bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physical and chemical evolution of PMDA‐ODA during thermal imidization
Authors: Ojeda Jaime R. , Mobley Juliana , Martin David C. 
Published: April 2003

AbstractThe processing of poly(imide) films from poly(amic acid) solutions involves the simultaneous loss of solvent and chemical conversion, and may involve structural reorganization such as orientation or crystallization. Here, we describe weight loss, solvent sorption. Fourier transform infrared (FTIR), and wide‐angle x‐ray scattering (WAXS) studies during thermal imidization of the commercially important poly(imide) PMDA‐ODA. The results indicate that imidization proceeds nearly to completion before significant crystallization occurs. The experimental data are interpreted in terms of a triangular phase diagram that makes it possible to plot the processing pathway during the conversion from poly(amic acid) solution to solid poly(imide). In constructing this triangular phase diagram the extent of imidization (i.e., the composition of the poly(amic acid‐co‐imide) copolymers during conversion) is treated as an independent thermodynamic variable. The form of the triangular phase diagram can be predicted from the Flory‐Huggins lattice theory of mixing. There is inevitably a two‐phase region present due to the relatively poor solubility of the poly(imide) in the poly(amic acid) solvent (NMP). The specific processing pathway taken depends on the relative amount of solvent loss and imidization during conversion. Further details about the triangular phase diagrams of poly(imides) will require such studies as solvent swelling at intermediate stages of conversion. © 1995 John Wiley & Sons, Inc.
NMR imaging of polyethylene pipes
Authors: Sardashti Maziar , Baldwin Bernard A. , O'Donnell Daniel J. 
Published: April 2003

Abstract1H nuclear magnetic resonance (NMR) imaging techniques have been used to image the extrusion aid (EA) in polyethylene (PE) pipe samples. The resulting two‐dimensional images show the distribution of EA within the pipe. EA is found to be uniformly distributed in a normal pipe. Examples of degraded pipes, due to exposure to extreme conditions, show migration of EA to the pipes' wall surfaces. NMR images of a normal pipe and two examples of damaged pipes are presented. The imaging technique and the results are discussed. © 1995 John Wiley & Sons, Inc.
Thermal isomerization and morphology of various polyacetylene films
Authors: Kyotani H. , Shimomura M. , Tanabe Y. , Akagi K. , Kasai T. , Zhang Y.‐X. , Shirakawa H. 
Published: April 2003

AbstractTwo DSC exotherms for cis‐trans thermal isomerization of polyacetylene (PA) films were found near 145 and 170°C. These exotherms are related to the higher‐order structure of PA films, depending on the sample preparation conditions. The high‐temperature peak corresponds to ordered crystallites (A state), which is prominent in conventional Shirakawa polyacetylene (S‐PA) and moderately stretchable PA (ms‐PA) films. The low‐temperature peak corresponds to disordered crystallites (B‐state) found in highly stretchable PA (hs‐x) films. The distribution of crystalline order in the B state depends on the materials. The A state is transformed to B state upon stretching of ms‐PA, but the B state is not transformed to A state by stretching. The supermolecular structure is discussed. © 1995 John Wiley & Sons, Inc.
Elastic modulus of the crystalline regions of cellulose triesters
Authors: Nishino Takashi , Takano Kiyofumi , Nakamae Katsuhiko , Saitaka Kiyoshi , Itakura Shyuichi , Azuma Jun'ichi , Okamura Keizo 
Published: April 2003

AbstractElastic moduli of the crystalline regions of cellulose triesters in the direction both parallel El and perpendicular Et to the chain axis are measured by x‐ray diffraction. El values for cellulose triesters are as follows: cellulose triacetate (CTA), 33.2 GPa; cellulose tripropionate (CTP), 21.6 GPa; cellulose tributyrate (CTB), 17.6 GPa; cellulose trivalerate (CTV), 17.9 Gpa. These are very small compared with that of cellulose I (134 GPa) and resemble each other despite the fact that the skeletal structure of CTP (32 helix) is much different from those of other cellulose triesters (2‐fold helix). The small El values for cellulose triesters can be explained by both the large cross‐sectional area of one molecule in the crystal lattice and the lack in intramolecular hydrogen bonds. Et values for cellulose triesters are as follows: CTA (310), 2.8 GPa; CTP (110), 1.4 GPa; (020), 2.1 GPa; (120), 2.2 GPa; CTB (110), 1.1 GPa. These are one of the smallest Et values already reported, and decrease with increasing the length of the side chain. Intermolecular interaction is considered to decrease with the length of acyl groups. The large Et value in the b direction of CTP reflects the dense packing of the chains in the crystal lattice. © 1995 John Wiley & Sons, Inc.
An X‐ray diffraction study of the different nematic mesophases of liquid‐crystalline poly(urethane‐ester)s
Authors: Francescangeli O. , Yang B. , Laus M. , Angeloni A. S. , Galli G. , Chiellini E. 
Published: April 2003

