bluuebunny/crossref_metadata_2025 huggingface dataset:
Dilute solution properties of styrene–acrylonitrile and styrene–methyl methacrylate copolymers. II. Short‐range and long‐range interactions from intrinsic viscosity data
Authors: Reddy C. Rami , Kalpagam V.
Published: April 2003

Experimental data on styrene–acrylonitrile (St–AN), and styrene–methyl methacrylate (St–MMA) copolymers reported in Part I of this series are tested by “two‐parameter” theoretical relations. The Fox–Flory (F–F) parameter K is estimated using the F–F, Stockmayer–Fixman (S–F), and Inagaki–Ptitsyn (I–P) equations. In general, the K values obtained by the F–F equation are low for the three St–AN copolymer samples in the systems studied while the values obtained from S–F and I–P equations agree within the limits of experimental error. Values of K obtained from Kurata–Stockmayer (K–S) equation for sample SA1 agree with values obtained by the S–F and I–P equations. The specific solvent effect on the K values is discussed. Values of the unperturbed dimension r̄02/M̄w, calculated from the K values estimated from the S–F equation and from the homopolymer data are compared. Except in one case, the calculated r̄02/M̄w values from homopolymer data are low in comparison with the values obtained from experimental data, which shows that the presence of the repulsive interactions between unlike monomer units brings about an expansion of copolymer molecule. The effect of composition on the steric factor σ values is discussed. The long‐range interaction parameter B, the excess interaction parameters ΔBAB, and χAB are calculated. The effects of composition and solvent on these parameters are discussed.
Dielectric behavior of aqueous solutions of sodium polyphosphates of low degree of polymerization
Authors: Van Beek W. M. , Odijk T. J. , Van Der Touw F. , Mandel M.
Published: April 2003

The dielectric relaxation behavior of three sodium polyphosphates with different but low degrees of polymerization in aqueous solution (without salt) has been investigated between 8 kHz and 100 MHz. The highest molecular weight sample (DP 338) exhibits two dispersion regions as is generally observed with synthetic polyelectrolytes at higher degrees of polymerization and is interpreted, according to the theory of van der Touw and Mandel, by attributing a certain flexibility to the polymer chain. The experimentally determined relaxation time of the high‐frequency dispersion is in fair agreement with the theoretically calculated value. For the lowest molecular weight sample (DP 112) the experimental results can best be described by a single dispersion curve pointing to a rigid, more or less stretched, conformation of the polyion in agreement with theoretical predictions. For the sample of intermediate molecular weight (DP 198) the situation is borderline as it is possible to describe the relaxation behavior by either one or two dispersion regions; it is, however, concluded from an analysis of the dielectric results that the average conformation is rather extended, but not completely rigid.
Deformation morphology of polyester single crystals
Authors: Shrawagi Suresh R. , Thomas Edwin L.
Published: April 2003

Truncated, six‐sided single crystals of a 10–16 linear polyester were grown from dilute solution in hexanol, deposited onto Mylar film, and uniaxially deformed at room temperature. For elongations below 10%, the crystals deform uniformly; however, above 20% elongation many cracks spanned by fibrils of 300 Å diameter develop approximately normal to the applied stress direction. Depending on the position of the crystal relative to the draw direction, lateral buckling pleats and cleavage cracks can also occur. Collapse of the nonplanar crystals onto the substrate with a resulting nonuniform adherence of the crystal influences the deformation. The deformation morphology is compared to that of truncated sixfold sector polyethylene crystals. Most notably, in contrast to polyethylene, {010} fold sectors do not deform differently from {110} fold sectors and phase boundaries between {110} and {010} fold sectors do not fracture easily.
Characterization of oriented low‐density polyethylene samples by differential scanning calorimetry
Authors: Pope D. P.
Published: April 2003

