bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of crystal texture in pvc gels by x‐ray diffraction and infrared dichroism
Authors: Guerrero S. J. , Keller A. , Soni P. L. , Geil P. H.
Published: April 2003

An enquiry is presented into the nature and origin of thermoreversible gelation of poly(vinyl chloride) (PVC). In line with a previous paper it is demonstrated by direct x‐ray diffraction evidence that the origin of the gelation is crystallization, and that this crystallinity can be conspicuously apparent even for the usual technological polymer. In addition some unusual diffraction effects become apparent such as do not obviously follow from existing notions of the PVC structure. Combined infrared dichroism and x‐ray studies revealed that these new effects are attributable to a two‐component nature of the crystallinity where the components are distinguished by their orientation behavior, lateral extension, and possibly morphology of the crystallites. Some of the crystals orient with their a axes (type A crystals) and some with their c axes (type B crystals) along the stretch direction. Other more complex orientability differences are also manifest during film formation. Crystals B are smaller, and are believed to correspond to the network forming junctions, hence to fringed micellar crystals. Crystals A have a less evident connection with the network and are hypothesized to be of lamellar character, the behavior of which is closely simulated by lamellar crystal additives (stabilizer crystals). High‐temperature x‐ray work revealed no melting of crystals even in the temperature range where endotherms appear in the thermograms.
Oriented polymers from solution. III. NMR of polyethylene/polypropylene blends
Authors: McBrierty V. J. , Douglass D. C. , Barham P. J.
Published: April 2003

T1, T2, and T1ρ measurements are reported for a blended fiber of polyethylene and polypropylene prepared by the “surface growth” technique. The data support the view that the fiber contains mixed crystalline regions of each pure component that may weakly interact via spin diffusion. A tentative model is proposed for the blended fiber.
Sequence distribution in ethylene‐propylene copolymers. I. Relations between multads and between multads and the 13C NMR spectrum
Authors: Smith Wendell V.
Published: April 2003

The theoretical relations between 13C NMR line intensities and monad, dyad, and triad populations are given. In some cases only approximations are possible. The relations between monads and dyads also between dyads and triads are given. Some necessary relations between line intensities are given which provide a basis for making corrections for differing Overhauser enhancements. Included in the discussion are three lines which have not previously been discussed.
Viscoelastic, dielectric, and piezoelectric behavior of solid amylose
Authors: Nishinari Katsuyoshi , Fukada Eiichi
Published: April 2003

Complex elastic, dielectric, and piezoelectric properties were measured on amylose films as a function of temperature and moisture content at 10 Hz. The real part of the complex Young's modulus of films containing a small amount of moisture was larger than that of a dry film. Peaks in the imaginary parts of these complex response functions were observed at about −80°C. The height of these peaks decreased when the specimen absorbed a little moisture. The activation energy for this peak as determined from an Arrhenius plot of the dielectric frequency dispersion was about 9.5 kcal/mole. This peak was ascribed to methylol rotation. The real part of piezoelectric e constant was shifted downwards when the specimen absorbed moisture. This was attributed to the instantaneous response in the case of a step function excitation. The structure of amylose was thought to be stabilized by moisture absorption, probably due to hydrogen bonding. The mechanism of methylol rotation was examined by dielectric measurements.
Studies of molecular aggregation of a polybenzimidazole in solution by fluorescence spectroscopy
Authors: Kojima Takakazu
Published: April 2003

A purified, well characterized sample of polybenzimidazole (PBI) has been studied by fluorescence spectroscopy in order to obtain information concerning molecular aggregation in solution. Fluorescence and excitation spectra of PBI and a model compound have been measured in N,N‐dimethylacetamide (DMA) and in formic acid (FA). The major emission band for PBI solutions is attributed an excited 1Lb state, which consists of 0‐0 and 0‐1 vibrational energy bands. Concentration quenching is attributed to reabsorption of the emitted light, and self‐quenching due to the formation of molecular aggregates. Therefore, the extent of molecular aggregation in solution is estimated from the self‐quenching constant. In the course of the investigation, a new fluorescence band was found for the PBI‐DMA solution; its intensity increased markedly due to overlapping of polymer coils. The formation of polyelectrolytes in PBI‐FA solutions was confirmed by viscometry. The major fluorescence band was found to originate from the excited 1Lb state and to shift to longer wavelengths upon addition of lithium bromide.
High‐pressure phases in polymers. V. Crystallization studies of synthetic cis‐polyisoprene
Authors: Edwards B. C. , Phillips P. J. , Sorenson D.
Published: April 2003

The effects of elevated pressure on the morphology and crystallization kinetics of cis‐polyisoprenes containing 2–2.5% trans units have been determined. Lamellar growth rates of both α and β crystals are enhanced by elevated pressure. The degree of enhancement of α‐crystal rates is much greater resulting in an effective suppression of β growth. Differences in lamellar growth rates between these polymers and cis‐polyisoprene result from different preexponent values. Hedritic or axialitic growth, presumably due to low‐molecular‐weight fractions, is observed in shish‐kebabs present in strained films. The high‐pressure hexagonal phase cannot be grown in these polymers.
Environmental stress cracking of polyethylene: Analysis of the three zones of behavior and determination of crack‐front dimensions
Authors: Shanahan M. E. R. , Schultz J.
Published: April 2003

