bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of linear low‐density polyethylene: Cross‐fractionation according to copolymer composition and molecular weight
Authors: Mirabella Francis M. , Ford Emory A.
Published: April 2003

The structure of ethylene copolymers modified by α‐olefins has become an area of intense investigation since the successful commercialization of so‐called linear low‐density polyethylene (LLDPE) resins. The molecular structure of a series of typical commercial LLDPE copolymers was investigated and compared to LDPE and HDPE. The commercial LLDPE resins studied contained about 7% by weight of butene‐1. The resins were fractionated according to short‐chain branching content by a technique called temperature rising elution fractionation. Size exclusion chromatography, x‐ray diffraction, 13C nuclear magnetic resonance, intrinsic viscosity, and differential scanning calorimetry were used to fully characterize the whole polymers as well as fractions of a selected LLDPE resin. A broad set of data was assembled in this work to investigate the short‐chain branching, long‐chain branching, and the molecular‐weight distribution of these commercial resins. The melting behavior of the LLDPE resins was found to be strikingly different from that of LDPE and HDPE. The broad and multimodal melting envelope of the LLDPE resins was found to be due to a broad and multimodal short‐chain branching distribution. No significant long‐chain branching was found in the LLDPE resins. The short‐chain branching was found to decrease with the increase of molecular weight in a typical commercial LLDPE resin. The unique physical properties of these resins are certainly strongly controlled by the expression of the distinctive heterogeneous comonomer incorporation in the solid‐state morphological structure. The physical and mechanical properties of these materials should be ultimately understandable on the basis of the unique morphology which results from the extremely heterogeneous incorporation of modifying α‐olefin in these commercial LLDPE resins.
Polymer blend complexes based on coordination chemistry
Authors: Agarwal P. K. , Duvdevani I. , Peiffer D. G. , Lundberg R. D.
Published: April 2003

The preparation, rheology, and mechanical properties of a family of blends composed of transition‐metal neutralized sulfonated ethylene‐propylene‐diene elastomers (S‐EPDM) and styrene‐4 vinylpyridine copolymers (SVP) are described. These polymeric materials contain relatively low levels of interacting groups (≤ 10 mol%), which are, however, sufficient for forming an intermolecular complex. A distinguishing characteristic of these blends is that the rheology and mechanical properties are strongly influenced by a coordination‐type bonding between the transition metal and the basic nitrogen unit. As a result, markedly improved and enhanced physical properties are observed, especially when the stoichometric ratio of the interacting moieties are approached (SO/N = 1/1). This enhancement in properties is clearly exhibited in melt viscosity data, dynamic mechanical data, and thermal data. The blend morphology is also altered by complex formation, as is observed in scanning electron microscopy of the blends from which one of the ingredients was selectively extracted. At the stoichometric ratio, the blend of the olefinic elastomeric ionomer and the styrenic thermoplastic copolymer approaches a single‐phase system. Such blends are otherwise completely immiscible when the coordination‐type interacting groups are absent from either of the individual components. Accordingly, it was observed that nontransition‐type (Na, Mg) counterions have only a marginal effect on the compatibility of these blends, as is the case in the completely unfunctionized blend components.
Static fatigue fracture of polyethylene: A morphological analysis
Authors: Barry D. , Delatycki O.
Published: April 2003

The fracture properties of a number of high‐density polyethylenes were evaluated and related to their morphology. The resistance to initiation of fracture is related to the resistance to voiding of the materials and the rate of coalescence of voids. The propensity of the materials to void has been shown to be related to the size of the amorphous region. The resistance to propagation of the fracture is also related to the above factors as well as the ease of stretching and rupture of fibrils. The ease of fibril formation has been shown to be related to the degree of perfection of the crystallites.
Effect of antiplasticization on gas sorption and transport. I. Polysulfone
Authors: Maeda Y. , Paul D. R.
Published: April 2003

The addition of tricresyl phosphate, N‐phenyl‐2‐naphthylamine, and 4,4′‐dichlorodiphenyl sulfone to polysulfone causes changes in thermal and mechanical properties of the glassy mixtures associated with antiplasticization, i.e., reduction in glass transition temperature and increase in stiffness. These changes are also found to be accompanied by reductions in sorption of carbon dioxide and the permeability coefficients for helium, carbon dioxide, and methane at low diluent concentrations with reversal of these trends at higher levels as also occurs for the mechanical properties. Detailed analyses of data for carbon dioxide are given in terms of the dual sorption and mobility models often used for glassy polymers. The mobility for gas transport was found to decrease with diluent addition. The major cause for the decreased sorption is the reduction in glass transition temperature accompanying addition of the diluents. The changes in transport behavior approximately parallel the changes in mechanical behavior. These trends are not even qualitatively correlated with estimates of the excess volume changes associated with addition of the diluents to polysulfone.
Chromism of soluble polythienylenes
Authors: Rughooputh S. D. D. V. , Hotta S. , Heeger A. J. , Wudl F.
Published: April 2003

Thermochromism and solvatochromism of solutions of poly(3‐alkylthienylenes) are reported. The experimental results indicate the presence of two coexisting phases: polymer in solution and polymer in microcrystalline aggregates. From the concentration independence of the thermochromism, it is concluded that the transition is fundamentally driven by a single chain mechanism, and that the aggregation (microcrystallization) of the poly(3‐alkylthienylene) macromolecules can occur only after the single chain conformational change has occurred.
X‐ray studies on the deformation of an aromatic polyimide
Authors: Russell T. P. , Brown H. R. , Grubb D. T.
Published: April 2003

