bluuebunny/crossref_metadata_2025_split huggingface dataset:
An NMR study of segmental motion in poly(isobutylene) and the relationship to translational diffusion of sorbed CO2
Authors: Bandis Athinodoros , Wen Wen‐Yang , Jones Elliot B. , Kaskan Peter , Zhu Yong , Jones Alan A. , Inglefield Paul T. , Bendler John T. 
Published: April 2003

AbstractThe spin‐lattice relaxation times as well as nuclear Overhauser enhancements (NOE) are determined for the methylene carbon of polyisobutylene (PIB). Three different correlation functions are used to treat the relaxation data to describe the local motion of the PIB backbone rubber. The first is the Hall‐Helfand function combined with restricted anisotropic rotational diffusion, the second is the Dejean‐Lauprêtre‐Monnerie function, and the third is the Williams‐Watts function combined with restricted anisotropic rotational diffusion. Spin‐lattice relaxation times are also determined on PIB under pressure of CO2 gas to check for changes in segmental motion in the presence of this penetrant. All the models give a satisfactory description for the local dynamics of the backbone carbon of the polymer chain, yielding comparable values for the time scale of conformational changes, apparent activation energies and distribution of correlation times. In addition, a proton line shape experiment is performed on bulk PIB as a function of temperature. The results are interpreted in terms of two motional components in the polymer chains: fast and slow ones. Applying a revised version of Rössler's formalism to our data, an average energy barrier is found which is consistent with the apparent activation energies. The apparent activation energy obtained for PIB, from the nuclear magnetic resonance (NMR) measurements, about 35 kJ, is slightly higher than the apparent activation energy for the translational diffusion of CO2 in PIB from NMR data. The distribution of correlation times and the correlation times themselves for segmental motion of the PIB and translational diffusion of CO2 in PIB are very similar, indicating a close link between the two motional processes. The distribution of correlation times is close to a single exponential in PIB consistent with Angell characterization of this material as a strong liquid. © 1994 John Wiley & Sons, Inc.
Tailored adhesion at polymer/nonpolymer interfaces
Authors: Smith Joshua W. , Kramer Edward J. , Mills Peter J. 
Published: April 2003

AbstractIn this investigation, block copolymers of deuterated polystyrene (dPS) and poly (2‐vinylpyridine) (PVP) have been used to modify the adhesion at polystyrene/soda lime glass interfaces. The fracture energy, Gs of these interfaces was measured using an asymmetric double cantilever beam specimen. The failure mechanism was investigated using forward recoil spectrometry (FRES) and Rutherford backscattering spectrometry (RBS). The areal density, ∑ of the dPS‐PVP block copolymer at the two fracture surfaces, as well as the fraction of the dPS block on the PS side of the fractured sample are measured directly by FRES. The fraction of the PVP block on the glass side of the interface can be found by quaternizing the PVP with methyl iodide and then using RBS to measure the amount of iodine on each fracture surface. Short dPS blocks (NdPS < 175) do not entangle effectively with the PS homopolymer and only very small increases in Gc can be achieved as the dPS block pulls out of the interface. If the dPS block is long (NdPS ≫ 175) and if ∑ is large, crazes can develop in the PS ahead of the crack. The crazed interface fails at low ∑ by breaking the block copolymer close to the styrene/vinylpyridine link. At higher ∑, if the PVP block is relatively short (NPVP = 95), the crazed interface fails by the PVP block being pulled off the glass. If both the PVP and dPS blocks are long (≫ 175), the Gc increases rapidly with increases in ∑, but the interface becomes so strong that the glass on the thinner side of the test specimen breaks. The dPS block and the PVP block are found on opposite sides of the fracture surface with most of the PVP on the glass and most of the dPS on the PS side of the interfaces. Finally, if the glass surface is modified by coating it with a self‐assembled hydrophobic monolayer produced from chlorodimethyloctadecylsilane (CDMOS), the interface becomes very weak and fails by pull‐off of the PVP from the CDMOS‐coated glass. Using these results it is possible to tailor the interfacial adhesion to produce a desired Gc within a wide range of possible values. © 1994 John Wiley & Sons, Inc.
Temperature‐dependent dielectric studies of fully cured diethylene glycol bis (allyl carbonate)
Authors: DeMeuse Mark T. 
Published: April 2003

