bluuebunny/crossref_metadata_2025_split huggingface dataset:
Charge transfer interactions in some poly[[o‐(trimethylsilyl)phenyl] acetylene]‐acceptor complexes
Authors: Kang E. T. , Neoh K. G. , Tan K. L. 
Published: April 2003

AbstractCharge transfer (CT) interactions between poly[[o‐(trimethylsilyl)phenyl]acetylene] or poly(o‐Me3SiPA) and some electron acceptors were studied by ultraviolet‐visible and infrared absorption spectroscopy and by x‐ray photoelectron spectroscopy, (XPS). The electron acceptors used included iodine, bromine, o‐chloranil, o‐bromanil, 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), and tetracyanoethylene (TCNE). Varying degrees of CT interactions were observed in all of the polymer/acceptor complexes studied. The electrical conductivities σ of the organic acceptor complexes exhibited a strong acceptor concentration dependence at low acceptor levels, with the DDQ complex exhibiting the highest σ. The extent of CT and the redistribution of charges resulting from the CT in all the complexes were revealed by XPS. The poly (o‐Me3SiPA)/I2 complex film lost iodine spontaneously while more than half of the bromine in the poly (o‐Me3SiPA)/Br2 complex existed as covalently bonded bromine, even at low halogen loading.
Effect of annealing on structure and permeability of poly [(l‐trimethylsilyl)‐l‐propyne]
Authors: Tasaka Shigeru , Inagaki Norihiro , Igawa Masaaki 
Published: April 2003

AbstractThe permeability of annealed poly (l‐(trimethylsilyl)‐l‐propyne) was studied from the viewpoint of structural information obtained from x‐ray diffraction and density. The sample cast from benzene solution had low density (0.82 g/cm3) and high permeability, whereas the annealed sample had a higher density (0.88 g/cm3) and permeability lower by two orders of magnitude. The smaller‐angle x‐ray diffraction peak for each sample, which was likely to reflect the distance between intermolecular chains, increased in intensity and shifted toward higher angle, corresponding to the change of the density with annealing. The logarithmic oxygen permeability was proportional to the density, namely the free volume fraction correlated with the diffusion coefficient and controlled by annealing and swelling by alcohols.
Relaxations of thermosets. VIII. Brillouin light scattering during the curing of diglycidyl ether of bisphenol‐A thermosets
Authors: Mangion M. B. M. , Vanderwal J. J. , Walton D. , Johari G. P. 
Published: April 2003

AbstractThe kinetics of sol‐gel‐glass transformations have been studied in the thermosets of diglycidyl ether of bisphenol A cured with diamino diphenyl methane and diamino diphenyl sulfone, at different temperatures using Brillouin light scattering. The Shape of the Brillouin peak is generally broad. This is attributed to the damping of elastic waves in the mixture of unpolymerized low‐molecular weight fluid and the polymer chains forming the networks. The Brillouin peak becomes sharp and narrow at complete curing of the thermosets. The phonon velocity increases and the attenuation decreases with the curing time. These changes occur in two steps with the second step appearing near the gelling time of the thermosets. A semilogarithmic plot of the time for the velocity and attenuation to reach half of their total change against the reciprocal temperature yields a straight line with different slopes for the two thermosets. It is suggested that Brillouin light scattering is a useful non‐destructive, in‐line, method for control in the processing of epoxy thermosets.
Structure and properties of complex transition‐metal (II) salts of ethylene‐methacrylic acid copolymer with 1,3‐bis (aminomethyl) cyclohexane
Authors: Hirasawa Eisaku , Tadano Kenji , Yano Shinichi 
Published: April 2003

AbstractThermal properties by differential scanning calorimetry, stiffness, and melt flow rate (MFR) were measured for the complex transition‐metal (Zn(II), Cu(II), Mn(II), and Co(II)) salts of ethylene‐methacrylic acid copolymer (EMAA) with 1,3‐bis(aminomethyl)‐cyclohexane (BAC). It was found that the strength of both ionic interactions of metal cations with carboxyl groups and coordination bonds of amino groups to metals differ among metal species. In particular, the complex Mn salts are weaker than the complex salts of the other transition metals, which corresponds with Irving‐Williams series of stability constants of transition metal‐ion complexes. Stiffness depends predominantly on the degree of crystallinity of ionic crystallites in ionic clusters, which depends on the ionic species.
Mechanical anisotropy in biaxially oriented polyvinyl chloride
Authors: Guney H. Yuksel , Oskay Taner , Ozkan H. Sinan 
Published: April 2003

