bluuebunny/crossref_metadata_2025_split huggingface dataset:
Driving force for hydraulic and pervaporative transport in homogeneous membranes
Authors: Paul D. R. , Paciotti J. D. 
Published: April 2003

AbstractExperiments were designed to demonstrate that the chemical potential gradient required for liquid transport through swollen network polymer membranes manifests itself as a concentration gradient and that the rate of transport is independent of how this gradient is established. The fluxes of various liquids through a crosslinked rubber membrane were measured in hydraulic and pervaporation modes of permeation. The pressure applied downstream in the latter act simply to fix the activity of the liquid in the downstream membrane surface. The experiments show the flux is a unique function of this activity, and it does not matter how it is established. Sorption data were used to convert these results into a plot of flux versus concentration differential across the membrane which was analyzed by Fick's law using a model for the concentration dependence of the diffusion coefficient. Measured ceiling fluxes for pervaporation for a number of liquids were found to be the same as those estimated from hydraulic permeation data. A simple mathematical representation for an ideal system is used as a pedagogical device to demonstrate the conclusions.
Nucleation and growth of crazes in amorphous polychlorotrifluoroethylene in liquid nitrogen
Authors: Brown Norman , Fischer S. 
Published: April 2003

AbstractThe density of mature crazes initially increases linearly with stress and then more rapidly at higher stresses. Once the crazes become observable then density was independent of time. The lowest stress at which an appreciable density of crazes was produced corresponds to the proportional limit. The average velocity of mature crazes was constant for a given stress and varied exponentially with the stress. The velocity depended on stress in the same way that the post‐yield point stress depended on strain rate, whereas the yield point varied differently being a nonlinear function of the logarithm of the strain rate.The density of crazes was quantitatively related to the concentration of surface defects at which the crazes nucleate. The craze velocity was directly related to the diffusion coefficient of N2into the polymer. The analysis indicates that bulk diffusion of the N2governs the craze velocity and that plasticization of the tip of the craze is most important for the nucleation and growth of a craze in PCTFE.
Effect of internal field on the birefringence of polyethylene crystals and on the anisotropy of polymer chains. I. Birefringence effects
Authors: Hong S. D. , Chang C. , Stein R. S. 
Published: April 2003

AbstractValues of the anisotropy of polarizability of methylene groups deduced from the refractive indexes of n‐paraffin crystals differ appreciably from those obtained from gas‐ or liquid‐phase measurements. The differences is attributed to the erroneous application of the Lorenz—Lorentz internal field to the anisotropic n‐paraffin crystal. A more detailed calculation of the internal field is carried out by detailed summation of the dipolar field over an idealized n‐paraffin crystal in which the molecular chains are replaced by anisotropic rods. With reasonable values of parameters and assumed crystal shape, the discrepancy in polarizability anisotropy is resolved.
Morphology and physical properties of triblock copolymers with crystalline end blocks
Authors: Kuo C. , McIntyre D. 
Published: April 2003

AbstractThe morphology of crystalline end‐block copolymers of poly(thiacyclobutane‐b‐isoprene‐b‐thiacyclobutane) (TCB–I–TCB) was studied by optical microscopy, electron microscopy, and small‐angle x‐ray scattering (SAXS). A spherulitic texture was observed for both the TCB homopolymer and the TCB–I–TCB block copolymers. Well‐defined phases arranged in an ordered structure exist when the films are cast above the melting temperature of the crystalline end blocks. The dimensions and the arrangements of the domains have been derived from both SAXS and electron microscope measurements. The deformation mechanism of the 41% end‐block copolymer sample was also examined by a combination of SAXS and stress–strain studies. It was found that the interdomain spacing increased along the stretching direction as the extension ratio was increased. The morphology changes from hexagonally packed cylinders to rowtype cylinders upon the application of stress.
Nonlinear viscoelasticity of polystyrene solutions. I. Strain‐dependent relaxation modulus
Authors: Fukuda Mitsutoshi , Osaki Kunihiro , Kurata Michio 
Published: April 2003

