bluuebunny/crossref_metadata_2025 huggingface dataset:
The dependence of slow crack growth in a linear polyethylene on test temperature and morphology
Authors: Lu Xici , Mcghie Andrew , Brown Norman
Published: April 2003

The slow crack growth behavior of a linear polyethylene with different morphologies was studied by using three point bending with a single edge notched specimen at testing tem‐peratures from 30 to 80°C. The morphology was varied by annealing the quenched material at temperatures from 86°C to 135°C. It was found that at test temperatures of 60°C or less, the changes in failure time with annealing temperature are very similar to the change in density with a maximum at 130°C. At testing temperatures above 60°C, the relationship of between failure time and annealing temperature is altered when the test is in the range of the α transition temperature. These results indicate that with respect to slow crack growth in the case of a homopolymer the strength of the crystals is relatively more important than the number of tie molecules. © 1993 John Wiley & Sons, Inc.
Miscible blends of modified poly(aryl ether ketones) with aromatic polyimides
Authors: Karcha Robert J. , Porter Roger S.
Published: April 2003

The phase behavior of binary blends of poly(ether ether ketone) (PEEK), sulfonated PEEK, and sulfamidated PEEK with aromatic polyimides is reported. PEEK was determined to be immiscible with a poly(amide imide) (TORLON 4000T). Blends of sulfonated and sulfamidated PEEK with this poly(amide imide), however, are reported here to be miscible in all proportions. Blends of sulfonated PEEK and a poly(ether imide) (ULTEM 1000) are also reported to be miscible. Spectroscopic investigations of the intermolecular interactions suggest that formation of electron donoracceptor complexes between the sulfonated/sulfamidated phenylene rings of the PEEKs and the n‐phenylene units of the polyimides are responsible for this miscibility. © 1993 John Wiley & Sons, Inc.
On the measurement of structural relaxation in polymers using positron annihilation lifetime spectroscopy
Authors: Li Xue Song , Boyce Mary C.
Published: April 2003

Positron annihilation lifetime spectroscopy has been identified as an effective means of characterizing the free volume content of amorphous polymers. The lifetime and intensity of the ortho‐positronium (o‐Ps) pick‐off annihilation has been found to correlate with the average size and density of free volume sites, respectively. Recently, PALS has been used to evaluate and monitor the physical aging and structural relaxation of polymers in terms of both initial state and evolution in state with time. However, during extended PALS measurements in insulating materials, an electric field can build up due to positron‐electron annihilation and can effectively reduce the probability of positronium formation. In this paper, an observed decrease in intensity associated with the o‐Ps annihilation component in the glassy polymers polycarbonate and polystyrene is found to be unrelated to structural relaxation of the materials over the time periods examined as reported earlier by others, and, instead, to be more likely a result of electric charge build‐up. © 1993 John Wiley & Sons, Inc.
Gas transport through homogeneous and asymmetric polyethersulfone membranes
Authors: Kumazawa H. , Wang J.‐S. , Sada E.
Published: April 2003

Both homogeneous and asymmetric polyethersulfone (PES) membranes were prepared by solvent casting. The sorption and permeation behavior of CO2, O2, and N2 using these two kinds of cast PES membranes and commercially available homogeneous PES film was investigated to extract the pressure dependence of gas permeability and the permselectivity for CO2 relative to N2, and to confirm the validity of the working assumption that a skin layer in an asymmetric membrane can be essentially replaced by a thick homogeneous dense membrane. The pressure dependence of the mean permeability coefficient to CO2 in homogeneous membranes obeys the dual‐mode mobility model. The ideal separation factor for CO2 relative to N2 at an upstream pressure of 0.5 MPa attains ca. 40, while the permeability to CO2 is about 2.7 Barrer at the same upstream pressure. The same separation factor in asymmetric membranes amounts to 35. The diffusion behavior for the skin layer in an asymmetric membrane with a thin skin layer can be simulated approximately by that in a homogeneous dense membrane. © 1993 John Wiley & Sons, Inc.
Melt spinning and mechanical properties of semirigid liquid‐crystal copolyesters
Authors: La Mantia F. P. , Valenza A. , Città V. , Pedretti U. , Roggero A.
Published: April 2003

Melt‐spinning and mechanical properties of fibers of a new class of semirigid thermotropic liquid‐crystal polymers are presented. These copolyesters are synthesized from 4‐4′‐dihydroxybiphenyl (B), 4‐hydroxybenzoic acid (H), and flexible units provided by aliphatic diacids. The flexible units depress the melting temperature without strongly depressing the mechanical properties. These liquid‐crystal polymers can be easily spun at high draw ratios. Indeed, unlike rigid liquid‐crystal polymers, relatively high draw ratios are needed to attain high mechanical strength. Tensile moduli of about 28 GPa and tensile strengths of about 350 MPa are obtained. © 1993 John Wiley & Sons, Inc.
Influence of the sulfonate countercation on the thermal stability of nafion perfluorosulfonate membranes
Authors: Feldheim Daniel L. , Lawson Del R. , Martin Charles R.
Published: April 2003

We report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation‐exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate‐coun‐terion interaction. © 1993 John Wiley & Sons, Inc.
Positron annihilation spectroscopy study of moisture absorption in protective epoxy coatings
Authors: Macqueen Richard C. , Granata Richard D.
Published: April 2003

