bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive blending via metal‐ligand coordination
Authors: Belfiore Laurence A. , McCurdie Mary Pat
Published: April 2003

d‐Block transition‐metal‐containing polymer blends which form coordination complexes are described in this treatise. The model compounds are zinc acetate dihydrate, copper acetate dihydrate, nickel acetate tetrahydrate, cobalt chloride hexahydrate, palladium chloride bis (acetonitrile), and the dimer of dichlorotricarbonylruthenium (II). Two classes of ligands are of interest. Poly (4‐vinylpyridine), P4VP, and copolymers that contain 4‐vinylpyridine repeat units form complexes with zinc, copper, nickel, cobalt, and ruthenium salts. Atactic 1,2‐polybutadiene contains olefinic sidegroups that displace weakly bound acetonitrile ligands and coordinate to palladium chloride. Thermal analysis via differential scanning calorimetry suggests that the glass transition temperature of the polymeric ligand is enhanced by these low‐molecular‐weight transition‐metal salts in binary and ternary blends. In some cases, d‐block salts function as transition‐metal compatibilizers for copolymers that would otherwise be immiscible. The isothermal ternary phase diagram for polybutadiene with palladium chloride highlights regions of gelation, precipitation, and transparent solutions during blend preparation in tetrahydrofuran. Fourier transform infrared spectroscopy provides molecular‐level data that support the concept of polymeric coordination complexes. High‐resolution carbon‐13 solid‐state NMR spectroscopy identifies (1) near‐neighbor interactions between polymeric pyridine ligands and the ruthenium salt, and (2) a considerable reduction in the molecular mobility of the polybutadiene chain backbone when it forms a coordination complex with palladium chloride. The elastic modulus of polybutadiene increases by three orders of magnitude when the palladium salt concentration is 4 mol % in a solid‐state glassy film. A thermodynamic interpretation of ligand field stabilization energies appropriate to tetrahedral cobalt and octahedral nickel complexes is employed to estimate the synergistic enhancement of the glass transition temperature, particularly when coordination crosslinks are present. ©1995 John Wiley & Sons, Inc.
Thermally stable polyimide isomers for membrane‐based gas separations at elevated temperatures
Authors: Costello L. M. , Koros W. J.
Published: April 2003

The temperature dependence of gas sorption and transport properties is examined for two polyimide isomers. The permeabilities and solubilities of five gases in these materials are reported over an extensive temperature range from 35 to 325°C. Also, the activation energies for permeation, the heats of sorption, and the activation energies for diffusion obtained for both polyimides are compared and correlated with physical properties of the polymers and penetrants. The influence of temperature on the selective properties of these membrane materials is discussed for three gas separations; He/N2, CO2/CH4, and O2/N2. Thorough analysis of these data provides insight into the influence of the subtle difference in chain structure of the two isomers. The performance of the 6FDA‐6Fp DA as a separation membrane at high temperatures suggests that it is an outstanding candidate for use in novel elevated temperature applications. ©1995 John Wiley & Sons, Inc.
Effect of size on the strength of polymeric fibers
Authors: Termonia Yves
Published: April 2003

Using a molecular model introduced previously, we study the effects of chain‐end segregation on the relationship between strength (σ) and diameter (d) in polymeric fibers. For segregated structures with a monodisperse molecular weight distribution, our results show a scaling law σ ∼ d−α, with α in the range [0.4–0.5], in agreement with experimental observation. A weaker dependence is found for polydisperse systems. Further investigation also reveals that macroscopic cracks have little influence on the fiber strength/diameter relationship, unless the crack width shows a faster than linear increase with fiber diameter. Finally, our model results also indicate a very weak dependence of fiber strength on its length, in good agreement with experimental observation. ©1995 John Wiley & Sons, Inc.
Multimodal sorption of nonionic dyes with two amino groups by various polymers from water
Authors: Shibusawa Takao , Nakamura Takashi
Published: April 2003