Previous work has shown that in the environmental stress cracking (ESC) of polyethylene, there are three major zones of behavior depending on the applied stress and the nature of the liquid environment. These three zones correspond to “pure” ESC (zone 1), ESC controlled by the speed of penetration of the liquid within a growing crack (zone 2), and behavior as in the absence of liquid (zone 3). Analysis of the transitions between zones has shown that, in the present case, a given liquid will either be capable of giving rise to all three types of behavior depending on the stress applied, or will be totally inactive. A related analysis has enabled the order of magnitude of the dimensions of the crack tip to be estimated and this has been found to be in the range of a micron.
Proton NMR studies of a polybenzimidazole in solution
Authors: Kojima Takakazu
Published: April 2003

Molecular aggregation of poly(4,4′‐diphenyl ether‐5,5′‐bibenzimidazole)(PBI) in solution has been studied by high resolution proton NMR. PBI and model compounds have been synthesized, purified, and characterized. Proton resonances in the NMR spectrum of PBI are assigned by comparison with the proton resonances of the model compounds. Spectra are studied by total line‐shape analysis, assuming each absorption curve to be Lorentzian. For PBI in N,N‐dimethylacetamide (DMAc), the resonance due to the proton of a hydroxyl group formed by proton exchange between the imino group of PBI and the carbonyl group of DMAc is observed. The activation energy for the proton exchange, obtained from Arrhenius plots of the temperature dependence of the chemical shifts of the hydroxyl proton and the imino proton, was found to increase in the order corresponding to dissociation energy of the NH···OC hydrogen bond. The chemical shifts in the NMR spectra of PBI‐DMAc solutions on the addition of LiCl are strongly dependent on the polymer‐salt ratio; and thereby the coordination position of LiCl to PBI is tentatively identified, assuming a pseudocontact LiCl‐induced shift. The dependence of the chemical shifts of protons in PBI on the dielectric constant of the solvent is demonstrated by using polar solvents of varying dielectric constant, such as N‐methylpyrrolidone, dimethylsulfoxide, and formic acid. The viscosity of the PBI‐DMAc solutions is reported at various temperatures and concentrations of LiCl. The results from viscometry are explicable in terms of the NMR observations.
Solution behavior of ionomers. I. Metal sulfonate ionomers in mixed solvents
Authors: Lundberg R. D. , Makowski H. S.
Published: April 2003

The solution behavior of metal sulfonate‐containing ionomers has been investigated in various mixed solvent systems. Ionomers, such as lightly sulfonated polystyrene (sodium salt) and sulfonated ethylene‐propylene‐diene terpolymer (metal salts) are generally insoluble in typical hydrocarbon solvents, but readily dissolve when small amounts of alcohols or other polar cosolvents are present. At relatively low polymer concentration these ionomers display unusually high thickening behavior in nonpolar solvents when compared with nonionic polymers because of association of the metal sulfonate groups. The addition of modest levels of polar cosolvent markedly decreases the solution viscosity and gives rise to viscosity‐temperature relationships different from those of conventional polymer solutions. For example, such solutions can display vicosities which increase, are relatively constant, or display maxima or minima over broad temperature ranges. These observations are interpreted as arising from a temperature‐dependent preferential interaction of the cosolvent with the sulfonate groups. While these ionomers can be regarded as polyelectrolytes of low charge density, they do not display the typical “polyelectrolyte” behavior often observed in aqueous solutions. This anomalous behavior is attributed to the fact that the metal sulfonate groups are largely un‐ionized in solvents of low dielectric constant. Therefore, the solution behavior is dominated by ion pair interactions rather than free ions.
Crosslinking chemistry and network structure in organic coatings. I. Cure of melamine formaldehyde/acrylic copolymer films
Authors: Bauer D. R. , Dickie R. A.
Published: April 2003

Crosslinking chemistry and network formation in hydroxy and carboxy functional acrylic copolymer resins cured with representative melamine‐formaldehyde crosslinking agents have been studied by infrared spectroscopy. Network formation in these systems is dominated by two reactions, the condensation of the hydroxy (or carboxy) functionality of the acrylic resin with melamine alkoxy groups to form acrylic‐melamine crosslinks, and the condensation of melamine hydroxy groups to form melamine‐melamine crosslinks. The extents of these reactions have been studied as functions of acrylic resin composition, melamine type and concentration, and cure time and temperature. For melamines with just methoxy functionality, the extent of formation of acrylic‐melamine crosslinks increased steadily with cure temperature. For melamines with substantial hydroxy functionality, the extent of formation of acrylic‐melamine crosslinks increased rapidly then leveled off with increasing cure temperature. The formation of melamine‐melamine crosslinks increased slowly with increasing cure temperature. From these data and a statistical model, effective crosslink densities were calculated. The crosslink densities correlated well with solvent resistance.
Crosslinking chemistry and network structure in organic coatings. II. Effect of catalysts on cure of melamine formaldehyde/acrylic copolymer films
Authors: Bauer D. R. , Dickie R. A.
Published: April 2003