AbstractAn x‐ray investigation on powder specimens and stretched oriented fibers of poly(urethaneester)s TDI‐CmCn, derived from various mesogenic alkylene di[4‐(ω‐hydroxyalkyloxy‐4‐oxybenzoyl)oxybenzoate]s (CmCn; m = 2, 4, or 6, and n = 4, 6, 8, or 10) and 2, 4‐toluenediisocyanate (TDI), is reported. Evidence is provided for the formation of two different nematic mesophases in the polymers, namely a cybotactic nematic and a conventional nematic mesophase. Whereas samples TDI‐C2C6, TDI‐C6C4, and TDI‐C6C10 formed one cybotactic nematic mesophase, samples TDI‐C4C6, TDI‐C6C6, and TDI‐C6C8 exhibited both cybotactic nematic and conventional nematic mesophases in a sequence with increasing temperature, which were connected by a first‐order transition. The analysis of the various features of the small‐angle x‐ray diffraction patterns indicates that two structural arrangements, namely smectic C‐like and conventional nematic structures, coexist inside the cybotactic nematic mesophase of these poly(urethane‐ester)s. © 1995 John Wiley & Sons, Inc.
Time‐resolved fluorescence study of 4‐dimethylaminobenzonitrile in nonhydrogen‐bonding polymers, using picosecond dye laser pulses as excitation source
Authors: Al‐Hassan Khader A. 
Published: April 2003

AbstractIt is shown that the time‐resolved fluorescence (TRF) spectra and the red edge effect (REE) phenomena are useful tools to observe the twisted intramolecular charge transfer (TICT) band, of 4‐dimethylaminobenzonitrile (DMABN) in nonhydrogen‐bonding polymers. The TRF results show that the relative intensity of the TICT band increases with the increase of time after excitation in all polymers used. The highest TICT relative intensity is observed in poly(butyl methacrylate) (PBMA) polymer matrix, which has a medium polarity and medium free volume compared with either poly(methylmethacrylate) (PHMA), which is more polar and more rigid, or poly(hexylmethacrylate) (PHMA), which is less polar and less rigid than PBMA polymer matrix. The lifetimes are rationalized to the opposite roles of local polarity and local free volume of polymer sites on TICT emission. © 1995 John Wiley & Sons, Inc.
Packing density and gas permeability of copolyimides containing bicyclo[2,2,2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride constituent
Authors: Chun Byong‐wa 
Published: April 2003

AbstractPacking density and gas permeability of two copolyimide series containing an alicyclic monomer, bicyclo[2,2,2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA), and a fluorinated monomer, hexafluoroisopropylidene,2,2‐bis(phthalic acid anhydride) (6FDA), were measured. Incorporation of a rigid BCDA segment in 6FDA polyimides either increases gas permeability or improves gas selectivity, depending on the base 6FDA polyimide. In the case of the highly gas permeable 6FDA polyimide, introduction of BCDA further increases gas permeability despite a loss in the amount of free volume. In the moderately gas permeable 6FDA polyimide, on the other hand, the introduction improves gas selectivity. © 1995 John Wiley & Sons, Inc.
Morphological changes in annealed ultrahigh molecular weight polyethylene (UHMWPE) gel‐films
Authors: Zhu Q. R. , Hong K. L. , Ji L. Q. , Qi R. R. , Zhou G. E. , Song M. S. , Wong Y. W. 
Published: April 2003

AbstractX‐ray diffraction of the UHMWPE gel‐films has shown that high heating rate annealing of the films causes deformation of the crystallites. The apparent crystal sizes change with the annealing temperature (Ta). With Ta below 110°C, the dimensions of the crystallites in c‐axis (Lc) increase associated with the decreasing in a‐axis (La) and b‐axis (Lb), but the changes are small because of the higher energy barrier. When Ta is raised to 138°C, Lc is nearly doubled its value at 60°C whereas Lb increases and La remains unchanged. IR spectral subtraction was applied to reveal the morphological changes of the gel‐films upon annealing. It has been found that bands of the same type of conformation have different sensitivities subject to the thermal treatment at different annealing temperatures. The results can be understood by assuming the changing process being completed through chain segments sliding along the (020) sectors. © 1995 John Wiley & Sons, Inc.
Permeation and sorption for oxygen and nitrogen into polyimide membranes
Authors: Toi Keio , Suzuki Hirotaka , Ikemoto Isao , Ito Tomoyasu , Kasai Tetsuo 
Published: April 2003