Sorption isotherms of nonionic dyes with two amino groups (one anthraquinone dye and two azo dyes) on various polymers from water were measured at 40–90°C (Nylon‐6 and cellulose film) and at 95°C (polyester microfiber). The isotherms were curved, convex to upward, in the range of low dye concentration Cs in water and almost linear in the range of medium to saturated Cs. The isotherms measured at low temperature (40°C for cellulose, 40–60°C for Nylon‐6, and at 95°C for polyester) were satisfactorily described by considering three concurrent modes of sorption. They are Nernst type partitioning and bimodal Langmuir sorption (sorption by the higher affinity sites with a small saturation value and that by the lower affinity sites with a large saturation value). However, for the sorption of the anthraquinone dye and one azo dye by Nylon‐6 film at high temperature (80–90°C), the amount of dye sorbed by the high affinity site decreased to negligibly small. Accordingly, the isotherms were expressed well by simple dual‐sorption model. © 1995 John Wiley & Sons, Inc.
NMR and DSC investigations of the miscibility of blends of cis‐1,4‐polyisoprene with polybutadienes of different microstructures
Authors: Bahani Mustapha , Lauprêtre Franco̧ise , Monnerie Lucien
Published: April 2003

Differential scanning calorimetry and torsional braid analysis investigations of the phase diagram of cis‐1,4‐polyisoprene/polybutadiene blends as a function of the polybutadiene microstructure were reported by several authors. Polybutadienes containing a high vinyl content were shown to be miscible with cis‐1,4‐polyisoprene on the DSC spatial scale, whereas polybutadienes containing a low vinyl content were immiscible. In this article, we used variable‐temperature determinations of 1H NMR free induction decays and low‐temperature, high‐resolution solid‐state 13C NMR measurements of proton spin‐lattice relaxation times in the rotating frame to probe the phase behavior of the cis‐1,4‐polyisoprene/polybutadiene blends at the smaller spatial scale of the NMR technique. Blends of cis‐1,4‐polyisoprene with a polybutadiene having a large number of vinyl 1,2 linkages appeared to be miscible on the molecular scale, in spite of small regions in which the polybutadiene component is not uniformily dispersed in the other polymer. On the contrary, blends in which the polybutadiene has a low content of vinyl 1,2 sequences were phase separated over the whole temperature range considered and no intermixed regions could be detected. The limiting case was observed with the polybutadiene containing 33 wt % vinyl 1,2 units, for which miscibility on a molecular scale is highly dependent on the blend composition. © 1995 John Wiley & Sons, Inc.
Effects of drawing on creep parameters of polyoxymethylene‐drawn fibers
Authors: Komatsu Tamikuni , Aoshima Atsushi
Published: April 2003

The effects of drawing on creep parameters (modulus, viscosity, and retardation time) of polyoxymethylenedrawn fibers were examined on the basis of a series‐parallel, four‐element, mechanical model. These parameters increased with the draw ratio. The change in the modulus was the same between the series and parallel components. This was true also for the viscosity, although the change in the viscosity was much greater than that in the modulus. This means that the series and parallel components are deformed in the same mode by drawing. The parallel viscosity increased with elapsed loading times according to an experimental power function; this was also derived from the usual rate equation for viscosity change in the amorphous component. In contrast, the series viscosity remained unchanged over the short creep range due to an extremely larger value than that of the parallel. © 1995 John Wiley & Sons, Inc.
NMR analysis of interaction between styrene‐divinylbenzene gel beads and small molecules
Authors: Ogino Kenji , Sato Hisaya
Published: April 2003

The interaction of small molecules such as cyclohexane, tetrahydrofuran, and acetonitrile with styrene‐divinylbenzene copolymer gel beads were investigated by 13C‐NMR spectroscopy. When the gel content was 0.1–0.3 g/mL, the 13C‐NMR spectrum of the solvent displayed two peaks. A sharp peak at lower magnetic field was assigned to the free solvent, and a broad one to the solvent affected by the gel. This signal splitting is attributed to the upfield shift caused by aromatic rings of styrene units in the polymer chain. The nitrile carbon of acetonitrile showed the largest upfield shift. The mobility of small molecules in gel beads was also investigated using the nuclear magnetic relaxation method. In the case of good solvents for gel beads, the mobility was affected by the cross‐linking density, whereas poor solvents exhibited little dependence of the cross‐linking density. © 1995 John Wiley & Sons, Inc.
Membrane formation by isothermal precipitation in polyamide‐formic acid‐water systems II. Precipitation dynamics
Authors: Cheng Liao‐Ping , Dwan An‐Hwa , Gryte Carl C.
Published: April 2003