AbstractThe mechanical anisotropy of polyvinyl chloride oriented in two perpendicular directions with different draw ratios has been studied. The results are compared with the anisotropy of uniaxial samples oriented at a common draw ratio. The propagation velocities of ultrasonic pulses have been measured by an immersion technique. Longitudinal wave velocities have been measured in three principal planes over a wide range of propagation directions. The limitations of measuring velocities in the planes containing the draw axes were mitigated by use of a special slicing technique. Measurements were performed at 2 MHz and 25°C. Velocities of the transverse waves were measured for incident wave angles greater than the critical angle. From these measurements, five elastic moduli were calculated for the uniaxially oriented samples, and nine elastic moduli were obtained for the biaxially oriented samples. In biaxially oriented samples, the moduli along the draw axes are directly proportional to the draw ratio in the same direction.
Molecular motion and 1H NMR relaxation of aqueous poly(N‐isopropylacrylamide) solution under high pressure
Authors: Ohta Hideo , Ando Isao , Fujishige Shoei , Kubota Kenji 
Published: April 2003

AbstractIn order to obtain useful information about the molecular motion and structure of poly(N‐isopropylacrylamide) (PNiPAM) in aqueous solution, proton spin‐lattice relaxation times, proton spin‐spin relaxation times, and volume changes were measured at pressures from 1 to 400 kg/cm2 as a function of temperature. We found that the molecular motion and the structure of water and PNiPAM in PNiPAM/water solution transitionally change at gelation temperature (31°C). The effect of pressure on such transitional changes is studied. It is suggested that application of pressure to the system prevents the gelation.
Prediction of the glass transition temperature of cycloaliphatic amine–epoxy networks
Authors: Won Yong‐Gu , Galy Jocelyne , Pascault Jean‐Pierre , Verdu Jacques 
Published: April 2003

AbstractStoichiometric, completely cured binary or ternary mixtures of the diglycidylether of bisphenol A (DGEBA), isophorone diamine (IPD), and trimethylcyclohexylamine (TMCA) monomers were studied by differential scanning calorimetry. The relations between the glass transition temperature Tg and the structure of the copolymer networks were investigated. Good predictions of Tg can be obtained on the basis of the following hypothesis: (1) the molar contributions MiT−1gi to the “copolymer effect” of difunctional groups are additive, (2) the crosslinking effect can be expressed by the DiMarzio relation in which the molar contribution of crosslink mers is an increasing function of the stiffness of linear segments. For the seven systems under study, the deviation between calculated and experimental Tg values is within experimental scatter.
Separation of styrene‐methacrylate copolymers by composition using normal and reversed‐phase high‐performance liquid chromatography
Authors: Sato Hisaya , Ogino Kenji , Maruo Susumu , Sasaki Masato 
Published: April 2003

AbstractThe separation of styrene‐methacrylate copolymers by chemical composition was studied using high‐performance liquid chromatography (HPLC). With the combination of acrylonitrile (polar) gel and nonpolar eluent or of styrene (nonpolar) gel and polar eluent, poly(styrene‐co‐methylmethacrylate) was separated by the adsorption mechanism. The former is designated as normal and the latter as reversed phase. With other combinations, the copolymer was separated mainly by fractional dissolution mechanism. The sample eluted slightly earlier as molecular weight decreased. The molecular weight effect on the reversed‐phase HPLC was smaller than that on the normal phase. A gel with an exclusion limit of 3 × 103 exhibited greater molecular weight dependence and worse resolution than a gel with an exclusion limit of 50 × 104.Poly(styrene‐co‐n‐butyl methacrylate) also was separated on the basis of chemical composition by normal and reverse‐phase HPLC. However, poly(styrene‐co‐t‐butyl methacrylate) was separated only by reverse‐phase HPLC. When octadecyl methacrylate gel was used instead of styrene gel in reverse‐phase HPLC, a good separation was not obtained. This indicates a specific interaction between the phenyl group of the styrene gel and the sample.
Heat capacities and entropies of linear, aliphatic polyesters
Authors: Varma‐Nair Manika , Pan Robert , Wunderlich Bernhard 
Published: April 2003