In a previous paper, the extents of reaction of various functional groups in different acrylic copolymer melamine‐formaldehyde crosslinked formulations were measured by infrared spectroscopy. From these data and a statistical model, various network structure parameters could be calculated. One of these, effective crosslink density, was found to correlate well with film solvent resistance. In this paper the effects of the addition of strong acid catalysts on cure chemistry and network structure are determined. Both solvent‐based and water‐based formulations have been studied. In the solvent‐based formulations studied, the addition of acid catalysts greatly enhanced the crosslinking reactions at low temperatures and dramatically lowered the cure temperature. Acid catalysts also lowered the cure temperature of a water‐based formulation based on a high (180°C) cure temperature melamine. In contrast, the addition of acid catalysts had a negligible effect on the cure chemistry of a water‐based formulation crosslinked with a low (130°C) cure temperature melamine. For this case the rate limiting process was found to be the rate of removal of neutralizing amine from the film. Cure temperatures in this system could only be lowered by replacing the amine used with a more volatile amine.
Equilibria of extended‐chain polymers exhibiting crystalline and liquid‐crystalline phases
Authors: Balbi C. , Bianchi E. , Ciferri A. , Tealdi A. , Krigbaum W. R.
Published: April 2003

The phase diagram of poly(p‐benzamide) (PBA) in N,N‐dimethylacetamide/LiCl solutions was determined for two PBA samples having weight‐average molecular weights of about 10,000. The various equilibria were studied using analytical, viscometric, and optical microscope measurements. The phase diagram at 25°C, taking as variables the concentration of polymer (Cp) and LiCl (Cs), involves several equilibria which can be summarized as follows: solid ↔ isotropic solution when 0.75 ≤ Cs ≤ 2 g/dl, solid ↔ anisotropic solution when 2 ≤ Cs ≤ 4 g/dl, isotropic solution ↔ anisotropic solution when 2 ≤ Cs ≤ 4 g/dl, and Cp > 6 g/dl, and dilute isotropic solution ↔ gel when Cs > 4 g/dl. In the Cp range in which the isotropic and anisotropic phases coexist, enrichment of the high‐molecular‐weight component of the polymer in the anisotropic phase becomes more marked as the volume fraction of the latter phase is decreased. The two PBA samples exhibit noticeable differences in solubility, absolute viscosity, and in their viscosity‐concentration behavior. The location of the maximum in the latter dependence does not necessarily coincide with the first appearance of the anisotropic phase. In the absence of a flow field, anisotropic solutions exhibit an irreversible increase in viscosity. Inclusion of the equilibria involving the crystalline state furnishes insight into some of the common observations for extended‐chain polymers. A diagram illustrates the superposition of the solubility curves for a crystalline polymer and the liquid‐crystal regions. This indicates that, for the high melting crystalline polymers, the crystalline phase should be stable relative to the concentrated anisotropic phase of the wide biphasic region.
A constitutive equation derived from the model of doi and edwards for concentrated polymer solutions and polymer melts
Authors: Doi Masao
Published: April 2003

In deriving a constitutive equation from a molecular model of polymers in concentrated solutions and melts, Doi and Edwards used a mathematical approximation, the “independent alignment approximation,” which has recently been shown to produce significant error in the particular case of stress relaxation following a double‐step strain in opposite direction. In the present paper, in order to examine the approximation in general cases, we derive a new constitutive equation without using the independent alignment approximation. The new equation is a nonlinear integro‐differential equation and is solved numerically for several cases, i.e., steady shear and elongational flows, and the transient flows after the start of shear and elongation. It is found that, in the cases examined here, the new constitutive equation gives nearly the same results as the old one: the rheological functions calculated from the two theories differ no more than 30%. This substantiates the expectation that the independent alignment approximation does not produce drastic error as long as the flow direction is not reversed.
Effect of solvent power on the adsorption of polystyrene onto a metal surface
Authors: Kawaguchi Masami , Takahashi Akira
Published: April 2003

The adsorption of linear polystyrenes from cyclohexane solutions onto a chrome plate of 35 (the theta temperature), 40, and 45°C was studied by ellipsometry. The adsorbance decreases with increasing temperature, while the extension of the adsorbed polymer layer increases. The adsorbance is almost independent of the molecular weight at these temperatures. The slope of a double logarithmic plot of extension versus molecular weight is 0.5 at the theta temperature, whereas at the higher temperatures the slope is a little larger. Both the adsorbance and the extension of the adsorbed layer change reversibly over a cycle of temperature change, indicating that a reversible conformational change has occurred. The expansion factor αt of the adsorbed layer is compared with the theoretical predictions of Hoeve and of Jones and Richmond. The expansion factor αt according to Hoeve's theory, was smaller than the measured value, whereas the expansion calculated by the Jones–Richmond theory is much larger than the measured value. It is concluded that the tail portions of adsorbed chains predominantly govern the extension of the adsorbed layer.
Transport properties of annealed, drawn low‐density polyethylene (LDPE)
Authors: De Candia F. , Russo R. , Vittoria V. , Peterlin A.
Published: April 2003