The deformation of the aromatic polyimide poly{N,N′‐bis(phenoxyphenyl)‐pyromellitimide} (PMDA‐ODA) has been investigated by x‐ray scattering. PMDA‐ODA, which exhibits a smecticlike ordering in the bulk can be elongated up to 70% at room temperature without a distinct yield point. Under strain, the diffraction pattern of the intramolecular spacing occurring at a Bragg spacing of 15.4 Å is elliptical. The ellipticity shows that the molecule changes its repeat distance along the chain axis. This may result from bond angle and bond length distortions. Consistent with this is a rapid recovery well below the glass transition temperature where all but 20% strain is recovered. This localized extension, however, cannot account fully for the macroscopic deformation applied, and, as such, a global orientation of the chains occurs, as evidenced by the arcing of the diffraction profiles. The retention of the intrachain reflection indicates that bundles of chain segments ordered in a smectic fashion orient as a unit maintaining a lateral chain‐segment alignment. Finally, the scattering vector at which a small‐angle scattering reflection occurs was found to be correlated to the coherence length determined by a Scherrer analysis of the ca. 15.4 Å intramolecular reflection. As the strain increased, the intensity and spacing of the small‐angle scattering reflection increased parallel to the stretching direction and decreased perpendicular to this. This suggests that the origin of the small‐angle scattering reflection arises from electron density fluctuations along the chain axis, as is typically seen in semicrystalline polymers.
Time‐temperature superposition and dynamic mechanical behavior of atactic polystyrene
Authors: Cavaille J. Y. , Jourdan Corinne , Perez J. , Monnerie L. , Johari G. P.
Published: April 2003

The dynamic mechanical behavior of monodisperse atactic polystyrene (mol. wt. 98,000) has been measured in the frequency range, 10−5 to 10 Hz and temperature range 359–374K. The time‐temperature superposition of the entire data in the frequency range of overlap seems less satisfactory in both the real and imaginary components of the complex shear modulus, G′ and G″, respectively. The lack of adequate superposition becomes pronounced in the tan ϕ (G″/G′) plots. The tan ϕ plots provide a more discerning criteria for the superposition than the G′ or G″ spectra.

An analysis based on an earlier model for anelastic deformation shows that of the several changes that may occur in the dynamic mechanical behavior on heating of polystyrene, the predominant ones are both an increase in the size of the microshear domains and the correlations of movement of segments near entanglements. These decrease the contribution to the modulus on heating near Tg so that the time‐temperature superposition is vitiated.
Mobility of anionic spin probes in water‐containing nylon 6 film
Authors: Hamada Kunihiro , Iijima Toshiro , McGregor Ralph
Published: April 2003

The rotational mobility of anionic spin probes in water‐containing nylon 6 film was investigated by means of electron spin resonance (ESR) measurements for comparison with the results for nonionic spin probes reported previously. The extrema separation of the ESR spectra, 2Az′ increased with time owing to the evaporation of water. In the higher temperature region, 2Az′ increased steeply with time at first, and then more slowly, whereas for the nonionic spin probes, 2Az′ increased gradually and monotonically with time. This fact suggests that the anionic probe molecules are more strongly affected by water than the nonionic ones, i.e., the former probes are located in hydrophilic regions and the latter in hydrophobic regions. T50G, which can be empirically correlated with the glass transition temperature of the polymer Tg decreased with increasing water content. The decreasing tendency for the anionic spin probes was stronger than that for the nonionic ones. This fact also indicates that the local environment around the probe molecules varies from probe to probe. The rotational correlation time τR decreased markedly with an increase in water content. The Arrhenius plots of τR showed two crossover points. The crossover points in the higher temperature region Tn decreased greatly with increasing water content. The difference in Tn between dried and water‐containing films was larger than that for T50G. The activation energy for rotation, E, also decreased with increasing water content. It is suggested that water concentrates around the anionic spin probes and makes their rotation much easier.
Chord intercepts in the two‐dimensional cell model
Authors: Schulze G. E. W. , Willers R.
Published: April 2003

The two‐dimensional cell model is defined by the following conditions of its formation: athermal nuclei may be randomly (Poisson) distributed in a thin amorphous film. From these nuclei spherulites may start to grow instantaneously, circularly, and at the same rate. Where two spherulites touch growth stops, and all points of contact form a straight intersection between neighboring spherulites. Finally, if the film contains spherulites only, each spherulite (cell) is completely limited by straight intersections, forming an irregular polygon. All irregular polygons of the film together form a planar irregular net of straight intersections. In quantitative microscopy this net is characterized by a “lineal analysis.” A straight line (Rosiwal's line) is arbitrarily put into the plane of the net. The net divides Rosiwal's line into chord intercepts of different lengths. The distribution of these lengths is analytically derived in the present paper by use of the theory of probability.
Ionic species produced by mechanical fracture of solid polymer. III. Anions from polytetrafluoroethylene
Authors: Sakaguchi M. , Kinpara H. , Hori Y. , Shimada S. , Kashiwabara H.
Published: April 2003