AbstractStrain‐dependent relaxation moduli G(t,s) were measured for polystyrene solutions in diethyl phthalate with a relaxometer of the cone‐and‐plate type. Ranges of molecular weight M and concentration c were from 1.23 × 106 to 7.62 × 106 and 0.112 to 0.329 g/cm3. Measurements were performed at various magnitudes of shear s ranging from 0.055 to 27.2. The relaxation modulus G(t,s) always decreased with increasing s and the relative amount of decrease (i.e.,–log[G(t,s)/G(t,0)]) increased as t increased. However, the detailed strain dependences of G(t,s) could be classified into two types according to the M and c of the solution. When cM < 106, the plot of log G(t,s) versus log t varied from a convex curve to an S‐shaped curve with increasing s. For solutions of cM > 106, the curves were still convex and S‐shaped at very small and large s, respectively, but in a certain range of s (approximately 3 < s < 7) log G(t,s) decreased rapidly at short times and then very slowly; a peculiar inflection and a plateau appeared on the plot of log G(t,s) versus log t. The strain‐dependent relaxation spectrum exhibited a trough at times corresponding to the plateau of log G(t,s). The longest relaxation time τ1(s) and the corresponding relaxation strength G1(s) were evaluated through the “Procedure X” of Tobolsky and Murakami. The relaxation time τ1(s) was independent of s for all the solutions studied while G1(s) decreased with s. The reduced relaxation strength G1(s)/G1(0) was a simple function of s (The plot of log G1(s)/G1(0) against log s was a convex curve) and was approximately independent of M and c in the range of cM <106. This behavior of G1(s)/G1(0) was in agreement with that observed for a polyisobutylene solution and seems to have wide applicability to many polymeric systems. On the other hand, log G1(s)/G1(0) as a function of log s decreased in two steps and decreased more rapidly when M or c was higher. It was suggested that in the range of cM < 106, a kind of geometrical factor might be responsible for a large part of the nonlinear behavior, while in the range of cM > 106, some “intrinsic” nonlinearity of the entanglement network system might be important.
Viscoelastic properties of heterogeneous network polymers from poly(D‐glutamic acid) and poly(oxyethylene glycol)
Authors: Mori Tetsuo , Tanaka Ryuichi , Tanaka Takehide 
Published: April 2003

AbstractA series of five heterogeneous network polymers was prepared from poly(D‐glutamic acid) (PDG) and poly(oxyethylene glycol) (PEG), and their dynamic mechanical properties were studied. The content of PDG was fixed at 60% by weight, and the molecular weight of PEG was changed to obtain networks with various crosslink densities. An increase in the PEG molecular weight from 330 to 880 caused considerable broadening of tan δ and E″ curves, and peak temperatures for tan δ and E″ decreased slightly. Curves of tan δ and E″ for PDG–PEG 4000 (indicating a PEG component of molecular weight 4,000) were much broader and the existence of two peaks was recognized. These findings and x‐ray photographs suggest that PDG–PEG 330, 570, and 880 give films of fairly uniform phase, but that PDG–PEG 1830 and 4000 give films with two‐phase structure. The factors influencing the dynamic mechanical properties in decreasing order of effectiveness are found to be the proportions by weight of PDG and PEG, the compatibility of PDG with PEG, the crosslink density, and the concentration of free carboxyl groups. The infrared spectra of these polymers indicate that at least part of the PDG component retains the α‐helix conformation.
A comparison of two techniques for inducing fibrous crystallization from solution
Authors: McHugh A. J. , Forrest E. H. 
Published: April 2003

AbstractExperimental results are presented and discussed comparing two techniques for inducing fibrous growth of polyethylene crystals from flowing solutions: a plunging cone device and a standard rotating cylinder (Couette) device. Comparison of crystal “overgrowth” diameter to spacing ratios for the several experiments with predictions based on an earlier postulated model lead to conclusions regarding the model inadequacy. A detailed comparison is made of the melting behavior of crystals produced by both flow fields and those results are discussed in light of a modified model for the growth process presented elsewhere. The conclusion is reached that differences in melting behavior may be attributed to differences in extension of the high molecular weight chains involved in the growth processes occurring in the two different flow fields.
High‐resolution preparative‐scale gel‐permeation chromatography
Authors: Kato Yoshio , Kametani Tomi , Furukawa Koichi , Hashimoto Tsutomu 
Published: April 2003