AbstractThe permeation rate curves and sorption rate curves of oxygen and nitrogen below 1.3 atm were measured for seven polyimides of which chemical structures were systematically changed. These rate curves were applied Fickian model curves. The Fick's law was found to hold from the pressure independencies of diffusion coefficients for both the experiments. The solubility was better described according to dual‐mode sorption model rather than Henry‐s law from the sorption experiments. The diffusivities of both the gases were correlated with packing density (reciprocal of specific free volume) of the polymer, except two polyimides. The packing density of these two polymers could not be successfully calculated from Bondi's method. However, all the diffusion coefficients decreased linearly with an increase in the cohesive energy density (CED), which was calculated by the group contribution method of van Krevelen. These results suggest that the gas diffusions in polyimides better correlate with CED than with the packing density. Therefore, the cohesive energy density may be considered as a more reliable indication of the efficient gas separation. © 1995 John Wiley & Sons, Inc.
Molecular design of multicomponent polymer systems XIX: Stability of cocontinuous phase morphologies in low‐density polyethylene–polystyrene blends emulsified by block copolymers
Authors: Harrats C. , Blacher S. , Fayt R. , Jerôme R. , Teyssié Ph. 
Published: April 2003

AbstractPolyethylene–polystyrene blends containing small amounts of polyethylene (20 wt %) display a cocontinuous phase morphology that is very unstable in the absence of an emulsifier. The kinetics of coalescence at high temperature is therefore very sensitive to differences in the interfacial activity of added polymeric emulsifiers. The morphology of blends added with a pure or a tapered hydrogenated polybutadiene‐b‐polystyrene block copolymer is investigated as a function of annealing time at 180°C. Various image treatments (standard granulometry, opening size granulometry distribution, and multiscaling analysis) were used to quantify the morphological evolution of these blends. The results clearly demonstrate that the tapered block copolymer is definitely more efficient than the corresponding pure diblock for stabilizing the cocontinuous structure of these blends. The differential behavior is assumed to results from differences in the tendency of the two copolymers to segregate and form their own domains. © 1995 John Wiley & Sons, Inc.
Tensile yielding and microstructures of blends of isotactic polypropylene and linear low‐density polyethylene
Authors: Liu Yan , Truss Rowan W. 
Published: April 2003

AbstractThin sheets of isotactic polypropylene (iPP) and linear low‐density polyethylene (LLDPE) blends were studied by tensile testing, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Eyring's two‐process yielding theory was used to analyze the data of yield stress as a function of strain rate and temperature, and satisfactory curve‐fitting results were obtained. Furthermore, stress whitening was found to have occurred in the necked regions of tensile specimens under a certain range of yielding conditions. These conditions corresponded to the activation of Process II yielding of Eyring's theory. The whitening was found to be a result of formation of microvoids that initiated at the interface between iPP and LLDPE. © 1995 John Wiley & Sons, Inc.
Spectroscopic studies of the effects of salt addition in the protonation and deprotonation of emeraldine films
Authors: Neoh K. G. , Kang E. T. , Tan K. L. 
Published: April 2003

AbstractEmeraldine base films were treated with HClO4 solutions of various concentrations, with and without the addition of NaClO4. The protonation of the films was studied using angle‐resolved x‐ray photoelectron spectroscopy (XPS), Fourier transform infra‐red (FTIR) absorption spectroscopy, and ultraviolet (UV)‐visible absorption spectroscopy. The protonation level can be substantially increased by the presence of salt if sufficient time is allowed for the anions to migrate into the bulk of the film. Conversely, in the partial deprotonation of emeraldine salt films, a higher retention of anions is observed in the presence of salt, even though the effect is not as pronounced as in the protonation process. © 1995 John Wiley & Sons, Inc.
Cooperative movements associated with the Curie transition in P(VDF‐TrFE) copolymers
Authors: Teyssedre G. , Bernes A. , Lacabanne C. 
Published: April 2003

