bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of spin trapping to redox‐initiated vinyl polymerization with thiourea as the reductant
Authors: Saha S. K. , Greenslade D. J.
Published: April 2003

An electron spin resonance (ESR) study confirms a free radical mechanism for aqueous vinyl polymerization initiated by three redox systems involving thiourea. The primary radical, NH2C (NH)S., could not be detected by ESR spectroscopy, perhaps because of its large g anisotropy and/or very short relaxation time. Propagating radicals are trapped from methyl‐methacrylate by 2‐methyl‐2‐nitroso propane (MNP) and their structures are found to be the same as those produced by either azo‐bis‐isobutyrnitrile or di‐t‐butyl peroxylate. The latter monomer, however, reacts with MNP in the absence of any initiator, giving different ESR lines.
Thermal and rheological properties of miscible polyethersulfone/polyimide blends
Authors: Liang K. , Grebowicz J. , Valles E. , Karasz F. E. , MacKnight W. J.
Published: April 2003

Blends of an aromatic polyethersulfone (commercial name Victrex) and a polyimide (commercial name Matrimid 5218), the condensation product of 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride and 5(6)‐amino‐1‐(4′‐aminophenyl)‐1,3,3′‐trimethylindane, were studied by differential scanning calorimetry, dynamic mechanical analysis, and rheological techniques. The blends appeared to be miscible over the whole range of compositions when cast as films or precipitated from solution in a number of solvents. After annealing above the apparent phase boundary, located aboveTg, the blends were irreversibly phase separated indicating that the observed phase boundary does not represent a true state of equilibrium. Only a narrow “processing window” was found for blends containing up to 20 wt % polyimide. Rheological measurements in this range of compositions indicated that blending polyethersulfone with polyimide increases the complex viscosity and the elastic modulus of the blends. For blends containing more than 10 wt % polyimide, abrupt changes in the rheological properties were observed at temperatures above the phase boundary. These changes may be consistent with the formation of a network structure (due to phase separation and/or crosslinking). Blends containing less than 10 wt % polyimide exhibited stable rheological properties after heating at 320°C for 20 min, indicating the existence of thermodynamic equilibrium.
The mechanism of fatigue failure in a polyethylene copolymer
Authors: Zhou Ying‐Qiu , Brown Norman
Published: April 2003

The fatigue behavior of an ethylene‐hexene copolymer was investigated. The effects of R, frequency, relative times under the maximum and minimum stress, and waveform were measured. The phenomenological aspects were related to the microscopic aspects of the failure process. The maximum stress produces damage by disentangling the molecules in the fibrils of the craze and the minimum stress produces damage by bending the fibrils. The net damage, which is a product of these two damage processes, has been represented by a simple equation which accounts for the phenomenological observations.
Effects of substituent groups of polyimides on sorption and diffusion of gases
Authors: Toi Keio , Ito Tomoyasu , Ikemoto Isao , Kasai Tetsuo
Published: April 2003

Sorption rate curves of CO2, N2, and He gases below 1 atm were measured for polyimide films prepared from benzophenone tetracarboxylic dianhydride (BTDA) with 3,5‐diaminotoluene trifluoride (DATF), 2,4‐diaminotoluene (DAT), m‐phenylenediamine (MPD), and diaminobenzoic acid (DABA). The molecular structures of these four polyimides differ only in the substituent groups of the diamine structure. These polyimides exhibit dualmode type sorption isotherms for carbon dioxide that are concave to the pressure axis, typical of glassy polymer/gas system. The apparent diffusion coefficients below 1 atm pressure of carbon dioxide for this series of compounds decrease in the order: BTDA‐DATF > BTDA‐DAT > BTDA‐MPD > BTDA‐DABA. A linear relation between the logarithm of the apparent diffusion coefficient and the reciprocal of free volume, calculated by the method of Bondi using density data, is found for these polyimides. However, this tendency is not observed for the other two gases. The activation energies of the apparent diffusion coefficients at 20 cmHg pressure of carbon dioxide increase with increasing cohesive energy density of the polyimides. The energy per mole of free volume elements in a liquidlike structure in each cohesive energy density may be equated to the activation energy and used to calculate the free volume. The values from the activation energy are almost the same as those from Bondi's method.
Orientation and mechanical properties of PBT and its blends with a liquid‐crystalline copolyester
Authors: Ajji A. , Brisson J. , Qu Y.
Published: April 2003

Blends of poly (butylene terephthalate) (PBT) and a liquid‐crystalline copolyester (60 mol % poly(p‐hydroxy benzoic acid)/40 mol % polyethylene terephthalate) (LCP) were prepared in the melt state. The investigation of mechanical properties indicated that, for the processing conditions used, neither the addition of up to 30 wt % LCP to PBT nor the cooling history affected significantly the tensile modulus E. For oriented specimens, a marked improvement of E was obtained for all the blends, and increased with the LCP content. This improvement was more marked for slowly cooled samples. X‐ray diffraction was used to quantify the orientation of the crystalline PBT and liquid‐crystalline LCP phases. It was shown that neither the thermal history nor the presence of up to 30 wt % LCP affected the orientation behavior of the PBT crystalline phase. For the LCP phase, measurements were not possible for concentrations lower than 10 wt %, and were more difficult and less precise than for PBT. Nevertheless, it was possible to show that a better orientation was obtained for the slowly cooled samples and for higher concentrations of LCP in the blends. This correlated with the enhancement of mechanical properties observed for the oriented samples.
129Xe NMR as a probe of polymer blends
Authors: Walton J. H. , Miller J. B. , Roland C. M.
Published: April 2003