The specific concentration ca of methylene chloride, the zero‐concentration diffusion coefficient D0, and the concentration coefficient γD of the diffusivity in drawn and annealed LDPE were measured. The influence of the drawing rate, of annealing with the ends of the sample free and fixed and the effects of time of standing at room temperature after annealing were investigated. The observed transport properties are in good agreement with the microfibrillar model of fibrous structure, its relaxation during annealing, and the slow crystallization of relaxed tie‐molecules upon standing at room temperature.
The use of synchrotron radiation for study of structural changes in polymers during phase transition and deformation
Authors: Forgács P. , Sheromov M. A. , Tolochko B. P. , Mezentsev N. A. , Pindurin V. F.
Published: April 2003

An experimental method using monochromatized synchrotron radiation for a wide‐angle x‐ray scattering study of polymers during phase transition and deformation is described. Results obtained on low‐density and high‐density polyethylenes and on polypropylene are given. Melting processes could be studied conveniently by making exposures during a temperature scan; a few seconds were found sufficient to obtain a diffraction spectrum. This way relatively fast crystallization processes and the structural change accompanying stress relaxation could be followed easily. The crystalline‐amorphous ratio was found to decrease continuously much below the melting temperature measured dilatometrically and by DSC, implying that in the αc‐relaxation transition region of polyethylene and polypropylene a structural change takes place. At the initial state of crystallization the 040 reflection in polypropylene was found to be stronger than the 110 one, while after crystallization has been completed this ratio was inverted. Equatorial spectra made after rapid uniaxial stretching of polypropylene sheet were found to exhibit a slight time dependence demonstrating that orientation went on after stretching had been stopped.
Melting and crystallization of poly(ethylene terephthalate) under pressure
Authors: Siegmann A. , Harget P. J.
Published: April 2003

A piston‐cylinder‐type high‐pressure dilatometer has been built and the effect of pressure on melting behavior of poly(ethylene terephthalate) (PET) has been studied. The melting temperature increases but the rate of change of the melting temperature decreases with increasing pressure. Poly(ethylene terephthalate) crystallized from the melt at elevated pressure and temperature was studied by thermal analysis, and wide‐angle and small‐angle x‐ray diffraction and electron microscopy. Chain‐extended PET crystals were observed for the first time and some of their properties are described. A similarity to extended‐chain polyethylene is suggested.
Abrupt dissolution of polydiacetylenes
Authors: Patel G. N. , Khanna Y. P.
Published: April 2003

Polydiacetylenes, where R(CH2)3,4OCONHCH2COO(CH2)1,3CH3 dissolve almost instantaneously within a narrow range of temperature (ca. 3°C). The enthalpy of dissolution of these polymers is determined by differential scanning calorimetry to be 25–46kJ/mole of the repeat unit. The abruptness of dissolution is due to breaking of intramolecular H bonds, which appears to be a cooperative phenomenon. Supporting infrared evidence is cited.
Conformational energies of para‐aromatic and aryl‐aliphatic polyamides: Relation to mesogenic character in solution
Authors: Lauprêtre F. , Monnerie L. , Fayolle B.
Published: April 2003

PCILO conformational calculations have been carried out on several model compounds of aromatic polyamide oxamides and polyamide hydrazides. The comparison of the entropy of the equilibrium conformations allows a classification of the various constitutive units into “rigid” segments, and “flexible” ones having respectively low or high entropies. From the results, it is possible to predict the mesogenic nature of solutions of a large number of aromatic polyamides, polyamide hydrazides, and polyamide oxamides.
Poling‐time dependence of the field‐induced phase transition and piezoelectric response of poly(vinylidene fluoride) films
Authors: Scheinbeim J. I. , Yoon C. H. , Pae K. D. , Newman B. A.
Published: April 2003

We have examined the poling time dependence of the field‐induced phase transition (from phase II to polar phase II) of biaxially oriented poly(vinylidene fluoride) films by x‐ray methods. These results were compared with the poling‐time dependence of the piezoelectric response (d31 and e31) determined using a piezotron Model U (Toyo Seiki, Tokyo). The piezoelectric response shows an initial rapid increase with poling time followed by a slow increase as the poling time increases. The x‐ray results show that the field‐induced phase transition is time dependent, and occurs first for those crystallites with their a axes perpendicular to the film surface. Crystallites with a in the plane of the film transform at a much slower rate. The data indicate that the poling time dependence of d31 and e31 (and, presumably, film polarization) are dependent on the transition rates.
Longitudinal acoustic mode in linear aliphatic polyesters
Authors: Wang Y. K. , Shu P. H. C. , Stein R. S. , Hsu S. L. , Kanamoto T.
Published: April 2003

The longitudinal acoustic mode has been observed in a series of linear aliphatic polyesters. In some cases, the vibrational frequencies observed do not strictly obey the expected inverse chain‐length relationship. Both the periodicity measured in small‐angle x‐ray diffraction and the chain length deduced from Raman spectroscopy are highly dependent on thermal history.
Diffusion in a multicomponent inhomogeneous multiphase system with moving boundaries. II. Increasing or decreasing volume (swelling or drying)
Authors: Rudolph F. B.
Published: April 2003

