bluuebunny/crossref_metadata_2025 huggingface dataset:
Blends of styrene/acrylic acid copolymers and acrylic polymers
Authors: Brannock G. R. , Barlow J. W. , Paul D. R.
Published: April 2003

The miscibility of a series of styrene/acrylic acid copolymers with various polyacrylate and polymethacrylate homopolymers, as well as a series of styrene/methyl methacrylate copolymers, has been investigated. According to the binary interaction model, the miscibility diagram for styrene/acrylic acid copolymers with styrene/methyl methacrylate copolymers indicates that acid and ester groups interact endothermically. The phase behavior of the homopolymers also implies this. The analysis ignores the association and self‐association observed for the polymer blends and the low‐molecular‐weight analogs used to model them. The heat of mixing of low‐molecular‐weight analogs depended greatly on both composition and acid structure.
Rheology of polymers that are initially in the disentangled state
Authors: Kotliar A. M. , Kumar R. , Back R. A.
Published: April 2003

An 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

The 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

The 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

The 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

Use 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

The 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

Positron 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

The 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

It 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

To 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

The 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

The 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

The 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

The 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

A 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

Extending 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

A 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

The 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

Thermomechanical 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

A 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

Results 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.
NMR studies of the structural development of high‐speed melt‐spun poly (ethylene terephthalate) fibers
Authors: Tzou D. L. , Desai P. , Abhiraman A. S. , Huang T.‐H
Published: April 2003

Lineshape simulation of 13C nuclear magnetic resonances was employed to characterize the structural development of poly (ethylene terephthalate) (PET) during fiber formation and subsequent processing. In all spectra the carbonyl (CA) and glycoethylene (GE) resonances can be simulated with two components. The intensity variation of these components has been interpreted quantitatively on the basis of four morphological components in the solid‐state structure, with clearly defined differences in order between them. The four components are, in decreasing structural order, (i) crystalline (C), (ii) noncrystalline with order in both CA and GE environments (NC1), (iii) noncrystalline with order only in the GE environment (NC2), and (iv) amorphous (NCA). The crystalline component has been taken here to correspond to the high‐density component which has been estimated from flotation and optical density measurements. Such an analysis reveals a smooth pattern of evolution of order within a range of conditions in melt spinning and subsequent thermomechanical processing of PET fibers. Cold drawing at room temperature was seen to induce substantial ordering only in the GE environment. In contrast, annealing at a temperature significantly above glass transition temperature (Tg) for 2 h appears to cause the conversion of amorphous component to crystalline from with little accumulation of the intermediate components.
Conformations and 13C NMR chemical shifts of some polyamides in the solid state as studied by high‐resolution 13C NMR spectroscopy
Authors: Kubo Kimihiro , Ando Isao , Shiibashi Toru , Yamanobe Takeshi , Komoto Tadashi
Published: April 2003

High‐resolution 13Carbon nuclear magnetic resonance (NMR) spectra of Nylons 4, 6, and 66 in the solid state were measured over a wide range of temperature. From the results, it was found that resonance lines of crystalline and noncrystalline components were separable and their chemical shifts were determined. The 13C chemical shift behavior is closely related to their conformation. The origin of the conformational effects on the chemical shifts is discussed.
Investigation of ethylene‐vinyl alcohol copolymers for surface modification of contact lenses
Authors: Ou S. H. , Ishida H. , Lando J. B.
Published: April 2003

Ethylene‐vinyl alcohol copolymers from 0 to 57 mol % of vinyl alcohol were investigated for potential contact lens surface modification. Films of the ethylene‐vinyl alcohol copolymers made by solution casting, showed that the copolymers with a high percentage of vinyl alcohol groups possessed excellent surface properties such as good wettability, low protein (albumin) and lipid adsorption, and no conformational change of the adsorbed protein. Utilizing the Langmuir‐Blodgett dipping technique, an ultrathin layer of ethylene‐vinyl alcohol copolymer was deposited on a silicone rubber substrate. This initial results confirm that wettability was improved and the amount of protein adsorbed was reduced significantly after only one deposition trip.
Solubility of water in polyimides: Quartz crystal microbalance measurements
Authors: Moylan Christopher R. , Best Margaret Evans , Ree Moonhor
Published: April 2003