AbstractSharp polymer fractions have been obtained in preparative‐scale gel‐permeation chromatography by use of a column set packed with polystyrene gel particles of about 10 μ diameter. When 0.13 g of standard polystyrene NBS 706 was fractionated per injection, fractions with polydispersities of about 1.02–1.03 were obtained over the molecular weight range 104–106. Effects of a injection volume, solution concentration, and fraction volume on fractionation efficiency were also investigated. Polydispersities of fractions increased appreciably with increasing amounts of polymer injected.
Pressure dependence of dielectric properties of chlorinated polyethylene vulcanizate. II. Free volume and configurational entropy theories
Authors: Naoki Motosuke , Nose Takuhei 
Published: April 2003

AbstractThe P–V–T relation and the heat capacity of a chlorinated polyethylene vulcanizate were measured. Several tests on the validity of thermodynamic treatments of the α relaxation process and the glass‐transition temperature were performed by using dielectric properties. From a study using excess variables, it was shown that the entropy theories represented by the equations of Goldstein and Adam–Gibbs' were slightly better than the free volume theory represented by Doolittle's equation. However the study provided no distinction between the two entropy theories. Some tests were also performed on the pressure dependence of the glass‐transition temperature, dTg/dP, and on H*V/H*V where H*V is the isochoric activation enthalpy and H*P is the isobaric activation enthalpy. Here, too, the entropy theories were better than the free volume theory. Goldstein's expression gave values of both dTg/dP and H*V/H*P closest to those from the dielectric experiments. The Adam–Gibbs' equation gave a temperature dependence for dTg/dP and H*V/H*P most similar to those from the experiments.
A rotational rheometer with a drag‐cup torque transducer
Authors: Berry Guy C. , Wong Chiu‐Ping 
Published: April 2003

AbstractA rotational cone‐and‐plate rheometer incorporating a drag‐cup torque transducer and a frictionless, wire suspension has been designed and constructed. The instrument design provides for a controlled atmosphere for the sample, including anhydrous conditions necessary for studies on solutions of polymers in strong acids. The rheometer can be used to determine the shear deformation in response to an applied stress, including creep, recovery, and the shear stress in response to an applied steady shear. Both transient and steady‐state measurements are possible. Illustrative examples of the instrument performance are given.
Degrading mixtures of monodisperse poly‐α‐methylstyrenes: Rates and anomalous molecular weight distributions
Authors: Roestamsjah  , Wall L. A. , Florin R. E. , Aldridge Mary H. , Fetters L. J. 
Published: April 2003

AbstractWhen a mixture of two monodisperse samples of poly‐α‐methylstyrene is thermally degraded, the components behave independently, as a first approximation, as shown by GPC and rate of volatilization data. The ratio Mw/Mn, before approaching the ultimate value of 2.0, first goes through a minimum at a much lower value.
ESR study of pressure dependence of free‐radical decay in irradiated polystyrene
Authors: Szocs F. , Plaček J. 
Published: April 2003

AbstractRadicals giving the usual triplet ESR spectrum have been generated in polystyrene by γ‐irradiation at room temperature. The decay of the radicals has been investigated in the temperature interval between 90° and 200° and pressures ranging from 1 to 8000 atm. The effect of pressure on the mechanism of the free‐radical decay is discussed. There are two regions of free‐radical decay showing different activation volumes: VI = 11.5 cm3/mole and VII = 66 cm3/mole. The correlation between molecular motion in the α‐relaxation region and radical decay is pointed out.
Crystallization of isotactic polystyrene from dilute solutions
Authors: Lemstra P. J. , Challa G. 
Published: April 2003

