bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photon correlation spectroscopy of syndiotactic poly (n‐butyl methacrylate) near the glass transition
Authors: Patterson G. D. , Jue P. K. , Ramsay D. J. , Stevens J. R. 
Published: April 2003

AbstractSlow relaxing longitudinal density fluctuations in bulk syndiotactic poly (n‐butyl methacrylate) [PBMA] were studied by photon correlation spectroscopy as a function of temperature from 70 to 90°C. The shape of the light‐scattering relaxation function broadened as the temperature approached the glass transition (Tg = 55°C). The average relaxation time shifted with temperature, consistent with previous studies of PBMA. The relaxation functions were analyzed in terms of a distribution of relaxation rates. The calculated distribution was clearly bimodal and the shape altered with temperature. The higher frequency peak in the distribution corresponds well with previous mechanical and dielectric relaxation studies of the intramolecular relaxation of the acrylate ester side chain. The resolution of the distribution into two modes is due to a well‐defined side‐chain motion with relaxation strength comparable to the primary glass‐rubber relaxation. © 1994 John Wiley & Sons, Inc.
Isothermal phase behavior of Nylon‐6, ‐66, and ‐610 polyamides in formic acid–water systems
Authors: Cheng Liao‐Ping , Dwan An‐Hwa , Gryte Carl C. 
Published: April 2003

AbstractConcentration‐dependent ternary interaction parameters are experimentally determined for the polyamide homopolymers, Nylon‐6, ‐66, ‐610, and for the Nylon‐66/610/6 terpolymer in formic acid‐water systems. The binodal envelope, the tie lines, and the crystallization isotherms at 25°C are given for each of the ternary systems. © 1994 John Wiley & Sons, Inc.
Phase separation and the kinetics of phase coarsening in commercial impact polypropylene copolymers
Authors: Mirabella, Jr. Francis M. 
Published: April 2003

AbstractThe phase segregation and subsequent minor phase coarsening of a commercial impact polypropylene copolymer was studied. The major components of the impact polypropylene copolymer studied were 82.4 wt % polypropylene homopolymer and 17.6 wt % ethylene‐propylene rubber (EPR). The system was artificially manipulated to ensure homogeneity by precipitation from solution with a nonsolvent. This ensured that the initial system did not exhibit large‐scale phase segregation. The homogeneous initial system was subjected to storage in the melt at 193°C for a series of times. The two‐phase morphology of commercial impact polypropylenes was generated in the melt state by storage in the melt for various periods of time from 5 s to 1 h. Small nuclei of particles appeared at short time and increased in volume with increasing time in the melt state. The coarsening of the minor phase EPR component was shown to follow the theoretically predicted d ∼ t1/3 and N ∼ t−1 (where d = diameter, N = number of particles, and t = time in the melt) relationships to a close approximation in accord with Ostwald ripening theory. At short times these relationships were not obeyed. The indication was that the long‐time coarsening regime was not entered until several minutes elapsed in the melt state. The particle size distribution was initially quite narrow and exhibited a trend of broadening at longer times of coarsening. This may be due to a shift from the short‐time regime to the long‐time coarsening regime. The initial polymer, which was precipitated from solution, was shown not to have undergone large‐scale phase segregation in that it exhibited a one‐phase morphology (i.e., no particles with > 0.1 μm diameter) as determined by 129Xe NMR spectroscopy. The precipitated blend produced incipient particle nuclei (> 0.1 μm diameter) after a very short time (5 s) in the melt state. © 1994 John Wiley & Sons, Inc.
The effect of crystallinity on chain mobility and free volume in the amorphous regions of a miscible polycarbonate/polyester blend
Authors: Zipper M. D. , Simon G. P. , Cherry P. , Hill A. J. 
Published: April 2003