Position annihilation spectroscopy (PAS) was used to measure the relative free‐volume fraction of protective epoxy coatings before and after exposure to liquid water at room temperature. The relative free volume fraction determined before water exposure was compared to the equilibrium water uptake of each coating and a correlation was found. The relative free‐volume fraction of the epoxy coatings decreased slightly after water exposure. This decrease is contrary to the free volume theory of plasticization, but is consistent with the antiplasticization process. Larger decreases in the relative free volume fraction were sought by repeating the water uptake experiments with nitrobenzene which in the bulk, liquid form quenches ortho‐positronium (o‐Ps). Since the o‐Ps lifetime remained approximately constant and the o‐Ps intensity decreased after nitrobenzene absorption, nitrcbenzene is believed to be inhibiting the formation of o‐Ps in the epoxy free volume cavities. Larger decreases in the relative free volume fractions were found after nitrobenzene exposure than after water exposure. These larger decreases are due to the fact that nitrobenzene is a better inhibitor of o‐Ps formation than water in the epoxy free volume cavities. Larger volume fractions of nitrobenzene were absorbed by the coatings than water and were interpreted to be due to interactions between nitrobenzene and the epoxies. © 1993 John Wiley & Sons, Inc.
Gas transport properties of poly(arylether bissulfone)s and poly(arylether bisketone)s
Authors: Aitken C. L. , Paul D. R. , Mohanty D. K.
Published: April 2003

The transport properties of the poly(arylether bissulfone) based on bisphenol A (PBSF) and the poly(arylether bisketone) s based on bisphenol A (PBK) and bisphenol S (PBK‐S) are reported at 35°C. Comparisons are made with the polysulfone and the polycarbonate also based on bisphenol A to determine the effect of the long, rigid bisketone and bissulfone groups on polymer properties. A direct comparison also is made between PBK and PBSF, which differ only by their ketone and sulfone groups. The bulkier sulfone group increases free volume and Tg more than the ketone group. This results in higher solubility and diffusivity coefficients for the bissulfone versus the bisketone polymer, both of which contribute to higher permeability coefficients. © 1993 John Wiley & Sons, Inc.
Molecular mobility in rubbery composites: Effect of filler particle size
Authors: Mahoney D. , Von Meerwall E.
Published: April 2003

We have measured proton NMR T2 relaxation spectra in Arco R45M OH‐terminated poly‐butadienes (PBs) cured with isophorone diisocyanate and filled with 65 wt % SiO2 particles of each of six different average sizes. Identifying the short T2 component with the gel, we find that the gel fraction is displaced from nominal NCO/OH stoichiometry, probably as a result of water adsorbed on filler particle surfaces. Near effective stoichiometry and in the presence of filler, molecular and segmental mobilities decrease, most strongly in specimens with the smallest filler particles. Comparison with parallel Monte Carlo simulations of the PB matrix geometry indicates that segmental mobility and sol migration decrease uniformly in a wide vicinity of the filler particles. Thus the rigidification of the matrix measured via NMR has a range of approximately 1‐3 μm from nearby filler particle surfaces, representing the rms diffusion distance of the light components of the sol during the T2 relaxation. © 1993 John Wiley & Sons, Inc.
Birefringence in polycarbonate: Molecular orientation induced by cooling stresses. I. Free quenching
Authors: Wimberger‐Friedl R. , De Bruin J. G.
Published: April 2003

The residual birefringence distributions in polycarbonate disks quenched in a liquid bath under various conditions are determined. Unbalanced distributions of approximately parabolic shape are obtained in the cross‐sections in general. A systematic influence of the initial quench temperature on the imblance of the birefringence distributions is observed, with higher initial temperatures leading to a strong shift of birefringence in the positive direction. The systematic variation of the birefringence distribution with quenching conditions is interpreted in terms of a stress and an orientation contribution. The distributions are predicted correctly by a numerical program making use of the linear stress‐optical rule with a different stress‐optical coefficient above and below the glass‐transition temperature. The contribution of molecular orientation is distinguished experimentally from the stress contribution by annealing experiments. © 1993 John Wiley & Sons, Inc.
Polyamide–polyester blends: An estimation of the amide–ester interaction
Authors: Ellis Thomas S.
Published: April 2003

Random copolyester‐amides derived from the cyclic monomers caprolactam, caprolactone, and laurolactam have been synthesized and characterized. Binary blend combinations based upon the latter and regular aliphatic polyamides and copolyamides have been investigated experimentally and the compositio/miscibility correlations determined. By treating the polymers involved as random copolymers on a microstructural scale, composed of methylene, amide, and ester groups, it has been possible to accommodate the experimental observations within the framework of a binary interaction model. A principal feature is that homogeneous mixtures can be obtained only when the chemical constitutions of the blend components do not differ from one another too greatly. Establishing the model on a scale dictated by an independent estimation of the methylene‐ester interaction, obtained by Paul, Barlow, and co‐workers, was found to give moderate agreement. However, a more precise description of the data could be obtained if the model was scaled from internal observations. Calculations indicate that all the segmental interactions are unfavorable for mixing. Although this some‐times can produce miscibility, it has been proposed that miscibility in blends composed of aliphatic polyesters, polyamides and their copolymers is driven entirely by the entropic contribution to the free energy of mixing. © 1993 Johnxs Wiley & Sons, Inc.
Solid‐state 13C nuclear magnetic resonance characterization of MDI‐based polyurethanes
Authors: Okamoto David T. , O'connell Ellen M. , Cooper Stuart L. , Root Thatcher W.
Published: April 2003

