bluuebunny/crossref_metadata_2025 huggingface dataset:
Single‐Molecule single crystals of isotactic polystyrene
Authors: Bu Haishan , Chen Erqiang , Xu Shengyong , Guo Kexin , Wunderlich Bernhard
Published: April 2003

Single‐molecule single crystals were grown from amorphous droplets of fractionated isotactic polystyrene. The crystals were analyzed by electron microscopy and electron diffraction. The molecular mass distribution could be matched with a statistical analysis of single‐molecule particles (amorphous and crystals). Proof was brought that single molecules of isotactic polystyrene do not reach equilibrium dimensions on crystallization, rather assume the lamellar morphology with chain‐folded macroconformation, also known from crystallization of polymolecular crystals. © 1994 John Wiley & Sons, Inc.

This article is a US Government work and, as such, is in the public domain in the United States of America. US Government contract No. DE‐AC05‐840R‐21400.
Adsorption‐desorption behavior of phenols on novel polymers containing the pyrrolidinone moiety
Authors: Atobe Ichiro , Takata Toshikazu , Endo Takeshi
Published: April 2003

Crosslinked polymers having a pyrrolidinone moiety (CPS, CPES, and CVP) were synthesized by radical copolymerization of 4‐(2‐oxo‐1‐pyrrolidinyl)methylstyrene, 4‐[2‐(2‐oxo‐1‐pyrrolidinyl)ethoxy]methylstyrene, or 2‐vinylpyrrolidinone with divinylbenzene in the presence of AIBN as a radical initiator. The adsorption‐desorption behavior of phenols on these polymers was investigated. The polymers with spacers between the polymer main chain and pyrrolidinone moiety appeared to have a superior adsorption capability to those without such spacers. The amount of phenol adsorbed on the polymers in a solvent decreased in the following order: water > chloroform > methanol. In methanol, the interaction between the polymers and phenol was suggested to come only from charge‐transfer stacking (C–T stacking), whereas in chloroform the interaction was caused mainly by both hydrogen bonding and C–T stacking. The interaction in water was attributed not only to both hydrogen bonding and C–T stacking, but also to a hydrophobic interaction. Characterization of polymers (CVP) containing adsorbed phenol was carried out by thermogravimetric analysis (TGA). The TGA curves indicated a two step weight‐decrease, namely the first step in the temperature ranging from ca. 100‐200°C was attributed to the desorption of phenol while the second step in the temperature ranging from ca. 350‐500°C was based on thermal decomposition of the polymers. The desorption of phenol adsorbed on the polymers in water indicated an inverse tendency to the adsorption; that is, the amount of phenol desorbed from the polymers without a spacer was more than those from the polymers with spacers. © 1994 John Wiley & Sons, Inc.
Plasma‐enhanced deposition of diamond‐like carbon films on high temperature tolerant polymers
Authors: Freeman Mathieu J. , Harding David R.
Published: April 2003

The feasibility of depositing carbon films with a diamond‐like structure on high temperature polymers, using established plasma‐enhanced chemical vapor deposition techniques, is explored. Potential uses for such a film will depend upon the adhesion of the film to the substrate, the properties of the deposited film, and the effect of the deposition process on the bulk properties of the polymer substrate.

Amorphous carbon (diamond‐like carbon) coatings with thicknesses ranging from 2 to 18 μm were deposited on polyimide substrates at temperatures below 420°C. Extended exposure to the plasma processing conditions caused no visible damage but halved the room‐temperature tensile strength of the polymer films. Diamond‐like carbon, graphitic carbon, and a precursor to the diamond‐like carbon structure, attributed to an aromatic carbon ring structure, were observed. The optical transparency of the coated polymer film was attenuated uniformly across the spectral range, 2.5‐22 μm. Static oxidation and limited thermal cycling of the coated polymer produced no widespread delamination of the coating from the substrate: neither the deposited film nor the coated regions of the polymer showed any effect when oxidized at 370°C, for 450 h. © 1994 John Wiley & Sons, Inc.
Thermal conductivity of poly(ether ether ketone) and its short‐fiber composites
Authors: Choy C. L. , Kwok K. W. , Leung W. P. , Lau Felix P.
Published: April 2003

The effects of crystallinity, orientation, and short‐fiber filler on the thermal diffusivity D and thermal conductivity K of poly (ether ether ketone) (PEEK) have been studied. Below the glass transition, D increases by less than 10% as the crystallinity increases from 0 to 0.3. For amorphous PEEK, there is an abrupt drop in D at the glass transition (Tg ⋍ 420 K). The drop is less prominent for the 30% crystalline sample and occurs at 20 K higher. At a draw ratio of 2.5, the axial thermal conductivity is 2.3 times higher while the transverse thermal conductivity is 30% lower than that of the unoriented material. For an injection‐molded bar of carbon fiber reinforced PEEK, the variation of D with position along the width or thickness direction is found to correlate well with the fiber orientation. By regarding the injection‐molded bar as a multidirectional laminate comprising a large number of unidirectional plies, the thermal conductivities along the longitudinal and transverse direction are calculated and found to agree closely with the experimental data. © 1994 John Wiley & Sons, Inc.
An improved model for mass transfer during the formation of polymeric membranes by the immersion‐precipitation process
Authors: Cheng Liao‐Ping , Soh Young S. , 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 a cellulose acetate polymeric membrane by a direct immersion‐precipitation of polymeric solutions in a nonsolvent bath. A material coordinate was employed to derive the mass transfer equations for the membrane solution and the convective mass transfer in the coagulation bath was 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 the experimental precipitation time and membrane morphologies observed in scanning electron photomicrographs. © 1994 John Wiley & Sons, Inc.
Light‐Scattering evidence of a “critical” concentration for polymer coil shrinking in dilute solution
Authors: Wu Chi
Published: April 2003