AbstractThe overall rate of crystallization of isotactic polystyrene from dilute solutions, 1% by weight, in trans‐decalin and benzyl alcohol was studied as a function of temperature using dilatometry. These solvents were chosen because the dissolution temperatures of crystalline isotactic polystyrene are practically the same in both solvents. The overall rate of crystallization as a function of crystallization temperature showed a maximum in both solvents at about 50°C. At lower crystallization temperatures the rate of crystallization is much lower. The overall rate of crystallization of isotactic polystyrene in benzyl alcohol is far larger than in trans‐decalin at the same undercooling throughout the temperature range, which is in apparent contradiction to present crystallization theories. At very large undercooling (Tc lower than about 0°C) the solutions of isotactic polystyrene in both solvents quickly become “rigid” gels. Surface replicas of freeze‐etched gels indicate that a fringed micelle type of crystallization takes place at these low temperatures. The transition from folded chain crystallization to fringed micelle crystallization may be due to a stiffening of the polymer chain below about 50°C, with a reduced rotational mobility of the phenyl groups on the chain. If very dilute solutions, below 0.5% by weight, are crystallized at these low temperatures no gels were formed but fibrous crystals are produced which could be observed under the polarizing microscope.
High‐pressure phases in polymers. I. Spherulitic growth kinetics in cis‐polyisoprene
Authors: Phillips P. J. , Edwards B. C. 
Published: April 2003

AbstractThis is the first paper in a series dealing with the crystallization of high polymers at elevated pressures. Through an extension of the thin‐film technique using osmium tetroxide staining, the measurement of lamellar growth kinetics at high pressures as well as the observation of micromorphological changes has proved possible. Three different morphological species of cis‐polyisoprene have been detected in the pressure–temperature plane. A review is given of the conditions governing their formation and the growth kinetics of lamellar crystals are discussed in detail. Secondary nucleation theory is obeyed, the major effect of pressure being to alter the kinetics through the thermodynamic transitions. Variations in lamellar thickness with pressure may be explained simply in terms of the elevation by pressure of the equilibrium melting point.
Molecular orbital calculation of the electronic structure of poly(N‐vinylcarbazole)
Authors: Hattori Kazuo , Wada Yasaku 
Published: April 2003

AbstractEnergy levels and molecular orbital wave functions of π‐electrons in a carbazole ring are calculated by the ω‐method. The result agrees well with observed optical absorption spectra of carbazole and poly(N‐vinylcarbazole) (PVCA). Molecular orbital wave functions are obtained for a PVCA chain in a 3/1 helix. The overlap integral between adjacent carbazole rings is evaluated for each molecular orbital of the ring. The result affords evidence for hole conduction in PVCA and explains the photoconductivity spectrum under high de field.
Dielectric study of low‐temperature relaxations in poly(isobutyl methacrylate), poly(n‐butyl methacrylate), poly(isopropyl methacrylate), and poly(4‐methylpentene‐1)
Authors: Shimizu Kazuharu , Yano Okimichi , Wada Yasaku 
Published: April 2003

AbstractIsochronal measurements of dielectric constant and loss are made for poly(isobutyl methacrylate) (PiBMA), poly(n‐butyl methacrylate) (PnBMA), poly(isopropyl methacrylate) (PiBMA), and poly(4‐methylpentene‐1) (P4MP1) at temperatures ranging from 4°K to 250°K. Loss peaks are found around 120°K (10–100 Hz) for PiBMA, PnBMA, and P4MP1. By comparing the activation energy with the calculated potential barrier for the internal rotation of alkyl group in the side chain, the motion responsible for the 120°K peak is concluded to be essentially the rotation of the isopropyl group as a whole for PiBMA and P4MP1 but, for PnBMA, the rotation of n‐propyl group accompanied by the rotation of the end ethyl group. Multiple paths of internal rotation are involved with the 120°K peaks of PiBMA and, in particular, PnBMA, which explain differences between PiBMA and PnBMA in the broadness and the temperature location of the 120°K peak. The 120°K peak is in general assigned to a side chain including a sequenceOCCC or CCCC. PiPMA without this sequence in the side chain does not show the 120°K peak, but it exhibits the 50°K peak (1 kHz) like poly(ethyl methacrylate). The 50°K peak is assigned to the rotation of ethyl or isopropyl group attached to COO group. Poly‐L‐valine in which the isopropyl group is directly attached to carbon does not have the 50°K peak. An additional loss peak at 20°K (1 kHz) for P4MP1 is also discussed on the basis of the calculated potential.
Dynamic mechanical properties of some novel ionene polymers
Authors: Tsutsui Tetsuo , Tanaka Ryuichi , Tanaka Takehide 
Published: April 2003