13C solid‐state nuclear magnetic resonance (NMR) experiments on linear polyurethanes and poly(ether‐urethane) block copolymers demonstrate that 13C spin‐lattice relaxation experiments in the laboratory [T1(C)] and rotating [T1p(C)] frames provide the most information about domain morphology in these microphase‐separated polymer systems. T1(H) TCH, and T1p(H) data are less useful in a 4,4′‐methylene bis(p‐phenyl isocyanate)‐1,4‐butanediol (MDI/BD) hard‐segment material, the MDI bridging methylene and the MDI urethane carbonyl T1(C and T1p(C) times fall in characteristic ranges for crystalline, amorphous, interfacial, and dissolved species. BD methylene carbons have short T1p(C) for crystalline and long T1p(C) for amorphous hard‐segment aggregates. The distinct T1p(C) and T1(C) fractins observed are attributed to the presence of several crystalline polymorphs. Both T1(C) results and DSC endotherms indicate that the crystalline polymorphs present in the poly(ether‐urethane) are less ordered than the types seen in the pure hard‐segment material. © 1993 John Wiley & Sons, Inc.
Isomer effects on transport properties of polyesters based on bisphenol‐A
Authors: Pessan L. A. , Koros W. J.
Published: April 2003

Pure gas sorption and transport properties of polyesters based on bisphenol‐A and both pure isophthalic and pure terephthalic acid chloride were obtained for He, N2, O2, CH4, and CO2 at 35°C. The polymers were synthesized in our laboratory and amorphous films were prepared with a specialized solvent casting procedure. The polymer containing m‐phenylene groups shows higher permselectivity for most of the gas pairs. The ideal selectivity of O2/N2 was increased by 33% when p‐phenylene units were replaced by m‐phenylene ones. On the other hand, the polyester containing only p‐phenylene groups, shows higher permeability to all the gases studied. The polymer based on pure terephthalic acid chloride has a 75% higher oxygen permeability and a 1.1‐fold higher carbon dioxide permeability than the isophthalic acid derivative. The polyester containing meta‐phenylene units has lower Tg, higher permselectivity, lower permeability, lower fractional free volume (FFV), and lower d‐spacing. The values of FFV, and lower d‐spacing. The values of FFV and d‐spacing were only slightly different between the two isomers. Moreover, for the sub‐Tgγ transition the maximum in tan δ occured at essentially the same temperature (−55°C). The polymer with a higher concentration of p‐phenylene units shows somewhat larger area under the γ‐peak, indicating slightly more sub‐Tg motion. The Distribution of FFV is considered to be the determining factor for the differences in transport properties observed. © 1993 John Wiley & Sons, Inc.
Crystallization of isotactic polypropylene and high‐density polyethylene under negative pressure resulting from uncompensated volume change
Authors: Piorkowska E. , Galeski A.
Published: April 2003

The melting behavior of spherulites in thin sections of isotactic polypropylene bulk samples and high‐density polyethylene thin films crystallized isothermally at various temperatures has been studied by polarized light microscopy. The regions around cavities and multiple boundary points between spherulites have higher melting temperatures than the other parts of spherulites crystallized in Regime III. The increase in melting temperature is explained as a result of crystallization under negative pressure arising locally in pockets of occluded melt due to density change during spherulitic crystallization. The negative pressure lowers locally the equilibrium melting temperature and therefore decreases the undercooling, which results in an increase in lamellar thickness. Sectioning of bulk samples releases frozen negative pressure and reveals the increase in melting temperature of those parts of spherulites that were crystallized at lower undercooling. © 1993 John Wiley & Sons, Inc.
Transverse heterogeneity in PET fibers
Authors: Tomlin D. W. , Roland C. M. , Slutsker L. I.
Published: April 2003

X‐ray scattering from a series of poly(ethylene terephthalate) (PET) fibers spun at differet speeds is analyzed to probe the morphology in the direction transverse to the fiber axis. Both the apparent crystal modulus, determined from the change in wide‐angle X‐ray scattering angle with fiber stretching, and the transverse degree of crystallinity indicate there is a substantial interfiberillar amorphous content. In the PET fiber spun at conventional speeds, only roughly one‐quarter of the fiber cross‐section is actually occupied by fibrils. The transverse crystallinity increases for fibers spun at speeds sufficient to cause crystallization in the spin line. The X‐ray moduli and fibril diameters are correspondingly larger in these high speed spun fibers. © 1993 John Wiley & Sons, Inc.
The amorphous phase in high‐speed spun PET fibers
Authors: Peng K. L. , Roland C. M.
Published: April 2003

Two phenomenogical descriptions of oriented semicrystalline polymers, the series‐parallel model and the series‐aggregate model, were applied to poly(ethylene terephthalate) (PET) fibers obtained at different spinning speeds. The mechanical behavior of the fibers conformed well to both models. The analyses indicate that PET fibers obtained by high‐speed spinning possess a more compliant interfibrillar amorphous phase. This feature may account for both the greater dimensional stability, as well as the more reversible mechanical behavior, exhibited by high‐speed spun PET. © 1993 John Wiley & Sons, Inc.
Molecular weight distribution in free radical polymerization with long‐chain branching
Authors: Tobita Hidetaka
Published: April 2003