The variation of polymer chain dimension with concentration in both dilute and extremely dilute solutions was monitored by measuring the diffusivity of narrowly distributed poly‐styrene standards in toluene at room temperature through a carefully designed dynamic light scattering experiment. As polystyrene concentration decreases, the measured translational diffusion coefficient levels off after a certain concentration, i.e., in terms of experimental results, there exists a “critical” concentration for polystyrene coil shrinking in dilute toluene solution. The existence of this critical concentration has been predicted by introducing the concept of screening length into the statistical thermodynamic calculation. In this paper, we report, for the first time, its laser light‐scattering evidence. © 1994 John Wiley & Sons, Inc.
Doi‐Edwards theory evaluation in double‐step strain flows
Authors: Venerus D. C. , Kahvand H.
Published: April 2003

It is widely accepted that for reversing double‐step strain deformations, predictions based on the Doi‐Edwards (DE) molecular theory without the independent alignment approximation (IAA) are superior to predictions obtained with the IAA, or equivalently, the Kaye‐Bernstein‐Kearsley‐Zapas (K‐BKZ) theory. This summation, however, is based on data obtained over limited ranges of strain and time: the time both between the step strains (t1) and following the second step strain (t–t1). In this study, a thorough evaluation of the DE theory is carried out using a comprehensive double‐step strain flow data set. The results of this study indicate that the DE theory is an improvement over the K‐BKZ theory in flows with strain reversal but only for cases when the criteria t1, t–t1 ≫ τk is satisfied. The constant τk, defined as the time beyond which the stress relaxation modulus is factorable: G(γ, t) = h(γ)G(t), is believed to represent the end of the chain retraction process in the DE theory. It appears that the dynamics of chain retraction have an important influence on double‐step strain behavior and, therefore, should be accounted for in molecular‐based theories devised to have general validity in this important deformation history. © 1994 John Wiley & Sons, Inc.
PVT properties of dodecane/polystyrene systems
Authors: Kim Dukjoon , Caruthers James M. , Peppas Nikolaos A.
Published: April 2003

The PVT properties of crosslinked polystyrene samples containing various amounts of dodecane were measured. The Tait equation was used to describe the PVT behavior of each system in both the glassy and rubbery regions. The glass transition temperature was determined from the abrupt change of the thermal expansion coefficient. Increase in the dodecane content in the samples resulted in a significant decrease of the difference between the expansion coefficients in the glassy and rubbery regions. Addition of dodecane lowered the glass transition temperature linearly. However, the dependence of the glass transition temperature on pressure was not affected by the presence of dodecane in the polymer samples. Above the glass transition temperature, the volume of the swollen polymer, Vm, could be determined by simple addition of the volumes of the pure components at the appropriate temperature and pressure; the volume change of mixing, δVm, was independent of temperature and pressure. Below the glass transition temperature, volume additivity of the two components was also applicable after appropriate adjustment of the glass transition temperature of the polymer to that of the dodecane/polymer samples. © 1994 John Wiley & Sons, Inc.
Dielectric relaxations in poly(thiocarbonates)
Authors: Calleja R. Díaz , Gargallo L. , Radić D.
Published: April 2003

The dielectric absorptions observed on six poly(thiocarbonates) (PTC) containing different substituents in the interphenylic carbon atom are subjected to a study. The α relaxation process associated with the glass transition temperature, which appears at the highest temperature studied, is overlapped with a strong conductive component. Between 80 and 100°C dielectric activity (β) is observed, which is related to structural relaxation phenomena. Polymers with double substitution on the interphenylic carbon atom show a γ relaxation with an activation energy of ca. 11 kcal mol−1 while those where the carbon atom is linked to a cyclohexyl group show higher activation energies and their respective characteristics. A cryogenic absorption around −120°C, for at least three polymers with an activation energy of about 5 kcal mol−1, is detected. © 1994 John Wiley & Sons, Inc.
Aspects of polymer surface characterization by inverse gas chromatography
Authors: Mukhopadhyay Prithu , Schreiber H. P.
Published: April 2003

The inverse gas chromatographic method has been used to evaluate dispersive surface energies and acid/base interaction values for a styrene/maleic anhydride copolymer over a substantial temperature range. Surface energy calculations require knowledge of the dimensions of adsorbed molecules; conventional values of these for linear alkanes result in reliable surface energy data at near‐ambient temperatures. Above about 60°C, however, more reliable surface energy data are obtained when the dimensions of the adsorbed species are corrected by density/temperature variations of the vapors. The copolymer studied was shown to be amphoteric, but with an appreciable prevalence of basic surface sites. © 1994 John Wiley & Sons, Inc.
Effect of styrene‐4‐vinyl pyridine diblock copolymer on morphological, thermal, and mechanical properties of poly(2,6‐dimethyl‐1,4‐phenylene ether)/polyethylene ionomer blends
Authors: Jo Won Ho , Jo Byoung Cheon , Cho Jae Cheol
Published: April 2003