The miscibility of two‐component polymer blends has been investigated using xenon‐129 (129Xe) nuclear magnetic resonance (NMR) to probe the phase morphology. The chemical shift of 129Xe dissolved in a given polymer is unique, thus heterogeneous blends with large domain sizes exhibit two 129Xe NMR lines. When a single resonance is obtained, the data are consistent with miscibility, yielding an upper bound on the domain size. The temperature dependence of the relative solubilities and chemical shifts of 129Xe dissolved in the pure components may allow a determination of the phase morphology in blends exhibiting a single resonance. The method is used to demonstrate that polychloroprene and 25% epoxidized 1,4‐polyisoprene form a miscible blend.
Sorption and diffusion of gases in a polyimide
Authors: Toi Keio , Ito Tomoyasu , Shirakawa Toshiaki , Ikemoto Isao
Published: April 2003

Sorption and diffusion of gases (CO2, N2, and He) in a polyimide (PI2080) film were measured by using an apparatus which gives the sorption rate curves from the initial state to the equilibrium state. Nonlinear isotherms observed for CO2 sorption were interpreted successfully in terms of the dual‐mode model for sorption in glassy polymers. Linear isotherms observed for N2 and He seemed to obey Henry's law. Two diffusion coefficients (DI and DE) were obtained using the short‐time method and the long‐time method for a Fickian diffusion model, together with the equilibrium solubility (Ce) from each experiment. The initial sorption rate curves agreed with the calculated curves using DI, however near sorption equilibrium the curves are in accord with the calculated curves using DE. These observations suggest that some relaxation process is superimposed on the diffusion process. The non‐Fickian transport data were correlated successfully with a model that combines time‐dependent diffusion and the Fickian model.
Characteristics and design procedure of hyperbolic dies
Authors: Chen Gao‐Yuan , Cuculo John A. , Tucker Paul A.
Published: April 2003

Nozzle profiles capable of generating constant extensional strain rates are termed hyperbolic dies. When used in polymer extrusion, they exhibit greater potential in inducing and retaining polymer molecular orientation than conventional capillary dies. Most mathematical expressions found in the literature involve several processing variables in describing and designing such nozzle profiles. This report reveals that a hyperbolic die profile, although rather complicated, can be expressed with equations in terms of two ordinary geometrical parameters—the exit diameter and the hyperbolic length. This finding greatly simplifies the design procedure of hyperbolic dies. The extensional strain rate of a hyperbolic die can be related to the length‐to‐diameter ratio for any given exit diameter. Examples of various types of die profiles are presented and their constant extensional strain‐rate characteristics are discussed.
Dual‐mode sorption of nonionic azo dyes by Nylon 6
Authors: Shibusawa Takao , Chigira Yasuhiro
Published: April 2003

Sorption isotherms of 2,4‐dinitroaniline and three 4‐amino‐azobenzene derivatives (nonionic dyes with adequate solubility in water) on Nylon 6 (film and fiber) from water were determined at various temperatures. The observed isotherms were curved, not linear. They were very well described in terms of the dual‐mode sorption model, Nernst‐type partitioning, plus Langmuir sorption. The contribution of the Langmuir sorption to the total dye sorption decreased with increasing temperature. The saturation value for the Langmuir sorption increased with the crystallinity of Nylon 6 film, suggesting that the Langmuir sorption is associated with the crystalline phase.
Miscible blends of zinc‐neutralized sulfonated polystyrene and poly(2,6‐dimethyl 1,4‐phenylene oxide)
Authors: Register Richard A. , Bell Theodore R.
Published: April 2003

Zinc‐neutralized sulfonated polystyrene ionomers (ZnSPS) and poly(2,6‐dimethyl 1,4‐phenylene oxide) homopolymer (PXE) form miscible blends up to at least 7.8 mol % sulfonation, as measured by thermal and mechanical criteria. The addition of an equal weight of PXE raises the glass transition temperature of ZnSPS by 40–50°C. However, this miscibility is not achieved by eradicating the microdomain structure present in ZnSPS, even though the PXE coils are considerably larger than the spacings between ionic aggregates. Small‐angle x‐ray scattering indicates that while the average interaggregate spacing is roughly the same in ZnSPS and its 50/50 blend with PXE at a given sulfonation level, the extent of phase separation is reduced upon PXE addition, indicating that more ionic groups are dispersed in the matrix. Factors influencing miscibility in the ZnSPS/PXE materials and related blends are discussed.
Counterion binding to poly(allylammonium) cation
Authors: Itaya Tomoyuki , Ochiai Hiroshi
Published: April 2003