The tetracyanoethylene anion radical (\documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document}) was detected by ESR spectroscopy in polytetrafluoroethylene (PTFE), which had been mechanically fractured in vacuo with tetracyanoethylene (TCNE) at 77 K. The assignment of \documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document} was carried out by ESR spectral simulation on the basis of an anisotropic effective hyperfine tensor that included a forbidden transition term. The \documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document} is formed by abstraction of an electron by TCNE from the anion that is produced by heterogeneous scission of the carbon‐carbon bond in the main chain of PTFE. At least 16% of the scission of the main chains of PTFE occurs by a heterogeneous process to produce the anions. Approximately 50% of the anions decay during annealing for 30 min at 220 K in the dark, and all anions decay within 15 min at 325 K.
Polymer–cosolvent systems. XI. Polystyrene dissolved in mixtures of diethyl ether and nitromethane
Authors: Cowie John M. G. , McEwen Iain J.
Published: April 2003

The ternary system nitromethane (1) +diethyl ether (2) +polystyrene (3) has been examined by determining the demixing behavior of the polymer in the temperature–solvent composition plane. Enhanced solvation of the polymer is evidenced by the ability of the mixture to dissolve very high molecular weight (107g/mol) polystyrene at intermediate solvent compositions compared with the behavior in the two solvents separately. The cosolvent action of the mixture is analyzed in terms of modern theories of polymer solution free volume.
Theoretical analysis of conformational energies, unperturbed dimensions, and dipole moments of poly(dichlorophosphazene)
Authors: Saiz Enrique
Published: April 2003

A theoretical analysis of the conformational energies of poly(dichlorophosphazene) (PDCP) is presented. The results indicate that the bond pair PNP possesses a considerable conformational freedom, whereas the bond pair NPN is relatively rigid. This difference explains the low glass transition temperatures Tg and large end‐to‐end distances measured for polyphosphazenes. A statistical model containing four rotational isomers (ie., trans, gauche, cis, and negative gauche) is developed and used to calculate unperturbed dimensions and dipole moments of PDCP. The results, obtained at 25°C with n = 400 skeletal bonds (200 repeating units), were Cn = 〈r2〉0/nl2 = 13.5; CT = 103d(ln〈r2〉0)/dT = −3.0 K−1; Dn = 〈μ2〉/nμ = 0.35; DT = 103d(ln〈μ2〉)/dT = −3.4 K−1. All the calculated magnitudes are extremely sensitive to the energy Eσ that controls the statistical weights of the conformations tg, tc, tg−, gt, ct, and g−t relative to tt for the bond pair PNP. A qualitative explanation for this sensitivity is discussed.
Double‐modulation and conventional ESR spectra of spin‐labeled crosslinked polystyrene
Authors: Andreis M. , Rakvin B. , Veksli Z.
Published: April 2003

The recently introduced method of detecting homogeneous linewidths from inhomogeneously broadened ESR spectra using the double‐modulation technique has been applied in parallel with the conventional method to study molecular motion in crosslinked polystyrene. The rotational correlation time in the slow‐motion region determined from the homogeneously broadened line varied from 1.68 × 10−5 to 8.0 × 10−6 s between 150 and 340 K. Double‐modulation spectra appear to be very sensitive to local motion at low solvent concentration. The influence of crosslink density and solvent concentration on both local and overall motion is analyzed.
Crystallization studies of poly(ε‐caprolactone).I. Morphology and kinetics
Authors: Phillips Paul J. , Rensch Gregory J. , Taylor Kevin D.
Published: April 2003

The crystallization behavior of three molecular weight samples of poly(ε‐caprolactone) has been studied as a function of temperature. Crystallization begins in the form of axialities and changes to spherulite growth as time progresses, presumably owing to the molecular weight distribution. Determinations of equilibrium melting point and analyses of growth kinetics are complicated by a major lamellar thickening process occurring at the crystallization temperature. Secondary nucleation analyses of spherulitic growth rates, carried out assuming a similar growth face to that of polyethylene, result in values of σσe. Use of the Thomas–Stavely relation to calculate a value of σ results in values of fold‐surface free energy, σe, similar to that of polyethylene.
Dynamic mechanical behavior of poly(vinyl‐methyl ether)‐poly(styrene) blends
Authors: Cavaille J. Y. , Perez J. , Jourdan C. , Johari G. P.
Published: April 2003

The dynamic mechanical behavior of 10 and 20% poly(vinyl methyl ether)‐polystyrene blends has been studied in the frequency range 10−5 Hz to 5 Hz and temperature range 100–450 K. Isochronal plots of modulus G′ and loss factor, tan ϕ, show the presence of one relaxation process at temperatures below the transition zone. A second relaxation process at intermediate temperatures but below Tg may be inferred from the breadth of the G″ frequency curves in the transition zone of both blends. This process, at 280 < T < 300 K, is independent of PVME concentration and seems to be associated with the local modes of motions of PS chains. The rheological behavior of the blends shows them to be compatible up to 20% PVME. Their G′ and G″ data cannot be shifted along a frequency axis to produce a satisfactory master curve. The departure from thermorheological simplicity is much more clearly observed in the tan ϕ than in the modulus‐frequency plots. This departure is due to the change in the segmental correlation effects, or length, with temperature near Tg. A molecular model of the growth of microshear domains with hierarchically constrained molecular motions, given elsewhere, quantitatively agrees with the dynamic mechanical behavior.
Dielectric relaxation and aging effect in interpenetrating network polymers of poly(urethane)‐poly(methyl methacrylate)
Authors: Mai C. , Johari G. P.
Published: April 2003