The compatibilizing effects of a styrene‐4‐vinyl pyridine diblock copolymer on the properties of immiscible poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE)/polyethylene ionomer (Surlyn) blends are investigated by examining the phase morphology and the thermal and mechanical properties. The block copolymer is synthesized by sequential anionic polymerization at −78°C and melt‐mixed with PPE and Surlyn at 290°C. When a small amount of block copolymer is present, the domain size of the dispersed phase becomes smaller. The tensile strength and elongation at break increase with addition of the block copolymer for PPE‐rich matrix blends, whereas the tensile strength increases but the elongation at break decreases for Surlyn‐rich matrix blends. These effects are interpreted in terms of the interfacial activity and the reinforcing effect of the block copolymer. From the experimental results, it is concluded that the block copolymer plays a role as an effective compatibilizer for PPE/Surlyn blends. © 1994 John Wiley & Sons, Inc.
Poly[(methylene oxide) oligo(ethylene oxide)] vs. poly(ethylene oxide) as hosts for neodymium compounds
Authors: Twomey Conor J. , Chen Shaw H. , Blanton Thomas N. , Schmid Ansgar , Marshall Kenneth L.
Published: April 2003

In view of the residual crystallinity in PEO found to limit the solubility of some Nd3+‐compounds, amorphous PEO (aPEO) was synthesized for exploration as an alternative host. Complexation, solubility limit, morphology, and response to moisture absorption in the doped systems were investigated using FTIR, DSC, TGA, and WAXD techniques. Representing a perturbation to the structural regularity present in PEO, aPEO was found to present lower solubilities for dopants (Nd(act)3 and Nd(acac)3, both characterized by a weak Nd3+–ether oxygen interaction. On the other hand, no difference in solubility was observed for dopant Nd(NO3)3, characterized by a strong Nd3+–ether oxygen interaction. Laser interferometry was employed to assess film homogeneity of the Nd(NO3)3‐doped systems across a 20‐mm diameter, and the measured peak‐to‐valley distortion values were observed to be encouraging for practical applications. © 1994 John Wiley & Sons, Inc.
Towards understanding the increase in strength of thermotropic polyesters with heat treatment
Authors: Warner S. B. , Lee J.
Published: April 2003

Thermotropic copolyester fibers of oxynaphthoate and oxybenzoate have been subjected to conditions that promote solid‐state polymerization as well as annealing. The annealing process causes the crystals to perfect with a simultaneous increase in heat of fusion and melting temperature. Solid‐state polymerization, a reaction rate‐controlled process, causes the polymer viscosity average molecular weight to increase by chain extension from about 14,000 g/mole to more than 87,000 g/mole with a simultaneous impressive increase in tenacity from about 10 g/d (1.2 GPa) to almost 30 g/d (3.7 GPa). To understand the changes in mechanical properties, we have modeled the fiber structure as short rod‐like molecules poorly bonded to a continuous matrix of parallel molecules. Lengthening of the reinforcing molecules facilitates better transfer of load from matrix to molecules, resulting in higher tenacity fibers. © 1994 John Wiley & Sons, Inc.
Thermal characterization of tetrafluoroethylene‐perfluoroalkylvinylether copolymers: Melting behavior and low‐temperature transitions
Authors: Pucciariello Rachele
Published: April 2003

Differential scanning calorimetry has been used to study the melting and the low‐temperature transitions of tetrafluoroethylene‐perfluoroalkylvinylether copolymers (PFA). Melting is similar to that of PTFE in that it is subject to superheating, moreover the melt‐crystallized samples show temperatures and heats of fusion lower than the native ones. At temperatures lower than room temperature, crystal‐crystal transitions are observed for copolymers containing 2 mol % of perfluoromethyl‐, perfluoroethyl‐, and perfluoro‐n‐propylvinylether. In the case of perfluoromethylvinylether as a comonomer, low‐temperature transitions are present only up to a content of 4 mol %. The effect on melting and low‐temperature transitions of both the comonomer content and of the type of side groups has been investigated. The temperatures and heats of transitions show the expected dependence as a function of the comonomer concentration and have been found to be independent on the chemical nature of the side group. © 1994 John Wiley & Sons, Inc.
Surface stress‐dependent adhesion to fluorinated polymers
Authors: Rye R. R.
Published: April 2003

Irradiation of thin commercial sheets of poly(tetrafluoroethylene) (PTFE) or a fluorinated ethylene‐propylene copolymer (FEP) yield essentially the same results with mass spectroscopy or x‐ray photoelectron spectroscopy (XPS). For both gas phase and surface (ca. 30 Å) products of irradiation, the same product distributions and exposure dependencies are observed. In addition, XPS of chemically etched (with sodium naphthalenide) PTFE and FEP shows the same extent of surface defluorination. In contrast to the more surface‐sensitive XPS, Rutherford backscattering spectroscopy of etched PTFE shows that the defluorination extends to depths of ca. 3000 Å, while with etched FEP defluorination extends to only a few hundred Angstroms. Scanning electron microscopy shows the FEP surface to be smooth and featureless both before and after chemical etching, while etched PTFE is characterized by a crazed surface with a high density of unidirectional cracks oriented perpendicular to long macroscopic scratches existing in the virgin surface. Adhesion of Cu to this etched PTFE has previously been shown to be sufficiently strong that failure is a result of near‐cohesive failure in the PTFE and not adhesive failure. Conversely, weak adhesion of Cu to etched FEP or to other smooth forms of fluorinated polymers, including polished PTFE, is observed. This correlation of strong adhesion with surface roughness and not with surface chemical changes is consistent with previous suggestions that a major component of adhesion to fluorinated polymers is mechanical interlocking. The differences between FEP and PTFE are discussed in terms of a model involving surface stresses expected from their different methods of manufacture: extrusion from the melt in the case of FEP and skiving from pressed cylinders in the case of PTFE. © 1994 John Wiley & Sons, Inc.
P‐V‐T properties of alternating poly(ethylene‐propylene) liquids
Authors: Chen S.‐j. , Chiew Y. C. , Gardecki J. A. , Nilsen S. , Radosz M.
Published: April 2003