AbstractNew measurements of the heat capacity in the melt of poly(trimethylene succinate) (PTMS), poly(trimethylene adipate) (PTMA), and poly(hexamethylene sebacate) (PHMS) from 310 to 400 K are presented. Based on these data and literature data on eight other molten polylactones and poly(ethylene sebacate) (PES), an addition scheme is developed for linear, aliphatic polyesters that leads to the equation:

which represents the ATHAS‐recommended melt heat capacities for all linear polyesters. Combining previously discussed solid heat capacities, derived from an approximate frequency spectrum, with the new liquid heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) could be derived using the ATHAS computation scheme. The average value of residual entropy at zero kelvin of 5.3 ± 1.8 J/(K mol) per mobile bead for glassy linear polysters was found to be somewhat higher than for many other polymers in the data bank, but closer to that observed for linear, aliphatic polyamides. The phase transitions of PTMS, PTMA, and PHMS are also analyzed using the quantitative baselines available from the heat capacity study.
Relaxations in thermosets. IX. Ionic conductivity and gelation of DGEBA‐based thermosets cured with pure and mixed amines
Authors: Mangion Michel B. M. , Johari G. P. 
Published: April 2003

AbstractThe results obtained during the isothermal curing of diglycidyl ether of bisphenol‐A‐based thermosets cross‐linked with pure diaminodiphenyl methane and pure diaminodiphenyl sulfone and with their mixtures have been analyzed to determine how the dc conductivity changes with time during the conversion of its liquid to a gel. The complex permittivity data are first analyzed to show that ac measurements can be used to obtain the ionic conductivity over a considerable period of the curing process. The procedure allows one to obtain the dc conductivity without having data as a function of frequency. The shape of the complex plane plots of the electrical modulus are semicircles, but with small deviations that appear at long times during the curing process. The dielectric consequences of the chemical changes with time during the cross‐linking of the thermoset are analogous to the frequency dependence of the complex permittivity of a liquid. The analysis shows that the dc conductivity σo of a thermoset during its cure follows a power law, σo∝ (tg—t)x, where t is the curing time (t < tg). The results can also be described equally well by a new equation, σo ∝ exp[—B/(to—t)], where x, tg, B, and to are empirical constants all of which vary with the temperature of the cure. tg is close to the time for gelation known from independent studies and to is close to but longer than the time for vitrification. These conclusions are discussed in terms of scaling concepts for the gelation phenomenon.
Characterization of a single sample of an unknown polymer by size exclusion chromatography
Authors: Vilenchik Lev Z. , Rubinsztajn S. , Zeldin Martel , Fife Wilmer K. 
Published: April 2003

AbstractThe relationship between viscosity constants, k', a and Kη from the equations of Huggins and Mark‐Kuhn‐Houwink has been considered. It is shown, theoretically, that the sum of k' and a must be constant for all flexible‐chain macromolecules irrespective of the solvent used. On this basis, a combination of chromatography and viscometry measurements can be used to characterize a new species. The method has been applied to the new polymer, poly[methyl(pyridin‐3‐yl) siloxane] (1) where no suitable calibration standards are available. The value of a, k', and Kη for 1 has been calculated. The calculated constants enabled an estimation of different average molecular weights (MnMwMz) and polydispersity (Mw/Mn) from a minimum of experimental data. The new method is general and can be applied to any homogeneous linear flexible‐chain nondraining macromolecule.
A raman LAM study of lamellar thickness of virgin polyethylene powder
Authors: Wang Li Hui , Ottani Stefano , Porter Roger S. 
Published: April 2003

AbstractThe lamellar thickness of polyethylene virgin reactor powder has been successfully measured using the Raman longitudinal acoustic mode (LAM). Relatively high lamellar thicknesses have been found. These values change with polymerization temperature in an unusual way, with lamellar thickness being larger for lower polymerization temperature, i.e., at higher undercooling for crystallization. Agreement within an experimental error of 10% has been obtained between values from LAM and those calculated by the Thompson—Gibbs equation from the melting point measured by differential scanning calorimetry.
Structure and thermochromic solid‐state phase transition of poly (3‐alkylthiophene)
Authors: Tashiro Kohji , Ono Keiko , Minagawa Yasuhisa , Kobayashi Masamichi , Kawai Tsuyoshi , Yoshino Katsumi 
Published: April 2003