Chloride ion activity coefficients in aqueous solutions of poly(allylamine) hydrochloride (PAA · HCl) have been determined both in the absence and the presence of simple salts. Without added salt, the activity coefficient depends on the polymer concentration. With added salt, the binding of added counterions by PAAH+ is evaluated from the release of chloride ion. The extent of interaction between counterions and PAAH+ at a given polymer concentration decreases in the order SO ≫ ClO > NO > Cl− > Br− > I−. This order of counterion selectivity agrees with the previous estimation of potentiometric titrations. The result shows that the hydration of the counterion, as well as its charge, plays an important part in counterion binding to the polyion.
A study of stress distribution in model composites by using finite‐element analysis. I. End effects
Authors: Fan Cun F. , Hsu Shaw L.
Published: April 2003

The stress distribution along a fiber in model polymer composites has been calculated using a finite‐element analysis technique. Earlier experimental studies suggested that the stress distribution for fibers with tapered ends is much more efficient in carrying an external load than is the case for fibers with blunt ends. Both thermal residual (compressive) stress and tensile stress distributions along the reinforcement fiber have been measured with high sensitivity and spatail resolution. For fibers with blunt ends, the measured stress distribution agrees well with the stress distribution expected for an idealized shear‐lag model. For tapered fibers, the stress distribution measured is a constant along the fiber and a critical length was not found. Finite‐element calculations agree well with these experimental data. In addition, the stress distribution in the fiber, i.e., the radial dependence and the relative strain in both the fiber and matrix, was calculated. A detailed description of possible failure modes for the discontinuous fiber composites is provided based mainly on the finite‐element calculation.
Conductivity and the electric modulus in polymers
Authors: Starkweather Howard W. , Avakian Peter
Published: April 2003

At relatively high temperatures and low frequencies the electrical properties of many polymers are dominated by ionic conductivity. In cases where the glass transition is obscured by conductivity, it can be revealed by treating the data in terms of the electric modulus. The magnitude of the activation energy for conductivity (24–67 kcal/mol) for Nylons 6, 66, and 6I, polybutylene terephthalate, and polycarbonate indicates that the transport of charged particles requires the motion of polymer segments.
Water sorption in poly(ammonium sulfopropylbetaines). I. Differential scanning calorimetry
Authors: Galin J. C. , Galin M.
Published: April 2003

The hydration of four amorphous acrylic and methacrylic poly(zwitterions) bearing the ammonium sulfopropylbetaine function as a side‐groups () was studied by differential scanning calorimetry over broad ranges of temperature (150‐400 K) and water content (weight fraction W1< 0.5). Analyses were made of the first‐order transitions and heat capacity of sorbed water, glass transition temperature (Tg) measurements. Nonfreezable bound water, about 7.7 ± 0.9 mol/monomeric unit, behaves as a single phase: Its mobility, fairly similar to that of bulk liquid water in viscoelastic systems at T > 250 K, decreases with temperature in the glassy systems, but never disappears, even at 185 K. The depression of the glass transition temperature of the hydrated polymers obeys Couchman's equation:Tg= ΣiWiΔCpiTgi/ ΣgiWiΔCpi. Freezable bound water, about 6.7 ± 0.9 mole/monomeric unit, shows multipeak melting endotherms in the range 242–272 K. Because of their charged sites, the hydration process of the poly(zwitterions) appears more similar to that of poly(electrolytes) than to that of uncharged hydrophilic polymers. © 1992 John Wiley & Sons, Inc.
Water sorption in poly(ammonium sulfopropylbetaines). II. Sorption isotherms
Authors: Galin J. C. , Galin M.
Published: April 2003

Water sorption by four amorphous acrylic and methacrylic poly(zwitterions) bearing ammonium sulfopropylbetaine side groups () was studied at a constant temperature of 23°C and over a broad range of water activity (0.14‐0.90). Whatever the physical state of the hydrated polymer, glassy or viscoelastic, water diffusion is Fickian (average diffusion coefficient D̄s in the range 2‐16 × 10−8 cm2 s−1), and the sorption isotherms may be quantitatively analyzed according to the Guggenheim‐Anderson‐De Boer amended BET equation for multilayer sorption processes. The number of sitebound water molecules per monomeric unit is in the range 1.5–2.0, and apparently there is no great energy difference between direct site binding and indirect binding in the successive solvation layers. The polymer‐water interaction parameter (−0.6 < χ Flory < 0.6) is an increasing function of the water content of the hydrated poly(zwitterions) over the whole composition range (water volume fraction < 0.5), without any clear transition from the glassy to the viscoelastic state. Clustering of water molecules (Zimm‐Lundberg theory) is never observed, even at high water content. Because of the charged structure of their dipolar units, the poly(zwitterions) show a water sorption process similar to that of the corresponding poly(electrolytes) of the tetra‐alkylammonium sulfonate type. © 1992 John Wiley & Sons, Inc.
Dynamic mechanical and gas transport properties of blends and random copolymers of bisphenol‐A polycarbonate and tetramethyl bisphenol‐A polycarbonate
Authors: Kim C. K. , Aguilar‐vega M. , Paul D. R.
Published: April 2003

Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol‐A and tetramethyl bisphenol‐A polycarbonates (PC‐TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H2, O2, Ar, N2, CH4, and CO2. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition. These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The γ relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers. © 1992 John Wiley & Sons, Inc.
Quasiharmonic treatment of infrared and raman vibrational frequency shifts induced by tensile deformation of polymer chains. II. Application to the polyoxymethylene and isotactic polypropylene single chains and the three‐dimensional orthorhombic polyethylene crystal
Authors: Tashiro Kohji , Minami Shintaro , Wu Gang , Kobayashi Masamichi
Published: April 2003

Quasiharmonic equations are derived for stress‐induced vibrational frequency shifts in the infrared and Raman spectra of polymer chains subjected to a tensile stress. The expressions are applied to the helical chains of polyoxymethylene and isotactic polypropylene. Observed frequency shifts can be reproduced well by using reasonable anharmonic force constants. A semiquantitative interpretation is given for the close relationship between stress‐induced vibrational frequency shifts and the deformation mechanism of the polymer chains. Stress‐induced frequency shifts are also calculated for an orthorhombic polyethylene crystal subjected to uniaxial tension along the chain axis or to hydrostatic pressure. The results consistently and reasonably reproduce observed data, not only for the intramolecular vibrational modes but also for the external lattice modes. © 1992 John Wiley & Sons, Inc.
Model filled polymers. IX. Synthesis of uniformly crosslinked polystyrene microbeads
Authors: Ding Zheng‐You , Ma Shenmin , Kriz Dennis , Aklonis J. J. , Salovey R.
Published: April 2003

Monodisperse sized crosslinked polystyrene (PS) beads prepared by reaction of styrene (S) and divinylbenzene (DVB), in batch emulsion copolymerization in the absence of emulsifiers, are not uniformly crosslinked, because DVB is more reactive than S. For copolymerization of 1 to 10 mol % DVB and S, within each crosslinked PS microbead, the crosslink density varies by a factor exceeding two and decreases with increased conversion. A semicontinuous copolymerization, involving incremental additions of DVB, produces uniformly crosslinked PS beads. For both copolymerization techniques, Tg correlates well with crosslink density and PS beads are spherical and monodisperse in size. © 1992 John Wiley & Sons, Inc.
Free volume in glassy poly(arylene ether ketone)s
Authors: Hinkley J. A. , Eftekhari A. , Crook R. A. , Jensen B. J. , Singh J. J.
Published: April 2003

Amorphous polyarylene ether ketones were examined in the glassy state by positron annihilation lifetime spectroscopy (PALS) and in the melt by standard rheological techniques. Specimens were well‐characterized fractions of two isomeric structures. PALS clearly shows that the polymer with meta linkages in its backbone contains larger voids (> 0.25 nm radius). Thus despite their similar bulk densities, the two materials must pack very differently on a local scale. On the other hand, the free volumes inferred from the WLF treatment of melt viscosity data are practically identical in both materials ca. 4% at Tg. The comparison between techniques sheds some light on the distribution of free volume. © 1992 John Wiley & Sons, Inc.
Bulk and microscopic properties of copolymer networks in mixed aqueous solvents
Authors: Varelas C. G. , Steiner C. A.
Published: April 2003

Amphiphilic films and hydrogels have been prepared from ethanol/water solutions containing a hydrocarbon‐grafted water‐soluble cellulose ether. These materials are characterized by dispersed hydrophobic microdomains which form spontaneously in the solvent due to the inherent incompatibility of the side chains with water. At low applied shear stress, the microdomains behave as temporary linkages of finite lifetimes, imparting viscoelastic properties to the networks. The molecular weight between microdomains was found to be independent of the volume fraction of polymer in the gel, and the number of linkages per backbone ranges from 22.8 ± 1.3 to 26.2 ± 1.5 over the frequency range 30–50 rad/s. The behavior of the solutions and gels was characterized using fluorescence and dynamic rheological measurements. It was demonstrated that the microdomains are capable of sequestering water‐insoluble solutes. © 1992 John Wiley & Sons, Inc.
Morphology of Nylon‐6 blends with styrenic polymers
Authors: Takeda Y. , Paul D. R.
Published: April 2003

The morphology of blends of styrenic polymers in a matrix of 75% Nylon‐6 prepared in a Brabender Plasti‐Corder was examined by scanning electron microscopy. Styrene/acrylonitrile copolymers (SAN) form smaller particles as the AN level increases owing to the corresponding decrease in the SAN–polyamide interfacial tension. Various styrenic polymers containing functional groups, maleic anhydride or oxazoline type, that can react with Nylon‐6 during melt processing were added to the SAN phase which also led to a decrease in the particle size owing to the graft copolymer formed in situ. The effects of functional group type, amount of functional groups per chain, amount of functional polymer added, and the miscibility of the styrene/maleic anhydride (SMA) and SAN copolymers on the morphology of the styrenic phase in the Nylon‐6 matrix are described. © 1992 John Wiley & Sons, Inc.
Dynamic light scattering from bulk poly(n‐hexylmethacrylate) near and above the glass transition
Authors: Giebel L. , Meier G. , Fytas G. , Fischer E. W.
Published: April 2003