The pressure‐volume‐temperature (P‐V‐T) properties of monodisperse alternating poly(ethylene‐propylene) (hydrogenated polyisoprene) melts of varying molecular weights are measured at 0.1 MPa < P < 200.1 MPa, and 290 K < T < 510 K in a dilatometer‐type apparatus. The Flory‐Orwoll‐Vrij (FOV), Modified Cell Model (MCM), Sanchez‐Lacombe (SL), and the Statistical Associating Fluid Theory (SAFT) equations of state are found to correlate the experimental data with excellent accuracy, except either at low pressures and high temperatures, or at high pressures and low temperatures. On average, MCM and SAFT fit the data slightly better than FOV and SL. The equation‐of‐state parameters are found to be independent of molecular weight, especially for SAFT, as required by the theory. © 1994 John Wiley & Sons, Inc.
Mechanical properties of unsaturated polyester resins in relation to their chemical structure: 2. Plastic deformation behavior
Authors: Melot D. , Escaig B. , Lefebvre J. M. , Eustache R. P. , Lauprêtre F.
Published: April 2003

The plastic deformation behavior of unsaturated polyester (UP) networks has been investigated in compression at constant strain‐rate over a wide temperature range. The temperature evolution of the activation parameters is directly related to the local molecular dynamics of the different networks previously characterized by dynamic mechanical spectroscopy and high resolution 13C solid‐state NMR. © 1994 John Wiley & sons, Inc.
TEM evidence for the existence of conducting islands in highly conductive polyaniline
Authors: Lux F. , Hinrichsen G. , Pohl M. M.
Published: April 2003

This article deals with the microlevel structure of the electronically conductive polymer, polyaniline, on the basis of the conducting islands model of Epstein et al. The paper presents, for the first time, TEM pictures of the microlevel structure of heavily doped polyaniline, possibly showing the conducting islands in the material. © 1994 John Wiley & Sons, Inc.
Compatibilization of polypropylene/poly (ethylene oxide) blends and crystallization behavior of the blends
Authors: Tang Tao , Huang Baotong
Published: April 2003

The compatibilization of incompatible polypropylene (PP)/poly(ethylene oxide) (PEO) blends was studied. The experimental results showed that the graft copolymer [(PP‐MA)‐g‐PEO] of maleated PP(PP‐MA) and mono‐hydroxyl PEO (PEO‐OH) was a good compatibilizer for the PP/PEO blends in which PP‐MA also had some compatibilization. The crystallization of the blends was affected by the compatibility between PP and PEO. The interfacial behavior of the compatibilizers had an important effect on crystallization behavior of the PP/PEO blends. PEO showed fractionated crystallization in the PP/PEO blends. This behavior was studied from the view point of the theory of fractionated crystallization. © 1994 John Wiley & Sons, Inc.
Specific heat capacity and melting/crystallization characteristics of polytridecanolactone
Authors: Skoglund Peter , Fransson Åke
Published: April 2003

An investigation of the thermodynamical properties of polytridecanolactone (PTDL) was made with the aid of a differential scanning calorimeter (DSC). PTDL is a linear polyester and belongs to the polylactones, which have been poorly investigated. In this paper we contribute with specific heat capacity in the range 180‐400 K, and melting and glass transition characteristics. Further, we present unique results corresponding to the effect of different cooling rates on crystallization temperatures and crystallization energies. PTDL has a melting temperature of 350 K, and a glass transition at about 237 K. The crystallization results show that PTDL crystallizes easily, with a crystallization degree of about 80%. In addition, the crystallization energy decreases with increasing cooling rate, and levels out at a constant value at higher cooling rates. The crystallization temperature, on the other hand, shows an increasing sensitivity of cooling rate, where the supercooling is increasing more rapidly at higher cooling rates. © 1994 John Wiley & Sons, Inc.
Polyimide‐polysiloxane‐segmented copolymers as high‐temperature polymer electrolytes
Authors: Tian S. B. , Pak Y. S. , Xu G.
Published: April 2003

Based on the fact that the flexibility of the polymer backbone will affect the ion transport and sometimes enhance the ionic conductivity, copolymer electrolytes of 1,2,4,5‐benzene‐tetracarboxylic dianhydride (PMDA), 4‐aminophenyl ether (ODA), and aminopropyldimethyl‐terminated polydimethylsiloxane (PSX), with or without doping of lithium triflate, have been prepared and investigated by infrared spectroscopy and electrical conductivity measurements. The PSX was found to be incorporated into PMDA‐ODA polyimide to form block copolymers, and the best conductivity (10‐7 s/cm at 300°C) is observed in the lithium triflate‐doped PMDA‐ODA‐PSX copolymer with a composition of 4PMDA: 3DA: 0.6PSX: 2LiCF3SO3. This conductivity is about 100 times better than the result of the lithium‐doped PMDA, ODA, and 2,5‐diaminobenzene sulfonic acid (DABSA) copolymer (4PMDA: 3DA:1DABSA:1LiCF3SO3) recently reported by this group. © 1994 John Wiley & Sons, Inc.
A study of tensile yielding of isotactic polypropylene
Authors: Liu Yan , Truss Rowan W.
Published: April 2003