AbstractStudies are presented of the dielectric properties of fully cured diethylene glycol bis (allyl carbonate) as a function of both frequency and temperature. It is shown that the characteristics of the fully cured system are dominated by a localized, secondary transition that is associated with motion of the carbonate unit. The glass transition is shown to contribute little to the dielectric properties within the temperature range 20–70°C. © 1994 John Wiley & Sons, Inc.
Estimation of interaction energies by the critical molecular weight method: 1. Blends with polycarbonates
Authors: Callaghan T. A. , Paul D. R. 
Published: April 2003

AbstractThe interaction energies between PS, Pα‐MS, and PMMA with several bisphenol‐A‐based polycarbonates were quantitatively determined from oligomer/oligomer, oligomer/homopolymer, and homopolymer/copolymer blends. Interaction energies were calculated from the Flory‐Huggins theory and the Sanchez‐Lacombe equation of state theory using experimental cloud points or miscibility boundaries. Alkyl addition to the phenyl rings of polycarbonate is favorable for miscibility with polystyrene whereas halogenation of the bisphenol connector unit is favorable for miscibility with poly(methyl methacrylate). Interaction energies are quantitatively ranked and described qualitatively in terms of changes in the electronic charge distribution of the polymer repeat units as calculated by SYBYL software. © 1994 John Wiley & Sons, Inc.
Depth‐profiling of polymer laminates using fourier transform infrared (ATR) spectroscopy: The barrier film technique
Authors: Pereira Marcia R. , Yarwood Jack 
Published: April 2003

AbstractWe report FTIR‐ATR spectra of a polymer laminate (PMMA/PVOH) at different base layer thicknesses and different angles of incidence on a ZnSe substrate. By varying this ‘barrier’ layer (of PMMA) we have demonstrated that different effective penetration depths into the PVOH are achieved, in very good agreement with the calculated electric fields as a function of distance away from the substrate surface. Such work forms the basis for depth profiling measurements in order to detect interfacial interactions between the polymer molecules. © 1994 John Wiley & Sons, Inc.
A generalization of dual mode transport theory for glassy polymers
Authors: Horas Jorge A. , Nieto F. 
Published: April 2003

AbstractThe polymer matrix, divided in a number of cells in which the penetrant molecules can be sorbed and migrate, is considered. Each cell has been assigned an effective energy value that obeys a particular distribution. The effective diffusion coefficient and its concentration and temperature dependence are determined. The origin of sorbed penetrant mobility is studied. Using a delta‐Dirac distribution for the site's energetic values, the model is reduced in the appropriate limit (low pressure) to other formulations of the dual transport model. More general results, allowing the site's energetic values to be drawn from a Gaussian distribution, are also given. © 1994 John Wiley & Sons, Inc.
Thermal diffusivity and electrical conductivity of electropolymerized polypyrrole films
Authors: Tsutsumi Naoto , Ishida Satoshi , Kiyotsukuri Tsuyoshi 
Published: April 2003

AbstractThis article presents measurement of thermal diffusivity and electrical conductivity of polypyrrole films prepared by electropolymerization. Thermal diffusivity was measured by laser radiometry (former flash radiometry). Electrical conductivity was determined by a conventional four‐probe method. Increase of thermal diffusivity is observed when increasing the supporting electrolyte concentration, which is also shared with the increase of electrical conductivity. Both thermal diffusivity and electrical conductivity significantly depended on the types of counter anion incorporating into polymer bulk. Thermal diffusivity of polypyrrole film is larger than that for common nonelectrical conductive polymers. Temperature profile of thermal diffusivity for as‐grown polypyrrole films shows that thermal diffusivity increases with increasing temperature (first running profile), whereas remeasured temperature profile of thermal diffusivity (second or third running profiles) shows the decrease of thermal diffusivity with increasing temperature. Electrical conductivity monotonically increases until the significant decrease of it occurs at the temperature above 130°C. Investigation of these temperature profiles of thermal diffusivity and electrical conductivity has been made by corresponding to thermal analysis data. © 1994 John Wiley & Sons, Inc.
The transport properties of polyimide isomers containing hexafluoroisopropylidene in the diamine residue
Authors: Coleman M. R. , Koros W. J. 
Published: April 2003