The mathematical solution of the following problem is given. Simultaneously with diffusion‐controlled mixing of two phases (e.g., gel formation), a third substance diffuses from one of the two pure phases into the other and through the inhomogeneous mixing phase which expands at a rate proportional to the square root of the time. The phases may change their volumes.
Transient decay studies of photophysical process in aromatic polymers. I. Multiexponential fluorescence decays in copolymers of 1‐vinylnaphthalene and methyl methacrylate
Authors: Phillips D. , Roberts A. J. , Soutar I.
Published: April 2003

The considerable potential of high resolution time‐resolved spectroscopic data for copolymer systems in elucidation of the intramolecular photophysical processes which occur in polymer systems is illustrated. Such information can not be gleaned solely from studies of homopolymers. Kinetic data and time resolved fluorescence spectra of copolymers of 1‐vinylnaphthalene and methyl methacrylate indicate that conventional kinetic schemes are inappropriate for the discription of excimer formation in 1‐vinylnaphthalene polymers. Evidence is presented for the presence of an emitting species in addition to the expected monomeric and excimeric forms. The nature of this third species is discussed and photophysical kinetic schemes are proposed to describe intramolecular excimer formation in such systems. Kinetic data have been derived for the principle deactivation pathways through investigation of the observed fluorescence decays upon the intrachain concentration of aromatic species.
Distortion of crystallites caused by heterogeneous chlorosulfonation of polyethylene
Authors: Bikson B. , Jagur‐Grodzinski J. , Vofsi D.
Published: April 2003

The effect of a heterogeneous chlorosulfonation on the crystalline regions of high‐density polyethylenes are investigated by x‐ray diffraction, differential scanning calorimetry, and infrared spectroscopy. The observed changes and their time dependence are discussed in terms of distortion of the crystallites, which is followed by relaxation processes leading to the elimination of the initially induced imperfections.
Anisotropy of NMR relaxation, and diffusion, of penetrants in stretched cis‐polyisoprene
Authors: von Meerwall E. , Ferguson R. D.
Published: April 2003

We have measured 1H and 19F NMR relaxation times T1, T1ρ, and T2, and diffusion constants, in trace penetrants hexafluorobenzene and n‐hexadecane dissolved in stretched cis‐polyisoprene, as function of temperature, rubber elongation, and angle with respect to the stretch direction. Values of T1 and T2 in the rubber were also measured. At all temperatures (—40 ≤ T ≤ 85°C), T1 in rubber and penetrants is isotropic and independent of elongation; the differences between rubber and penetrants are related to penetrant diffusion. All T2 above—15°C are anisotropic and elongation dependent, and follow a motional narrowing model. For the penetrants, averaging the dipolar interactions implies averaging over a diffusion path; this correctly reproduces the observed much higher T2 anisotropy in the penetrants. Penetrant diffusion rates, however, are essentially isotropic and elongation independent. These effects depend only weakly on the shape of the penetrant molecules.
Five‐line model for the description of radial x‐ray diffractometer scans of nylon 6 yarns
Authors: Heuvel H. M. , Huisman R.
Published: April 2003

Types of nylon 6 yarn which contain large γ crystals cannot be described by a model comprising three Pearson VII curves, as we formerly proposed. Hence, a new extended computer program has been developed containing five Pearson VII lines. Two lines are related to the α phase, two to γ‐phase crystals, and the fifth describes the amorphous contribution. Some physical relations between parameters could be derived and were incorporated into the computer program. This program provides extremely good fits to all equatorial diffractometer scans which can be obtained from nylon 6 yarns, including those containing large γ crystals. The parameter accuracy is quite satisfactory for diffractometer traces with well‐resolved peaks from both α and γ crystals. However, if the traces are poorly resolved or the samples do not contain a sufficient amount of the γ modification, resulting in a lack of detailed information, the parameter accuracy can be rather poor. For those cases special versions of the computer program were developed which contain further empirical interrelations between parameters. With these programs crystal sizes and molecular distances within the crystals of both the α and β modifications can be determined. The method has also been applied to radial scans at various small azimuthal angles with respect to the equator. In that way the relative amounts of the α and γ crystals as well as their orientation factors could be determined. Various aspects of this investigation are illustrated by some examples.
Characterization of Ziegler–Natta catalyst by ESCA
Authors: Furuta Motonobu
Published: April 2003

The surface composition of TiCl3‐based Ziegler—Natta catalysts prepared by various methods was analyzed by ESCA to correlate the total amount of surface titanium with the catalyst activity in propylene polymerization. The ESCA peak ratio (Ti 2P3/2/Cl 2P) of the catalysts was measured to estimate the surface composition. The titanium index defined as the product of the (Ti/Cl peak ratio and surface area) was closely correlated with the catalyst activity in polymerization. This indicates that surface titanium concentration and surface area determine the catalyst activity. It was also found that removal of surface aluminum and chlorine at the catalyst preparation stage results in concentration of titanium at the surface and an increase in surface area.
Dielectric relaxation phenomena in a series of polyhydroxyether copolymers of bisphenol‐A—endcapped polyethylene glycol with epichlorohydrin
Authors: Pochan J. M. , Gruber R. J. , Pochan D. F.
Published: April 2003