A new theory to predict the molecular weight distribution in free radical polymerization that includes chain transfer to polymer is proposed. This theory is based on the branching density distribution of the primary polymer molecules. The branching density distribution provides the information on how each chain is connected to other chains, and therefore, a full molecular weight distribution can be calculated by application of the Monte Carlo simulation. The present theory accounts for the history of the generated branched structure and can be applied to various reaction systems that involve branching and crosslinking regardless of the reactor types used. The present simulation confirmed the validity of the method of moments in a batch polymerization proposed earlier. It was shown clearly why gelation never occurs by chain transfer to polymer without the assistance of other interlinking reaction such as bimolecular termination by combination. © 1993 John Wiley & Sons, Inc.
Self‐nucleation and recrystallization of isotactic polypropylene (α phase) investigated by differential scanning calorimetry
Authors: Fillon B. , Wittmann J. C. , Lotz B. , Thierry A.
Published: April 2003

The crystallization behavior after partial or complete melting of the α phase of iPP is examined by combined differential scanning calorimetry (DSC) and optical microscopy: calorimetric results are directly correlated with corresponding morphologies of microtome sections of DSC samples. On partial melting at various temperatures (hereafter referred to as Ts) located in a narrow range (4°C) below and near Tm, the number of nuclei increases (as in classical self‐nucleation experiments), by several orders of magnitude; on subsequent cooling, the crystallization peak is shifted by up to 25°C. After partial melting in the lower part of the Ts range and recrystallization, the polymers display a prominent morphology “memory effect” whereby a phantom pattern of the initial spherulite morphology is maintained.

After partial melting in the upper part of the Ts range the initial morphology is erased and self‐nucleation affects only the total number of nuclei. The present experimental procedures make it possible to define, under “standard” conditions, the crystallization range of the polymer and in particular, the maximum crystallization temperature achievable when “ideally” nucleated. © John Wiley & Sons, Inc.
Miscibility of blends of poly(2,6‐dimethyl 1,4‐phenylene oxide) with polystyrene‐based ionomers and copolymers
Authors: Bazuin C. G. , Rancourt L. , Villeneuve S. , Soldera A.
Published: April 2003

Blends of poly(2,6‐dimethyl 1,4‐phenylene oxide) (PPhO) with the copolymer poly(styrene‐co‐methacrylic acid) (PS‐MAA) and the ionomer poly(styrene‐co‐sodium methacrylate) (PS‐MAA‐Na), up to 10 mol% co‐unit content, were investigated by dynamic mechanical thermal measurements. The PPhO/PS‐MAA‐Na blends are compared with PS/PS‐MAA‐Na blends. The blends of PPhO with PS‐MAA are no longer miscible at 10 mol% acid content; this is attributed to a copolymer effect induced by the reduction of PS‐PPhO interactions due to the presence of the MAA group which does not interact favorably with PPhO. The blends of PPhO with the ionomer are already immiscible at the lowest ion content studied (2.4 mol%), but become increasingly so as ion content is increased. Despite favorable PS‐PPhO interactions, these blends are only a little more miscible than the PS/PS‐MAA‐Na blends. This is attributed to a combination of the increasing importance of the ionomer cluster phase (from which the homopolymer chains presumably are excluded) as ion content is increased, and of a copolymer effect between the homopolymers and the unclustered phase of the ionomer. These results are compared with published data indicating that blends of PPhO with another biphasic ionomer, zinc sulfonated polystyrene, are miscible. The contrasting behavior is rationalized in part by the suggestion that the copolymer effect between PPhO and the unclustered phase of the latter ionomer, but not of the former, is absent; this is related to multiplet structure and sizes. The analysis made of the above systems is extended to predict what might be the miscibility behavior between PPhO and other PS‐based ionomer and related copolymer systems. © 1993 John Wiley & Sons, Inc.
The influence of physical aging on the creep rupture behavior of polystyrene
Authors: Arnold J. C.
Published: April 2003

The effects of postannealing aging time on the brittle fracture behavior of polystyrene were studied. A combination of mechanical properties, including creep and creep rupture under constant load and the behavior under constant extension rate deformation were examined for polystyrene samples of different prior aging times (from 1h to 2 months). The specimens and fracture surfaces were examined by optical microscopy and SEM to observe any change in the fracture behavior. It was found that longer aging times caused not only a change in the time‐dependent modulus of the material but also a significant decrease in the creep rupture life and a decrease in strain to failure. It was found that the reasons for this are that although aging delays craze formation, craze breakdown and ultimate failure are accelerated by aging. The importance of these findings are discussed, particularly in relation to failure criteria involving the use of critical strains. © 1993 John Wiley & Sons, Inc.
NMR and x‐ray studies on the morphology of thermoreversible polyacrylonitrile gels
Authors: Herbert Ian R. , Tipping Alison , Bashir Zahir
Published: April 2003

The morphology of thermoreversible polyacrylonitrile–propylene carbonate (PAN‐PC) gels was examined using solid‐state carbon‐13 nuclear magnetic resonance (NMR) spectroscopy and x‐ray diffraction. Following complete dissolution of the polymer at elevated temperature and cooling of the concentrated PAN‐PC solutions, a gel was formed. The PAN‐PC gels consisted of regions of mobile polymer chains, rich in PC, “cross‐linked” by regions of rigid polymer. The mobile regions of the gels showed solution‐type NMR spectra with resolution of tacticity effects. The rigid component detected by NMR would correspond to the crysttallites detected previously by x‐ray diffraction. Wide‐angle x‐ray diffractograms of the gels showed different peaks when compared with the dry polymer powder. After solvent extraction and drying of the gel, the diffractogram reverted to that of the original dry powder. This new result is the strongest evidence to support the view advanced earlier that the new peaks found in the diffraction pattern of the wet gels arises from solvated polymer crystallites rather than from ordinary polymer crystallites. © 1993 John Wiley & Sons, Inc.
Poisson ratios and upper bounds of intrinsic birefringence from brillouin scattering of oriented polymers
Authors: Krbecek H. , Krüger J. K. , Pietralla M.
Published: April 2003