The yielding behavior of isotactic polypropylene (iPP) sheets prepared by hot pressing was studied by tensile testing. The corresponding microstructural changes in the specimens after testing were investigated by image analysis, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The yielding of iPP was found to follow a two‐process Eyring yielding model. In the necked regions, stress‐whitening occurred only in specimens tested over a certain range of strain rates and temperatures. The occurrence of the stress‐whitening was correlated well with the activation of Process II in the two‐process Eyring model. SEM revealed that the stress‐whitening in the necked regions was associated with the formation of craze‐like structures that were parallel to the loading direction. Furthermore, DSC analysis showed that the necked regions of the unwhitened tensile specimens had an additional low‐temperature melting peak. However, no additional melting peaks were found in the stress‐whitened specimens. © 1994 John Wiley & Sons, Inc.
FTIR‐ATR studies of drawing and poling in polymer bilaminate films
Authors: Chen Gang Chi , Su Ji , Fina Leslie J.
Published: April 2003

A large increase in the remnant polarization of drawn and poled poly(vinylidene fluoride) (PVF2)/nylon 11 bilaminates compared with the individual films observed in other studies provides the motivation for the examination of dipole orientation in variously treated single and bilaminate films with FTIR‐ATR spectroscopy. Four ATR spectra are collected from each surface using two sample orientations and two light polarizations for each incident light angle. The incident light angle is varied to obtain information about the change in structure with depth. Computer simulations of the experimental optics using anisotropic optical constants aides in the interpretation of experimental results. As the result of simple one‐way drawing in PVF2 and nylon 11, anisotropy in dipole orientation is observed in the plane transverse to the draw direction. In both single and bilaminate films, the average direction of the amide plane in nylon 11 and the CF2 dipoles in PVF2 resides in the plane of the film, perpendicular to the subsequent poling field direction as a result of one‐way drawing. The transverse plane orientation is depth dependent in nylon 11 in both single and bilaminate films and is attributed to a surface‐induced effect. Poling fields of 1.6 MV/cm produce large differences between the surfaces of single films and the bilaminates. At the interior interface of the drawn and poled bilaminates, the PVF2 and nylon 11 dipoles important in polarization appear to be random. The structural implications of this as well as other observations from the spectra are interpreted in terms of the large remnant bulk polarization in the poled bilaminate. © 1994 John Wiley & Sons, Inc.
23Na NMR in urethane cross‐linked polyether solid polymer electrolytes
Authors: Forsyth M. , Smith M. E. , Meakin P. , MacFarlane D. R.
Published: April 2003

Sodium triflate/polyether urethane polymer electrolytes ranging in concentration from 0.05 molal to 1.75 molal have been investigated via 23Na static solid‐state NMR. Room temperature spectra and spin lattice relaxation times were consistent with a single narrow resonance indicating the presence of only mobile ionic species. The concentration and temperature dependence of relaxation times, chemical shifts, and linewidth have been investigated. The results suggest either a single species or rapid exchange between a number of species (even at temperatures below the glass transition temperature, Tg). The linewidth decreases with increasing concentration of ions and remains temperature independent below Tg. Below Tg a maximum quadrupolar interaction constant of 2 MHz is calculated. The addition of plasticizer to the polymer electrolyte causes significant chemical shift changes that depend on the solvent donicity of the plasticizer. The linewidth and T1 relaxation times also depend on the Tg of the plasticized systems. Previous 23Na NMR literature results are reviewed and qualitative models developed to account for the variation in results. © 1994 John Wiley & Sons, Inc.
Analysis of the cure‐dependent dielectric relaxation behavior of an epoxy resin
Authors: Deng Yong , Martin George C.
Published: April 2003

The dielectric relaxation behavior of an epoxy‐amine resin was investigated using the Williams‐Watts relaxation function. Phenomenologically, the dielectric features of the resin during cure are similar to those of stable materials. The distribution parameter of the dipole relaxation decreases from the onset of cure to a conversion near the gel point and then maintains a constant value. Based on the experimental observations and theoretical considerations, a single‐frequency approach has been proposed for extracting the relaxation time of maximum loss. The relaxation data so obtained are independent of the measurement frequency and are in agreement with those acquired directly from the dipole loss peaks. © 1994 John Wiley & Sons, Inc.
Ostwald ripening in an immiscible hydrogenated polybutadiene and high‐density polyethylene blend
Authors: Mirabella, Jr. Francis M. , Barley Jeffrey S.
Published: April 2003

