bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheology of polymers that are initially in the disentangled state
Authors: Kotliar A. M. , Kumar R. , Back R. A. 
Published: April 2003

AbstractAn attempt was made to measure the effects of molecular entanglements on the rheological properties of polymer melts. Two classes of polymers were studied; glassy atactic polystyrene polymers covering a 60‐fold range in molecular weight, and semicrystalline high‐density polyethylene from two sources covering about a twofold range in molecular weight. The entanglements initially present were removed or greatly reduced in number by freeze drying the polystyrene polymers from dilute solutions below and above C*, the critical overlap concentration, and by slowly crystallizing the polyethylene from very dilute solutions. Since only minor rheological changes were observed with polystyrene, it would appear that the initially isolated coils interpenetrate more rapidly than is indicated by the results of Liu and Morawetz, or that the rheological behavior is rather insensitive to whether the flow obstacles are intermolecular or intramolecular. The enhancement of the viscosity and elasticity observed with polyethylene polymers indicate the importance of the crystallization step on the local melt topology of the polymer chains.
Structure of ultrathin polyethylene layers in multilayer films
Authors: Pan S. J. , Im J. , Hill M. J. , Keller A. , Hiltner A. , Baer E. 
Published: April 2003

AbstractThe crystalline structures of “microlayer” and “nanolayer” polyethylene have been examined in coextruded films comprised of alternating layers of high‐density polyethylene and polystyrene. Transmission electron microscopy (TEM), small‐angle x‐ray scattering (SAXS), and wide‐angle x‐ray scattering (WAXS) reveal that microlayer polyethylene, where the layer thickness is on the order of several microns, crystallizes with the normal unoriented lamellar morphology. In nanolayer films, where the film thickness of tens of nanometers is on the size scale of molecular dimensions, lamellae are oriented with the long axes perpendicular to the extrusion direction in a row‐nucleated morphology similar to structures described in the literature. The lamellae are partially twisted about the long axes. The preferred twist angles of ±40° orient the lamellar surfaces normal to the layer surface. The row‐nucleated morphology imparts highly anisotropic mechanical properties to the nanolayer polyethylene.
Influence of the surface treatment of graphitized carbon fibers on the curing of an amine‐catalyzed epoxy‐anhydride system
Authors: Sellitti C. , Koenig J. L. , Ishida H. 
Published: April 2003

AbstractThe surface of graphitized carbon fibers is oxidatively treated by nitric acid. Fourier transform infrared attenuated total reflection spectroscopy has been utilized to monitor the influence of the surface species on the curing of an epoxy system. A curve‐fitting program is used to deconvolve the overlapped infrared bands. The integrated intensities of the ester, anhydride, epoxy, and carboxylic acid, plotted against the curing time, clearly show the dependence of the crosslinking process on the concentration of the surface species. The surface groups themselves act as a catalyst: there exists an optimal concentration below which an activation of the curing process occurs. Above that concentration, a retardation of the curing process has been detected.
Effect of microheterogeneities on the diffusion of gases through glassy polymers
Authors: Horas J. A. , Reyes E. R. , Magnin J. E. 
Published: April 2003

AbstractThe diffusion of gases through glassy polymers is studied and the effective diffusion coefficient Deff is represented as the result of the superposition of two fundamental mechanisms, namely slipping and hopping. Deff is calculated by a two‐point correlation method. Comparisons are made with experimental data of Meares for diffusion coefficients of Kr, O2, He, and A in poly(vinyl acetate) in the glassy state. Good fits are obtained and yield significant parameters.
Test of the validity of the classical kinetic theory of polymer crystallization
Authors: Point J. J. , Colet M. C. , Dosiere M. 
Published: April 2003

AbstractUse of the accepted theories of polymer crystallization to interpret crystal growth rate data for a polyethylene fraction from dilute xylene solution leads to the conclusion that crystallization cannot proceed in either in regime I or regime II, nor in an intermediate regime. This apparent paradox means that the classical theory of polymer crystallization does not give the right order of magnitude of the rate of initiation and of the rate of spreading of a secondary nucleus.
Miscibility of poly (styrene‐co‐methylmethacrylate)s differing in composition
Authors: Kohl P. R. , Seifert A. M. , Hellmann G. P. 
Published: April 2003