To overcome the difficulties in measuring high‐frequency shear constants of polymeric materials by ultrasonic or Brillouin scattering technques, we extrapolate results from oriented materials to zero birefringence. Shear constants C44 in the high‐frequency limit (GHz) are determined for polyethylene, poly(ethylene terephthalate), poly(vinyl chloride), poly(methyl methacrylate), and polycarbonate using Brillouin scattering. Accurate values of Poisson's ratio are derived. The extrapolation to full orientation using an amended Moseley relation gives upper bounds for the “intrinsic birefringence.” Changes in the character of the orientation process are easily detected by monitoring the mode numbers, which are defined by analogy to Poisson's ratio. Extrapolation of these ratios to their upper bound 0.5 gives an independent check of the maximum intrinsic birefringence. © 1993 John Wiley & Sons, Inc.
Physical modifications of propylene/ethylene–propylen–diene–monomer rubber surfaces. I. Determination of surface composition and surface order by fourier transform infrared–attenuated total reflectance
Authors: Bonnerup C. , Gatenholm P.
Published: April 2003

The aim of this study was to introduce a new method for determining the surface composition and surface order of PP/EPDM (propylene/ethylene–diene–monomer rubber) blends, based on surface‐enhanced infrared spectroscopy. PP/EPDM blends were characterized by Fourier transfer IR–attentuated total reflectance (FTIR‐ATR) using two different internal reflection elements, Ge and KRS‐5. These elements provide information at different depths and show differences in relative band intensities. A linear relationship between the ratio of the bands at 2850 and 2920 cm−1 EPDM content was obtained when well‐defined compositions of PP and EPDM mixtures were used. Changes in crystallinity were measured by the ratio of the bands at 2959 and 2951 cm−1. For comparison, bands in the lower region of the spectrum and DSC and WAXS measurments were used. It was shown by two calibration methods that FTIR‐ATR can provide information on surface composition and surface crystallinity at very low penetration depths. This new method indicates that injection‐molded sample show a lower surface order and lower EPDM content at the surface than is seen in bulk. © 1993 John Wiley & Sons, Inc.
Lattice treatment of thermodynamic properties of ring and linear polymer mixtures
Authors: Léonard J.
Published: April 2003

Expressions for the entropy and free energy of mixing a solvent with a mixture of linear and cyclic polymer molecules are derived. The entropy of mixing is deduced from the number of ways of arranging on a honeycomb lattice a mixture of totally flexible molecules made up of NR rings and NC chains. An equation is obtained through the combination of two independent expressions for the number of ways of arranging rings and chains. The free energy of mixing is deduced from the entropy and the enthalpy of mixing, using two distinct interaction parameters for ring and for chain molecules. The chemical potentials for solvent, ring polymer, and linear polymer are derived from the free energy of mixing. These quantities are found to be functions of the mole fraction of rings in the polymer mixture. © 1993 John Wiley & Sons, Inc.
A method for evaluating structural distortion from X‐ray scattering patterns with broad peaks and its application to thermally stabilized acrylic fibers
Authors: Shioya M. , Takaku A.
Published: April 2003

A method has been proposed for evaluating the lattice distortion that yields broad X‐ray scattering peaks. The long‐period structure of thermally stabilized acrylic fibers has been analyzed by applying this method to the meridional small‐angle X‐ray scattering. The period length of the acrylic fibers increases during stabilization, while the distortion of the period remains unchanged, maintaining a coefficient of variation of about 0.3. It is concluded from a simulation using a model lattice that the cyclization of molecular segments proceeds faster in disordered regions than in crystalline regions, and that the cyclization in the crystalline regions proceeds preferentially from crystallities separated by smaller cyclized regions. © 1993 John Wiley & Sons, Inc.
NMR approach to properties of polymeric membranes. Kinetics of membrane formation
Authors: Viallat Annie , Perez Sylvie
Published: April 2003

Nuclear magnetic resonance (NMR) is used to characterize properties of polyetherimide membranes obtained from a phase inversion process. At the end of the phase inversion and prior to the subsequent thermal treatments, the membrane is made of a porous structure filled of solvent and nonsolvent molecules embedded in a concentrated polymer–solvent matrix in the glassy state. The confinement of the small solvent and non solvent molecules in the porous system leads to a restriction of their mobility. The kinetics of membrane formation is observed from NMR. It is found that the penetration of non‐solvent and the propagation of the glassy phase into the system obey simple diffusion laws. © 1993 John Wiley & Sons, Inc.
Photophysical processes in aromatic polyimides. Studies with model compounds
Authors: Hasegawa Masatoshi , Shindo Yoichi , Sugimura Tokuko , Ohshima Shigeru , Horie Kazuyuki , Kochi Masakatsu , Yokota Rikio , Mita Itaru
Published: April 2003