An analysis is presented, which describes the isothermal ternary diffusion process encountered in the formation of the aliphatic polyamide membranes such as Nylon‐66 by direct immersion‐precipitation of a polymeric solution in a nonsolvent bath. A material coordinate is employed to derive the mass transfer equations for the membrane solution. The convective mass transfer in the coagulation bath is taken into account by solving the hydrodynamic boundary layer equations. Diffusion coefficients were measured and used to deduce ternary phenomenological coefficients. The computed results are found to agree with measured precipitation times and with membrane morphologies observed by scanning electron photomicrographs. © 1995 John Wiley & Sons, Inc.
About the microstructure of PCVD prepared crystal mats of statistical oligo‐vinylidene‐fluoride‐trifluoroethylene in relation to other fluorinated polymers
Authors: Fischer C. , Krüger J. K. , Bohn K.‐P. , Vogt U. , Schreiber J. , Jiménez R. , Wolf D. , Legrand J. F. , Alnot P. , Servet B.
Published: April 2003

The room temperature phase of the physical/chemical vapor‐deposited statistical co‐oligomer VDF/TrFE(70/30) has been characterized by different experimental methods such as small‐angle x‐ray scattering, wide‐angle x‐ray diffraction, size‐exclusion chromatography, infrared absorption and optical refractometry. The characterization of the elastic properties was carried out using high‐performance Brillouin spectroscopy in connection with special scattering geometries. The co‐oligomer VDF/TrFE(70/30) was obtained by cracking the parent statistical copolymer and subsequently vapor depositing the shortened chains on highly oriented PTFE substrates (PIA‐technique). The room temperature phase of the resulting oriented waxy crystal mats of VDF/TrFE(70/30) is predominantly ferroelectric. The physical properties are very different to those of similarly PIA‐prepared n‐alkanes, perfluoroalkanes, and blockfluoroalkanes. The microstructure of VDF/TrFE(70/30) is interpreted in terms of partially crystalline nano‐sized structures giving rise to a marked freezing process below room temperature. © 1995 John wiley & Sons, Inc.
Nanofoam porosity by infrared spectroscopy
Authors: Sanchez M. I. , Hedrick J. L. , Russell T. P.
Published: April 2003

Infrared spectroscopy has been used to determine the porosity of polymer nanofoams produced from block copolymers of an aromatic polyimide with either poly(propylene oxide) or poly(α‐methyl styrene). It is shown that, with an independent measurement of the film thickness, both the absorption bands and the interference fringes can yield an accurate measure of the void content. The results obtained are in quantitative agreement with density gradient methods. © 1995 John Wiley & Sons, Inc.
Effect of orientation on the relative dispersion of PMDA‐ODA polyimide and polypropylene
Authors: Cha Cheol Y. , Samuels Robert J.
Published: April 2003

The relative dispersion of birefringence, Db, is determined for isotactic polypropylene and Kapton HA PMDA‐ODA polyimide films. Db is then used to identify the dependence of dispersion on the orientation of polymers and is interpreted in terms of fringe jumping. Optical relationships between the in‐plane birefringence and wavelength are formulated to predict the in‐plane birefringence of oriented Kapton HA PMDA‐ODA polyimide films at any wavelength. These relations can be used for the direct comparison of the in‐plane birefringence of Kapton PMDA‐ODA polyimide films obtained from different optical techniques (i.e., polarized microscopy, polarized refractometry, wave guide coupling, etc.). © 1995 John Wiley & Sons, Inc.
Gas permeability and stability of poly(1‐trimethylsilyl‐1‐propyne‐co‐1‐phenyl‐1‐propyne) membranes
Authors: Nagai Kazukiyo , Higuchi Akon , Nakagawa Tsutomu
Published: April 2003