Dielectric relaxation spectra of a series of polyhydroxyether copolymers have been obtained. It has been shown that the systems exhibit very similar relaxation spectra with the α(Tg) process a function of molecular weight. All systems exhibit two secondary relaxations: β (ca. 240 K) and γ (ca. 180 K). These have been assigned as hydroxyl motion and main‐chain motion, respectively. The peak positions are not functions of composition in the ranges studied. The effect of sorbed water on the relaxation spectra is discussed.
Dielectric loss of polyethylene at very low temperatures in the frequency range from 1 kHz to 100 MHz
Authors: Yano Okimichi , Saito Susumu , Sato Yoshio , Takeda Toshifumi , Tanaka Atsushi , Wada Yasaku
Published: April 2003

The dielectric loss of high‐density polyethylene was measured from 1 kHz to 100 MHz with the improved calorimetric method at liquid‐helium temperature for samples with different oxidation times t. Two loss peaks, centered at ca. 4 kHz and at 1 MHz, both increase in height with increasing t. On the bases of these results along with previously reported ones, the low‐frequency and high‐frequency losses are ascribed to the tunneling of protons of OH groups in crystalline and amorphous regions, respectively.
Molecular dynamics and rheological properties of concentrated solutions of rodlike polymers in isotropic and liquid crystalline phases
Authors: Doi Masao
Published: April 2003

A molecular theory is presented for the dynamics of rodlike polymers in concentrated solutions. The theory describes the rotational motion of rods in both the isotropic phase and the liquid crystalline phase. Combined with the molecular expression of the stress tensor, it also gives a unified rheological constitutive equation which predicts the nonlinear viscoelasticity in both phases. As an illustrative example, the steady‐state viscosity η at zero‐shear‐rate is calculated. The predicted dependence of η on molecular weight and concentration agrees fairly well with experiments.
Crazing in two polystyrene/polybutadiene block copolymers
Authors: Argon A. S. , Cohen R. E. , Jang B. Z. , Sande J. B. Vander
Published: April 2003

Crazing was investigated in two commercial polystyrene/polybutadiene block copolymers made by the Phillips Petroleum Co. and marketed under the trade names of KRO‐1 and KRO‐3 resins. The two block copolymers each with 23% polybutadiene (PB), have radically different microstructure and radically different crazing behavior, leading to strains to fracture of 0.1 and 1.0, respectively. Of these, the KRO‐1 Resin has a phase microstructure that consists of randomly wavy and often interconnected rods of PB of 20 nm diameter surrounded by polystyrene (PS). The microstructure of KRO‐3 Resin consists of lamellae of PB with 20 nm thickness and large aspect ratio which range in packing from regular aligned lamellar domains with randomly varying misorientation in the annealed material, to randomly corrugated and wavy sheets in the as‐received material. Crazes in KRO‐1 Resin have well delineated planar shapes with a conventional, tufty craze matter structure which suggests growth by the now well‐established meniscus instability mechanism proposed by one of us. In KRO‐3 Resin, on the other hand, crazing involves profuse cavitation if the PB lamellae, giving rise to less well delineated zones of cavitational growth dispersed over the volume and suggests a mechanism of craze growth by stable, interfacial cavitational degradation in a process zone ahead of the craze tip. The measured stress and temperature dependences of craze velocities in these two polymers is in partial support of the suggested mechanisms which are also developed in outline.
Measurements of light scattering changes induced by a strong optical field in solutions of tRNA
Authors: Dobek A.
Published: April 2003

Changes in light scattering induced by a strong laser beam, as predicted theoretically by Kielich, were measured for unfractionated yeast transfer ribonucleic acid (tRNA) solutions. The vertically polarized electric field of a strong laser pulse (λ = 1060nm) amounted to 4.5 × 103 esu cgs; its duration was 10 nsec. A weak incident laser beam (λ = 630nm) was also polarized vertically and the vertical and horizontal intensity components of the light scattered through 90° at the latter wavelength were measured. These measurements together with previous results from measurements of Rayleigh light scattering and light scattering in a magnetic field permitted evaluation of the tensor of third‐order polarizability (c = 3 × 10−30 esu cgs, c = −373 × 10−30 esu cgs) and the anisotropy of the third‐order polarizability components with its sign (δc = +56 × 10−2, δc = +0.25 × 10−2 for tRNA monomer and aggregate, respectively). The new method described may be useful for studies of macromolecules and macromolecular complexes of biological importance.
Rigid‐backbone polymers. XVIII. Strictly alternating rigid‐flexible polyamides
Authors: Aharoni Shaul M.
Published: April 2003

It is shown that in strictly alternating rigid‐flexible copolyamides with the axial ratio x of their rigid elements between 3 and 3.5, lyotropic liquid crystallinity exists in solutions of 25–40% poiymer. For polymers having 4.0 < x < 4.5, anisotropic solutions appear in the concentration range 15–25%. These axial ratios are substantially smaller than the value of xc = 6.4 predicted by theories for independent rodlike particles, but are in qualitative agreement with recent theoretical calculations taking cognizance of the connection of rodlike elements by flexible residues in the polymer chain. It is further shown that solid solutions of a model compound in an alternating rigid‐flexible polymer may be prepared, provided there exists shape and size similarity between the model compound and the polymeric repeat unit.
Structure and morphology of heavily deformed single crystals of a polydiacetylene. I. Electron microscopy and x‐ray diffraction
Authors: Young R. J. , Read R. T. , Batchelder D. N. , Bloor D.
Published: April 2003