AbstractThe mutual miscibility of random poly (styrene‐co‐methylmethacrylate)s with different compositions but a constant molecular weight of Mw ≅ 150,000 was studied at room temperature and at 180°C. Compatibility was analyzed with films cast from solutions with different solvents. The reliability of the analytical technique is discussed. The miscibility windows {x, yx}, which define the limits of miscibility of the blends of a given copolymer P (SxMMA1−x) with other copolymers P (SyMMA1−y), were determined for all x. The widths |x − yx| of these windows are, contrary to the predictions of the Flory–Huggins model, different for yx > x and yx > x, and depend strongly on x. Miscibility is better for blends with a high MMA content. The windows are markedly wider at room temperature. Many blends are, therefore, “semicompatible,” i.e., have a critical point of the LCST type between room temperature and 180°C.
Positron annihilation in amine‐cured epoxy polymers—pressure dependence
Authors: Wang Y. Y. , Nakanishi H. , Jean Y. C. , Sandreczki T. C. 
Published: April 2003

AbstractPositron annihilation spectroscopy has been used to study free volume in an arnine‐cured epoxy as a function of external pressure at temperatures above and below the glass transition temperature. The observed ortho‐positronium lifetime τ3 and formation probability I3 decreased with increasing pressure. The decrease in τ3 is interpreted in terms of a corresponding decrease in average free‐volume hole size over the range from 0.135 to 0.045 nm3. The fractional free‐volume and the free‐volume compressibility in the epoxy are calculated as functions of pressure at 100°C.
Effects of orientation on the dielectric glass–rubber relaxation of amorphous networks
Authors: Diaz‐Calleja Ricardo , Riande Evaristo , Guzmán Julio 
Published: April 2003

AbstractThe effects of the orientation on the dielectric glass–rubber relaxation of elongated poly(diethylene glycol isophthalate) networks, are studied. Orientation of the chains shifts the maximum of the α peak, at any frequency, to slightly lower temperature, as occurs in the case of mechanical relaxations. The dielectric behavior is interpreted in terms of the free volume theory. It is found that the ratio of the relative free volume to the parameter B at the glass transition temperature, where B is related to the minimum hole size required for local segmental motions, is almost independent of the elongation ratio λ. Cole–Cole diagrams are circular in the low‐frequency region, but at high frequencies the curves approach the abscissa along straight lines, which are nearly parallel for different values of λ. The difference between the dielectric constant at zero and infinite frequencies (ε0 − ε∞) is a linear function of the elongation ratio, and the Frölich theory suggests strong correlations between the relaxing species. The dielectric behavior of oriented networks is interpreted by using both the coupling model and a model which assumes the presence of defects around which the relaxation processes take place.
Vibrational assignments for the CCL stretching region of the Raman spectrum of poly(vinyl chloride)
Authors: Bower D. I. , Jackson R. S. 
Published: April 2003

AbstractIt is shown that, by assuming that each of the peaks resolved in the CCl stretching region of the Raman spectra of a series of poly(vinyl chloride) gels can be associated with a definite triad structure, most of the peaks can he assigned to syndiotactic, isotactic, or heterotactic triad configurations without reference to the spectra of model compounds or to vibrational calculations. The results are in general agreement with most previous assignments except for the assignment of the peak at 646 cm–1. Previously this was assigned to syndiotactic material, but it is here assigned to a structure consisting of consecutive syndiotactic, isotactic, and syndiotactic placements in a conformation not very distorted from the planar zigzag conformation.
Effects of annealing on the polarization switching of phase I poly(vinylidene fluoride)
Authors: Takase Y. , Scheinbeim J. I. , Newman B. A. 
Published: April 2003