AbstractThe effect of modification of the central moiety of the dianhydride residue and isomerism on the gas transport and physical properties were compared for six polyimides containing the hexafluoroisopropylidene group in the diamine residue. Substitution of bulkier groups within the dianhydride residue resulted in disruption of chain packing and slight increases in resistance to chain motions which led to an increase in permeability with little loss in selectivity. The permeabilities and diffusivities in the meta connected polyimide isomers were considerably lower than in the para connected polyimide isomers. Similarly, the permselectivities in the meta connected isomers were consistently higher than in the para connected isomers. These lower permeabilities and higher permselectivities were a result of the more dense packing and a significant suppression of small scale motions in the meta connected isomers. The suppression of segmental mobility in the meta connected isomers was indicated by an increase in the sub Tg transition temperatures in these materials relative to the para connected isomers. The differences in transport properties for these polyimides were attributed to contributions by several factors, including: (1) total free volume (2) distribution of free volume (3) intersegmental resistance to chain motions, and (4) intrasegmental resistance to chain motions. © 1994 John Wiley & Sons, Inc.
Properties of polystyrene‐poly(methylmethacrylate) random and diblock copolymers in dilute and semidilute solutions
Authors: Kent Michael S. , Tirrell Matthew , Lodge Timothy P. 
Published: April 2003

AbstractSolution properties for random and diblock copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA) have been measured by dynamic and total intensity light scattering in solvents of differing quality. The results are compared with the corresponding properties for PS and PMMA homopolymers of similar molecular weight, in order to determine if interactions between unlike monomers are significant. The hydrodynamic radius (Rh) and diffusion second virial coefficient (kd) for the random copolymer are found to be larger than the corresponding values for the homopolymers in a solvent which is near‐theta for the two homopolymers, whereas no such effect is observed for the block copolymer. This suggests that most intrachain interactions occur a relatively short distance along the chain backbone. In a mutual good solvent Rh and kd of the random copolymer are comparable to the average of the values for the homopolymers, indicating that in a good solvent monomer/solvent interactions dominate over monomer/monomer interactions. For an isolated diblock copolymer in a mutual good solvent, there is no evidence that interactions between unlike monomers lead to additional expansion of the entire molecule, as measured by Rh, nor expansion of the individual blocks as probed by light scattering with one block optically masked. However, at low but finite concentration there is evidence (the coefficients of the binary interaction terms in the viscosity and the mutual diffusion coefficient, and the second and third virial coefficients) that a weak ordering effect may exist in block copolymer solutions, far from the conditions where microphase separation occurs. Finally, measurements of ternary polymer‐polymer‐solvent solutions show no dependence on monomer composition or monomer distribution for the tracer diffusion of probe PS‐PMMA copolymers in a PMMA/toluene matrix. This indicate that the frictional interaction is largely unaffected by interactions between unlike monomers. However, there is evidence that the thermodynamic interaction is more unfavorable between a random copolymer and the homopolymer matrix than between a diblock and the matrix. © 1994 John Wiley & Sons, Inc.
Structural studies of poly(paraphenylene), poly(2,5‐thienylene) and their derivatives by solid‐state NMR of 1H and 13C
Authors: Erdmann K. , Czerwinski W. , Gerstein B. C. , Pruski M. 
Published: April 2003

AbstractTransient techniques in NMR of 1H and 13C were used to study the chemical and physical structures of solid poly(p‐phenylene) (PPP), poly(2,6‐dimethyl‐p‐phenylene oxide) (PDMPO), poly(p‐phenylene sulfide) (PPS), poly(p‐biphenylene sulfide) (PPBS), poly(p‐phenylene selenide) (PPSe), poly(p‐biphenylene selenide) (PPBSe), poly(2,5‐thienylene) (PT), poly(3‐methyl‐2,5‐thienylene) (PMT), and poly(p‐phenylene‐co‐2,5‐thienlyene) (PPPT) of different monomer ratios. 13C NMR confirmed the expected chemical structure for homopolymers, and indicated a random distribution of monomer units in PPPT. Relative fractions of crystalline and interfacial regions were determined by measurements of 1H magnetic relaxation, 13C CP/MAS NMR, and XRD. © 1994 John Wiley & Sons, Inc.
Carbon tetrachloride‐induced crack healing in polycarbonate
Authors: Wu Terhou , Lee Sanboh 
Published: April 2003