The structure and morphology of heavily deformed single crystals of a diacetylene polymer have been studied using a combination of x‐ray diffraction and electron microscopy. Crystals have been deformed by both rolling and hammering. The crystals remain intact during deformation and can be reduced in thickness by a factor of over 5 in directions perpendicular to their chain axes. It is found that the chain orientation is maintained during both hammering and rolling. A greenish‐colored surface skin develops during both types of deformation but the structure of the interior of the crystals depends upon the type of deformation employed. The interior of the hammered crystals consists of crystal blocks ca. 50 μm thick formed by cleavage perpendicular to the chain direction whereas the rolled crystals tend to be fibrous with no evidence of molecular fracture. The possible deformation mechanisms which have given rise to the different structures have been discussed.
Sorption of organic vapors by polystyrene
Authors: Saeki S. , Holste J. C. , Bonner D. C.
Published: April 2003

Activity coefficients of benzene, toluene, cyclohexane, carbon tetrachloride, chloroform, and dichloromethane in binary solutions with polystyrene at 23.5°C have been determined using a piezo‐electric sorption apparatus. The investigated solvent concentration ranges were 15 to 39 wt % for benzene, 14 to 29 wt % for toluene, 15 to 28 wt % for cyclohexane, 26 to 38 wt % for carbon tetrachloride, 24 to 46 wt % for chloroform, and 21 to 41 wt % for dichloromethane. The polystyrene (weight‐averaged) molecular weights were 1.1 × 105 and 6.0 × 105 g/gmole. The weight‐fraction activity coefficients (Ω1 = a1/w1) of cyclohexane, toluene, and carbon tetrachloride in polystyrene solutions determined in this work agree within experimental error with previously published values determined by measurement of vapor pressure lowering and vapor absorption by thin films. We find disagreement, at low solvent concentrations, between our results for benzene and chloroform and previously published results. We have analyzed our results using Flory's version of corresponding‐states polymer solution theory. The theory can account, qualitatively, for the cyclohexane and carbon tetrachloride results. It cannot account for the toluene, benzene, dichloromethane, or chloroform results.
Spectroscopic studies of solutions, suspensions, and precipitates of poly(1,6‐di‐p‐toluene sulfonyloxy‐2,4‐hexadiyne)
Authors: Bloor D. , Batchelder D. N. , Ando D. J. , Read R. T. , Young R. J.
Published: April 2003

Optical‐absorption, fluorescence, and Raman spectra for solutions, suspensions, and precipitates of poly(1,6‐di‐p‐toluene sulfonoxy‐2,4‐hexadiyne) in and from nitrobenzene, acetone, and chloroform are presented. These are interpreted in terms of the occurrence of two forms of the polymer chain; a quasicrystalline form with properties close to those of single crystal polymer and a chain‐extended form occurring in solution and colloidal particles, with an absorption energy of about 2.5 eV (20,000 cm−1). No evidence is found for the presence of very short polymer chains in partially polymerized monomer at low conversion. The relationship of these results to those for deformed single crystals is briefly discussed.
Laser Raman spectroscopy of polyacrylamide
Authors: Gupta Manoj K. , Bansil Rama
Published: April 2003

The Raman spectra of polyacrylamide and its covalently crosslinked gel (with N,N′‐methylenebis‐acrylamide as the crosslinking agent) in the region of 200–3600 cm−1 are discussed. The vibrational band assignments for polyacrylamide are made on the basis of a comparison with the spectra of acrylamide, acrylic acid, polyacrylic acid, poly(vinyl alcohol), and other vinyl polymers. The Raman spectra of polyacrylamide in the solid phase and in aqueous solution have similar spectral features. The Raman spectra of gels with low crosslink content and of polyacrylamide in aqueous solution are comparable except that one new band, predominantly due to the residual monomer, appears in the gel phase. An analysis based on polarized Raman, infrared and NMR spectra, model building, and group theoretical calculations suggests a structure dominated by isotactic species.
Heterogeneous reactions of polyethylene. II. Distortion of crystallites due to chlorination
Authors: Bikson B. , Jagur‐Grodzinski J. , Vofsi D.
Published: April 2003

The effect of heterogeneous chlorination of high‐density polyethylene on its crystalline regions was investigated by NMR, x‐ray diffraction, differential scanning calorimetry, and infrared spectroscopy. Crystallites remained inaccessible to attack by chlorine, even after extensive chlorination, however, their perfection was affected by extensive chlorination of the adjacent amorphous regions.
Measurements of infrared frequency shifts in stressed polymers
Authors: Wool R. P.
Published: April 2003

A difference‐spectrum method is used to measure vibrational frequency shifts in mechanically stressed polymers. It is shown that the peak‐to‐peak height of the difference‐spectrum intensity profile is a linear function of small frequency shifts with a slope inversely proportional to the band halfwidth for Lorentzian or Gaussian bands. The method is applied to measure frequency shifts in uniaxially stressed ultraoriented isotactic polypropylene films, using a double beam infrared grating dispersion spectrometer with a nonstressed sample in the reference beam. It is shown that frequency shifts can be measured with an accuracy of better than 0.01 cm−1 using the difference‐spectrum method.
Cellulose–hydrazine complexes
Authors: Lee David M. , Blackwell John
Published: April 2003