Emission mechanism in an aromatic polyimide, PI(BPDA/PDA), derived from biphenyltetracarboxylic dianhydride and p‐phenylene diamine were studied with ultraviolet visible absorption and fluorescence spectra of a series of the model compounds. The excitation spectrum of the intermolecular charge‐transfer (CT) fluorescence peaking around 550 nm of PI(BPDA/PDA) thin film was completely consistent with the absorption spectrum, indicating that the intermolecular CT fluorescence emission of PI(BPDA/PDA) film is not caused by direct excitation of the CT absorption band, but by light absorption due to structural units in the polymer backbone. The UV‐vis. absorption spectra of the model compounds corresponding to the structural units in PI(BPDA/PDA) showed that the longest wavelength absorption band is due to the biphenylbisimide moiety. The band was assigned as π, π* transition with the polarization spectrum of the model compound. The fluorescence spectra of the model compounds changed sensitively depending on the conformation around N‐phenyl bond. The lifetime measurement for the model compounds suggested that intramolecular CT process occurs very rapidly. © 1993 John Wiley & Sons, Inc.
Analysis of mechanical behavior in cold‐drawing deformation of polymers
Authors: Xixiong Zhu
Published: April 2003

When stretched under uniaxial stress, ductile polymers usually exhibit unstable plastic deformation, which embodies two phases: (a) yielding with the formation of a neck and (b) cold‐drawing with the propagation of necking shoulders. The mechanical state associated with this deformation behavior is analyzed. The discussion is divided into three parts. The first part is a general treatment of the constitutive function of flow stress in the plastic state, in which a series of relations among various characterizing parameters are formulated. The second part provides three mechanical criteria for necking deformation and propagation of necking shoulders: the condition of unstable plastic deformation requiring \documentclass{article}\pagestyle{empty}\begin{document}$ D_P = - \left( {\partial {{\ln \dot \varepsilon } \mathord{\left/ {\vphantom {{\ln \dot \varepsilon } {\partial \varepsilon }}} \right. \kern-\nulldelimiterspace} {\partial \varepsilon }}} \right)_P < 0 $\end{document} the stabilizing deformation mode, which requires \documentclass{article}\pagestyle{empty}\begin{document}$ \gamma _p = \left( {{{dD_p } \mathord{\left/ {\vphantom {{dD_p } {d\varepsilon }}} \right. \kern-\nulldelimiterspace} {d\varepsilon }}} \right)_P > 0 $\end{document} and the obvious localization of unstable plastic deformation. The third part describes a mathematical model which can be used in calculations to fit the contour of the necking shoulder. This model is developed according to rational considerations for the relation of In \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} to ε. Experimental data on PE rod specimens are well fitted by this model. © 1993 John Wiley & Sons, Inc.
NMR study of the propagation center in cationic polymerization of N‐benzoyl‐8‐octanelactam. I. The structure of model living oligomers
Authors: Kříž J. , Puffr R.
Published: April 2003

Model living oligomers of N‐benzoyl‐8‐octanelactam initiated by the model octanoylium hexachloroantimonate, SbCl5, and by Ph3C+ AsF6−, were studied by 1H and 13C one‐ and two‐dimensional nuclear magnetic resonance using the COSY, S‐INEPT, COLOC, and ROESY methods. If prepared in the more solvating mixture of 1,1,2,2‐tetrachloroethane (TCE) with 1,2‐dichlorobenzene, the oligomers were found to be linear with the acylium ion as a living group on one end; in TCE only, the oligomers are highly branched. In both cases, the propagation center appears to be strongly coordinated to the nearest benzoylamide chain group. © 1993 John Wiley & Sons, Inc.
Liquid crystalline main chain polymers with a poly(p‐phenyleneterephthalate) backbone. 2. Fiber spinning and mechanical properties of polyesters with alkoxy side chains
Authors: Damman S. B. , Mercx F. P. M.
Published: April 2003

Fiber spinning and mechanical properties of four rigid polyesters with alkoxy substituents of different length and placement were evaluated. Properties of oriented fibers from the polymer with dodecyloxy substituents on the terephthalate moiety, PTA12HQ, were significantly affected by the crystal modification. At room temperature the following properties (tensile modulus E, tensile strength σb, and strain at break εb) could be obtained: E = 9.5 GPa, σb = 85 MPa and εb = 1.1% for phase Lf (the “frozen in layered mesophase”); E = 10.4 GPa, σb = 59 MPa and εb = 0.6% for modification A; E = 17.3 GPa, σb = 158 MPa and εb = 1.2% for modification B. Because of the higher amount of main chains per cross sectional area the polymer with hexyloxy side chains, PTA6HQ, showed better properties at a comparable degree of molecular orientation: E = 24 GPa, σb = 270 MPa, εb = 1.4%. Fibers obtained from the polyester with dodecyloxy substituents on the hydroquinone moiety, PTAHQ12, were too brittle to handle. The polyester with dodecyloxy substituents on both moieties, PTA12HQ12, was spun from the isotropic melt. Because of the obtained low degree of orientation, properties (E = 1 GPa, σb = 40 MPa, and εb = 6.3%) were governed by interactions between the chains (the main chains are not load‐bearing). © 1993 John Wiley & Sons, Inc.
Dynamic rheo‐optical characterization of a low‐density polyethylene/perdeuterated high‐density polyethylene blend by two‐dimensional step‐scan FTIR spectroscopy
Authors: Gregoriou Vasilis G. , Noda Isao , Dowrey Anthony E. , Marcott Curtis , Chao James L. , Palmer Richard A.
Published: April 2003