The long‐time regime coarsening in a phase‐segregated blend of hydrogenated polybutadiene (HPB) with high‐density polyethylene (HDPE) was studied. The blend consisted of 10 wt% of HPB in a HDPE matrix. The morphology of the system was studied by etching the HPB particles from the HDPE matrix and observing the etched specimens in a scanning electron microscope. The average volume of the HPB particles was found to increase with storage time in the melt, and to follow a temporal exponent of 1 in agreement with the predictions of the Ostwald ripening theory. This indicated that the particles coarsen by the evaporation‐condensation mechanism on which the Ostwald ripening theory is based. The rate constant from the Ostwald ripening theory was calculated and compared to the rate constant determined from the experimental data. The theoretical rate constant, K, calculated from Ostwald ripening theory, was 3.6 × 10−18 cm3/s compared to an experimentally determined rate constant of 4.8 × 10−18 cm3/s. The agreement between the theoretical and experimental rate constants was quite good. The significance attached to the good agreement between the theoretical and experimental rate constants might be mollified to some extent by the uncertainty involved in the parameters used to calculate the theoretical rate constant; viz. the interfacial tension, mutual‐diffusion coefficient, and equilibrium concentration of the HPB in the matrix phase that are not known to high accuracy. In reality, because other theories were used to determine the interfacial tension, mutual‐diffusion coefficient, and equilibrium phase compositions, this study was a test of several theories simultaneously. However, the agreement of the experimental temporal exponent and rate constant with the predictions of Ostwald ripening theory strongly indicates that the HPB/HDPE system coarsens by the evaporation‐condensation mechanism upon which the Ostwald ripening theory is based. © 1994 John Wiley & Sons, Inc.
The influence of short branches on the α, β and γ‐relaxation processes of ultra‐high strength polyethylene fibers
Authors: Ohta Yasuo , Yasuda Hiroshi
Published: April 2003

Dynamic mechanical measurements were conducted for several kinds of ultra–high‐strength polyethylene fibers with different methyl branch contents. As is the case with conventional polyethylene materials, UHSPE fibers also exhibit α, β, and γ‐relaxation dispersions. Each relaxation process is the function of both the tensile moduli and the branch contents of UHSPE fibers. It was also found that the γ‐process of UHSPE fibers is dominated mainly by the localized molecular motion in the crystalline part, such as a dislocation mode of crystallite defects, which is very sensitive to the branching content. From the time and temperature superposition of the frequency dispersion experiments, it was found that activation energies for both the α2‐process and α3‐process increase proportionally to the methyl branch content, while the α1‐process is not so affected by the branch content. This result shows that the incorporated branch sites in the crystalline part effectively hinder the chain‐to‐chain slippage; meanwhile, they have not hindered the slippage at the grain boundary so far, which also enables us to explain the creep improvement of UHSPE fibers through branch incorporation with the same mechanism. © 1994 John Wiley & Sons, Inc.
Investigation of the microstructure of poly(diallyldimethyl‐ammonium chloride) by nitrogen‐14(15) NMR spectroscopy
Authors: Masterman T. Craig , Dando Neal R. , Weaver Douglas G. , Seyferth Dietmar
Published: April 2003

CPMAS 13C and 15N solid‐state NMR spectroscopy, as well as solution state 14N NMR spectroscopy, was used to investigate the microstructure of poly (diallyldimethylammonium chloride). The results of these studies, supported by 14N NMR studies of model compounds, were in agreement with the earlier conclusion of other workers (via solution state 13C NMR spectroscopy) that the polymer consists of a chain of five‐membered pyrrolidinium rings, A. magnified image © 1994 John Wiley & Sons, Inc.
Polymer‐solvent demixing under tension. Isotope and pressure effects on liquid‐liquid transitions, VII. Propionitrile–polystyrene solutions at negative pressure
Authors: Imre Attila , Van Hook W. Alexander
Published: April 2003

Liquid‐liquid demixing in propionitrile‐polystyrene solutions has been observed (−2 < P/MPa < 4) using a Berthelot tube technique. The experimental isopleths join smoothly to ones gathered at positive pressure by another technique. The equation of state used to describe the transitions thus appears to be valid across the entire liquid range. © 1994 John Wiley & Sons, Inc.
The effect of water on the transport of oxygen through nylon‐6 films
Authors: Gavara Rafael , Hernandez Ruben J.
Published: April 2003

The effect of presence of water on the transport of oxygen through films of Nylon‐6 was evaluated at 5, 23, and 40°C by permeation experiments. Through the oxygen permeability experiments it was found that the diffusion of oxygen through Nylon‐6 is not a simple Fickian process and the total diffusion process can be expressed by a bimodal diffusion mechanism. Permeability, solubility, and diffusion coefficients were determined as a function of water activity for both mechanisms. The effect of sorbed water on the oxygen diffusion and solubility in the polymer is presented as a function of the state of water in the polymer and as a result of the molecular competition between water and oxygen. © 1994 John Wiley & Sons, Inc.
Analytic model for surface‐induced molecular weight segregation in thermoplastic composites
Authors: Pangelinan Adriano B. , McCullough R. L. , Kelley Michael J.
Published: April 2003

An analytic model based on a random‐walk formulation for absorbing barriers is presented. The range of applicability of the model is established from results derived from Monte Carlo simulations. The model takes into account the influences of neutral, repulsive, and attractive polymer‐surface interactions on the spatial variation of species concentrations in the vicinity of a surface. The model predicts that the lower molecular weight species of a polydisperse mixture will accumulate in the vicinity of a surface to create an interphase region. The extent of this surface‐perturbed interphase region is on the order of three times the radius of gyration of the longest species of the mixture. The degree of molecular weight segregation is dependent upon the breadth of the molecular weight distribution. © 1994 John Wiley & Sons. Inc.
Luminescent polymers with discrete emitter units
Authors: Musfeldt J. L. , Reynolds John R. , Tanner D. B. , Ruiz Jose P. , Wang Jiping , Pomerantz Martin
Published: April 2003