Photon correlation spectra of polarized scattered light from poly(n‐hexylmethacrylate) PHMA (Mw = 1.6·105, Tg = −5°C) have been studied in the temperature range of −2–25°C. The experimental time correlation functions over the time range 10−6−102 s were represented by the Kohlrausch‐Williams‐Watts (KWW) function exp{−(t/τ)β} with a virtually temperature‐independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass‐rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass‐rubber or α‐relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10−6 s near Tg. © 1992 John Wiley & Sons, Inc.
Thermoreversible gels of polyacrylonitrile
Authors: Bashir Z.
Published: April 2003

Polyacrylonitrile (PAN) is soluble at room temperature in some ionic aqueous media and in many polar organic liquids such as dimethyl sulfoxide, but the polymer will not crystallize from these solvents. It is known, however, that PAN will from single crystals from dilute propylene carbonate (PC) solutions. It was found that on cooling concentrated PAN‐PC solutions, thermoreversible gels were formed. The gels showed x‐ray diffraction peaks and calorimetry indicated first‐order dissolution endotherms and crystallization exotherms. Thus, on cooling, crystallization of the polymer from this solvent was identified as the cause for gelation of concentrated solutions. © 1992 John Wiley & Sons, Inc.
Analysis of polymer films by diffuse reflectance FTIR spectroscopy: Characterization of terminal carboxyl functionalities
Authors: de Donato P. , Cases J. M. , Humbert B. , Lutgen P. , Feyder G.
Published: April 2003

Fourier transform infrared (FTIR) spectroscopy in the diffuse reflectance mode was used to study polyethylene terephthalate (PET) films. The polymer film (12 μm, molecular weight M1 = 18,000) was placed on a finely powdered KBr matrix, used as a reference. Infrared spectra exhibited a new band at 1684 cm−1, not usually reported in the literature. This band is assigned to the CO stretching vibration of a terminal acidic function in the presence of internal hydrogen bonds. In the carbonyl region, artifacts created by specular reflection are also discussed. The assignment of the band at 1684 cm−1 is confirmed by transmission measurements on the overtone of carbonyl group (3335 cm−1), using polymer films with thicknesses greater than 200 μm and by comparison with polymer of different molecular weight. These acidic functions can be used to monitor the rate of polymerization. It is therefore possible to obtain information on the polymerization rate of PET films, using diffuse reflectance and transmission analysis, directly on the solid. © 1992 John Wiley & Sons, Inc.
Flow birefringence studies of a concentrated polystyrene solution in a two‐roll mill. I. Steady flow and start‐up of steady flow
Authors: Geffroy Enrique , Leal L. Gary
Published: April 2003

We have studied a 4.8 volume percent solution of a narrow distribution polystyrene with molecular weight 3.84 × 106 in flows generated by a co‐rotating two‐roll mill. These flows have a stagnation point at the midpoint between the roller axes. Further, they are linear, two‐dimensional, and the magnitudes of the strain‐rates are greater than the vorticity. The overall objective of our studies is to explore the dynamics of concentrated polymer solutions which are in the highly deformed state that is generated in the two‐roll mill. Birefringence data are presented for both steady flow and start‐up of steady flow in the two‐roll mill. The steady and transient data are used to analyze the linear and nonlinear viscoelastic regions of material behavior. In the nonlinear regime, the birefringence upon start‐up shows an initial overshoot followed by a strong undershoot that is enhanced as the ratio of elongation to rotation is increased (i.e., the flow becomes increasingly extensional in character.) We attribute this undershoot, which does not seem to appear in simple shear flows, or flows close to simple shear flow, to polymer segment stretching following an initial period of segment reorientation. Model studies are currently underway to test this notion. © 1992 John Wiley & Sons, Inc.
Prediction of miscibility regions in ternary blends of poly(styrene‐stat‐acrylonitrile), poly(acrylonitrile‐stat‐methyl methacrylate), and poly(styrene‐stat‐methyl methacrylate)
Authors: Cowie J. M. G. , Li Guangxian , Ferguson R. , McEwen I. J.
Published: April 2003

The miscibilities of ternary copolymer blends prepared from poly(styrene‐stat‐acrylonitrile), poly(styrene‐stat‐methyl methacrylate), and poly(methyl methacrylate‐stat‐acrylonitrile) were predicted by calculating the interaction parameter, χblend, for various blend combinations, from the corresponding binary segmental interaction parameters estimated from previous work. Binodal and spinodal curves were calculated using the Flory‐Huggins theory and it was observed that the most accurate estimate of the boundary between miscible and immiscible blends was given by the spinodal. It has also been demonstrated that in some of the ternary blends with fixed copolymer compositions the miscibility of the blend can be altered by changing the ratio of the three components in the mixture. Conditions for miscibility in this ternary system, and possibly a general feature of all such systems, are (a) that at least two of the binary interaction parameters χij are less than the critical value χcrit, while the third should not be too much larger, that is, one of the copolymers may act as a compatibilizer for the other two copolymers, (b) that the difference Δχ = /χ12 − χ13/ is small. © 1992 John Wiley & Sons, Inc.
Direct measurement of free‐volume hole distributions in polymers by using a positronium probe
Authors: Jean Y. C. , Deng Q.
Published: April 2003