The solubility of water vapor in four different polyimides at 100% relative humidity and 22°C was measured by means of a quartz crystal microbalance system. The results confirm earlier conclusions that diffusion in these polymers is Fickian, and are sufficiently precise that the order of solubilities is unambiguous. The differences between the values are interpreted in terms of morphological variations rather than variations in chemical affinity for water. Diffusion coefficients are also reported.
Effects of orientation on the mechanical and dielectric relaxation behavior of cycloaliphatic polyester networks
Authors: Díaz‐Calleja Ricardo , Riande Evaristo , Guzmán Julio
Published: April 2003

The mechanical and dielectric relaxation behavior of strained and unstrained networks, prepared from hydroxyl‐terminated poly(diethylene glycol‐trans‐1,4‐cyclohexane dicarboxylate) (PDGC), is studied over a wide interval of frequencies and temperatures. The mechanical relaxation spectrum exhibits a glass‐rubber absorption, designated β, located in the vicinity of 0°C at 0.1 Hz, followed by a β relaxation which appears to be the result of two overlapping peaks centered at −80°C (β1) and −110°C(β2). These two peaks coalesce into a single peak in the case of strained networks. The dielectric relaxation spectrum also exhibits an α absorption followed by a subglass β relaxation whose width decreases as the elongation ratio λ increases. The activation energy associated with the mechanical β1 appears to increase as λ increases. However, the activation energy of the dielectric β process does not show a clear dependence on the elongation ratio. The analysis of the conformational characteristics of PDGC chains indicates that rotational transitions through the CcyC* bonds of the acid residue would give rise to high dielectric activity. Conformational changes about the CH2CH2 bonds of the glycol residue would produce significant mechanical activity but, comparatively, low dielectric activity. The glass‐rubber absorption is slightly displaced toward the high‐temperature side as the elongation ration increases, suggesting that the entropic effects overcome the volume effects. The glass‐rubber transition is interpreted in terms of the free volume theory.
Molecular deformation of high‐modulus polyethylene fibers studied by micro‐raman spectroscopy
Authors: Kip Bert J. , Van Eijk Marcel C. P. , Meier Robert J.
Published: April 2003

Raman spectra of the CC stretching region of strained gel‐spun ultradrawn ultrahighmolecular weight polyethylene fibers were recorded. On the low‐wavenumber side of both the asymmetric and symmetric band, an additional broad band appeared during straining of the fiber, indicating the presence of CC bonds exhibiting high strain. The fraction of such CC bonds was estimated to be 40%. At 4% strain, the shifts of the CC stretching bands were found to increase linearly with the initial Young's modulus. From Raman spectra, information about strain distribution can be obtained. Considering the observed differences in strain distribution between fibers produced in a different way, it can be understood why one sample can be drawn to a higher extent without rupture of CC bonds. The results were discussed in conjunction with results of X‐ray measurements reported by Prasad and Grubb. It is suggested that the fibers can be described by two crystalline fractions mixed on the molecular level and an additional small amount of a third fraction with a low Young's modulus.
Light scattering and size exclusion chromatography of semi‐flexible polyimide precursors
Authors: Kim Seong H. , Cotts Patricia M.
Published: April 2003