AbstractHomopolymers and blends of polycarbonate/ThermX have been investigated by differential scanning calorimetry, dynamic mechanical analysis, density measurements, and positron annihilation lifetime spectroscopy. The study focuses on the chain mobility and free volume in the amorphous miscible regions of the blends and how this mobility and free volume are affected by increasing crystallinity. It is proposed that judicious annealing, which results in increasing crystallinity (while avoiding ageing or transesterification), induces a constraint on the amorphous region leading to an increase in Tg and coalescence of free volume sites. © 1994 John Wiley & Sons, Inc.
Degradation on freezing dilute polystyrene solutions in p‐xylene
Authors: Zysman Viviane , Nguyen Tuan Q. , Kausch Henning‐H. 
Published: April 2003

AbstractChain scission was observed during the crystallization of p‐xylene in dilute polystyrene solutions. Degradation yields were determined by gel permeation chromatography, as a function of the number of freeze‐and‐thaw cycles, polymer concentration, and initial polymer molecular weight (M). The rate constant for chain scission Kc increases with the polymer chain length, from 0.021%/cycle at M = 110·103 to 4.7%/cycle at M = 8.5·106. Over the two decades range of investigated molecular weights, Kc follows an empirical scaling law of the form Kc ∼ (M − Mlim)1.17578, where Mlim is a limiting molecular weight ≅ 29,000 g. mol−1 below which no degradation could be induced. Some propensity for midchain scission was detected, although this tendency was much weaker in comparison to flow‐induced degradation.A chain scission model based on crack propagation failed to reproduce the experimental results. To explain the observed dependence of Kc with the square of the radius of gyration, an interfacial stress transmission mechanism between the crystallization fronts and the polymer coil has been proposed. © 1994 John Wiley & Sons, Inc.
Stress in polyimide coatings
Authors: Coburn John C. , Pottiger Michael T. , Noe Susan C. , Senturia Stephen D. 
Published: April 2003

AbstractThe effect of film thickness on in‐plane molecular orientation and stress in polyimide films prepared from pyromellitic dianhydride with 4,4′‐oxydianline was investigated using a prism coupling technique to measure the refractive index. Film thickness was controlled by varying both solution concentration and spinning conditions. Birefringence, the difference between the in‐plane and out‐of‐plane refractive indices, was used to characterize the in‐plane molecular orientation. The observed birefringence is a combination of the birefringence resulting from molecular orientation and the birefringence induced by the residual stress present in the films. The birefringence decreases with increasing film thickness over the range of thicknesses studied (3–20 μm) indicating that the molecular orientation decreases with increasing film thickness. The in‐plane coefficient of linear thermal expansion (CTE), controlled by the level of orientation in the film, increases from 18 to 32 × 10−6/°C over the same thickness range. The birefringence of free‐standing films was lower than that of adhered films due to the release of residual stress in the film once the film is removed from the substrate. The residual film stress arises primarily from the mismatch in CTEs between the polyimide film and the substrate to which the film is adhered. Thus, since the film anisotropy decreases with increasing thickness, the film stress increases with increasing thickness. Residual stress calculated by integrating the product of the film modulus and the CTE mismatch assuming temperature‐dependent properties is comparable to experimentally measured film stress. Ignoring the temperature dependence of the film properties leads to an overestimation of stress. Moisture uptake was used to study the stress dependence of the optical properties. Moisture uptake increases both the in‐plane and out‐of‐plane refractive indices by equal amounts in free‐standing films due to an isotropic increase in the polarizability. In adhered films, an increase in moisture uptake leads to a decrease in the birefringence due to a swelling‐induced decrease in the residual film stress. © 1994 John Wiley & Sons, Inc.
Miscibility predictions for poly(phenylene sulfide): Heats of mixing of model compounds
Authors: Landry Christine J. T. , Teegarden David M. 
Published: April 2003