The melting behavior of samples of oriented low‐density polyethylene is examined as a function of annealing temperature and time, subsequent heat treatment, and irradiation dose. Three types of endotherm are identified which are attributed to primary melting of the lamellae, to melting of the products of reorganization during the scan, and to melting of material crystallized during cooling from the original annealing temperature. Irradiation was found to suppress the refolding which normally occurs when a sample is heated above its annealing temperature, but also produces an increase in melting point. The behavior of similar samples prepared from high‐density polyethylene is briefly considered.
Photoconductivity of poly(N‐acryloylcarbazole)
Authors: Okamoto Ken‐Ichi , Itaya Akira , Kusabayashi Shigekazu
Published: April 2003

The photoconductivity of poly(N‐acryloylcarbazole) (PACz), with the pendant carbazolyl group only a short distance from the skeletal chain of the polymer but separated from it by a carbonyl group, is investigated and compared with that of poly(N‐vinylcarbazole) (PVCz). There is no significant difference between PACz and PVCz in the temperature, light intensity, and spectral dependences of the photocurrent. The photoconductivity of PACz, however, is much inferior to that of PVCz and even to that of poly(N‐carbazolylethylvinylether), a representative vinyl polymer with pendant carbazolyl groups far from the skeletal chain. The poor photoconductivity of PACz is discussed in relation to the intensity of the electronic interaction between neighboring carbazolyl groups in the polymer chain and to singlet exciton migration. It is attributed mainly to an extremely low efficiency of extrinsic carrier generation via a singlet exciton, which is due to the poor electron‐donating character and the extremely short lifetime of a singlet exciton in the presence of the carbonyl group.
The thermal degradation of polyoxymethylene produced by solid‐state polymerization
Authors: Pearson A. W. N. , Groves G. W.
Published: April 2003

The thermal degradation of polyoxymethylene produced by the solid‐state polymerization of trioxane crystals has been studied. Changes in small‐angle and wide‐angle x‐ray patterns, weight loss, and density have been measured in specimens heated in air at 175°C, 185°C, and 195°C. The polyoxymethylene contained material in two different crystallographic orientations, which behaved differently. Material in the so‐called “twin” orientation melted preferentially at 185°C and 195°C, and at 185°C resolidified on cooling in parallel to the main orientation, in a lamellar structure. At 195°C, randomly oriented material was produced on resolidification. At 175°C, there was no evidence of melting or the formation of a lamellar structure, but the twin material was preferentially degraded so that only material in the main orientation remained after a time of 1500 min. The more rapid loss by degradation of the twin material was attributed to its having a lower molecular weight than the material in the main orientation.
Quantitative information from x‐ray diffraction of nylon‐6 yarns. I. Development of a model for the analytical description of equatorial x‐ray profiles
Authors: Heuvel H. M. , Huisman R. , Lind K. C. J. B.
Published: April 2003

A wide‐angle x‐ray method has been developed by which quantitative structural information can be obtained on nylon‐6 yarns. To this end, experimental equatorial diffractometer scans measured in transmission were fitted to a mathematical model describing the profiles as the envelopes of three bell‐shaped functions. Four different models were investigated using, respectively, Gauss, Lorentz (Cauchy), Logistic, and Pearson‐VII functions. The last model, which can be regarded as a generalized Lorentz function, gave the best fit. On the basis of a statistical analysis of the results of well‐separated x‐ray peaks, two parameters could be fixed. Another reduction of the number of parameters was achieved by interrelating the peak areas of the two outer reflections. These reductions widened the applicability of a computer program based on the aforementioned model to highly overlapping x‐ray peaks. So the whole variety of x‐ray scans, which can be obtained from nylon‐6 yarns made under widely varying process conditions, can be well described. The fitting procedures provide unique solutions and hence objectively determined parameters.
Kinetics of swollen surface layer formation in poly(vinyl chloride)–solvent system
Authors: Lapčík L. , Panák J. , Kellö V. , Polavka J.
Published: April 2003