Optical absorption and photo‐luminescence measurements were performed on a series of semiconducting polymers, based upon phenylene linkages, that have discrete emitter units. In these polymers, broken conjugation has been achieved in two ways: by introducing metalinkages between various numbers of para‐connected aromatic groups or by severe steric distortion of a fully conjugated main chain. In either case, electronic states are localized on relatively small units, resulting in a large (π, π*) band gap. The band gap decreases with increasing emitter unit conjugation, as expected. Blue light emission was observed from these materials, with the peak emission wavelength red shifted (by greater than 1 eV on average) from the peak absorption. © 1994 John Wiley & Sons, Inc.
Curie transition, ferroelectric crystal structure, and ferroelectricity of a VDF/TrFE(75/25) copolymer 1. The effect of the consecutive annealing in the ferroelectric state on curie transition and ferroelectric crystal structure
Authors: Kim Kap Jin , Kim Gwan Bum , Vanlencia Catherine L. , Rabolt John F.
Published: April 2003

We have completely deconvoluted multiple ferroelectric‐to‐paraelectric phase transitions of a VDF/TrFE copolymer often observed on DSC by consecutive annealing below the Curie transition temperature and obtained three clear endothermic peaks resolved well from each other. We could also increase the Curie transition temperature by using the consecutive annealing performed in the ferroelectric state. Annealing time, as well as annealing temperature, was found to affect the Curie transition behavior significantly. Each ferroelectric crystalline phase was characterized by IR, Raman scattering, x‐ray diffraction, and DSC measurements. The ferroelectric phase, having higher Curie transition temperature, has been found to have more trans sequences and less gauche defects and to require larger thermal energy for the Curie transition. © 1994 John Wiley & Sons, Inc.
Density profile of spin cast polymethylmethacrylate thin films
Authors: Wu Wen‐li , Orts William J. , Van Zanten John H. , Fanconi Bruno M.
Published: April 2003

The density profiles of polymethylmethacrylate (PMMA) thin films on silicon (111) single crystal wafers were investigated via neutron reflectivity measurements. Films were prepared by spin casting PMMA onto silicon wafers from o‐xylene solution followed by annealing under vacuum at 90°C for 5 h. A ∼45 Å thick layer at the free polymer surface was observed in the as‐prepared samples that has a density about half the value of bulk PMMA. After heating above 110°C, this diffuse layer disappeared and the thin film density profile was transformed to one with a sharp free polymer surface. This transition was found to be irreversible. © 1994 John Wiley & Sons, Inc.
An experimental study on saturation swelling of styrene–acryronitrile copolymer particles with styrene and acrylonitrile monomers
Authors: Nomura Mamoru , Liu Xiang , Ishitani Kouichi , Fujita Kazumi
Published: April 2003

The saturation swelling behavior of styrene and acrylonitrile (SAN) copolymer particles with a styrene (St) and acrylonitrile (AN) comonomer mixture was investigated experimentally. The effects of the copolymer composition and the compositional inhomogeneity in SAN Copolymer particles on their swelling behavior were examined. The experimental results show that both the copolymer composition and the compositional inhomogeneity in SAN copolymer particles have little or no influence on the swellability of SAN copolymer particles with a St and AN comonomer mixture, as long as the weight fraction of AN monomer units in SAN copolymer particles is less than a certain value between 0.6 and 0.8. With increasing AN content in the copolymer particles beyond this value, however, the swellability of SAN copolymer particles gradually decreases. Semiempirical equations are proposed, which correlate the saturation concentration of each monomer in SAN copolymer particles as a function of the comonomer composition in the monomer droplets and the overall copolymer composition in SAN copolymer particles. © 1994 John Wiley & Sons, Inc.
Morphology of melt‐pressed latex films examined by scanning and freeze‐fracture electron microscopy
Authors: Sosnowski Stanislaw , Li Lin , Winnik Mitchell A. , Clubb Brian , Shivers Richard
Published: April 2003

We report freeze‐fracture transmission electron microscopy (FFTEM) and scanning electron microscopy (SEM) studies of films prepared by melt‐pressing micrometer‐size polystyrene (PS) and poly(methyl methacrylate) (PMMA) latex samples prepared by surfactant‐free emulsion polymerization. Film samples were prepared in two ways intended to influence the nature of packing in the solid: slow evaporation of water at 40°C and 1 atm, or freezedrying. These powder samples were then gently pressed into transparent films using a Carver press. Samples prepared from freeze‐dried latex are much less ordered then those from slowly dried dispersions. Two kinds of close packing, face‐centered cubic (fcc) and body‐centered cubic (bcc), may exist in different parts of an individual sample. An excellent example of bcc ordering was observed in a sample prepared by slowly drying a PMMA latex dispersion. Under very similar conditions, small regions of both fcc and bcc ordering were observed in PS samples. However, distortion of ideal bcc or fcc packing produces the same pattern of fracture. © 1994 John Wiley & Sons, Inc.
Synthesis and mesophase characterization of liquid crystalline polyesters with bulky, rigid, lateral substituents
Authors: Khan N. , Price D. M. , Bashir Z.
Published: April 2003