Cellulose–hydrazine complexes have been prepared by soaking cellulose fibers in anhydrous hydrazine, and their structures have been investigated by x‐ray diffraction. The unit cells for the complexes formed by native ramie (cellulose I) and by Mercerized ramie and Fortisan (both cellulose II) have different dimensions, but all contain sections of four chains; and the x‐ray patterns suggest significant changes in the chain stagger, as compared with the uncomplexed structures. The differences between the Mercerized ramie and Fortisan complexes may reflect the differences in morphology and crystallinity of these materials. Reconversion to cellulose is effected by soaking in water. For the cellulose II complexes a hydrate intermediate is observed in this process. The hydrate is a two‐chain unit cell and contains approximately one water molecule per glucose residue.
Application of scaling concepts to sedimentation phenomena in semidilute macromolecular solutions
Authors: Roots Jaan , Nyström Bo
Published: April 2003

Sedimentation velocity data on polystyrene in a good solvent (toluene) and in a theta solvent (cyclopentane), over a large concentration range are reported. Under good‐solvent conditions the exponent β in the apparent scaling law describing the concentration dependence of the sedimentation coefficient (s ∝ cβ) in the semidiiute region is found to be concentration dependent. However, a power law fit to data for the highest molecular weight (M = 20.6 × 106) in the concentration region (c < 2 kg m−3) yields a value β = −0.59, somewhat smaller than that (−0.54) predicted theoretically. This discrepancy and the observed curvature in logs vs. logc at higher concentrations are discussed. Under theta‐solvent conditions, on the other hand, the concentration dependence of s in the semidilute regime can be represented by a simple power law, with β = −1.0, in excellent agreement with the theoretical prediction. The crossover concentration c*, separating the dilute and semidilute concentration regimes, was found to be well defined and located at c = 1/[η]. c* varies with molecular weight as M−0.73 and M−0.50 under good‐solvent and theta‐solvent conditions, respectively.
SAXS instrumental broadening and the order dependence of peak width
Authors: Harrison I. R. , Kozmiski S. J. , Varnell W. D. , Wang J.‐I.
Published: April 2003

The width at half‐height of SAXS discrete diffraction peaks has been used to compute the number of polyethylene lamellae in a stack. The dependence of this width on diffraction order reflects the nature and magnitude of lattice fluctuations. Within the literature there have been conflicting reports on this order dependence and hence on the nature of the lattice fluctuations. Previous studies have neglected the effects of instrumental broadening. These present studies show that instrumental effects can account for some 40% of the observed first‐order peak width and drastically change the ratio of peak widths as a function of order. These studies, carried out on isothermally grown polyethylene single‐crystal mats, also demonstrate the importance of the functions chosen to represent the various broadening factors. A mat was made up consisting of randomly stacked lamella with two distinct fold periods. The scattering from this mixed mat could not be described by either of the prevailing theories.
Model polyurethane elastomers prepared from noncrystallizable poly(propylene oxide) chains
Authors: Sung P.‐H. , Mark J. E.
Published: April 2003

Elastomers of controlled molecular structure were prepared from hydroxyl‐terminated atactic poly(propylene oxide) (PPO) chains having number‐average molecular weights Mn in the range 800–4360 g mole−1. The chains were end‐linked into noncrystallizable trifunctional networks using a specially prepared aromatic triisocyanate. The networks thus obtained were studied with regard to their stress–strain isotherms in the unswollen state, in elongation at 25°C, and with regard to their equilibrium swelling in benzene at 61°C. Values of the modulus in the limit at high deformation were in good agreement with corresponding results previously obtained on networks of poly(dimethylsiloxane) (PDMS). This is of considerable importance since use of the widely used “plateau modulus” as a measure of interchain entangling would suggest that the networks of PPO would have a much higher density of such entanglements than would the corresponding networks of PDMS. The close similarity between the moduli of the two types of networks therefore argues against the idea that such entanglements make large contributions to the equilibrium elastomeric properties of a polymer network. These values of the high deformation modulus are also in good agreement with recent molecular theories as applied to the nonaffine deformation of a “phantom” network. The values of the low deformation modulus were considerably smaller than the values predicted for an affine deformation, however, suggesting that the junction points were not firmly embedded in the network structure. This is presumably due to the relatively low degree of chain‐junction entangling in the case of relatively short network chains. The swelling equilibrium results were in very good agreement with the new theory of network swelling developed by Flory.
Infrared spectroscopic study of solvent‐induced structural changes in poly(ethylene terephthalate) film
Authors: Khan A. H. , Venkatesh G. M.
Published: April 2003

It is found from polarized infrared spectroscopy that treatment of oriented poly(ethylene terephthalate) (PET) film with strongly interacting solvents such as s‐tetrachloroethane, nitrobenzene, dimethylformamide, and benzyl alcohol results in disorientation of polymer chains. Partial transformation from trans to gauche conformation takes place on thermal treatment and, to a larger extent, on solvent treatment. Increasing sharpness of the 988 cm−1 band on solvent treatment indicates the formation of regular chain folds. Some new spectral features are discussed.