bluuebunny/crossref_metadata_2025_split huggingface dataset:
Positron annihilation spectroscopy study of moisture absorption in protective epoxy coatings
Authors: Macqueen Richard C. , Granata Richard D. 
Published: April 2003

AbstractPosition 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

AbstractThe 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

AbstractWe 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

AbstractThe 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

AbstractRandom 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

Abstract13C 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

AbstractPure 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

AbstractThe 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

AbstractX‐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

AbstractTwo 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

AbstractA 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

AbstractThe 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

AbstractBlends 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

AbstractThe 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

AbstractThe 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

AbstractTo 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

AbstractThe 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

AbstractExpressions 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

AbstractA 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.