Measurement of the molecular weight, radius, and molecular weight distribution of polyimide precursors (amic acids and easters) is quite difficult due to strong polymer–solvent interactions, electrostatic interactions, and the possibility of partial imidization in solution. The large quantities of solvent and high dilutions necessary in liquid chromatography make this technique the most sensitive to these effects. The distortions in the chromatogram from these effects can make assessment of the molecular weight distribution from a polystyrene calibration very tenuous. Use of a light‐scattering detector permits direct measurement of the scattering intensity (and thus the molecular weight), as the sample elutes from the column. For the esters, anomalous peaks and unexpectedly large apparent values for both the molecular weight and molecular weight distribution are shown to be due primarily to partial imidization in solution catalyzed by basic solvent impurities. Chromatographic results obtained in neutralized solvent are in agreement with light‐scattering results obtained at higher concentrations.
Phase behavior of polystyrene–polyisoprene–toluene systems in the temperature range 15–45°c
Authors: Tseng Hsiao‐show , Lloyd Douglas R. , Ward Thomas C.
Published: April 2003

The phase behavior of narrow molecular weight distribution samples of polystyrene and polyisoprene in the presence of toluene was investigated by means of gel permeation chromatography. Equilibrium phase diagrams, tie lines, and critical points for a number of partially miscible polystyrene‐polyisoprene‐toluene systems were generated at 15 and 30°C and 1 atm pressure. The data were combined with previously reported results at 45°C. Using the experimentally determined phase compositions along with literature values of the polymer–solvent interaction parameters, the polymer–polymer interaction parameters were evaluated using the Flory–Huggins theory. The influence of temperature, polymer molecular weight, and polymer–solvant interaction parameters on the size, shape, and location of the equilibrium phase curve, the location of the critical point, and the polymer–polymer interaction parameter was studied.
Chemical modification of poly(substituted‐acetylene). I. Synthesis and gas permeability of poly(1‐trimethylsilyl‐1‐propyne)/poly (dimethylsiloxane) graft copolymer
Authors: Nagase Yu , Ueda Tomoko , Matsui Kiyohide , Uchikura Masaki
Published: April 2003

In order to improve the selectivity and the stability and the stability for gas permeation of poly (1‐trimethylsilyl‐1‐propyne) (PTMSP) membrane, it was chemically modified by grafting polydimethylsiloxane (PDMS) chains. The graft copolymers were synthesized by four different methods via metallation of PTMSP with n‐butyllithium. PDMS content of the graft co‐polymers was controlled in the range of 4–92 mol %. Very tough, thin membranes could be prepared from these graft copolymers using a solvent casting method. Thermal property and gas permeability of the copolymer membranes thus obtained were evaluated. These membranes were relatively thermally stable, and the softening points were over about 150°C. Oxygen permeability coefficients Po2 and selectivity Po2/PN2 of PTMSP/PDMS graft copolymers depended on the PDMS content, the former was in the range of 1 X 10−8 to 2 × 10−7 cm3 (STP)· cm/(cm2· s · cm. Hg) and the latter was 2.0–3.1. Minimum values of PO2 and PN2 occured at PDMS content of about 55 mol %. The introduction of more than 60 mol % of PDMS resulted in oxygen permeability coefficient which was maintained for more than one moth (PO2 = 2 − 6 × 10 −8 cm 3 (STP)· cm/(cm2·s·cm Hg), PO2/PN2 = 2.3–2.7).
A model of fibril deformation in crazes
Authors: Leonov A. I. , Brown H. R.
Published: April 2003

A theoretical model is proposed to describe quantitatively the steady‐state deformations of fibrils in crazes. In the model, the total force is represented as the sum of high elastic, plastic (actually, nonlinear viscous), and surface tension forces; the first two being modeled by using elongational rheology and the third represented in exact form. The model description is reduced to a boundary value problem for a second‐order ordinary differential equation describing the profile of fibrils. This problem results in an energy balance which, in turn, leads readily to a thermodynamic description of the equilibrium conditions for the deformations of homogeneous fibrils far from the interface (z → ∞). Two possible regimes of fibril deformation were found, depending on the periodicity of the fibrils in the craze. The first is Paredes and Fischer's regime of static deformations of fibrils under action of elastic forces and surface tension where the periodicity is determined by the condition for the static regime to exist. The second is Kramer's drawing regime where the fibril periodicity is found from the Fields and Achby maximization of craze tip advance speed. The choice between these two regimes is made to minimize the complete Gibbs' free energy including surface tension for the equilibrium state of fibrils at z → ∞. The model predicts that the static regime usually appears under moderate stresses and changes for the drawing regime when stresses increase. Hence, this model solves the contradictions between the static and drawing approaches proposed in literature. Examples of both the static and drawing regimes of fibril deformations are demonstrated and some comparisons with data are represented.
Ferroelectric polarization switching in nylon‐11
Authors: Lee J. W. , Takase Y. , Newman B. A. , Scheinbeim J. I.
Published: April 2003