AbstractCalorimetry was used to gain insight into the thermodynamics of mixing of unlike species, designed to represent organic polymers. These results are to be useful in predicting miscibility between various polymers and poly(arylene sulfides). Phenyl sulfide (PS) and phenyl disulfide (PSS) were used as models for poly(phenylene sulfide) (PPS) and were mixed with model compounds that are representative of other polymer classes. The enthalpy of mixing was measured for a large number of combinations. The results are interpreted in terms of a summation of the effects of specific interactions and dispersive forces. It is seen from these data that the presence of aromatic side groups enhances the miscibility of the species with the poly(phenylene sulfide) model compound. Furthermore, exothermic heats of mixing were observed between the PPS model and compound. Furthermore, exothermic heats of mixing were observed between the PPS model and compounds that contain carbonyl, amide, or amine moieties. Finally, the sulfur atom in PPS seems to play only a minor role in determining its interactions with other species. Replacing sulfur with oxygen (or even an alkyl group) is seen to have very little effect on the heats of mixing results. © 1994 John Wiley & Sons, Inc.
Physical and chemical properties of tussah silk fibroin films
Authors: Tsukada Masuhiro , Freddi Giuliano , Gotoh Yoko , Kasai Nobutami 
Published: April 2003

AbstractPhysical and chemical structure, as well as thermal behavior of solution‐cast regenerated films, prepared from tussah (Antheraea pernyi) silk fibroin, were compared with those of solution‐cast native films, in order to ascertain whether treatment (degumming, dissolution) used for preparation affected their properties. Regenerated fibroin films exhibited a higher thermal stability than native ones, as shown by differential scanning calorimetry, thermomechanical analysis, and dynamic mechanical behavior. Glass transition temperature and other relevant thermal transitions of the regenerated silk specimen shifted to higher temperatures compared with those of native specimen. Molecular conformation and crystalline structure did not show significant differences between the two kinds of silk films. Amino acid composition and molecular weight, however, distribution changed markedly after dissolving tussah silk fibroin fiber in concentrated LiSCN in polypeptide size was the main features for the regenerated silk fibroin. © 1994 John Wiley & Sons, Inc.
Cellulose‐polyamide 66 blends. I. Processing and characterization
Authors: Garcia‐Ramirez M. , Cavaillé J. Y. , Dupeyre D. , Péguy A. 
Published: April 2003

AbstractEach homopolymer, cellulose and polyamide 66 (PA66), was separately dissolved in a mixture of N‐methyl morpholine N‐oxide and phenol (80/20 w/w). Then, the two solutions were mixed together. This step leads to the crystallization of PA66 in small aggregates (about 1 μ) regularly dispersed in the cellulose solution. It appeared that this morphology remains independent of further processing such as spinning or casting. Finally, fibers or films were precipitated in methanol. The entire preparation technique used here results mainly in two‐phase systems in which PA66 domains are embedded in an amorphous cellulose matrix. The specimens obtained were at first characterized by differential scanning calorimetry, scanning electron microscopy, and wide angle x‐ray scattering. © 1994 John Wiley & Sons, Inc.
Relaxations in thermosets. XXVI. Ultrasonic studies of the temperature dependence of curing kinetics of diglycidyl ether of bisphenol‐A with catalyst
Authors: Alig I. , Nancke K. , Johari G. P. 
Published: April 2003

AbstractLongitudinal velocity and attenuation of the unreacted diglycidyl ether of bisphenol‐A and dimethylbenzylamine mixture have been measured for 1 MHz ultrasonic frequency. These are combined with our earlier data [Alig et al., Acta Polymerica, Vol. 40, p. 590 (1989)], which were measured during the curing process of the thermoset, and then analyzed in terms of a process involving a negative feedback between molecular diffusion and chemical reaction. The complex plane plots of the real and imaginary components of the longitudinal modulus are fitted to a stretched exponential relation, and the structural relaxation time is calculated at different stages of curing at temperatures in the range 333‐403 K. The results are compared against the calorimetric, dielectric, and viscosity measurements and it is shown that, at least for two cases, gelation time can be observed from the longitudinal modulus data. © 1994 John Wiley & Sons, Inc.
An x‐ray pole figure analysis on biaxially deformed polyethylene film
Authors: Pazur Richard J. , Prud'homme Robert E. 
Published: April 2003