AbstractIn order to clarify the structural changes that occur in the thermochromic phase transition of poly (3‐dodecylthiophene) [P3DT] and poly (3‐hexylthiophene) [P3HT], the temperature dependence of x‐ray diffraction and Fourier transform infrared spectra was measured. (1) Orthogonal unit‐cell parameters were determined at room temperature: a=25.83 Å, b=7.75 Å, c (fiber axis)=7.77 Å for P3DT and a=16.63 Å, b=7.75 Å, and c=7.77 Å for P3HT. A large variation of the a‐axis length between P3DT and P3HT indicates the extended trans conformation for the alkyl side chains which are oriented along the lateral a‐axis direction. (2) The interplanar spacing, intensity, and integral width of the x‐ray (h00) and (00l) reflections were found to change drastically in the transition region. (3) Polarized infrared measurements at high temperature revealed a marked increase of the gauche band intensity for the alkyl side group modes followed by a decrease in the band intensity of the thiophene ring modes. (4) The layer reflections of the x‐ray fiber diagram become diffuse at high temperatures, indicating that the transition occurs in a liquidcrystalline manner with the orientation of the main chain axes preserved but with almost no axial correlation between the neighboring main chains. These results provide experimental support for the structural model proposed earlier: as the temperature increases, the trans‐type side chains begin to disorder by introduction of gauche bonds. This disordering disrupts the regularity of the main chain conformation and decreases the effective length of the polythiophene conjugated system.
The influence of crystallinity distribution on small‐angle x‐ray scattering from semicrystalline polymers
Authors: Lee Y. D. , Phillips P. J. , Lin J. S. 
Published: April 2003

AbstractTheoretical x‐ray scattering curves have been developed for the lamellar structure in semicrystalline polymers in which there are present distributions of lamellar thickness and crystallinity. The models have been tested against samples of linear low‐density, low‐density and crosslinked polyethylenes. When variation in crystallinity is present in a material, a major effect is an increase in the magnitude of near‐zero angle scattering. The Bragg maximum can appear as an ill‐defined hump on an apparently high level of background scattering. The shape of the Bragg peak is influenced more by crystallinity distribution than by lamellar thickness distribution. Of the polymers we have studied so far only linear low density polyethylene shows significant crystallinity distribution effects. A “rule‐of‐thumb” method for rapid estimation of crystallinity distribution effects has been developed, obviating the need for lengthy simulation.
A model for dynamic relaxations in amorphous polymers. I. Conceptual framework, formal implementation of simplest version, and application to poly(ester carbonates)
Authors: Bicerano Jozef 
Published: April 2003

AbstractA new model for the dynamic relaxations occurring below the glass transition temperature in amorphous polymers is introduced. This model combines ideas from theoretical solidstate physics, thermodynamics, and statistical mechanics. Formal analogies are made between the dynamic relaxations and phase transitions. The concepts of percolation theory are briefly discussed. The molecular level motions which might be giving rise to each dynamic relaxation are incorporated within this framework. The simplest version of the model is then formally implemented within the context of bisphenol‐A polycarbonate (BPAPC) and its poly (ester carbonates) (PEC). The following results are calculated: (1) Characteristic temperatures (Tc) for BPAPC, similar to γ1, and γ2 relaxation temperatures observed by dynamic mechanical spectroscopy (DMS) at commonly used measurement frequencies. (2) Tc for the β2 relaxation in tetrabromo‐BPAPC much higher than the Tc in BPAPC. (3) A slow and monotonic increase in both the intensity and the Tcof the γ2 relaxation with an increasing fraction of terephthalate comonomer in PEC copolymers. It is hoped that this model, which is admittedly tentative at this time, will be useful as a working hypothesis. The next paper of this series will provide extensions and generalizations of the model, and its application to the poly (alkyl methacrylates).
Solution behavior of random copolymers of styrene with sodium‐2‐acrylamido‐2‐methylpropane sulfonate
Authors: Wang Zhulun , Wang Jian , Chu Benjamin , Peiffer Dennis G. 
Published: April 2003