Dynamic mechanical analysis coupled with polarized step‐scan FTIR transmission and two‐dimensional correlation analysis (2D FTIR) has been used to monitor the submolecular orientational responses of the components of a semicrystalline 50 : 50 blend of low‐density polyethylene (LDPE) and perdeuterated high‐density polyethylene (d*‐HDPE) to a small amplitude uniaxial 23.47 Hz sinusoidal mechanical strain. Perdeuteration of the HDPE component allowed the distinction of its response from that of the LDPE in the blend samples. The experiments were carried out at room temperature. Analysis of the data indicates that the crystalline parts of the two components reorient at different rates, with the functional groups of the high‐density portion reorienting faster, in general, than those of the LDPE in response to the mechanical strain. © 1993 John Wiley & Sons, Inc.
Higher order hydrodynamic interactions in the calculation of polymer transport properties
Authors: Phillies George D. J. , Kirkitelos Paul C.
Published: April 2003

Higher order hydrodynamics interactions are short‐range modifications to the Oseen tensor Tij and its self‐interaction counterpart Tii. They differ from the Oseen tensor in having terms of higher order than the first in a/R, a being a bead radius and R being a bead‐bead distance. Effects of higher order hydrodynamic interactions on whole chain–whole chain hydrodynamic interactions are here computed. Higher order hydrodynamic interactions are shown to lead to a concentration dependence of the diffusion and friction coefficients of a free monomer. However, while higher order interactions make contributions of the same nature to the drag coefficients of a monomer and of a whole chain, the contributions are not simply multiplicative, removing a justification for the common practice of correcting polymer solution transport data for “monomer friction effects” via a normalization with data on friction coefficients of free monomers. © 1993 John Wiley & Sons, Inc.
Structure and electrical conductivity of ion‐implanted rigid‐rod and ladder polymers
Authors: Wang C. S. , Burkett J. , Lee C. Y‐C , Arnold F. E.
Published: April 2003

Isotropic and oriented thin films of rigid‐rod, rigid‐rod pseudo‐ladder, and ladder polymers were ion‐bombarded with 84Kr+ to a dose of 4 × 1016 ions/cm2. The bombardment was conducted at two conditions: one at 190 keV energy with 0.12 μA/cm2 current density and the other at 200 keV energy with 2.0 μA/cm2 current density. With the low current density, the polymers developed a uniform ion‐bombarded layer of about 0.35 μm at the surface. This layer showed an electrical conductivity on the order of 10−3s/cm at ambient conditions, an enhancement of 6 to 9 orders of magnitude from the pristine polymers. The enhanced conductivity was found to decrease to 10−6s/cm after the implanted krypton was removed by heating under reduced pressure. It suggests that the enhanced conductivity was due to a synergistic effect of structural change of the polymers and chemical doping by the im‐planted ions. With the high current density, most polymer films, except that of rigid‐rod pseudo‐ladder poly(p‐(2,5‐dihydroxy) phenylene benzobisthiazole) (DPBT), developed an additional fibrous network structure over the uniform ion‐bombarded layer. The comparable conductivity, 53 to 157 s/cm, measured for the various ion‐bombarded films in‐dicated that neither the molecular structure, rigid‐rod or ladder, nor the molecular packing order, isotropic or oriented, constituted significant effect on the conductivity of ion‐bombarded polymers. Since krypton could not be detected in the polymers ion‐bombarded with high current density, the enhanced conductivity was attributed to the structural change of the polymers. The DPBT films ion‐bombarded with high current density showed holes of micron size, probably due to the decomposition of hydroxy pendents from the rigid‐rod backbone. © 1993 John Wiley & Sons, Inc.
Thermally stimulated current and DSC studies of the broadened glass transition in liquid crystalline polymers
Authors: Sauer Bryan B. , Beckerbauer Richard , Wang Lixiao
Published: April 2003

The high sensitivity of the thermally stimulated current, thermal sampling (TS) method is emphasized in a study of the breadth of the glass transition in several liquid‐crystalline polymers (LCPs). Differential scanning calorimetry (DSC) was performed on all samples to further quantify the glass transition regions. For “random” copolyester LCPs with widely varying degrees of crystallinity, including highly amorphous samples, very broad glass tran‐sition regions were observed. One semicrystalline alternating copolyester and a series of semicrystalline azomethine LCPs were studied as examples of structurally regular polymers. These exhibited relatively sharp glass transitions more comparable to ordinary isotropic amorphous or semicrystalline polymers. The broad glass transitions in the random copolyesters are attributed to structural heterogeneity of the chains. In one example of a moderate‐crystallinity random copolyester LCP (Vectra), glass transitions ranging up to ca. 150°C in breadth were determined by the thermal sampling (TS) method and DSC. In other lower crystallinity copolyester LCPs, the main glass transition temperature as determined by DSC was comparable to that determined by TSC although cooperative relaxations of a minor fraction of the overall relaxing species were detected well below the main Tg, by the TS method and not by DSC. Rapid quenches from the isotropic melt to an isotropic glass were possible with one LCP. The anisotropic and isotropic glassy states for this LCP were found to have the same breadth of the glass transition as was determined by the TS method, although TSC and DSC show that Tg is shifted downward by ca. 15°C in the anisotropic glass as compared to the isotropic glass. © 1993 John Wiley & Sons, Inc.
Tracer diffusion of star‐branched polystyrenes in poly(vinyl methyl ether) gels
Authors: Won J. , Lodge T. P.
Published: April 2003