AbstractCrack healing induced by carbon tetrachloride in polycarbonate has been studied at temperatures in the range of 40–60°C. The carbon tetrachloride treatment reduces the glass transition temperature of polycarbonate. Crack healing is observed because the effective glass transition temperature in polycarbonate is reduced to below the test temperature by the carbon tetrachloride treatment. Two distinctive stages of crack healing are divided based on the recovery of mechanical strength and fractograph. The first stage corresponds to the progressive healing due to the convolution of wetting and self‐diffusion, which has a constant crack closure rate. Immediately following the first stage, the second stage, corresponding to the self‐diffusion of polymer chain, enhances the quality of healing behavior. The transport of carbon tetrachloride in polycarbonate consists of case I (concentration gradient controlled) and case II (relaxation controlled) behaviors. The direction of case II is opposite to that of case I. The solubility decreases with increasing temperature, but diffusivity and velocity for mass transfer, crack closure rate, and diffusion coefficient for the diffusion front have the opposite trend. The first stage of crack healing is controlled by case II transport. The transport of carbon tetrachloride changes the fracture behavior of polycarbonate from ductile to brittle. A comparison of crack healing in polycarbonate and poly (methyl methacrylate) is made. © 1994 John Wiley & Sons, Inc.
Electrical conduction in a nonconjugated polymer doped with SnCl4 and SbCl5
Authors: Yu Guo‐Qing , Thakur M. 
Published: April 2003

AbstractThe electrical and optical properties of 1,4‐cis‐polyisoprene before and after doping with SnCl4 and SbCl5 were investigated. The material becomes reddish brown and black upon doping with SnCl4 and SbCl5, respectively, and the conductivity increases by about 11 orders of magnitude. The optical absorption, infrared spectra, elemental analyses, and the studies of reversibility upon compensation indicate that radical cation formation is the most likely mechanism for electrical conduction in these complexes. The results are consistent with previously published articles involving iodine doping. © 1994 © John Wiley & Sons, Inc.
Characterizing domain mixing effects in hydrogen bond‐compatibilized polymer blends
Authors: Taylor‐Smith Ralph E. , Register Richard A. 
Published: April 2003

AbstractThe nature and extent of phase mixing in blends of hydroxyl‐functionalized polystyrene and poly(ethyl acrylate) (PS/PEA), where the driving force for mixing is hydrogen bonding, are characterized by several techniques. Small‐angle x‐ray scattering (SAXS) shows a reduction in average domain size with increasing functionalization level, a result also evident from scanning electron microscopy (SEM). Together, the two techniques reveal a very broad distribution of domain sizes. At high functionalization levels, both SAXS and SEM indicate a high degree of “in‐domain” mixing, with little or no pure PS or PEA remaining in the blends. Mathematical modeling of dynamic mechanical thermal analysis (DMTA) data is employed to quantify this progression. Initially, mixing is primarily interfacial, but as the functionalization level increases, the mixed interphase rapidly grows to occupy the entire material. In agreement with the SAXS and SEM results, DMTA modeling shows that further increases in the functionalization level suppress the amplitude of composition variations in the sample. The onset of extensive in‐domain mixing coincides with the marked changes in stress‐strain behavior observed previously in these materials. © 1994 John Wiley & Sons, Inc.
Temperature effect on solvent diffusion in rigid and semirigid polyimide films
Authors: Chang Ying‐Lun , Jou Jow‐Huei 
Published: April 2003

AbstractThe diffusion of NMP (n‐methyl‐pyrrolidinone) solvent in a semirigid rod‐like PMDA‐ODA (pyromellitic dianhydride‐4,4′‐oxydianiline) film coated on silicon is found to be case I diffusion at temperatures ranging from 30 to 90°C by the use of a bending beam technique. The diffusion constant increases for the 7.4 μm PMDA‐ODA film (which was cured at 300°C) from 3.3 to 318 × 10−11 cm2/s as the diffusion temperature increases from 30 to 90°C. The corresponding hygroscopic stress in the direction parallel to the film decreases with the increase of temperature, possibly due to the softening of the film at elevated temperatures. The diffusion mechanism, however, changes from case II to case I in a rigid rod‐like PMDA‐PDA (pyromellitic dianhydride‐p‐phenylenediamine) film when the diffusion temperature increases. The change in the diffusion mechanism occurs at a higher temperature for thinner films, presumably due to higher ordering and/or orientation in the films. The activation energy for NMP diffusion in the PMDA‐ODA films markedly decreases from 93 to 59 kJ/mole as the film thickness increases from 2.2 μm to 11.3 μm. This may also be attributed to decreased ordering in thicker films. © 1994 John Wiley & Sons, Inc.
Correlation between the fractal dimension of fracture surfaces and fracture toughness for ductile polymer materials
Authors: Lyu Suping , Zhu Xiaoguang , Qi Zongneng 
Published: April 2003