The synthesis and characterization of aromatic polyesters containing various symmetrically di‐substituted hydroquinone monomers is described. The homopolyesters made from these monomers and terephthalic acid (TA) did not melt. Copolyesters of TA with mono‐ and di‐substituted hydroquinone formed liquid crystalline melts. Optical microscopy showed schlieren, marbled, and droplet textures characteristic of the nematic phase. DSC experiments were also in accord with mesophase formation as multiple transitions characteristic of first‐order phase changes were found. In general, the crystal‐nematic transition was about 300°C, whereas the nematic‐isotropic change was over 400°C. All the polyesters were prone to decomposition near or above the isotropization temperature. © 1994 John Wiley & Sons, Inc.
Effect of degree of acetylation and solvent on the chiroptical properties of lyotropic (acetyl) (ethyl) cellulose solutions
Authors: Guo J.‐X. , Gray D. G.
Published: April 2003

(Acetyl) (ethyl) cellulose (AEC) polymers with an ethyl degree of substitution (DS) of 2.5 and acetyl DS ranging from 0 to 0.5 dissolve readily in a wide range of organic solvents and form chiral nematic liquid crystalline phases in concentrated solution. The chiroptical properties of these liquid crystals are strongly influenced by the acetyl content and solvent. In dichloromethane, dibromomethane, chloroform, bromoform, m‐cresol, acetic acid, and aqueous phenol, the AEC lyotropic mesophases all show a handedness inversion as the acetyl DS of the polymers is increased, changing from left‐ to right‐handed supermolecular helicoidal structures. The temperature dependence of the pitch for these mesophases is also reversed from negative to positive with increasing acetyl DS in all the above solvents except aqueous phenol, in which the corresponding AEC mesophases change from positive to negative. The optical microscopic, optical diffraction, and ORD evidence provide a unique indication that the reversal of the handedness and temperature dependence for the AEC mesophases occurs at a compensated degree of acetylation, DA*. The corresponding compensated mesophases show an infinite pitch and behave optically like nematic mesophases. The value of the DA* is dependent on solvent. In dichloroacetic acid, AEC liquid crystals remain right‐handed, independent of the acetyl DS. At given concentration and temperature, the long pitch samples flow much more readily than short pitch samples. © 1994 John Wiley & Sons, Inc.
Temperature dependence of molecular motions in bulk polystyrene
Authors: Blackburn F. R. , Cicerone Marcus T. , Ediger M. D.
Published: April 2003

Time‐resolved optical spectroscopy is used to investigate the reorientation of three rigid probes and one labeled chain in bulk polystyrene. Orientational correlation times for these probes and labels are found to be in the range of 10−8–10−10 s at temperatures of 180–300°C. Consistent with previous studies, the attachment of a chromophore into the chain backbone slows its dynamics by about an order of magnitude. The temperature dependences of the correlation times are similar to the temperature dependence of the viscosity. When combined with probe reorientation times near and below Tg, these results indicate that probe reorientation tracks the temperature dependence of the viscosity quite well over twelve decades in time. In contrast, literature results for the translational diffusion of similarly sized probes indicates a substantially weaker temperature dependence near Tg. Thus it appears that a fundamental change in the mechanism of probe motion occurs near Tg. © 1994 John Wiley & Sons, Inc.
A scattering study on intermicellar interactions and structures of polymeric micelles
Authors: Chu Benjamin , Wu Guangwei , Schneider Dieter K.
Published: April 2003

The micellar structure is usually considered to be composed of a hard sphere (liquid) core and a heavily solvated corona. Therefore, the correction for intermicellar interactions at finite concentrations can be relatively complicated. In this article, small‐angle neutron scattering of a copolymer, known as Pluronic L64 (PEO13PPO30PEO13), in o‐xylene in the presence of D2O is used to demonstrate that, based on the hard sphere approximation, intermicellar interactions can be corrected by representing the micellar size as having an equivalent hard sphere radius. The procedure remains valid even if the micellar shape becomes asymmetric, with axial ratios of 3 ˜ 4. For the present system, the equivalent hard sphere radius corresponds to the micellar core radius plus one‐half of the micellar shell thickness. With the equivalent hard sphere approach, the scattering behavior of the micelle could be described by using a core‐shell structure. © 1994 John Wiley & Sons, Inc.
Investigation of dipolar reorientation dynamics of pure bulk polymers using second harmonic generation
Authors: Guan H. W. , Pauley M. A. , Brett T. , Wang C. H.
Published: April 2003

Second harmonic generation (SHG) in three corona‐poled, pure, bulk polymers is studied as a function of temperature. It is found that this technique readily yields dynamical information that is complementary to that obtained from the technique of dielectric relaxation (DR). The SHG results are compared to those from DR in the same temperature ranges above Tg. It is found that in the temperature ranges examined, the relaxation times obtained from SHG are several orders fo magnitude longer than those measured by dielectric relaxation. This is explained as being due to the strong correlation between oriented dipoles and to trapped charges injected by the poling process. Fitting measured data to the Williams‐Landau‐Ferry (WLF) equation indicates that more free volume is needed in SHG for dipolar reorientation than is needed in DR. An SHG relaxation elongation phenomenon at constant temperature is found to occur in the pure bulk polymers and is similar to that found in chromophore‐doped polymers previously studied. The SHG technique is developed as a new tool to directly study the reorientational dynamics of polar polymer segments. © 1994 John Wiley & Sons, Inc.