We have directly measured the free‐volume hole distributions in semicrystalline polypropylene by positron lifetime annihilation spectroscopy. A Laplace inversion technique was engaged to analyze the positron lifetime spectra measured under quasi‐isotropic external pressures of 0, 4.2, and 14.7 kbar into continuous lifetime distributions. The hole radii distributions as determined from the ortho‐positronium lifetime distributions are found to be between 4.0 and 0.5 Å and to have maxima at 3.0, 1.9, and 1.1 Å under the external pressures of 0, 4.2, and 14.7 kbar, respectively. © 1992 John Wiley & Sons, Inc.
Temperature and stress effects in the creep of aramid fibers under transient moisture conditions and discussions on the mechanisms
Authors: Wang John Z. , Dillard D. A. , Ward T. C.
Published: April 2003

In a previous study, a mechanosorptive phenomenon in poly(p‐phenylene terephthalamide) fibers was reported. In this article, the mechanosorptive creep mechanism of aramid fibers and the temperature and stress influences on the mechanosorptive creep behavior of aramid fibers are addressed. Test results indicate that logarithmic creep rates and the mechanosorptive effects increase with temperature. The creep activation energies of the fibers tested are: 20 kJ/mole for the cyclic moisture condition, 4.4 kJ/mole for a high equilibrium moisture condition (RH = 95%), and 7.8 kJ/mole for a low equilibrium moisture condition (RH = 5%). Increase in stress may increase the logarithmic creep rates but may reduce the mechanosorptive effect. Aramid fibers contain hydrogen bonds between rodlike crystallites oriented at small angles relative to the fiber axis. Transient moisture conditions may cause slippage of hydrogen bonded elements and result in accelerated crystallite rotations due to breakage of hydrogen bonds, thus causing increases in logarithmic creep rate. The obtained activation energies and the reduction in fiber elastic compliance due to creep deformation support the proposed mechanisms. © 1992 John Wiley & Sons, Inc.
Thermal elimination of isobutene from meta and para tert‐di‐butyl pyromellitic acid
Authors: Johnson C. , Xu Huizhu , Wunder S. L. , Houlihan F. M. , Chin E.
Published: April 2003

An investigation of the kinetics of the thermal elimination of isobutene from the meta and para isomers of the tert‐butyl diesters of pyromellitic acid has been carried out using Fourier transform‐Raman spectroscopy and mass spectroscopy. These studies indicate that the elimination of the tert‐butyl group occurs at a temperature 26°C lower for the meta isomer than for the para isomer; the maximum rate of elimination occurs at 184°C for the former and at 210°C for the latter. Analysis of the Raman spectra of the compounds indicates that this effect results from the better packing arrangement in the para monomer compared with the meta monomer. Formation of pyromellitic dianhydride in the tert‐butyl diesters of pyromellitic acid occurred only after formation of the pyromellitic acid; thus it occurred at lower temperatures for the meta isomer. When the meta and para tert‐butyl diesters of pyromellitic acid are dissolved at 1% concentration in poly (vinyl acetate), the elimination of isobutene occurs at 173°C for both isomers, indicating that it is the differences in crystal packing which give rise to the 26°C difference in the solid‐state samples. For the meta, para, and 50/50 mixed isomers of the tert‐butyl esters of oxydianiline/pyromellitic dianhydride polyamic acid, the elimination of the tert‐butyl group occurs at the same temperature (177°C). This result indicates that the packing arrangement of the tert‐butyl group is disrupted in the polymer chain, so that intermolecular bonding does not hinder thermal deprotection of the tert‐butyl group from the polymer. © 1992 John Wiley & Sons, Inc.
Diffusion of camphorquinone in uniaxially drawn polycarbonate films
Authors: Xia J. L. , Wang C. H.
Published: April 2003

Employing the laser‐induced holographic grating relaxation technique, we have measured tracer diffusion coefficients of a phtochromous dye, camphorquinone, in uniaxially drawn polycarbonate films as a function of stretch ratio. Anisotropy in the tracer diffusion coefficient has been observed with D∥ greater than D⟂ by at least a factor of 4 for the film stretched to the stretch ratio δ = 2.3. The diffusion coefficient along the direction of stretch D∥ increases significantly with increasing δ, whereas D⟂ decreases slightly with increasing δ. The stretch ratio dependence of D∥ and D⟂ is interpreted according to a modified free volume theory. The strain rate and stretch temperature dependence of the anisotropic tracer diffusion coefficient has also been investigated. © 1992 John Wiley & Sons, Inc.
Dielectric properties of a PMMA/E7 polymer‐dispersed liquid crystal
Authors: Zhong Z. Z. , Schuele D. E. , Gordon W. L. , Adamic K. J. , Akins R. B.
Published: April 2003