The permittivity and loss of poly(methyl methacrylate) (PMMA) network crosslinked with trimethylol‐1,1,1 propane and its interpenetrating network polymers with 10, 34, and 50% (by weight) poly(urethane) have been measured from 100 to 400 K over a frequency range of 12 to 1 × 105 Hz. Two relaxation processes, γ and β, are observed in the PMMA network, and a third process, αpu, in the 10% poly(urethane) IPN. At higher concentrations of poly(urethane), the γ process is removed from the temperature‐frequency range of our study. Crosslinking in pure PMMA slows the segmental motions involved in the β process and raises its activation energy. Physical aging of the 10 wt% poly(urethane)‐PMMA causes its γ process to become indiscernible and the αpu process to become better resolved. A discussion of these results in terms of local regions of segmental motion is provided.
Submillimeter infrared absorption and chain conformations of poly(vinylidene fluoride) and copolymers. I. Crystalline and amorphous contributions
Authors: Latour M. , Moreira R. L.
Published: April 2003

Far infrared spectra of poly(vinylidene fluoride) and several copolymers (with hexafluoropropylene, chlorotrifluoroethylene, and tetrafluoroethylene) have been obtained between 15 and 55 cm−1. After correction of the interference phenomenon affecting the measurements, the absorption coefficient and the imaginary part of the dielectric constant have been calculated. We show how these parameters are affected by the chain conformation and copolymer composition. The behavior of the crystalline and amorphous phases have been studied. The effects of mechanical and electrical stresses are considered.
Gas sorption and transport in substituted polycarbonates
Authors: Muruganandam N. , Koros W. J. , Paul D. R.
Published: April 2003

The effects of molecular structure manipulation of polycarbonates on sorption and transport of various gases were studied using tetramethyl, tetrachloro, and tetrabromo substitutions onto the aromatic rings of bisphenol A polycarbonate. Solubility and permeability measurements were made at 35°C over the pressure range of 1–20 atm for a variety of gases, namely CO2, CH4, O2, N2, and He. A threefold to fourfold increase in permeability was caused by the tetramethyl substitution, whereas the tetrachloro and tetrabromo substitutions reduced the permeability relative to the tetramethyl substitution. Lower activation energies for transport were found for the tetramethyl polycarbonate relative to the unsubstituted polycarbonate. Permeability coefficients were factored into solubility and diffusion coefficients. Sorption levels increased for all substitutions, but among the substituted polymers the levels remain practically the same. Solubility data were analyzed in terms of the dual sorption model. The Henry's law solubility coefficients obtained from this analysis were found to be consistent with a predictive equation developed for rubbery polymers. The usual correlation for predicting the Langmuir sorption capacity of the model overestimates the values for the substituted polycarbonates, and a proposal for the cause of this is offered. Thermal expansion of these polymers was measured using dilatometry, and the results are used in the interpretation of the sorption data. Diffusion phenomena are explained by segmental mobility and free volume considerations. The effects of CO2 exposure history on sorption and transport were also investigated.
Effects of chain length distribution on viscoelastic properties of entangled linear polymers: Blending laws for binary blends
Authors: Kim Hee Young , Chung In Jae
Published: April 2003

The reptation idea of de Gennes and the tube model theory of Doi and Edwards are extended to explain the terminal viscoelastic properties of binary blends in the highly entangled state of two linear monodisperse polymers with different molecular weights M1 and M2. A modified tube model is proposed that considers the significance of the constraint release by local tube renewal in accounting for the relaxation process of the higher molecular weight chain. Its relaxation by both reptation and the constraint release is remodeled as the disengagement by pure reptation of an equivalent primitive chain. From knowledge of the longest relaxation times of the blend components, the stress equation is formulated from which blending laws of viscoelastic properties for the binary blends are derived. To force better agreement between theory and experiment at the pure monodisperse limits of the blends, a crude treatment to include the effect of contour‐length fluctuation in the equivalent‐chain model is also discussed. Theoretical predictions of the zero‐shear viscosity and steady‐state shear compliance are shown to be in good agreement with literature data on undiluted polystyrenes and polybutadienes over a wide range of the blend composition and M2/M1 ratio. The asymptotic of the laws for blends with M2/M1 → 1 and 0 are comparable to those from the relaxation spectrum proposed by others earlier on the basis of the tube model.
Diffusion in concentrated polymer solutions: Encapsulated FENE dumbbell model results
Authors: Brunn P. O.
Published: April 2003

Structure‐property relations for the encapsulated FENE dumbbell correlate well with experimental observations for concentrated polymer solutions. Relying on rigorous kinetic theory results, we derive an expression for the polymeric mass flux relative to the mass‐average velocity (diffusive flux). The form of this flux implies non‐Fickian diffusion with its own intrinsic time scale. For steady flow in an infinitely long tube nonuniform concentration profiles are predicted.
Influence of dopant ion and synthesis variables on mechanical properties of polypyrrole films
Authors: Buckley L. J. , Roylance D. K. , Wnek G. E.
Published: April 2003