AbstractThe thermal and dielectric behavior of β‐PVDF and a series of random P(VDF‐TrFE) copolymers with various chemical composition has been investigated in the temperature range of their Curie transition. Dielectric relaxations and phase transitions were characterized by means of differential scanning calorimetry and thermostimulated current spectroscopy. The thermal hysteresis associated with the first order character of the Curie transition decreases as the TrFE content increases, and vanishes for P(VDF‐TrFE) 50/50. For the latter, the distribution in lamellar thickness and the dependence of the conformational order in the ferroelectric phase upon thermal history yield an intricate thermal behavior. For the overall investigated polymers, the TSC mode associated with the ferro/para‐electric transition is described by a distribution in relaxation times obeying a compensation law. This behavior has been interpreted based on cooperative movements in the ferroelectric phase in the vicinity of the transition temperature. These molecular movements are precursors of the transition. It is valid for β‐PVDF, as well as for P(VDF‐TrFE) copolymers which for the compensation temperature corresponds to the transition temperature. So, the Curie temperature of PVDF has been found at 170°C, i.e. the melting point. ©1995 John Wiley & Sons, Inc.
Free volumes in liquid‐crystalline main‐chain polymer probed by positron annihilation
Authors: Uedono A. , Sadamoto R. , Kawano T. , Tanigawa S. , Uryu T. 
Published: April 2003

AbstractFree volumes in a copolymer consisting of p‐hydroxybenzoic acid (HBA) and poly(ethylene terephthalate) (PET) were probed by positron annihilation technique. Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured in the temperature range between 30 and 230°C. Above the glass transition temperature (ca. 60°C), the lifetime of ortho‐positronium (o‐Ps) annihilated in the free volumes and its annihilation probability were found to increase with increasing specimen temperature. These facts were attributed to the increase both in the size of the free volumes and in the concentration of such regions due to rearrangements of molecules. From the observed lifetime of o‐Ps, it was found that the size of the free volumes increases from 0.05 nm3 to 0.1 nm3 in the temperature range between 30 and 230°C. At solid‐mesophase transition temperature (150–220°C), the size of the free volumes monotonously increases, while the increase in the concentration of such regions saturates at 174°C. The clear relationship between the data obtained by the positron annihilation and those obtained by differential scanning calorimetry was confirmed. ©1995 John Wiley & Sons, Inc.
Laser light‐scattering investigation of the density of pauci‐chain polystyrene microlatices
Authors: Wu Chi , Kwong Chan Kam 
Published: April 2003

AbstractThe average density (〈ρ〉) of the pauci‐chain polystyrene microlatices (PCPS), which contains a few linear polystyrene chains, was investigated by laser light scattering (LLS) including both angular dependence of absolute integrated scattered intensity (static LLS) and of the line‐width distribution G(Γ) (dynamic LLS). In static LLS, the weight‐average particle mass (Mw) and the z‐average radius of gyration (Rg) were measured; and simultaneously in dynamic LLS, the hydrodynamic radius distribution was obtained from Laplace inversion of very precisely measured intensity‐intensity time correlation function. A combination of both the static and dynamic LLS results leads us to a value of 〈ρ〉. For comparison, we also determined 〈ρ〉 of conventional multichain polystyrene latex (MCPS) by following the same LLS procedure. It was found that 〈ρ〉MCPS = 〈bulk〉 = 1.05 g/cm3, but 〈ρ〉PCPS = 0.92 g/cm3. This difference in density suggests that the intersegmental distance in MCPS or bulk polystyrene is smaller than that in PCPS, even the chains in PCPS are confined to a smaller volume. This might attribute to the fact, namely the intersegmental approaching inside PCPS is mainly the intrachain crossing which is more difficult in comparison with the interchain crossing inside MCPS or bulk polystyrene.
Ionic conduction in LiScn/Dimethylformamide/Poly(propylene oxide) system II. Mobility of lithium and thiocyanate ions
Authors: Mitani Kazuishi , Adachi Keiichiro 
Published: April 2003

AbstractIonic conductivity σ, shear viscosity η, and glass transition temperature Tg were measured on systems composed of lithiumthiocyanate LiSCN, N,N‐dimethylformamide (DMF), and poly (propylene oxide) (PPO) over wide ranges of LiSCN concentration C and DMF content Φ. Using the dissociation constant of LiSCN reported in Part I, we have determined the concentration n of Li+ and SCN− ions and then the mobility μ from σ. Data indicate that in the binary system of LiSCN/PPO, the σ versus C curve exhibits a maximum ca. C = 0.3 mol/L. In low C range, μ is independent of C but decreases with C in the range of C > 0.3 mol/L. Similar n dependence of μ is seen in the ternary systems containing DMF. The ratio of μ0/μ (C) is lower than the ratio of viscosity η(C)/η0 where μ0 and η0 indicate the values at infinite dilution of LiSCN. Thus the friction coefficient ςion for the translational diffusion of the ions is not proportional to the macroscopic viscosity. Relationship between μ and the monomeric friction ςp for the segmental motion of the PPO chains is also discussed based on the data of Tg and the Williams‐Landel‐Ferry equation. ©1995 John Wiley & Sons, Inc.
Hooke numbers of polymers
Authors: Elias Hans‐Georg 
Published: April 2003