AbstractTo obtain information about microscopic processes involved in the polarization switching in uniaxially oriented poly (vinylidene fluoride) film, a least‐squares estimation of nonlinear parameters was developed to yield parameters of an equation which describes the nucleation and domain growth process. Time domain measurements of polarization reversal revealed that switching times decreased as the annealing temperature Ta increased (67.0, 52.4, and 41.3 μs at –20°C under a 200 MV/m pulse field for the as‐stretched samples, the samples being annealed at 120 and 160°C, respectively). The analysis showed that the value of the domain growth speed increased as Ta increased. This is consistent with x‐ray diffraction data which indicated that the annealing process brought about better chain packing and increased crystallite perfection. The analysis also showed that the nucleation probability significantly increased as Ta increased. This result was interpreted in terms of a morphological transformation, which was indicated by the decrease in elastic modulus with increasing Ta with no corresponding loss of orientation. It is suggested that the annealing process brought about an increase in the number of nucleation sites as a result of a transformation from a fibrous structure to a crystal‐amorphous series structure which has increased boundary zone area.
A fourier‐transform infrared spectroscopic study of the surface hydrolysis of polythiazyl
Authors: Ancelin H. , Hauptman Z. V. , Banister A. J. , Yarwood J. 
Published: April 2003

AbstractThe hydrolysis of (SN)x, in air at room temperature and 90% relative humidity has been studied using the attenuated total reflectance (ATR) method. Decomposition gave rise to strong bands at 3210 and 3150 cm–1 [v3 and v1 (NH)], 1420 cm–1 (vb NH), 1220 cm–1 (SO), 1089 and 610 cm–1 [v1 and v3 (SO)]. For the first 3 days, the decay of the 808 and 690 cm–1 bands of (SN)x was first order, with a half life of about 30 h. The spectroscopic data were consistent with the rapid formation of SO2NH2 and SNH chain end groups with subsequent relatively slow hydrolysis to (NH4)2SO4, sulfur, and fresh hydrolysable chain ends.
Relaxations of thermosets. IV. A dielectric study of crosslinking of diglycidyl ether of bisphenol‐a by two curing agents
Authors: Mangion M. B. M. , Johari G. P. 
Published: April 2003

AbstractThe dielectric permittivity ϵ′ and loss ϵ″ during the crosslinking or curing of diglycidyl ether of bisphenol‐A with diaminodiphenyl methane and diaminodiphenyl sulfone have been measured from the sol to gel to glass‐formation regions. The ϵ′ monotonically decreases with time and the ϵ″ initially decreases, then increases to a peak value and finally reaches extremely low values characteristic of the glassy state. These features shift to shorter times with an increase in the temperature of curing. Complex‐plane plots of ϵ′ and ϵ″ have the shape of an are skewed at both the short‐time and the long‐time intercepts and resemble Cole–Cole plots of ϵ*. Thus the dielectric consequences of the chemical changes with time during the cross‐linking of a thermoset are analogous to the frequency dependence of ϵ* in an amorphous solid. The time dependence of ϵ* follows a stretched exponential decay, ϕ(t) = exp [− (t/τ)γ] where 0 < γ < 1. The parameter γ is in the range 0.2 to 0.4, and increases with a decrease in the curing temperature. Additional curing at longer times produces polymer segments in the network with a high reorientation rate. This is observed as deviations from the shape of a skewed arc at the limiting long‐time intercept and appears as a secondary relaxation during the curing process, but at very long times. The ϵ′ and ϵ″ have been analyzed and the roles of dc conductivity, Δϵ, and γ in determining the shape of the curing isotherms have been estimated. A representation of the data in the complex electrical modulus, M*, formalism shows the occurrence of two relaxation processes during the period of a typical isothermal cure. The feature observed at the shortest time is due to conductivity relaxation and the subsequent feature is due to the dipolar relaxation processes during the curing. The time of cure at which the relaxation rate reaches a fixed value follows an exponential relation with the reciprocal curing temperature with parameters which are characteristic of a thermoset. The decrease in dc conductivity during sol → gel conversion follows the scaling law used in the description of a critical phenomenon.
Rheology of galactomannan‐borax gels
Authors: Pezron E. , Ricard A. , Leibler L. 
Published: April 2003