Dielectric measurement on a polymer‐dispersed liquid crystal (PDLC) has been carried out in the frequency range from 10 Hz to 1 MHz and over the temperature range from 100 to 330 K. The PDLC sample was prepared by thermally induced phase separation of a 50% mixture by weight of commercially available liquid crystal E7 with PMMA and was sandwiched between two indium tin oxide glass plates separated by 40 μm spacers to form a “window.” The dielectric spectrum at low temperature (220–250 K) shows two distinct relaxation processes. Which occur at about 5 K lower than those in pure E7 having Tg ≈ 209 K. From differential scanning calorimetry data, the nematic transition of LC droplets in the PDLC is at 258 K, about 6 K lower than that of pure E7. The Maxwell‐Wagner effect has been observed in the low‐frequency side as the temperature increases from 280 to 320 K. At room temperature, the loss peak associated with the Maxwell‐Wagner effect shows an amplitude dependence with excitation level but no frequency shift. The effect of different concentrations of E7 in PDLC samples at a given temperature shows the 50% mixture has the “fastest” relaxation frequency in such a dispersed heterogeneous system. © 1992 John Wiley & Sons, Inc.
Lamellar and whisker single crystals of poly(2,6‐oxynaphthoate)
Authors: Liu J. , Rybnikar F. , Geil P. H.
Published: April 2003

Electron diffraction from single crystal lamellae and whiskers of poly(2,6‐oxynaphthoate) reveals the presence of at least 3 unit cells. The equatorial reflections in the patterns from the whiskers correspond to the dominant (phase I) hk0 diffraction pattern from the lamellae; phase I is monoclinic with 2 chemical repeats per physical repeat. The intensity distributions in the hk0 patterns of phase I and II resemble those of the same phases in poly(p‐oxybenzoate). The hk0 reflections of phase III suggest a common internapthalene unit spacing, but variable lateral (and possibly axial) shifts; apparently related orthorhombic and monoclinic patterns, with variable γ*, are observed. At elevated temperature, above the crystalliquid crystal transition (ca. 330°C), quadrant reflections are retained; the change in the hk0 pattern from any given crystal is gradual, extending over some 40°C. Above the liquid crystal‐liquid crystal transition (ca. 460°C) the pattern can be interpreted in terms of nematic or possibly smectic A packing. © 1992 John Wiley & Sons, Inc.
Optical anisotropy of polymeric films measured by waveguide propagation mode determination
Authors: Bai S. J. , Spry R. J. , Zelmon D. E. , Ramabadran U. , Jackson J.
Published: April 2003

Extruded thin films of a liquid‐crystalline charge‐conjugated rigid‐rod polymer poly(p‐phenylenebenzobisthiazole), PBT, and a semicrystalline thermoplastic polyethylene‐terephthalate (Mylar) were fabricated and examined for film thickness, refractive index, and linear attenuation coefficient. Optical waveguide modes were successfully induced on the polymeric films using a prism coupler at λ = 633 and 1300 nm. Highly consistent thickness values were obtained for the polymeric films. In addition, the anisotropic nature of the optical properties was determined using TE and TM propagation modes. A refractive index as high as 2.3 was observed on PBT film. The refractive index data suggested that the PBT and Mylar films were optically anisotropic with refractive indices n⟂ (out‐of‐plane) invariably smaller than n∥ (in‐plane). Large anisotropy was also discovered in the linear attenuation coefficient α, with α∥/α⟂ ≈ 50 for the Mylar films. Complementary polarimetric and spectroscopic interference measurements were also applied to investigate the optical anisotropy of the extruded polymeric films. © 1992 John Wiley & Sons, Inc.
Bulk rigid‐rod molecular composites of articulated rod copolymers with thermoplastic pendants
Authors: Bai S. J. , Dotrong M. , Evers R. C.
Published: April 2003

Bulk rigid‐rod molecular composites were successfully obtained by powder consolidation of a copolymer containing both the reinforcing rigid‐rod segments and the thermoplastic matrix. By chemically linking the reinforcing segments and the matrix molecule, the copolymer was designed to minimize phase separation in the molecular composite. The copolymer was an articulated rigid‐rod poly(p‐phenylenebenzobisthiazole), aPBT, with an aromatic poly(ether ketone), mPEK, thermoplastic pendant grafted at the points of articulation. The copolymer powder was pre‐formed and compression molded at an elevated temperature, which resulted in bulk rigid‐rod molecular composites with three‐dimensionally isotropic properties. Compared to the neat mPEK homopolymer, significant increases in glass transition temperature Tg and tensile properties have been realized for the aPBT‐g(mPEK) copolymers with low rod content. Taking into account the aspect ratio of the aPBT, the bulk rigid‐rod molecular composite showed a tensile modulus as predicted by the Halpin‐Tsai equation. In addition, x‐ray scattering revealed minimal rod aggregation. However, for the copolymer of higher rod content, significant phase separation was observed in the copolymer powder, which resulted in a decrease in Tg as well as reinforcement efficiency of the bulk rigid‐rod molecular composite as compared to those derived from the copolymers of low rod content. © 1992 John Wiley & Sons, Inc.
Extension of miyazawa's equations to the case of an arbitrary number of junction atoms in a molecular helix
Authors: Kandakov A. V. , Ginzburg B. M.
Published: April 2003

An algorithm is proposed for the construction of Miyazawa's equations with an arbitrary number of junction atoms in the repeat unit of the macromolecule. In these equations the helical parameters of an infinite polymer chain and the internal parameters of the chain, bond lengths, bond angles, and internal rotation angles, are interrelated. © 1993 John Wiley & Sons, Inc.
Study of crystalline orientation in drawn ultra‐high–molecular weight polyethylene films
Authors: Lafrance Claude‐Paul , Debigaré Josée , Prud'homme Robert E.
Published: April 2003