AbstractThe nonaqueous solution behavior of random copolymers of styrene (ST) with sodium‐2‐acrylamido‐2‐methylpropane sulfonate (Na‐AMPS) [poly(ST‐Na‐AMPS)] has been investigated using the transient electric birefringence (TEB) technique. The copolymers with varying high sulfonate contents (about 30–70 mol%), bridging the gap between conventional ionomers and classical polyelectrolytes, were dissolved in the solvent methylformamide (MFA) with a high permittivity ϵ of ca. 190. The solutions showed a negative birefringence at electric field strength E of the order of kV/cm. A typical Kerr effect was observed at low polymer concentrations C of ca. 10−3g/mL and electric field strengths of the order of kV/cm. However, the detailed, TEB studies demonstrated different behavior at two concentration regimes in dilute solution. At a low concentration regime (e.g., C ≤ 1 × 10−3g/mL for the copolymer with a 66.7 mol % sulfonate content) where the reduced viscosity exhibited a pronounced polyelectrolyte effect, the birefringence signal pattern showed a maximum before reaching a steady value. Additionally, during the rise at an applied electric field strength beyond a threshold value, it was observed that the nonexponential field‐free decay was slower than the single exponential field‐induced rise. The observed anomalous behavior was similar to those of a polyelectrolyte [sodium poly (styrene sulfonate)] in aqueous solution and might be attributed to the perturbation of the molecular shape by the applied electric field. At the higher concentration regime (e.g., C ≥ 4 × 10−3g/mL for the same copolymer with a 66.7 mol % sulfonate content) where the polyelectrolyte effects started to diminish as indicated by the viscosity study, the birefringence shape showed no variation with an increased electric field strength and the field‐free decay turned out to be faster than the single exponential rise. The dissociation of ionic aggregates was tentatively interpreted to be responsible for this observation. It seems that by simply varying the polymer concentration, poly (ST‐Na‐AMPS) could behave either as a polyelectrolyte or as an ionomer in a single polar organic solvent.
Cryodilation of thermoplastic PEBA elastomers
Authors: Okoroafor E. , Rault J. 
Published: April 2003

AbstractPEBA block copolymers, poly(ether‐block‐amide), containing low concentrations of polyamide are thermoplastic elastomers. These materials, when strained at room temperature and then relaxed, exhibit dilation during cooling to low temperatures (ca.–10°C). This effect, of the order of 5–15%, depending on the concentration of the different blocks, is due to oriented crystallization of the soft polyether segments.
Dynamic mechanical analysis of RIM nylon‐6
Authors: Ning Xin , Ishida Hatsuo 
Published: April 2003

AbstractThe β relaxation process was shown to occur at different temperatures and exhibit a different activation energy for dry and wet samples prepared by reaction injection molding (RIM) of Nylon‐6. By employing a low operating frequency and controlled low moisture levels, it became possible to distinguish the two β relaxation processes, β1 and β2, in one sample by dynamic mechanical spectroscopy. It was shown that while β1 was associated with moisture in the sample, β2 was related to a structural mechanism independent of moisture. The effect of moisture content on the chain‐chain association (α relaxation process) and chain‐water association (β1, relaxation process) in nylon‐6 was assessed. The annealing mechanism of RIM Nylon‐6 at 85°C was probed by both dynamic mechanical spectroscopy and x‐ray diffraction.
The glass transition temperature of nonstoichiometric epoxy–amine networks
Authors: Vallo C. I. , Frontini P. M. , Williams R. J. J. 
Published: April 2003

AbstractGlass transition temperatures (Tg) of nonstoichiometric epoxy‐amine networks based on the diglycidylether of bisphenol A (DGEBA), are analyzed in terms of the network structure. In most cases reasonable predictions of Tg can be made using an empirical equation reported by L. E. Nielsen together with the experimental Tg value of the stoichiometric network and statistical calculations of the concentration of elastic chains. It is stated that in these rigid networks the concentration of elastic chains is the main structural factor associated to the variations of Tg with stoichiometry. For flexible networks based on the diglycidylether of butanediol (DGEBD), the effect of elastic chains on the Tg value is much less significant.
Oscillatory measurement of linear viscoelasticity: Dynamic moduli revisited
Authors: Conde Luis , Rubio Miguel A. , Fairén Victor , Riande Evaristo 
Published: April 2003

AbstractThe current technique for the measurement of linear viscoelastic dynamic moduli is reconsidered. The transfer function analysis reveals the existence of nonlinear components in the response of the sample in a wide range of excitation frequencies around the reasonances of the measuring system. This analysis permits the disclosure of the components of the response which behave in accordance to linear viscoelastic theory and separates the undesirable nonlinear components. This results in partial corrections of the anomalous behavior of the calculated dynamic moduli through the standard technique.