethanol has a larger effect than acetone since ethanol hydrogen bonds to the acrylate group. However, if the concentration of ethanol is increased above ca. 10 wt %, it self‐associates and reverts to antisolvent behavior, forcing the copolymer out of solution. For nonpolar polyethylene–propane mixtures, the polar cosolvents behave as traditional an‐tisolvents. In poly(methyl acrylate)–chlorodifluoromethane mixtures, both polar cosolvents enlarge the single‐phase region. The cloud‐point curves for the (co)polymer–propane–acetone mixtures are modeled reasonably well using the Sanchez–Lacombe equation of state with two adjustable mixture parameters. No attempt is made to model the mixtures that exhibit hydrogen bonding. © 1993 John Wiley & Sons, Inc.
Kinetics of phase separation in polymer blends. Calculations based on nonlinear theory
Authors: Wang Zheng‐Yu , Konno Mikio , Saito Shozaburo
Published: April 2003

Suzuki's scaling theory for transient phenomena is applied to the calculation of the kinetics of phase separation in the early‐to‐intermediate stage based on a nonlinear theory proposed by Langer, Bar‐on, and Miller (LBM). Calculated results are compared with experimental data on light scattering from a polymer blend system. Deviations from predictions of Cahn's linearized theory in the early time range of phase separation can be explained well by the proposed method of calculation. Nonlinear effects are found to play an essential role in characterizing the light scattering behavior of phase separation in the intermediate stage. Time evolutions of the single‐point distribution function of composition are calculated, and the results are in good agreement with those reported in digital imaging analysis experiments and computer simulations of the time‐dependent Ginzburg‐Landau equation. The influence of asymmetry of free‐energy on the single‐point distribution function is also investigated in this study. © 1993 John Wiley & Sons, Inc.
Optical analysis of dichroism measurements in polymer science
Authors: Wold Erik , Bremer Johannes , Hunderi Ola
Published: April 2003

The polarization properties of an optical system, source–interferometer–polarizer–polymer film–detector, have been calculated. Using Mueller matrices, the intensity has been obtained as a function of polarizer angle. It is shown in some detail how polarization of the beam in both interferometer and detector optics distort the spectra. The contributions from the finite extinction ratio of the polarizer are also calculated and intensity variations caused by beam‐wandering are discussed. It is shown that the commonly used procedure for correcting the spectra is wrong. Better methods for correcting the spectra are proposed. The influence of a uniaxial refractive index on the data is discussed, and experimental methods that can deal with refraction effects are presented. © 1993 John Wiley & Sons, Inc.
Toughening of epoxies via craze‐like damage
Authors: Sue H.‐J. , Garcia‐Meitin E. I. , Orchard N. A.
Published: April 2003

The fracture behavior of a core‐shell rubber (CSR) modified epoxy is investigated using both fracture mechanics and microscopy tools. The CSR‐modified epoxy is found to be toughened via numerous line‐array cavitations of the CSR particles, followed by plastic flow of the epoxy matrix. The toughening effect via the above craze‐like damage process is found to be as effective as that of the well‐known widespread rubber cavitation/matrix shear yielding mechanisms. The conditions for triggering the craze‐like damage appear to be both stress state and rubber concentration dependent. The type of rubber tougheners utilized also plays a critical role in triggering this rather unusual craze‐like damage in epoxy systems. © 1993 John Wiley & Sons, Inc.
The effect of amorphous orientation on the oxygen permeability of polypropylene films
Authors: Taraiya A. K. , Orchard G. A. J. , Ward I. M.
Published: April 2003

Oxygen permeability measurements have been made on uniaxially and biaxially oriented polypropylene samples. X‐ray diffraction pole‐figure measurements provided the crystalline orientation functions. These results combined with density and refractive index measurements provided the amorphous orientation functions based on the two‐phase model. A good correlation has been found between the amorphous orientation and the oxygen permeability of the samples. © 1993 John Wiley & Sons, Inc.
High‐resolution solid‐state 13C NMR study of ethylcellulose films
Authors: Kimura Tsunehisa , Azuma Jun‐Ichi , Gray Derek G.
Published: April 2003

Ethylcellulose films cast from concentrated solutions of chloroform, benzene, and carbon tetrachloride were subjected to the NMR relaxation measurements including 1H spin‐lattice relaxation time (T1H), rotating‐frame 1H spin‐lattice relaxation time (T1ρH), and 13C spin‐lattice relaxation time (T1C). The values of T1ρH for carbons in the glucose units of ethyl‐cellulose were of the same order of magnitude as those reported for the crystalline and noncrystalline regions of ramie cellulose. The values of T1C for unsubstituted C2, C3 carbons were smaller than those for the corresponding carbons in the noncrystalline region of native celluloses. The T1C values for unsubstituted C2, C3, and substituted C6 carbons showed a small but definite dependence on the solvent from which the films were cast. © 1993 John Wiley & Sons, Inc.