A wide‐angle x‐ray diffraction (WAXD) study of the development of molecular orientation in the crystalline phase of ultra‐high–molecular weight polyethylene films prepared by the gelation–crystallization method is presented. WAXD scans of the undrawn films show that the lamellae are oriented in the plane of the films. Upon drawing at 130°C, the orientation of the molecular chains changes from the direction normal to the film surface (ND) to the elongation direction. The decrease of the 200/020 intensity ratio at low draw ration (λ <10) indicates that double orientation develops during the transformation from the lamellar to the fibrillar morphology, with the a‐axis oriented parallel to ND. The orientation distributions of the 110, 200, 020, and 002 planes of the orthorhombic unit cell of polyethylene were studied and characterized by the coefficients of a Legendre polynomial series. At a draw ratio of 4.5, the second‐order coefficient, 〈P2(cos χ〉, already gets close to its limiting value, but it is shown that higher order coefficients of the polynomial series can be used to describe the evolution of the orentation, even up to λ = 50. The coefficients relative to the molecular chain orientation, 〈Pn(cos χ)〉c, can be calculated from different crystalline reflections. Curve‐fitting calculations were made in order to improve the correlation between the results obtained from the orientation distribution of the 110, 020, and 002 planes. A Person VII function was found to give a better fit of the experimental curves than Gaussian or Lorentzian equations. © 1993 John Wiley & Sons, Inc.
The effect of increased crystallization on the electrical properties of nylon‐12
Authors: Pathmanathan K. , Johari G. P.
Published: April 2003

The dielectric properties of 30% crystalline dry Nylon‐12 have been measured over the frequency range 10–105 Hz and temperature range 300–450 K, and the effect of its annealing at 423 K investigated both by dielectric measurement and differential scanning calorimetry. Annealing causes its crystallization to α phase, which increase the dc conductivity and decreases the contribution to orientation polarization, but does not alter the shape of the relaxation spectrum. The orientation polarization in Nylon‐12 involves two processes, each of which occurs above the glass‐transition temperature of Nylon‐12, but only the spectra of the lowest temperature process could be clearly resolved. © 1993 John Wiley & Sons, Inc.
Effect of the addition of amine diluents on the physical properties of poly(methyl methacrylate‐co‐methacrylic acid) copolymers obtained by partial hydrolysis of PMMA
Authors: Smith P. , Goulet L.
Published: April 2003

Atactic poly(methyl methacrylate) was partially hydrolyzed in concentrated sulfuric acid to obtain methacrylic acid contents (MAA) of 3–12 mol %. The resulting copolymers were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography. The dynamic mechanical properties of these copolymers were studied in the glass transition region at a frequency of 1 Hz following neutralization with various low‐molecular weight linear (e.g., octylamine) and rigid (e.g., 1‐adamantanamine, ADA) primary amines. While the addition of linear amines to the copolymers was found to depress Tg, the addition of ADA had relatively little effect. FTIR spectra of all these blends indicated that proton transfer occurred from the MAA units to the amines, resulting in H‐bonded ion pairs which behaved mechanically as grafts. Itwas concluded that the ion pairs resulting from protonation of the ADA units by MAA are less effective at reducing free volume than similar ones resulting from the reaction of a sulfonic acid with ADA. © 1993 John Wiley & Sons, Inc.
Study of orientational order in a nematic polysiloxane by utilizing the “guest–host” effect
Authors: Wolarz Eryk , Bauman Danuta
Published: April 2003

A nematogenic side‐chain polysiloxane is investigated by means of absorption and fluo‐rescence spectroscopy.4‐Dimethylamino‐4′‐nitrostilbene (DANS) is dissolved in the poly‐meric matrix as a guest probe. The orientational order and the molecular distribution function have been determined from measurements of polarized absorption and fluorescence spectra. It has been found that fluorescence spectroscopy affords a method for determination of the phase transition temperatures of liquid–crystalline polymers. © 1993 John Wiley & Sons, Inc.
Modeling strategy for systems with both stepwise and chainwise chemistry revisited. The directionality effect on the build‐up of the network structure
Authors: Riccardi Carmen C. , Williams Roberto J. J.
Published: April 2003

A comparison of rigorous and approximate models for the build‐up of epoxy‐amine networks with simultaneous etherification is presented. Contrary to a recent publication, it is shown that naïve statistical models perform very well in predicting statistical parameters when the different directions of network growth are distinguished in the statement of the recursive procedure. Slightly lower values of gel conversions are predicted by the approximate model, a fact that is consistent with the wider distribution of chain lengths resulting from the random recombination procedure. © 1993 John Wiley & Sons, Inc.
On catenate network formation by end‐linking reactions
Authors: Iwata Kazuyoshi , Ohtsuki Toshiya
Published: April 2003

Catenate network formation by end‐linking reactions of linear chains with bifunctional regents is studied theoretically and by computer simulations. It is found that the reaction cannot reach its stationary limit, and catenate networks are never formed by this method. An alternative method that will lead to catenate networks nearly in the topological equilibrium state is proposed. It is pointed out that catenate networks are an ideal system for studying the role of entanglement in rubber elasticity. © 1993 John Wiley & Sons, Inc.