A significant reduction in the gas permeability of the poly(1‐trimethylsilyl‐1‐propyne) (PMSP) membrane was investigated in terms of the membrane thickness and the storage environment. The effects of physical aging were observed with thinner membranes and under vacuum conditions compared with storage in air. The decrease in the permeability coefficient was dependent on the decrease in the hole saturation constant of Langmuir adsorption (C'H), which is related to the volume of the microvoids. Physical aging in the PMSP membrane affected not only the glassy domain but also the rubbery one. To stabilize the permeability of the PMSP membrane, a poly(1‐trimethylsilyl‐1‐propyne‐co‐1‐phenyl‐1‐propyne) [poly(TMSP‐co‐PP)] membrane was prepared. Poly(TMSP‐co‐PP) has the same unit of poly(1‐phenyl‐1‐propyne), which membrane has stable permeability. The poly(TMSP‐co‐PP) with less than 20 mol % PP content was estimated to be a random copolymer based on theoretical gas permeation analysis. In the poly(TMSP‐co‐PP) membrane, the relation between the PP content and C'H was similar to the relation between the PP content and the gas permeability. The stability of the permeability was dependent on the PP content. The poly(TMSP‐co‐PP) membrane containing 10 mol % PP had both high permeability and good stability under some of the aging conditions performed in this work. © 1995 John Wiley & Sons, Inc.
Rotational and translational diffusion of low molecular weight substances in polyblock copolymers with soft and rigid blocks
Authors: Krykin M. A. , Dadaly A. A. , Gasyuk O. V. , Ozerin A. N. , Rebrov A. V. , Shmukler R. A. , Storozhuk I. P. , Wasserman A. M.
Published: April 2003

The rotational diffusion of spin‐probes and the translational diffusion of n‐pentane in a series of random‐block copolymers (BSP) have been studied as a function of composition and block lengths. It was shown that the local diffusion properties of the BCP microphases depend on these two characteristics of BCP. © 1995 John Wiley & Sons, Inc.
The glass temperature of dendritic polymers
Authors: Stutz Herbert
Published: April 2003

A theoretical treatment of the glass temperature of dendritic polymers is presented. The influences of polymer backbone, end group, initiator core, branching unit, composition and functionality are discussed. In dendritic polymers the glass temperature is dependent only on the generation number of dendritic growth and thus only on the molecular weight of a dendron, but not on the molecular weight of the whole molecule. It is governed primarily by the backbone glass temperature and depends little on branching functionality. Only minor differences between linear polymer and dendrite are obtained, since the influences of end groups and branching compensate each other to a large extent. © 1995 John Wiley & Sons, Inc.
Composite spectral density functions for the interpretation of the 13C NMR relaxation behavior of polymers containing hydrocarbon side chains. Free and restricted side chain motion
Authors: Spyros A. , Dais Photis
Published: April 2003

13C NMR NT1 and NOE have been calculated by using composite spectral density functions describing polymer chain segmental motion and internal rotation of a hydrocarbon side chain attached to the polymer backbone. Numerical results at two magnetic fields are presented as a function of the various motional parameters characterizing the various models. NT1 and NOE relaxation parameters are well behaved and appear to have practical value for describing the dynamics of these systems. The models have been applied to the relaxation data of poly(n‐butyl methacrylate) and poly(n‐hexyl methacrylate) in toluene solutions. The dynamics of the two polymers are characterized by a very localized backbone motion and restricted internal rotation about successive CC bonds of the side chains. © 1995 John Wiley & Sons, Inc.
Molecular images of [M(phthalocyaninato)O]n, where M = Si and Ge: Microphases and structures of crystal domains
Authors: Wu Junhua , Zou Bensan , Pan Ziang , Du Xueli , Zhou Xiao
Published: April 2003