AbstractThe orientational states induced upon two‐step biaxially stretching low‐density polyethylene at 25°C have been investigated. A pole figure analysis of the (200), (020), and (002) crystalline planes has been employed to elucidate the evolution of the molecular crystalline orientation as a function of biaxial stretching. The initial uniaxial‐like orientation induced along the extrusion direction of the films was gradually lost upon transverse stretching and, consequently, replaced by a biaxial orientation as suggested by the orientation functions. In these cases, the a crystallographic axis was observed to be strongly oriented along the film normal, thus confining the c and b axes to the film plane. The pole figures clearly indicate that the c and b axes are preferentially aligned 45° with respect to the stretching directions. This unique orientational state of the orthorhombic unit cell of polyethylene has been termed a biaxial‐double orientation. Birefringence measurements on the biaxial samples indicated that the amorphous and crystalline regions are simultaneously biaxially oriented. The evolution of the crystalline orientation as a function of stretching was conveniently followed on a White/Spruiell orientation triangle. Quantification was hindered, however, by the presence of different crystal populations in the biaxially stretched samples. © 1994 John Wiley & Sons, Inc.
Structural stabilization of phase separating PC/polyester blends through interfacial modification by transesterification reaction
Authors: Yoon H. , Feng Y. , Qiu Y. , Han C. C. 
Published: April 2003

AbstractCompetition between phase separation and transesterification in immiscible polymer blends of polycarbonate (PC) and a copolyester (PET) is studied as a function of time and temperature by differential scanning calorimetry (DSC) and small‐angle neutron scattering (SANS). We found that (1) Global structure coarsens at T ≤ 200°C due to the dominance of phase separation over transesterification and melts at T ≤ 220°C due to the dominance of transesterification at the domain interface. However, transesterification is slow but still significant even at T ≤ 200°C. (2) An intricate balance of transesterification and phase separation rates controls global and interfacial structures. (3) Interfacial structures become measurable under certain conditions, and the interfacial thickness between PC or PET and the copolymers generated by transesterification increases with time. (4) DSC results are consistent with results obtained by SANS, but the latter is more sensitive than the former and differentiates the structural change at different length scales caused by phase separation and transesterification. © 1994 John Wiley & Sons, Inc.
Intramolecular formation of excimers in model compounds for polyesters obtained from 2,6‐naphthalene dicarboxylic acid and cyclohexanediols
Authors: Bravo Julio , Mendicuti Francisco , Mattice Wayne L. 
Published: April 2003

AbstractThe fluorescence in dilute solution has been measured as a function of solvent viscosity for four bichromophoric models for polyesters with naphthalene in the rigid aromatic unit and diols derived from cyclohexane as the flexible spacer. The spacers are 1,2‐cis‐cyclohexanediol, 1,2‐trans‐cyclohexanediol, a 1:2 mixture of 1,3‐cis‐ and 1,3‐trans‐cyclohexanediols, and a 1:2 mixture of 1,4‐cis‐ and 1,4‐trans‐cyclohexanediols. The shape of the emission spectra for the molecules in this series is less sensitive to the viscosity of the medium than was the case for an analogous series in which a methylene or oxyethylene spacer replaces the cyclohexanediol spacer. The dependence of the excimer emission on the type of spacer is different also in the series in which the rigid units contain naphthalene or benzene. When the rigid units contain naphthalene, excimer formation is maximal if the spacer contains 1,2‐trans‐cyclohexanediol, but this spacer produces a molecule with a very small tendency for excimer formation in its polymers with terephthalate. A conformational analysis correctly concludes that the spacer most conducive to excimer formation should be 1,2‐trans‐cyclohexanediol, but it does not identify the correct order of the remaining three bichromophoric model compounds. The problem may reside in the method for taking into account the finite width of the torsional well associated with each rotational isomer. © 1994 John Wiley & Sons, Inc.
Stoichiometry and morphology in terbium nitrate‐poly(ethylene oxide) macromolecular complex
Authors: Twomey Conor J. , Chen Shaw H. , Blanton Thomas N. , Schmid Ansgar , Marshall Kenneth L. 
Published: April 2003