Oxidized, conductive poly(pyrrolylium anion) films [poly(pyrrolylium) = PP+ where there exists about one cation per three pyrrole rings] have been prepared electrochemically in an effort to study the effect of counteranion structure and preparation conditions on the composition, order (crystallinity), and mechanical properties of the films. The counteranion principally employed was p‐toluene‐sulfonate (OTs−), although benzenesulfonate (BZs−), p‐ethylbenzene‐sulfonate (EBs−), and p‐dodecylbenzenesulfonate (DBs−) were incorporated in several polypyrrole films. It was found that the amount of OTs− incorporated increased with increasing potential during synthesis, suggesting a parallel increase in the extent of oxidation of the polymer. Mechanical testing of the same films demonstrated that the ultimate tensile strength decreased as the electrode potential and current density during synthesis increased. X‐ray diffraction indicated that the degree of order (reflected by the widths of the diffraction lines), albeit quite small, is dependent upon the anion species and synthesis conditions. Interestingly, samples with the highest degree of order exhibit the highest electrical conductivities.
Interaction via diffusion of polymer crystals in growing spherulites
Authors: Keith H. D. , Padden F. J.
Published: April 2003

Previous calculations of how diffusion ranges should be averaged when polymer molecules of various lengths are segregated at crystal growth fronts have been extended. Crystals of acicular or lamellar habit are addressed directly, necessarily using more approximate methods, and earlier conclusions regarding appropriate averaging are reaffirmed. Results also lead to a better understanding of why crystalline texture in polyethylene spherulites appears to scale with the averaged diffusion range at crystallization temperatures within regime II but not at higher temperatures within regime I.
The thermotropic and lyotropic liquid‐crystalline properties of acetoacetoxypropyl cellulose
Authors: Pawlowski Walter P. , Gilbert Richard D. , Fornes Raymond E. , Purrington Suzanne T.
Published: April 2003

Acetoacetoxypropyl cellulose, formed by the acetoacetylation of hydroxypropyl cellulose using a diketene/acetone adduct at elevated temperature, forms both thermotropic and lyotropic liquid‐crystalline phases. DSC and hot‐stage polarized light microscopy confirmed the thermotropic nature of the bulk polymer. Thin layers showed green reflection colors at room temperature. The wavelength λ0of selective reflection was measured spectrophotometrically. The crystalline structure of the polymer was investigated using x‐ray diffraction. A lyotropic mesophase formed in acetic acid at ≥ 40 wt% polymer. The value of λ0for the lyotropic cholesteric mesophase was determined by optical rotatory dispersion (ORD) and circular dichroism (CD) of a thin layer of a wholly anisotropic solution.
Crystallization, thermal behavior, and compatibility in isotactic polystyrene/poly(o‐chlorostyrene‐co‐p‐chlorostyrene) blends
Authors: Silvestre C. , Cimmino S. , Karasz F. E. , MacKnight W. J.
Published: April 2003

The dependence of the kinetics of crystallization and melting behavior in isotactic polystyrene/poly‐o‐chlorostyrene‐co‐p‐chlorostyrene (iPS/Po‐CIS‐co‐p‐CIS) blends on temperature, thermal history, and blend composition has been investigated. The crystallization rate at a given temperature and copolymer composition decreases with increasing copolymer content in the blend when the samples are premelted. These effects can be ascribed to the reduction of mobility of the crystallizable chains due to the presence of the copolymer and to the decrease in the number of heterogenous iPS nuclei as a result of the premelting process. The Avrami exponent values and the analysis of the blend morphology indicate that the growth mechanism of the crystals is strongly influenced by thermal treatment. There is no measurable change in the melting temperature of iPS in the blends, with composition indicating that, on the basis of the Flory‐Huggins approximation of the thermodynamics of polymer mixing, the net interaction parameter at the melting temperature is close to zero. From the comparison of the phase diagram for the isotactic polystyrene‐containing blend with that of the atactic‐containing blend, it can be concluded that in the amorphous state polystyrene with a regular configuration is slightly less compatible with the P(o‐CIS‐co‐p‐CIS) than is polystyrene with random configuration.
Formation of ordered phases of (hydroxypropyl)cellulose in miscible and immiscible isobutyric acid‐water mixtures
Authors: Laivins G. V. , Sixou P.
Published: April 2003

(Hydroxypropyl)cellulose (HPC) is known to form birefringent liquid‐crystalline phases at elevated polymer concentrations in either water or isobutyric acid (IBA). The HPC concentration at which the polymeric phase exhibits birefringence decreases as the IBA content in mixed H2O/IBA solvents decreases, even though the concentration ϕic for the formation of an ordered phase of HPC in water is greater than that in IBA. Water is a spectator component and apparently does not participate in the formation of a birefringent phase when IBA is present. A birefringent phase forms once the concentration of HPC in the solution omitting the H2O equals the ϕic of binary HPC/IBA solutions for temperatures from 23 to 95°C. The strong preferential affinity of HPC for IBA is visually evident as an HPC coagulate separates from dilute solution when the solvent mixture contains as little as 5% IBA. The coagulate dissolves to give a monophasic isotropic solution as the IBA content in the solvent is increased. A heterogeneous system in which a clear supernatant fluid covers a pearly white polymeric phase forms when the solvent mixture is immiscible and the HPC content is less than 50%. At high HPC content, the classical appearance associated with concentrated HPC solutions is seen. The optical and rheological properties of the heterogeneous systems are compared with those of homogeneous solutions at several HPC concentrations.
Ion implantation doping and electrical properties of high‐temperature ladder polymers
Authors: Jenekhe Samson A. , Tibbetts Stanley J.
Published: April 2003