AbstractA microcrack‐shear band chain model for the fracture of ductile materials is proposed. The fractal dimension (D) of the fracture surfaces is derived and correlated with the fracture toughness (KIc) of ductile materials. The fractal dimension of the fracture surface is predicted to have an inverse trend with the fracture toughness. The theoretical results are consistent with the experimental results of some polymers and metals. © 1994 John Wiley & Sons, Inc.
Effect of cross‐link density on the morphology, thermal and mechanical properties of flexible molded polyurea/urethane foams and films
Authors: Thomas Oomman , Priester, Jr. Ralph D. , Hinze Ken J. , Latham Dwight D. 
Published: April 2003

AbstractThe effect of cross‐link density on the morphology and properties of two flexible molded foam samples was studied. Film samples based on the same foam formulations were also fabricated to study the feasibility of using them for the characterization of complex foam products. Fourier transform infrared spectroscopy (FTIR) and small angle X‐ray scattering (SAXS) data show that films and foam samples have entirely different hard domain ordering. The results of the study of morphology indicate that an increase in cross‐link density appears to increases phase mixing in film and foam samples. Differential scanning calorimetry (DSC) studies indicate that the soft segment glass transition temperature (Tg) is independent of cross‐link density (at levels studied). But for both film and foam samples, morphology clearly dicates the manner in which moisture interacts with the hard domains. Results of the stress‐strain behavior indicate that an increase in cross‐link density increases the modulus and decreases the elongation at break. Mooney‐Rivilin modeling of the stress‐elongation behavior of film shows that the higher cross‐link density sample gives more nonaffine behavior, possibly due to a heterogeneous distribution of hard domains. Similar modeling of the foams was not possible because of their linear stress response to surprisingly high elongation. The results of the power law modeling of stress relaxation response indicates that with an increase in cross‐link density (covalent and virtual), the power law exponent decreases as expected. At levels of cross‐linking and hard segment content studied, stroke‐controlled equilibrium hysteresis was independent of cross‐link density. Normalized dynamic mechanical spectra (DMS) show that the film samples have higher rubbery plateau modulus. The magnitude of the area under the tan δ curve at Tg indicates greater flexibility of polymer segments in foam sample. Structure‐property relationships of cellular materials can be established by characterizing film samples because a parallel trend exists between each group. © 1994 John Wiley & Sons, Inc.
Partial carbonization of aramid fibers
Authors: Zhang Quichen , Liang Ying , Warner Steven B. 
Published: April 2003

AbstractHeat treatment of aramid fiber was conducted in the temperature range 300–710°C nominally for 10 and 30 s in both static air and flowing nitrogen atmosphere. Crystallinity, crystal orientation, and crystallite size were determined using x‐ray diffraction. Fibers with a skin–core structure were produced at intermediate temperatures, as revealed by scanning electron microscopy of fibers after partial dissolution of the fiber in 95–98% sulfuric acid. The skin, which forms in both nitrogen and air, is amorphous and brittle. It is insoluble in sulfuric acid, suggesting it is a cross‐linked polymer. Formation of the skin may be facilitated by the removal of an aggressive chemical species that forms during heat treatment. The species may diffuse out of the outer layer of the fiber, allowing it to cross‐link. The molecular weight of the dissolved core, analyzed using intrinsic viscosity, decreases with increasing heat treatment temperature. The tenacity, modulus, elongation‐to‐break, and toughness of fibers with a skin–core structure decrease with heat treatment and the fiber loses its fibrillar character. Mechanical property reductions are greater in air than nitrogen. X‐ray data are also consistent with the notion that oxygen assists attack of crystals at high temperatures. Scanning electron microscopy shows that fibers have become skin–core composites with quite different mechanical properties between the two regions. A fiber failure mechanism is proposed. © 1994 John Wiley & Sons, Inc.