AbstractThe rheological behavior of semidilute galactomannan solutions in the presence of borax has been studied. The effects of polymer and borate concentrations, ionic strength, pH, and temperature are investigated and discussed. The shape of the viscoelastic functions of galactomannan–borax gels is similar to that for semidilute or concentrated polymer solutions. In 1 M NaCl, electrostatic effects are screened and the characteristic moduli of the gels appear to be determined by the number of interchain crosslinks. The elastic plateau modulus varies linearly with the free borate concentration and with the 2.6 power of the galactomannan concentration. Time–temperature type superposition is applicable if a vertical shift is introduced to account for the exothermic nature of the complexation reactions. Moreover, it seems possible to control the gel reversibility and the lifetime of crosslinks by changing the complexation kinetics via the pH.
Equilibrium partitioning of long‐chain polymers between bulk solution and pores in the presence of short‐range attractions
Authors: Davidson Marc G. , Deen William M. 
Published: April 2003

AbstractThe partitioning of linear polymers between small pores and bulk solution is examined theoretically for the case of long‐chain molecules which are attracted by the walls of cylindrical or slitlike pores. The polymer is considered to be a freely jointed chain of N mass points connected by rectilinear segments of length l. The interaction potential is represented as a square well with width comparable to l. It is assumed that N is very large and that l is much smaller than the pore radius, allowing the calculations to be performed by solving a “diffusion equation” with a suitable source term. The results presented cover a wide range of interaction potentials and relative polymer and pore sizes. A critical interaction potential is identified for which entropic and enthalpic effects exactly cancel, resulting in equal concentrations in the pore and bulk solution. As the critical potential is approached, the solution to the diffusion equation rapidly changes character. The critical potential may be interpreted as defining a transition from “free” to weakly adsorbed polymer.
Modeling strategy for systems with both stepwise and chainwise chemistry: Amine‐epoxy networks with etherification
Authors: Gupta Anshu M. , Macosko Christopher W. 
Published: April 2003

AbstractA comparison between the entirely statistical and the combined kinetic and statistical model for amine‐epoxy networks, both studied previously in the literature is made. The chemistry studied involves the generation of a secondary site which reacts in the network through chainwise addition rather than the stepwise addition mode of the primary reaction. It is shown that the combined model is exact and the naïve statistical models are approximate. The assumptions underlying the two models are delineated. It is shown, that under certain circumstances, the predictions of the two models can differ by several hundred percent. Further, the combined model is extended to predict the postgel properties of the network.
Characterization of thermal diffusion of copolymers in solution by thermal field‐flow fractionation
Authors: Schimpf Martin E. , Giddings J. Calvin 
Published: April 2003

AbstractExtending our earlier measurements of homopolymer thermal diffusion, we characterize here the thermal diffusion of nine copolymers in toluene by thermal field‐flow fractionation (thermal FFF). The copolymers are organized into groups whose members differ in one major aspect only. These differences include monomer ratios in random copolymers, block arrangements in block copolymer pairs having both linear and star‐shaped configurations, and arm numbers and arm molecular weights in star‐shaped copolymers. By examining the influence (or lack thereof) of these distinctive features on the thermal diffusion coefficient DT, the general phenomenon of thermal diffusion in polymer solutions is further characterized. Specifically, two principal observations are made. First, for copolymers subject to the radial segregation of its monomers, thermal diffusion appears to be dominated by the monomers preferentially located in the outer (free‐draining) region of the solvated polymer molecule. Second, for copolymers lacking monomer segregation, DT can be described by a weighted average of the DT values of the corresponding homopolymers, where the weighting factors are the mole‐fractions of each monomer type in the copolymer.
Interdiffusion in complex polymer systems used in the formation of microporous coatings
Authors: Patsis A. V. , Henriques E. H. , Frisch H. L. 
Published: April 2003