Cold‐drawn Nylon‐11 films, which were prepared by stretching the melt‐quenched films to a draw ratio of 2.8: 1 at room temperature, were found to exhibit an electric displacement versus electric field hysteresis loop. The results confirmed that the Nylon‐11 film exhibited ferroelectric behavior at or below room temperature. The coercive fields were 65, 98, 125, 160, and 215 MV/m at 20, 0, −20, −40, and −60°C and the remanent polarization at −20°C (where there was considerably less dc conduction) was 56 mC/m2. Switching of the polarization was almost completed within 20 ms.
Effect of annealing on the ferroelectric behavior of nylon ‐ 11 and nylon ‐ 7
Authors: Lee J. W. , Takase Y. , Newman B. A. , Scheinbeim J. I.
Published: April 2003

We have discovered recently that melt‐quenched and cold‐drawn Nylon ‐ 11 films exhibit very clear ferroelectric hysteresis behavior. In the present study, a remanent polarization as high as 86 mC/m2 has been found in Nylon ‐ 7 samples; this is significantly higher than that usually observed in poly (vinylidene fluoride) films. The effect of annealing on the electric displacement versus electric field characteristics of both Nylon ‐ 11 and Nylon ‐ 7 films have been studied and show an increased coercive field (62 to 115 MV/m for Nylon ‐ 11 and 79 to 97 MV/m for Nylon ‐ 7) and a decreased remanent polarization (51 to 17.3 mC/m2 for Nylon ‐ 11 and 86 to 70.5 mC/m2 for Nylon ‐ 7) with increasing annealing temperature from 25 to 145°C.
Nonintegral and integral folding crystal growth in low‐molecular mass poly(ethylene oxide) fractions. I. Isothermal lamellar thickening and thinning
Authors: Cheng Stephen Z. D. , Zhang Anqiu , Chen Jianhua , Heberer Daniel P.
Published: April 2003

The overall crystallization and crystal melting of one low‐molecular mass poly(ethylene oxide) (PEO) fraction (MW 3000) have been investigated by differential scanning calorimetry (DSC) and in situ small‐angle x‐ray scattering (SAXS). The salient new results indicate that initial transient crystals with nonintegral folding (NIF) chain lengths form over a wide range of crystallization temperatures. This NIF structure subsequently transforms into crystal forms with integral folding (IF). The PEO IF crystals consist of the extended chain (n = 0) crystal and the once‐folded chain (n = 1) crystal, while the NIF has an intermediate fold length. The NIF → IF transformation occurs either by lamellar thickening or thinning. The NIF crystal is less stable than the IF(n = 1) crystal, but its growth is more rapid. Crystallization of the PEO (MW 3000) fraction is thus recognized as a compromise between the direction of the thermodynamic driving force and the kinetic pathway. Some potential consequences of these observations are also addressed.
Gas transport properties of liquid crystalline poly (ethylene terephthalate‐co‐p‐oxybenzoate)
Authors: Weinkauf D. H. , Paul D. R.
Published: April 2003