The kinetics of formation of a swollen surface layer by diffusion of liquid solvent into solid poly(vinyl chloride) in the glassy state has been studied. The apparent Fickian diffusion coefficients of cyclohexanone, cyclopentanone, tetrahydropyrane, 1,2‐dichloroethane, N,N‐dimethyl‐formamide, and monohalogen derivatives of benzene in PVC is calculated with the use of Crank's model for discontinuous change of diffusion coefficient with concentration. It is found that the apparent activation energy for diffusion is in the range 6–17 kcal/mole and is dependent on the polarity of the solvent molecule.
Phase structure in a polyurethane above soft segment Tg via calorimetric and NMR techniques
Authors: Froix M. F. , Pochan J. M.
Published: April 2003

There is much controversy in the literature concerning the nature of the thermal transitions observed for segmented polyurethanes. In this study calorimetric and NMR data on a polyurethane reveal ordered structures similar to that previously observed. However, based on a recently observed semi‐ordered polymeric phase and the observation of a time‐dependent calorimetric effect not observed previously, the data are interpreted in terms of a high‐temperature short‐range order and a low‐temperature long‐range order. The former appears to form faster and annealing of both ordered phases increases their thermal stability.
Isotactic poly(pentene‐1): Form III
Authors: Moser M. , Boudeulle M. , Chanzy H.
Published: April 2003

A new crystalline form of isotactic poly(pentene‐1) was obtained from dilute solution in amyl acetate. We have designated it as form III. The morphology and structure of isothermally crystallized samples were investigated by electron microscopy and electron and x‐ray diffraction. This crystalline modification can be indexed on an orthorhombic unit cell (cell dimensions: a = 21.20 ± 0.05 Å, b = 11.48 ± 0.05 Å, c = 14.39 ± 0.05 Å (fiber axis) and probable space group P212121).
The effect of ion aggregation on some melt properties of styrene ionomers
Authors: Shohamy E. , Eisenberg A.
Published: April 2003

The dynamic modulus, G′, and viscosity, η′, in the melt were determined for styrene ionomers containing up to 7.7 mole‐% sodium methacrylate in the frequency range of 10−2 to 40 rad/sec, at various temperatures. The same parameters were determined for the methyl ester of these ionomers, as well as for some acid samples. It was found that in the temperature range studied the time–temperature superposition principle was applicable to the salts as well as to the esters and acids. Furthermore, it was found that the shapes of the G′ versus ω plots for the three types of polymers were identical for a particular molecular weight and comonomer concentration, and independent of whether the sample was in the acid, ester, or salt form. The temperatures required to achieve superposition were, however, quite different. This temperature difference, ΔT (between the salt and the ester), was found to be a function of the ion concentration, c. The shape of the plot of ΔT versus c suggests that the structure of the ionic aggregates changes in the range of 4–5 mole‐% of ions.
Deformation structures in solid‐state extruded polyethylene
Authors: Kolbeck A. G. , Uhlmann D. R.
Published: April 2003

Deformation structures resembling kink bands have previously been reported in a number of oriented semicrystalline polymers which have undergone various modes of deformation. In the present work, such structures have been observed and studied in solid‐state extruded polyethylene which has been processed to give a biaxial, “single crystal” texture. Deformation of this material by bending followed by unbending has been observed to lead to shear during the bending stage and to void formation during the unbending stage. The kink bands which form during this treatment exhibit a single morphology regardless of the axis of bending so long as the direction of compression during bending is parallel to the original extrusion direction. Besides intracrystalline slip, which is known to contribute at least in part to the process of kink band formation, mechanisms involving interlamellar slip and interfibrillar slip are also considered. These mechanisms are considered in terms of three distinct experimental observations: the relationship between the kink boundary and the x‐ray long period, the process of void formation during unbending, and the single characteristic morphology of the kink bands.
Investigation of relaxation processes in linear polyethylene in the 10−9 sec region by means of high‐resolution neutron spectroscopy
Authors: Peterlin‐Neumaier T. , Springer T.
Published: April 2003