AbstractA model is presented for the development of membranes upon the contact of polymer solutions with nonsolvents under coagulating conditions in which the membranes increase in thickness with time. Good support for the model is presented in the form of experimental measurement of solvent diffusion rates in the formation of porous membranes from polyvinyl chloride blends with polyurethanes using dimethylformamide as the polymer solvent and water as the coagulant. Qualitative observations are described for the effect of solvent/nonsolvent interdiffusion rates on the pore structures of the membranes.
Dynamic mechanical spectrometry of nylon‐12
Authors: Varlet J. , Cavaillé J. Y. , Perez J. , Johari G. P. 
Published: April 2003

AbstractThe shear modulus and loss of ca. 30% crystalline nylon‐12 have been measured over the temperature range 100–440 K and frequency range 10−4−1 Hz. The effect of water and physical aging of the amorphous regions on the relaxation spectra have been investigated. Absorbed water decreases both the temperature and height of the γ‐relaxation peak, induces a β‐relaxation peak, and decreases the temperature of the α‐relaxation peak. These results are interpreted in terms of the hydrogen‐bonding effect of water on nylon‐12 monomer and polymer. The G″ spectrum of the polymer has a half‐width of ca. 6 decades of frequency, and neither the G″, nor G″, nor the tan ϕ spectra can be superposed by shifting along the frequency axis. The large half‐width is attributed to the random distribution of crystalline regions in the polymer. The results are further discussed in terms of hydrogen‐bonding, with or without H2O, and compared with the properties of other nylons.
Model‐filled polymers. II. Stability of polystyrene beads in a polystyrene matrix
Authors: Gandhi K. , Park M. , Sun L. , Zou D. , Li C. X. , Lee Y. D. , Aklonis J. J. , Salovey R. 
Published: April 2003

AbstractThermomechanical degradation, as a result of mixing at 175°C during the preparation of polystyrene composites containing monodisperse (0.45μm) crosslinked polystyrene beads, often leads to a uniform decrease in rheological properties on increasing the concentration or on reducing the crosslink density of the beads. The extent of such degradation depends on the molecular weight of polystyrene and on the crosslink density of the polystyrene beads. Scission fragments from decomposed beads may induce free radical degradation of the polystyrene matrix. Degradation during mixing of the beads and the matrix is suppressed by mixing crosslinked beads in a polystyrene solution, and removing the solvent, or by melt mixing after adding 0.2% BHT. Polystyrene beads and composites show thermally induced weight loss on heating above 330°C in nitrogen or above 250°C in air. Networks of increased crosslink density are of enhanced thermal stability on heating in the absence of shear.
Multiple dark‐field STEM: A new method for beam‐sensitive polymers
Authors: White J. R. , Chapman J. N. , McVitie S. 
Published: April 2003

AbstractA new method for recording multiple dark‐field transmission electron micrographs using a scanning transmission electron microscope fitted with a quadrant detector is described. Simultaneous multiple recording is particularly advantageous when studying electron beamsensitive polymers and images of crystals of poly(butylene terephthalate) are presented by way of example. Resolution levels of ca. 10 nm are demonstrated.
Volume‐dependent rate processes in an epoxy resin
Authors: Bero Craig A. , Plazek Donald J. 
Published: April 2003

AbstractResults for four different volume‐dependent rate processes of an epoxy resin, Epon 1001F, fully cured with a stoichiometric amount of 4,4′‐diamino diphenyl sulfone are presented: (1) specific volume measurements at constant rates of cooling; (2) time‐dependent volume measurements after rapid temperature changes; (3) elongational creep compliance measurements; and (4) shear creep compliance measurements. Voluminal and shear retardation spectra are compared as are the temperature time scale shift factors, aT obtained from the four processes. Volume–temperature cooling curves show the decreasing glass temperature with decreasing rate of cooling, but appear to reach the glass line at a constant temperature regardless of the rate of cooling. This narrowing of the “transition range” is not predicted by the Kovacs, Aklonis, Hutchinson, and Ramos (KAHR) multiparameter model, which assumes thermorheological simplicity.