Gas transport properties are reported for a series of films prepared from thermotropic poly (ethylene terephthalate‐co‐p‐oxybenzoate), or PET/PHB, having compositions of 60 and 80 mol % PHB. The mesomorphic and crystalline morphology of the copolyester films was examined by cross‐polarized light microscopy, differential scanning calorimetry (DSC), and x‐ray diffraction. Melt‐processed films of both compositions appeared to exhibit an entirely anisotropic morphology with low levels of conventional crystallinity. Solution‐cast films prepared from the 60 mol % material were found to contain a large fraction of isotropic regions, which become ordered upon annealing above the glass transition. Permeability measurements were made for He, H2, O2, N2, and CO2 at 35°C and the diffusivities were computed from time‐lag data. The largely anisotropic films exhibit good barrier properties resulting from very low solubility coefficients. The partially isotropic 60 mol % films show much higher permeability coefficients driven primarily by increased solubility coefficients, while diffusivity is affected to a lesser extent. These results appear to contrast with what is observed in semicrystalline systems where increased crystalline order results in more dramatic reductions in penetrant mobility.
X‐ray scattering studies of the structure of aqueous hydroxy‐propylcellulose solutions
Authors: Wignall G. D. , Annis B. K. , Triolo R.
Published: April 2003

X‐ray diffraction studies have been undertaken on aqueous solutions of hydroxy propylcellulose (HPC) over a wide range of the scattering vector Q. The experiments revealed only modest differences in local structure on a distance scale ca. 5–300 Å despite the fact that they covered concentrations generally interpreted as ranging from the isotropic (35.1 wt %) to the anisotropic liquid crystalline (LC) phase (53.5 wt %). Several models were used to interpret the small‐angle scattering data, and each gave similar structural parameters and extrapolated intensities (Q → 0) for both solutions. Peaks were observed with d‐spacings ca. 12–17 Å in both materials. Wide‐angle x‐ray scattering (WAXS) showed slightly increased local order over a size range ca. 5–20 Å for the anisotropic solution, and this is consistent with a greater intensity of the 13 Å peak in this material. It is difficult to reconcile these findings with an interpretation of the LC state involving major differences with the isotropic phase and a high degree of orientational order extending over long length scales.
Gas permeability of a new silicone ring polymer: Isotactic poly(phenyl silsesquioxane)
Authors: Mi Y. , Stern S. A.
Published: April 2003

The permeability of isotactic poly(phenyl silsesquioxane) (PPSQ) to O2 and N2 at 25.0°C and to CO2 and CH4 at 35.0°C was measured at low pressures by the “time‐lag” method. PPSQ is a glassy silicone polymer with an 8‐atom ring structure of alternating Si and O atoms. The CO2/CH4 selectivity of PPSQ is markedly higher than that of other silicone polymers, whereas its O2/N2 selectivity appears to be only slightly higher. PPSQ is not as effective a “molecular sieve” as would be expected from its ring structure, possibly because its relatively large mean interchain distance suggests that this polymer has a large mean free volume.
Relaxations in thermosets. VI. Effects of crosslinking on sub‐Tg relaxations during the curing and aging of epoxide‐based thermosets
Authors: Mangion M. B. M. , Johari G. P.
Published: April 2003

The dielectric permittivity and loss of diglycidyl ether of bisphenol‐A‐based thermosets cured with diaminodiphenyl methane and diaminodiphenyl sulfone have been measured over a temperature range 77–400 K after curing or aging for a predetermined duration. Of the two sub‐Tg relaxations, the height of the γ relaxation peak monotonically decreases during both the cure and postcure periods, and the height of the β relaxation peak first increases to a maximum value and then decreases. This decrease is attributed to physical aging effects. The height of the α‐relaxation peak decreases. The γ‐ and β‐relaxation peaks become increasingly separated in temperature. A concept of accumulated equivalent curing time which is based upon known chemical kinetics has been introduced for use in both theoretical and practical aspects of the study of thermosets. It is shown that substantial curing of the sample occurs during its slow heating to the curing temperature. The use of this concept in the curing of thermosets is illustrated. A procedure for the analysis of the distribution of relaxation times from a set of results limited in both frequency and temperature range is described. The distribution parameter is 0.20 and 0.16 for the γ and β process, respectively, and remains constant with postcuring and physical aging. The distribution parameter for the α process decreases from 0.60 to 0.36 on curing.
The effect of pressure on gas permeation through semicrystalline polymers above the glass transition temperature
Authors: Naito Yasutoshi , Mizoguchi Keishin , Terada Katsuhiko , Kamiya Yoshinori
Published: April 2003