Results are presented of neutron incoherent scattering experiments on isotropic linear polyethylene samples of high (80%) and low (48%) crystallinity in the temperature range between −180°C and +85°C for values of the scattering vector between 0.29 Å−1 and 1.81 Å−1 obtained with a high resolution backscattering spectrometer (Δħω = 0.25 − 1.0 μeV) and between 0.57 Å−1 and 2.4 Å−1 with a time‐of‐flight spectrometer (Δħω = 420 μeV). From a comparison of the results on these samples one concludes that relaxation takes place predominantly in the noncrystalline regions. This motion cannot be adequately accounted for by any of the existing models for the γ‐process. Therefore, a more liquidlike motion is suggested. Diffusion of shorter chain segments has also been ruled out since it is too slow to be observed. A simplified model of protonic jumps between equidistant sites located on the periphery of a circle of radius 2.5 Å reproduces the experimental results well. For the average time between successive CH2‐group reorientations one obtains τ1 = τ0 exp(EactRT) with τ0 = (2.0 ± 1.5) × 10−13 sec and Eact = (4.5 ± 1.0) kcal/mole. The values join up well with those for the γ‐process observed by NMR. It has been concluded that 60–90% of the protons in the noncrystalline regions participate in this motion.
The temperature dependence of the equilibrium and instantaneous compliances of low molecular weight polystyrene melts
Authors: Gray R. W. , Harrison G. , Lamb John
Published: April 2003

The equilibrium compliance of three low molecular weight polystyrene melts has been determined over the range 15–70°K above Tg from dynamic viscoelastic measurements using alternating shear. Results are favorably compared with the previous results of Plazek and O'Rourke obtained from creep measurements, but agreement with predictions based on the Rouse theory is obtained only in the case of the highest molecular weight sample.
Swelling of nylon 6 film due to water sorption
Authors: Inoue Kazuo , Hoshino Sadao
Published: April 2003

Dimensional changes in nylon 6 film on absorption and desorption of water were studied as functions of time and the amount of absorbed water. For absorption, a plot of film expansion versus the square root of time was sigmoidal in the initial region and did not coincide with the sorption curve: the latter was linear in the same region. This behavior is very similar to that reported for nylon 6 fiber by Kunzman. A theoretical analysis based on certain assumptions about the molecular state of nylon 6 gave good agreement with experimental results. By this analysis it was shown that the characteristic swelling behavior arises from instantaneous relaxation of the polymer molecules and is not connected with a time lag between water absorption and expansion of the polymer, as Kunzman proposed.
An x‐ray and conformational study of Kapton H
Authors: Conte G. , D'Ilario L. , Pavel N. V. , Giglio E.
Published: April 2003

Potential energy calculations were performed on the isolated chain of Kapton H (KH) in order to obtain information on the most probable conformations. A model with a COC angle of 130° and with the segments joining the ether oxygens forming a planar zigzag chain satisfactorily fits the x‐ray experimental data. Although the equatorial reflections are very few and diffuse, it seems likely that the space group is P21 and the unit cell parameters are a = 4.66 Å, b = 32.9 Å, c = 5.96 Å, β = 100°. The observed density is in agreement with two monomers in the unit cell. An intrachain vector distribution map was computed by rotating (angle θ) the pyromellitic acid dimide (DIPA) unit about the NC bond in the KH monomer. This map was compared with a one‐dimensional Patterson synthesis calculated along b, the fiber axis, to establish the value of θ. Van der Waals' energy calculations were subsequently accomplished in the crystal as a function of θ and of the rotation around the helical axis of the KH chains. The results allowed us to choose a reasonable macromolecular conformation and packing in the crystal. KH is mainly ordered along the fiber axis but shows little order in the packing of adjacent helixes. The macromolecules are held together by Van der Waals' and, probably, by charge‐transfer forces.
Mutual selective exclusion of unlike polymers in dilute solution and its measurement by light scattering
Authors: Kratochvíl Pavel , Vorlíček Jiří
Published: April 2003