We report the first ion implantation doping studies on high‐temperature ladder polymers and show that insulting films of the benzimidazobenzophenanthroline‐type ladder polymer (BBL) can be doped by boron, argon, and krypton implantation to conductivities as high as 224 S/cm at a dose of 4.0 × 1016/cm2 while retaining the excellent mechanical properties of the pristine films. Effects of dose (ions/cm2) and beam current density (microamps/cm2) on electrical conductivity at fixed ion energies are reported. The temperature dependence of the conductivity indicates that the implanted ladder polymer films are semiconductors. Spatially selective implantation, creating regions of conducting lines in an insulating matrix, which suggests microelectronic device applications of the ladder polymers, is demonstrated.
Experimental analysis of the molecular theory of rubber elasticity
Authors: Sanjuan J. , Llorente M. A.
Published: April 2003

Stress‐strain and birefringence‐strain experiments, on polybutadiene and poly(methyl‐3,3,3, trifluoropropyl siloxane) elastomeric networks of various degrees of crosslinking have been carried out in order to evaluate the recent molecular theory of rubber elasticity of Erman and Flory, which is based on the idea of constraints imposed by entangled network chains on crosslink fluctuations. Previously published results on polyoxypylene and poly(dimethylsiloxane) networks have also been analyzed. In general, the theory describes the elastic behavior of all these systems satisfactorily. Stress‐strain and birefringence data can be interpreted using the same set of parameters. The most important theoretical parameter κ, which is a measure of the severity of constraints, varies with the elastic modulus as predicted by theory. However, the relationship is not a universal one, as was originally suggested.
The effects of solvent type on the concentration dependence of the compression modulus of thermoreversible isotactic polystyrene gels
Authors: McKenna G. B. , Guenet J.‐M.
Published: April 2003

Solutions of isotactic polystyrene in either trans‐decalin or 1‐chlorodecane were transformed into gels by quenching from a high temperature (ca. 180°C) to −20°C. The relaxation modulus in compression of these gels was measured over a range of concentrations of from 0.04 g/g to 0.40 g/g. At 22°C, the gels show a double logarithmic stress relaxation rate, m, which is higher than for PVC and gelatin gel systems. 120 s isochronal modulus concentration diagrams exhibit non‐power law behavior, i.e., not only is the general trend such that the double logarithmic slope decreases with increasing concentration, but there are also regions in which abrupt changes in modulus occur over narrow ranges in concentrations. These features in the concentration dependence of the modulus are less pronounced than those found previously1 in isotactic polystyrene/cis‐decalin gels. The behavior is interpreted to be inconsistent with a fringed micelle picture of the gel structure. Preliminary results are reported indicating that polymer fraction and temperature of gel formation can significantly affect the modulus of the gels.
Synthesis and properties of polycyanoethylmethylsiloxane polyurea urethane elastomers: A study of segmental compatibility
Authors: Li C. , Yu X. , Speckhard T. A. , Cooper S. L.
Published: April 2003

A series of polyurea urethane block polymers based on either aminopropyl‐terminated polycyanoethylmethylsiloxane (PCEMS) soft segments or soft segment blends of PCEMS and polytetramethylene oxide (PTMO) were synthesized. The hard segments consisted of 4,4′‐methylenediphenylene diisocyanate (MDI) chain‐extended with 1,4‐butanediol. The hard segment content varied from 11 to 36%, whereas the PTMO weight fraction in the soft segment blends varied from 0.1 to 0.9. The cyanoethyl side group concentration was also varied during the synthesis of the PCEMS oligomer. The morphology and properties of these polymers were studied by differential scanning calorimetry, infrared spectroscopy, dynamic mechanical and tensile testing, and small‐angle x‐ray scattering. These materials exhibited microphase separation of the hard and soft segments; however, attaching polar cyanoethyl side groups along the apolar siloxane chains promoted phase mixing in comparison with polydimethylsiloxane‐based polyurethanes. The increased phase mixing is postulated to lead to improved interfacial adhesion and thus can account for the observed improvement in ultimate tensile properties compared with polydimethylsiloxane‐based polyurethanes. Both hard segment content and cyanoethyl concentration are important factors governing the morphological and tensile properties of these polymers.
Morphology of a liquid‐crystalline polyester film
Authors: Bhattacharya S. K. , Misra A. , Stein R. S.
Published: April 2003

Morphological studies are reported for a thermotropic liquid crystalline polyester. Small angle light scattering studies were carried out as a function of temperature using Hv and Vv polarization with photographic as well as photometric techniques. No scattering was observed from a thin film cast from a dilute solution of the polymer in a highly volatile solvent. When the film was heated, scattering of light was observed above the glass transition temperature of the polyester. The scattering was found to be azimuthally dependent with Vv intensities being much higher than the corresponding Hv intensities. The size of the morphological features responsible for SALS patterns were calculated and were found not to change significantly with temperature ranging from glass transition temperature to the solid‐nematic transition temperature of the polyester. The WAXS pattern of solution cast polymer was representative of an amorphous structure. Solution cast films heat treated under various conditions (all above the Tg of the polymer) contained crystalline as well as amorphous structures. The maximum apparent crystallinity for annealed samples was of the order of 30%.
Rotating frame proton spin‐lattice relaxation measurements of poly (ethylene oxides)
Authors: Wobst M.
Published: April 2003