AbstractThe Tb (NO3)3‐PEO system was characterized to have a solubility limit equivalent to n ≅ 6.5 and a coordination number of 12.4 ± 0.1, compared to 5.0 and 10.9 ± 0.1 for the Nd(NO3)3‐PEO system. The greater coordination involving Tb3+ appears to be responsible for the lower asymptotic glass transition temperature at high doping levels of the Tb(NO3)3‐PEO complex. In both systems, anhydrous amorphous complexes were obtained below the respective solubility limits, over which apparent solubilities were found to be enhanced by the presence of tightly bound moisture while retaining the amorphous character of the complexes. Whereas partial precipitation was observed in the Tb(NO3)3‐PEO system upon exposure to ambient moisture, both complexation and amorphous character were found to persist in the Nd(NO3)3‐PEO system in the presence of absorbed moisture. © 1994 John Wiley & Sons, Inc.
Crystallization and thermoreversible gelation of poly(butylene terephthalate)–epoxy mixtures
Authors: Nichols Mark E. , Robertson Richard E. 
Published: April 2003

AbstractThe thermoreversible gelation of solutions of poly(butylene terephthalate) (PBT) and a liquid diglycidyl ether of bisphenol‐A epoxy has been investigated. The morphology of the gels and the conditions under which they form have been characterized by optical microscopy, thermal analysis, and x‐ray scattering. Gels were found to form under two different conditions and with different morphologies. Gels formed after a considerable delay when homogenous PBT‐epoxy solutions were cooled to slightly below the dissolution temperature of crystalline PBT. These gels contained large, irregular PBT spherulites and smaller birefringent interspherulitic matter. The melting of these gels and the onset of macroscopic flow coincided with the melting of the interspherulitic matter, and occurred before the melting of the large spherulites. Thermoreversible gels formed very quickly when PBT‐epoxy solutions were self‐nucleated by heating a dispersion of crystalline PBT in epoxy slightly and briefly above the dissolution temperature and then cooling. These gels displayed only a weak background birefringence and were molten when the weak birefringence disappeared. In both cases, gelation occurred by the formation of a three‐dimensional PBT network in the epoxy liquid, and the nodes of the network were crystalline PBT particles. $ 1994 John Wiley & Sons, Inc.
Gas sorption and transport properties of bisphenol‐I‐polycarbonate
Authors: Hägg M.‐B. , Koros W. J. , Schmidhauser J. C. 
Published: April 2003

AbstractGas sorption and transport characterization of a new polymer in the polycarbonate family, based on the bisphenol of 3,3,5‐trimethylcyclohexane‐1‐one (BPI) is reported at 35°C. By comparison with properties of other known polycarbonates, the effects of inhibition of both packing and segmental motion due to the introduction of the bulky substituent in the backbone are elucidated. The Tg of the material was measured with differential scanning calorimeter (DSC) and was found to be unusually high for a polycarbonate (233°C). This indicates a successful inhibition of the large‐scale segmental mobility of the polymer. Variable 13C NMR analysis indicated that rotation of one phenylene ring has an unusually high (ca. 10 kcal) energy barrier, whereas the other phenylene ring has a more typical rotation profile (barrier < 3 kcal). The density was measured and found to be low (1.107 g/cm3), indicating a high fractional free volume (FFV) for the polymer. Consistent with expectations, the introduction of the bulky‐substituted cyclohexane group gave high permeabilities for the various gases tested (N2, O2, He, CH4, CO2) compared to most standard polycarbonates. On the other hand, the permselectivities were typical for standard polycarbonates. The solubility coefficients of all gases were rather high, as expected for a polymer with such an open structure. © 1994 John Wiley & Sons, Inc.
Charge transport in poly(methylphenylsilane): The case for superimposed disorder and polaron effects
Authors: Bässler H. , Borsenberger P. M. , Perry R. J. 
Published: April 2003

AbstractCareful analysis of the temperature dependence of the hole mobility in poly (methylphenylsilane) indicates that the functional dependence is between an Arrhenius law and a ln μ ∝ T−2 law as predicted by a model of disorder‐controlled hopping. This is attributed to the superposition of disorder and polaron effects. A method is presented for separating the two contributions. The evolution of time‐of‐flight photocurrent transients with decreasing temperature is consistent with the disorder parameter derived from the temperature dependence of the mobility. © 1994 John Wiley & Sons, Inc.