A method is proposed to analyze the effect of pressure on permeation of gases through semicrystalline polymers above the glass transition temperature. The method utilizes similarities in molecular diameters of the gases and differences in their solubilities. Two polymers, polyethylene and polypropylene, and a series of gases are chosen for an application of the method, and the effect of pressure on the permeabilities for 10 gases is measured in the pressure range 1–130 atm at 25°C. For polymers, the logarithm of the permeability coefficient is linear in the pressure for each gas, with negative slope for slightly soluble gases (He, Ne, H2, N2, O2, and Ar) and positive slope for highly soluble gases (CH4, Kr, CO2, and N2O). Analyzing these slopes by the method proposed permits contributions of hydrostatic pressure and concentration to the pressure dependence of permeation to be evaluated. On the basis of the results, the mechanism of gas permeation in rubbery films under high pressures is discussed.
Mathematical modeling of seeded miniemulsion copolymerization for oil‐soluble initiator
Authors: Rodriguez Valmore S. , Asua Jose M. , El‐Aasser Mohamed S. , Silebi Cesar A.
Published: April 2003

A mathematical model of seeded miniemulsion copolymerization of styrene‐methyl methacrylate for oil‐soluble initiator is presented. The mathematical model includes the mass transfer, from the miniemulsion droplets to the polymer particles, by both molecular diffusion and collision between miniemulsion droplets and the polymer particles. The mathematical model also includes the calculation of both the distribution of partices with i radicals and the average number of radicals per particle in the miniemulsion copolymerization using oil‐soluble initator. Studies were carried out on the mass transfer coefficients of monomers across the interface between the miniemulsion droplet and the aqueous phase, hexadecane concentration in the miniemulsion droplets, the miniemulsion droplet sizes, and the collision between miniemulsion droplets. The results indicated that the copolymerization of styrene‐methyl methacrylate was not a mass transfer controlled process. The mass transfer by collision between miniemulsion droplets and polymer particles plays an important role and was included in the model in order to predict the experimental data of seeded miniemulsion copolymerization.
Kinetic analysis of cis‐trans thermal isomerization of polyacetylene
Authors: Tanabe Yoshikazu , Kyotani Hiroko , Shimomura Masaki , Akagi Kazuo , Suezaki Minoru , Kasai Takanori , Shirakawa Hideki
Published: April 2003

A single broad exothermic peak due to cis‐trans isomerization appears near 140°C in the differential scanning calorimetry (DSC) curve of polyacetylene (PA) films, polymerized by a nonsolvent method using a high‐temperature‐aged catalyst. This exothermic peakis described by a two‐state model, in which population probabilities for cis and trans states are assumed to change through the forward and backward reactions. The enthalpy difference between the two states is 1.69 kcal/mol, which was derived from the slope of the plot of heat of isomerization versus cis content. The activation energy was determined experimentally from the heating‐rate dependence of the peak temperature. A single activated process with an activation energy of 28 kcal/mol was observed for the PA film. Other parameters such as the preexponential factor were estimated by comparing theoretical and experimental DSC curves.
Small‐angle neutron and x‐ray scattering study of swollen nylon‐6
Authors: Pleštil Josef , Baldrian Josef , Ostanevich Yurii M. , Bezzabotnov Vadim Yu
Published: April 2003

Results of swelling and small‐angle scattering experiments on samples of nylon‐6 swollen with heavy water are discussed on the basis of the lamellar and switchboard models. The small‐angle neutron scattering (SANS) intensity is very sensitive to the distribution of water in swollen samples, while the small‐angle x‐ray scattering (SAXS) data characterize the dry samples. The observed values of the mean‐square fluctuation of scattering‐density can be explained by a model with assumed inhomogeneous swelling of the amorphous phase.