The tracer diffusion of 3‐, 4‐, and 12‐arm polystyrene (PS) stars in poly(vinyl methyl ether) (PVME) gels has been measured by dynamic light scattering (DLS). The intensity correlation functions were analyzed by two methods. One was that employed previously in a DLS study of linear PS diffusion in PVME gels [N. A. Rotstein and T. P. Lodge, Macromolecules, Vol. 24. p. 1316 (1992)], and the other was based on consideration of possible nonergodicity effects [P. N. Pusey and W. van Megen, Physica A, Vol. 157, p. 705 (1990)]. Both methods gave equivalent results, suggesting that nonergodicity plays a small role in this system. This conclusion is not unreasonable, given that the PVME gels are almost isorefractive with the solvent (toluene), and that the signal is dominated by scattering from the PS chains. The resulting star diffusivities are consistently less than or equal to those for linear probes of comparable size, with the difference increasing with molecular weight. The diffusivities are also less than or equal to those obtained for the same stars in PVME solutions. A weak dependence on the number of arms is also observed. Finally, the mobility of a given star in a gel is much more sensitive to variations in the average molecular weight between cross‐links than is the mobility of a linear chain. All of these features in the data are broadly consistent with the reptation hypothesis. © 1993 John Wiley & Sons, Inc.
Scattering experiments on polymer solutions
Authors: Chu Benjamin
Published: April 2003

Laser light‐scattering characterization of poly(tetrafluoroethylene) (PTFE) in a perfluoroalkane (perfluorotetracosane) or oligomers of poly(chlorotrifluoroethylene) at temperatures near the crystalline melting point of PTFE and studies of the coil‐to‐globule transition for polystyrene in cyclohexane are reviewed. Discussions on approach to solving some experimental problems are emphasized. © 1993 John Wiley & Sons, Inc.
Ion‐Exchange equilibria in cationic polyelectrolytes
Authors: Ríos Hernán E. , Ternero Gerardo A. , Barraza Raúl G. , Gamboa Irma C.
Published: April 2003

A method which allows the evaluation of phenomenological ion exchange constants Kex is proposed and tested in a cationic polyelectrolyte system. Results for nitrate/chloride exchange are nearly constant over the entire concentration range studied. However, for nitrate/bromide exchange, the results depend on the polyelectrolyte concentration, with Kex following the same trend as the mean activity coefficient for the polyion bromide. For polyion fluoride, a conformational change is probably induced as nitrate is added to the solution and the result deviates from the linear relationship predicted by the method. Benzene sulfonate behaves like a hydrophilic anion, whereas tosylate and ethylbenzene sulfonate also induce conformational changes by hydrophobic interactions. These results are supported by viscosity measurements and agree well with those recently reported by Satoh, who considered changes in apparent molar volume. © 1994 John Wiley & Sons, Inc.
Study of the miscibility of poly(vinyl pyridines) with poly(vinyl acetate), poly(vinyl alcohol) and their copolymers
Authors: Cesteros L. C. , Isasi J. R. , Katime Issa
Published: April 2003

Miscibility of poly(4‐vinyl pyridine) (P4VP) and poly(2‐vinyl pyridine) (P2VP) with poly(viny acetate) (PVAc), poly(vinyl alcohol) PVA and poly(vinyl acetate‐co‐alcohol) (ACA copolymers) has been investigated over a wide composition range. Differentiaal scanning calorimetry (DSC) results indicate that P2VP is immiscible with PVAC, PVA, and their copolymers over the whole composition range. In turn, P4VP appears to be immiscible with PVAC and PVA, but miscible with some ACA copolymers in certain range of composition. The P4VP‐ACA phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with composition for miscible mixtures was found to follow the Gordon‐Taylor equation, with the parameter κ dependent upon copolymer composition. FTIR analysis of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups and the nitrogen of the pyridinic ring, which appear to be decisive for miscibility. © 1994 John Wiley & Sons, Inc.
Effects of methylene chloride sorption on the properties of poly(ether ether ketone)
Authors: Arzak A. , Eguiazábal J. I. , Nazábal J.
Published: April 2003

Sorption of methylene chloride by poly(ether ether ketone) (PEEK) has been studied for both amorphous and highly crystalline polymer. After the determination of sorption and desorption curves, the crystallinity of the two materials after desorption was determined both by density and X‐ray measurements. The experimental results indicate the existence of solvent‐induced crystallization in initially amorphous PEEK and a virtual lack of this process in highly crystalline PEEK. In the latter case, the observed density increase is attributed to solvent compression and a decrease in free volume. The mechanical behavior of both PEEKs is consistent with their crystallinity levels. The mechanical behavior of both PEEKs before and after sorption allows us to discern the separate effects of the two processes to which the presence of methylene chloride in PEEK gives rise, i.e., plasticization and solvent‐induced crystallization. © 1994 John Wiley & Sons, Inc.
Deformation effects on ionic transport in polymeric films
Authors: Sakamoto W. K. , Gonzalez E. R. , Zimmerman R. L. , Rúvolo‐Filho A.
Published: April 2003

When a periodical deformation is applied to a cellophane film through which an ion flux is established by a concentration gradient, an electrical signal, synchronous with the deformation, can be detected on electrodes placed on both sides of the membrane. This signal was studied as a function of the amplitude and frequency of the deformation and the ionic concentration. Ionic resistance, permeability, water content and ionic concentration measurements were carried out in order to explain the particular dependence of the signal with the ionic concentration. © 1994 John Wiley & Sons, Inc.