Measurements of Tlρ as a function of temperature have been made on two polyethylene oxides (PEO) with molecular masses of 5,000 and 30,000. The T1ρ measurements show biexponential behavior of the relaxation function in the temperature range from 170 K to 350 K. The intensities of the components of the relaxation function are constant over this temperature range in agreement with the crystallinities of the samples. The two relaxation times can be associated with the crystalline and amorphous component; the relaxation time minima describe the α relaxation in the crystalline regions of PEO and the glass transition in amorphous PEO.
Effects of thermal treatment on biaxially oriented poly(ethylene terephthalate). II. The anisotropic glass temperature
Authors: Vallat M.‐F. , Plazek D. J.
Published: April 2003

Thermal properties of an anisotropic biaxially oriented Poly(ethylene terephthalate) (PET) were determined before and after further deformation of the Mylar film. Film shrinkage in different planar directions was monitored during and following initial heating. After stabilization for three days at 140°C, glass temperatures Tg were determined from the decrease in length of film strips and were found to vary in the different in‐plane directions. An increase in anisotropy brought about by additional deformation in the direction of the greatest orientation enhanced the Tg difference from 8 to 16°C. Tg is highest in the direction of greatest orientation.
Compatibility and mesophase separation in blends of α‐helical polyglutamates
Authors: Sasaki S. , Nagao M. , Gotoh M. , Uematsu I.
Published: April 2003

Blends composed of the α‐helical polymers, poly‐L‐glutamates [(NHCαHRC′O)n, R = CH2CH2COO(CH2)m(C6H5] (Lm) and the corresponding D enantiomers (Dm), have been studied by x‐ray diffraction and viscoelastic measurements. Binary blends of L2, D2, L3, and D3 are compatible and form isomorphous mixed crystals at all compositions, whereas other pairs, with the exception of L1/D1, are incompatible. The demixing process is described for a ternary system consisting of L1, D3, and a diluent chloroform at 40°C. The phase diagram comprises four regions, I, IA, A, and AA, with increasing polymer concentration; I: isotropic, A: anisotropic, IA: I–A biphasic, and AA: A–A biphasic. The IA biphasic gap is greater in the ternary system than in the binary ones. The high‐molecular‐weight component (D3) is partitioned into the A phase in the IA region. The AA separation originates from incompatibility of the polymers. The phase behavior is discussed on the basis of the Abe‐Flory theory by incorporating the polymer‐polymer interaction parameter.
Transport of carbon dioxide and methane in glassy aromatic polyesters
Authors: Sheu F. R. , Chern R. T. , Stannett V. T. , Hopfenberg H. B.
Published: April 2003

Solubilities and diffusivities of CO2 and CH4 in two aromatic polyesters [Ardel® poly(bisphenol A phthalate) (PAr) and poly(phenolphthalein phthalate) (PPha)] and one polycarbonate [Lexan® (PC)], generated from independent sorption and permeation measurements at 35°C and up to 25 atm, are compared. The permeability ratio for CO2 over CH4, at 20 atm and 35°C, ranges from 24 for PC, to 21 for PAr, and 27 for PPha. However, the permeability of PPha and PAr are 40 and 120% higher, respectively, than that of PC. Less than 21% change in the gas diffusivity was observed; therefore, a major portion of the observed higher permeability of PPha and PAr is attributed to an increase in the gas solubility. These data are interpreted qualitatively in terms of changes in the calculated packing density, chain torsional mobility of the polymer, and gas‐polymer attraction.
Analyzing polymer crazing as quasifracture
Authors: Sun B. N. , Hsiao C. C.
Published: April 2003

This paper deals with a viscoelastic boundary element method for analyzing a polymer quasifracture usually called a craze in polymers. A time‐dependent boundary stiffness is considered on the quasifracture envelope surface. The viscoelastic property of the glassy polymer is represented by a generalized Kelvin model with multiple retardation times. According to the linear viscoelastic correspondence principle, the associated elasticity solution can be solved by applying the general integral boundary element method. Then the viscoelastic solution in the time domain can be obtained by applying a collocation Laplace inversion transformation. Using these methods, the quasifracture problem composed of an isolated craze opening with time‐dependent stiffness traction in a stressed rectangular plate is analyzed. The displacement profile and the stress distribution around the craze envelope surface are computed.
Heat of fusion of poly(4‐methylpentene‐1)
Authors: Charlet Gérard , Delmas Geneviève
Published: April 2003

The heat of fusion of perfectly crystalline poly(4‐methylpentene‐1) (P4MP1), ΔHu, has been determined by two methods. Melting point depressions (A) in concentrated solutions in naphthalene and cyclododecane, and in infinitely dilute solutions in 39 solvents, led to ΔHu = 5.5 ± 0.3 kJ mol−1 (65 ± 4 J g−1). The second method (B) involved new measurements of the crystalline volume Vu,c as a function of temperature, in order to calculate ΔHu from the Clausius‐Clapeyron equation: extrapolation to the melting point gave Vu,c = 109.2 cm3 mol−1 (1.298 cm3 g−1) (I), which is in good agreement with the result of Tanigami et al.1 (II) but appreciably lower than the value reported by Zoller et al.2 (III). Possible reasons for the discrepancy are discussed. The values of ΔHu from methods A and BIII are in excellent agreement, whereas BI and BII give a higher figure. There is at present no reason to prefer one set of values to the other, although the degree of crystallinity estimated from the low ΔHu and the experimental heat of fusion is in the 75–85% range, in excellent agreement with x‐ray diffraction data. Depending on the selected ΔHu, the entropy of fusion is either similar or lower than for other branched polyolefins. The results are discussed in terms of order in the melt, order seemingly relevant to the understanding of the mechanism of formation of the noncrystalline thermoreversible gels of P4MP1.
Infrared reflection‐absorption spectroscopy of polyacrylonitrile on copper and aluminium surfaces
Authors: Wu C. R. , Liedberg B.
Published: April 2003