This contribution is a study of the crystal structures and crystal domains in the thin epitaxially growing films of [M(Pc)O]n (M = Si and Ge, Pc = phthalocyaninato) revealed by high‐resolution electron microscopy. Microphases detectable only on the microscopic level were observed: (a) γ‐phase for [Si(Pc)O]n, orthorhombic system, a = 1.38 nm, b = 5.52 nm, c = 0.66 nm; and (b) α‐phase for [Ge(Pc)O]n, base‐centered orthorhombic, a = 1.33 nm, b = 2.66 nm, c = 0.35 nm. Translation and rotation crystal domains were visualized on the nanometeric scale. The high‐resolution images are rich in irregularity and provide direct information on the defects and imperfections in the polymer films. © 1995 John Wiley & Sons, Inc.
Viscoelasticity and birefringence of polyisoprene
Authors: Okamoto Hirotaka , Inoue Tadashi , Osaki Kunihiro
Published: April 2003

The complex Young's modulus, E*(ω), and the complex strain‐optical coefficient, O*(ω), which is the ratio of the birefringence to the strain, were measured for polyisoprene (PIP) over a frequency range of 1 ∼ 130 Hz and a temperature range of 22 ∼ −100°C. The imaginary part of O*, O″, was positive at low frequencies and negative at high frequencies. The real part, O′, was always positive and showed a maximum. The complicated behavior of O* could be understood by the assumption that E* = ER* + EG* and O* = CRER* + CGEG*, where ER* and EG* were complex quantities and CR and CG were constants. The CR value, equal to the ordinary stress‐optical coefficient measured in the rubbery plateau zone, was 2.0 × 10−9 Pa−1. The CG value, defined as the ratio O″/E″ in the glassy zone, was −1.1 × 10−11 Pa−1. The EG*, which was the major component of E* in the glassy zone, showed almost the same frequency dependence as that of polystyrene and polycarbonate. The ER*, which was dominant in the rubbery zone, was described well by the bead‐spring theory. The temperature dependence of the EG* was stronger than that of the ER*. This difference caused the breakdown of the thermorheological simplicity for E* and O* around the glass‐to‐rubber transition zone. © 1995 John Wiley & Sons, Inc.
Mutual diffusion and thermodynamics in the blends of polystyrene and tetramethylbisphenol‐A polycarbonate
Authors: Kim Eugene , Kramer Edward J. , Osby John O. , Walsh David J.
Published: April 2003

A study was made of miscible polymer blends of deuterated polystyrene (d‐PS) and tetramethylbisphenol‐A polycarbonate (TMPC). The Flory interaction parameter χ was obtained from the relation between mutual and tracer diffusion coefficients, D̃ and D*, which were measured by forward recoil spectrometry. The temperature dependence of diffusion at PS weight fractions ω of 0.25 and 0.5, and the composition dependence at temperatures 45°C above the glass transition temperature, Tg, were investigated. A stronger dependence of χ on both temperature (at ω = 0.5) and composition was observed in comparison with other miscible binary polymer blends involving PS. Analysis using the generalized lattice‐fluid model of Sanchez and Balazs1 showed that the incorporation of a significant specific interaction is needed to explain the temperature dependence of χ. The diffusion coefficients obtained in the one‐phase region were extrapolated to the two‐phase region, and these were compared with the effective diffusion coefficient extracted from phase separation dynamics measured by light scattering.2 A significant discrepancy between the extrapolated and effective diffusion coefficients was observed. © 1995 John Wiley & Sons, Inc.
Comparison of rheological properties of cross‐linked and thermal‐mechanically degraded HDPE
Authors: Harlin Ali , Heino Eeva‐Leena
Published: April 2003

Rheological properties of a high‐density polyethylene (HDPE) subjected to thermal‐mechanical degradation were compared with those of the HDPE degraded by the addition of small quantities of peroxides as free radical initiator. The high molecular weight fraction of HDPE changes quantitatively during processing, which has a remarkable effect on the rheological properties of the material, when the MWD narrows and the HMW tail decreases. The molecular weight distribution, especially the highest molecular weight fraction, is concluded to be more important than the long chain for HDPE rheology. © 1995 John Wiley & Sons, Inc.
Dynamic aspects of phase decomposition in reactive blends of polycarbonate and syndiotactic polymethyl methacrylate
Authors: Ko Che‐Chian , Kyu Thein , Smith Steven D.
Published: April 2003