AbstractNovel ionic polymers of the type
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x,y‐oxyethylene ionenes (x,y‐OEI), have been synthesized, for x and y varying from 2 to 5. The 2,2‐, 2,3‐, 2,4‐, and 3,3‐OEI are crystalline; the 3,4‐, 4,4‐, 4,5‐, and 5,5‐OEI are amorphous. The temperature dependence of the dynamic mechanical properties of these polymers, studied by torsional braid analysis over a temperature range from −170° to +150°C, shows two types of dispersion in each polymer. The dispersions lying between −6° and +90°C appear to be primary dispersions due to the amorphous phase. The dispersions between −110° and 0°C, on the other hand, are attributed to local modes. The temperature of the primary dispersion depends linearly on the charge density along the main chains of the polymer. However, the dependence of the local mode dispersion temperature on the charge density shows no regular pattern. Both dispersions are greatly influenced by the presence of absorbed water. Measurements of Tg at various water contents reveal the existence of abnormal plasticizing effects by water.
Mechanics of peeling of rubbery materials. I. Peel strength and energy dissipation
Authors: Igarashi Takashi 
Published: April 2003

AbstractThe peel strength found in the trousers‐type peeling process is treated for the case in which the adherends, assumed to be flexible but inextensible are bonded by rubbery viscoelastic adhesives.Taking into consideration energy dissipation during deformation of the adhesive, Griffith's criterion is extended to the peeling of viscoelastic materials. For the peeling force per unit width f it is deduced that 2f = Γ + u′h, where T is twice the surface energy, u' is the energy dissipation per unit volume of adhesive, and h is the thickness of the adhesive layer. Values of u' obtained from peeling tests for various thicknesses are compared with those from the tensile tests and found to agree with the above relation. The deduction that the peel strength is independent of the thickness for adhesives with no energy dissipation is also verified experimentally.
Effect of molecular weight on the crystalline structure of polytetrafluoroethylene as‐polymerized
Authors: Suwa Takeshi , Seguchi Tadao , Takehisa Masaaki , Machi Sueo 
Published: April 2003

AbstractMelting and crystallization behavior of polytetrafluoroethylene as polymerized in emulsion and suspension is shown to depend on molecular weight. DSC heating curves for virgin PTFE with low molecular weight below 3 × 105 have a single peak, whereas curves for higher molecular weight samples have double peaks. With increasing heating rate the areas of higher melting peaks become larger than the lower melting peaks. The morphology of polymer exhibiting double melting peaks is mainly folded ribbons or granular particles. The phenomenon of double melting is explained on the basis of two different crystalline states which correspond to the “fold regions” and the “linear segments” in a folded ribbon.The melting temperature of virgin PTFE is almost constant at ca. 330°C for molecular weights below 1 × 106, and rises as the molecular weight increases above 1 × 106. The heat of melting of virgin PTFE is nearly independent of molecular weight.On the basis of these results, we propose a model for melting and crystallization of low and high molecular weight PTFE and for the crystal structure.
A study of the fold surface structure of polyethylene single crystals by means of selective degradation with ozone
Authors: Patel G. N. , Keller A. 
Published: April 2003

AbstractPrevious studies on the fold surface of polyethylene single crystals by means of selective degradation with ozone, together with associated GPC analysis, have been taken further. This refined method led to improved accuracy and reproducibility which enabled new and more quantitative information to be obtained than was possible earlier, and this in turn has led to new conclusions as regards the nature of the fold surface. The postulated picture of the existence of a distribution of fold lengths has received further support together with much additional information about the nature of the distribution itself. Also, differences in this respect between different crystal types have become apparent. The salient feature of the newly mapped distribution is that the majority of the folds terminate within closely defined limits with one minority fraction protruding beyond this level while another is buried within the crystal interior. The protruding folds become progressively looser and can be visualized as collapsed chains on the top surface while the folds which are buried more deeply become gradually sharper when progressing towards the crystal interior. The data on which these conclusions are based can be expressed in quantitative terms by which it could be assessed that there are differences between crystals formed at 90°C and 70°C the latter having a larger proportion of loose folds along the top surface of the crystal. A reasonable agreement between results of GPC and low‐angle x‐ray analysis gives support to these conclusions.