Infrared reflection‐absorption spectroscopy has been used to study the chemical structure of thin films of pyrolyzed polyacrylonitrile (PAN) on copper and aluminium surfaces. The formation of a conjugated CCC backbone occurs at temperatures as low as 200°C for PAN on copper, whereas the same reaction on aluminium requires pyrolysis at 300°C in order to be completed. These temperatures are, respectively, about 200 and 100°C lower than those previously reported for bulk PAN. Pyrolysis of PAN on copper at 200°C also results in diffusion of copper atoms (ions) into the polymer network followed by Cu(I)N°C complexing. Conclusive evidence is obtained for end‐on coordination through nitrogen lone pair orbitals of the CN groups. We propose a chemical structure of PAN on copper that is different to that in the bulk and on aluminium.
Dispersion polymerization of styrene in ethanol: Monomer partitioning behavior and locus of polymerization
Authors: Lu Y. Y. , El‐Aasser M. S. , Vanderhoff J. W.
Published: April 2003

A thermodynamic model has been proposed for the simulation of monomer partitioning behavior in the dispersion polymerization of styrene in ethanol. The monomer concentration in the polymer particles is very low (20 vol% at 5% conversion) and decreases further as the polymerization proceeds. It is independent of stabilizer concentration but is strongly dependent on initial monomer concentration. The partitio
n coefficient ([Mp]/[Mc]) of styrene increases from 0.8 to 1.1 with incresing conversion. There are two polymerization loci in dispersion polymerization, namely the continuous and polymer phases. Competition between solution and heterogeneous polymerization has been observed in this system. The rate of dispersion polymerization is dependent on initial monomer concentration but is independent of initiator concentration at higher conversions. The molecular weight of the polymers produced by this process increases with increasing conversion and decreases with increasing initiator concentration.
Ionic products in ground polymer. IV. Anions in poly(vinylidene fluoride)
Authors: Sakaguchi Masato , Kinpara Hiromu , Hori Yasuro , Shimada Shigetaka , Kashiwabara Hisatsugu
Published: April 2003

When poly(vinylidene fluoride) (PVDF) was ground with tetracyanoethylene (TCNE) powder in a vibration glass ball mill in vacuum in the dark at 77 K, the TCNE anion radical (TCNE‐) was detected in the mixture by ESR spectroscopy. The TCNE.‐ is formed by the abstraction of electrons by TCNE from the anion that is produced by a heterogeneous bond scission of carbon‐carbon bonds in the polymer main chain. The assignment of TCNE.‐ was carried out by the ESR spectral simulation on the basis of an anisotropic effective hyperfine tensor that includes a forbidden transition term. At least 85% of the bond scission of the PVDF main chain is induced by a heterogeneous process to produce ionic products. The yield of these mechanions seems to increase with the polarity of carbon‐carbon bond owing to a substituent group bonded to the carbon in the polymer main chain.
Miniemulsion copolymerization of vinyl acetate and butyl acrylate. II. Mathematical model for the monomer transport
Authors: Delgado Joaquin , El‐Aasser Mohamed S. , Silebi Cesar A. , Vanderhoff John W. , Guillot Jean
Published: April 2003

A mathematical model is presented to describe the monomer transport between monomer droplets, aqueous phase, and polymer particles during the course of an emulsion polymerization. The model was used to investigate the role of the cosurfactant (hexadecane) in the miniemulsion copolymerization of 50:50 molar ratio vinyl acetate‐butyl acrylate monomer mixture, as well as the effect of the different components and process variables on the rate of copolymerization, monomer distribution between phases, and composition of the copolymer.
A technique for measuring the crosslink densities in both phases of a vulcanizate blend
Authors: Honiball D. , Mcgill W. J.
Published: April 2003

The magnitude of the depression of the freezing point of a solvent in a swollen vulcanizate is dependent on the crosslink density. It is shown that use of such measurements, coupled with the conventional swelling technique, allows the crosslink density in both phases of a vulcanized blend to be determined.
Mechanical anisotropy in rolled nylon 66
Authors: Choy C. L. , Leung W. P. , Ong E. L. , Wang Yimin
Published: April 2003

The nine independent stiffness constants Cpq for rolled nylon 66 at thickness reduction ratios λt = 2.4, 4.9, 7.6 have been measured from −40 to 50°C by an ultrasonic method at 10 MHz. Analysis of x‐ray pole figures indicates that at high λt the material has a uniplanar‐axial texture, with hydrogen‐bonded (010) planes parallel to the roll plane and the molecular chains along the roll direction. The mechanical behavior is determined not only by the alignment of molecular chains and hydrogen bonds but also by the microfibrillar morphology. On the basis of this idea the magnitudes of the tensile moduli along the three principal axes can be understood in terms of the Takayanagi model. The effects of water absorption have also been investigated.