AbstractHooke numbers He ≡ σb/(E) are calculated from published ultimate tensile strengths σb, tensile moduli E, and ultimate elongations ϵb. Data for common thermoplastics and natural fibers each follow a function He = [1 + (ϵb/ϵcrit)ab]−1/b with a Hookean region I (He = 1) at ϵb ≪ ϵcrit, a non‐Hookean region III at ϵb ≫ crit, and a transition region II for ϵb ≈ ϵcrit. Only non‐Hookean regions III were found for semisimultaneous interpenetrating networks from polyisobutylene‐polymethyl methacrylate, thermoplastic elastomers from segmented polyamide‐polyethers, molecular composites from poly(p‐phenylene benzobisthiazole) and poly[2,5(6)‐benzimidazole], and three groups of various synthetic fibers. The Hooke numbers of lyotropic and thermotropic liquid‐crystalline polymers vary with the heat treatment and depend on orientation angles for orientation angles greater than ca. 10°. Hooke numbers much greater than 1 are observed for highly stressed polymers. ©1995 John Wiley & Sons, Inc.
Shear‐precipitated chitosan powders, fibrids, and fibrid papers: Observations on their formation and characterization
Authors: Salmon Sonja , Hudson Samuel M. 
Published: April 2003

AbstractChitosan powders and fibrids were prepared by shear precipitation of dissolved chitosan in a coagulating solution of sodium hydroxide. Following neutralization by washing and an alcohol dehydration step, the white to off‐white powders were fine and free flowing. The dried fibrids had a highly oriented, ribbon‐like shape that in bulk gave a lofty appearance and soft hand. Chitosan fibrids were readily converted to sheet structures by typical paper‐making procedures. The resulting chitosan papers were either smooth, flexible, and largely translucent when pressed dry from the moist mat, or were soft and opaque white when the moist mat was soaked in alcohol before drying. X‐ray diffraction, SEM, and optical microscopy were used to characterize the different chitosan powders, fibrids, and papers. Chitosan fibrid papers were found to have tensile properties comparable to that of cellulosic papers, though the wet strength and water sorption of chitosan fibrid papers was higher than that of the cellulose controls. ©1995 John Wiley & Sons, Inc.
Viscosity behavior of poly(glyceryl methacrylate) in the presence of borate and phenylboronate ions
Authors: Keita G. , Ricard A. , Audebert R. 
Published: April 2003

AbstractThe viscosity behavior of polyelectrolyte solutions induced by borate or phenylboronate complexation with poly(glyceryl methacrylate) (PGM) has been investigated. In dilute solutions borate ions can form monodiol (1/1) complexes and didiol (2/1) intramolecular complexes. Both types of complex are anionic. Thus, the polymer is characterized by the existence of charged sites on the chain and loops formed by intramolecular complexation. On the contrary, phenylboronate can only give monodiol 1/1 complexes. In the presence of passive salt, the charges are screened. By addition of borate ion to a PGM solution, a decrease of the initial polymer viscosity due to loop formation is first observed, then the anionic charges fixed on the chain by complex formation induce an expansion of the polyelectrolyte and the viscosity of the solution increases. The situation is different for the PGM‐phenyl boronate system, where no intramolecular crosslink is present. In this case the viscosity of the solution increases with phenyl boronate concentration. But for a fixed complexing ion concentration it will tend to that of the neutral polymer when NaCl is added. ©1995 John Wiley & Sons, Inc.
Retardation of dissolution and surface modification of high‐modulus poly(ethylene) fiber by the synergetic action of solvent and stress
Authors: Vaykhansky L. E. , Cohen Y. 
Published: April 2003

AbstractRetardation of dissolution of highly oriented polyethylene fibers exposed to solvent under a constant tensile force has been investigated in comparison to free conditions. Beyond a critical value of the applied force, the time for dissolution increases sharply by several orders of magnitude. This effect is significant only in fibers with high initial orientation. It is attributed to the existence of a network of oriented crystallites. We have utilized this effect for surface modification of highly oriented PE fibers, by exposure to solvent at different temperatures and applied stress. At a relatively low load the action of the solvent displays pronounced effects: roughening of the fiber surface, formation of a nonoriented crystalline phase, enhancement of adhesion to epoxy resin with some loss of strength. ©1995 John Wiley & Sons, Inc.