Dynamics of phase separation in bisphenol‐A polycarbonate (PC)/syndiotactic polymethyl methacrylate (sPMMA) blends has been investigated by means of time‐resolved light scattering. Solvent‐cast films of the PC/sPMMA blends were transparent, suggestive of miscible character. Several temperature jumps were carried out at a 50/50 PC/sPMMA composition from a homogeneous state (room temperature) into a two‐phase regime. The process of phase separation first occurred for some considerable period, then it was followed by phase dissolution driven by chemical reaction. The thermodegradative reaction of sPMMA triggered the dissolution process by probably forming PC/sPMMA graft or random copolymers at the interface, which eventually resulted in a single phase. However, annealing at elevated temperatures for an extended period could lead to cross‐linking, and thus a two‐phase structure could be fixed permanently. The early stage of spinodal decomposition was interpreted in terms of the linearized Cahn‐Hilliard theory. In the late stages of spinodal decomposition, the relationship between scattering peak wavenumber and time was found to obey a power law, but the exponents showed a strong dependence on temperature jumps. The temporal universal scaling failed due to the influence of the chemical reaction. © 1995 John Wiley & Sons, Inc.
Miscibility studies of poly(3‐octylthiophene)/poly(ethylene‐co‐vinylacetate) blends with a solvatochromatic shift in the solid state
Authors: Levon K. , Chu E. , Ho K.‐S. , Kwei T. K. , Mao J. , Zheng W.‐Y. , Laakso J.
Published: April 2003

The mixing of electrically conducting polymers in the undoped state with flexible polymers has been limited due to the stiffness of the delocalized coplanar backbone. The substitution with alkyl side chains has resulted in the distortion of the aromatic rings in the backbone with an increase of the flexibility. The alkyl substituents also prevent the thiophene back‐bones from packing together, thus making blending with other polymers promising. We have investigated the phase behavior of poly(3‐octylthiophene) (P3OT) with a flexible polymer, poly(ethylene‐co‐vinylacetate) (vinylacetate composition 20%, EVA20), and defined a miscibility window based on melting point data, on cloud point measurements, and on analysis by optical microscopy. The miscible region has been studied by UV‐VIS and CPMAS NMR spectroscopies. A UV absorption in the visible region originates from a π‐π * transition in the delocalized structure of P3OT, and a change in the length of the conjugated segment in the backbone results in a shift of this absorption. A gradual solvatochromatic shift of P3OT in the solid state with dilution was observed in the miscible region. T1 relaxation times for the methylene carbons in solid state show a gradual change in the relaxation process as a function of composition. © 1995 John Wiley & Sons, Inc.
A molecular composite approach to the thermal expansion behavior for anisotropic crystalline polymers
Authors: Zahran R. R. , Kardos J. L.
Published: April 2003

The dimensional stability of crystalline polymers such as polyethylene and polypropylene is a critical property in structural applications requiring known dimensional stability. It is essential to evaluate how such structural systems will respond when exposed to thermal fluctuations. Utilizing the molecular composite approach, oriented polyethylene has been modeled as a macroscopic composite of its constituent crystalline and amorphous phases. The molecular composite model, originally developed to describe the isotropic behavior of crystalline polymers, has been refined to account for the anisotropic micromorphological behavior of oriented polyethylene solids. This refinement accounts for the deformation and orientation of both constituent phases; the variation of the amorphous phase mechanical and expansional properties due to the taut tie molecules has likewise been considered. Furthermore, a theoretical expression relating the crystalline orientation descriptors, λ and fc, has been developed. A detailed calculational format for the prediction of the expansivity of oriented polyethylene is outlined. The overall pattern of anisotropic dimensional behavior has been correctly predicted when compared with experimentally measured thermal expansivities of various types of polyethylene. © 1995 John Wiley & Sons, Inc.
Physical and chemical evolution of PMDA‐ODA during thermal imidization
Authors: Ojeda Jaime R. , Mobley Juliana , Martin David C.
Published: April 2003

The 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

1H 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

Two 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

Elastic 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

An 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

It 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

Packing 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

X‐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

The 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

Polyethylene–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

Thin 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

Emeraldine 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

The 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

Free 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

The 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

Ionic 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

Hooke 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

Chitosan 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.