The interaction of unlike polymer molecules (components 2 and 4) in a ternary solution can be regarded as selective exclusion or desorption of one polymer by another. A relation is derived between the coefficient of selective sorption and the interaction parameters A24 and A244 which are analogs of the second and third virial coefficients. The ratio between the apparent light‐scattering molecular weight and the true value for a polymer solute in a ternary system with one component of a binary solvent polymeric is more involved than in a ternary system in which both solvent components are of low molecular weight. Under certain conditions, the introduction of polymer component 2 into a dilute solution of polymer component 4 may lead to a decrease in the total intensity of scattered light.
A simple phenomenological approach to the thermal behavior of glasses during uniform heating or cooling
Authors: Hutchinson J. M. , Kovacs A. J.
Published: April 2003

Thermal behavior of glasses, as observed from the isobaric variations of volume, v, and enthalpy, H, is analyzed in terms of retardation kinetics. A phenomenological theory involving a single retardation time, τ, is developed, assuming that molecular mobility is controlled essentially by the actual free volume, or configurational entropy of the glassy specimen. The characteristic features of the v and H isobars, as derived from the theory, are examined as a function of the thermal history of a typical glassy specimen. The respective contributions of temperature and structural parameters to τ, are also discussed in terms of the characteristic parameters of the isobars. The theoretical predictions are compared with some dilatometric data obtained with an atactic polystyrene. The comparison reveals the limitations of the theoretical treatment and suggests that glass‐transition phenomena involve more than one retardation mechanism.
Determination of composition of ethylene–propylene copolymers by intrinsic viscosity
Authors: Delmas Geneviève , Daviet Viviane , Filiatrault Danielle
Published: April 2003

Intrinsic viscosities have been measured at 25° on five ethylene–propylene copolymer samples ranging in composition from 33 to 75 mole‐% ethylene. The solvents used were n‐C8 and n‐C16 linear alkanes and two branched alkanes, 2,2,4‐trimethylpentane and 2,2,4,4,6,8,8‐heptamethylnonane (br‐C16). This choice was based on the supposition that the branched solvent would prefer the propylene segments and the linear solvent the ethylene segments, due to similarity in shape and possibly in orientational order. It was found that [η]n − [η]br ≡ Δ[η] is indeed negative for propylene‐rich copolymers, zero for a 56% ethylene copolymer, and positive for ethylene‐rich copolymers. The Stockmayer–Fixman relation was used to obtain from Δ[η] a molecular‐weight independent function of composition. The quantities (Δ[η]/[η])(1 + aM−1/2) and Δ[η]/M are linear with the mole percent ethylene in the range investigated with 200 ≤ a ≤ 2000. The possibility of using these results for composition determination in ethylene–propylene copolymers is discussed. Intrinsic viscosities in the same solvents are reported for two samples of a terpolymer with ethylidene norbornene.
The drawing behavior of linear polyethylene. I. Rate of drawing as a function of polymer molecular weight and initial thermal treatment
Authors: Capaccio G. , Crompton T. A. , Ward I. M.
Published: April 2003

The drawing behavior of a series of linear polyethylene homopolymers with weight‐average molecular weight (M̄w) ranging from 67,800 to ∼3,500,000 and variable distribution (M̄w/M̄n = 5.1−20.9) has been studied. Sheets were prepared by two distinct routes: either by quenching the molten polymer into cold water or by slow cooling below the crystallization temperature (∼120°C) followed by quenching into cold water.

When the samples (2 cm long) were drawn in air at 75°C using a crosshead speed of 10 cm/min it was found that for low M̄w polymers the initial thermal treatment has a dramatic effect on the rate at which the local deformation proceeds in the necked region. At high M̄w such effects are negligible. An important result was that comparatively high draw ratios (λ > 17) and correspondingly high Young's moduli could be obtained for a polymer with M̄w as high as 312,000. It is shown how some of the structural features of the initial materials (mainly studied by optical microscopy, small‐angle x‐ray scattering and low‐frequency laser Raman spectroscopy) can be interpreted in terms of the molecular weight and molecular weight distribution of the polymers. Although crystallization and morphology can be important at low M̄w, it suggested that the concept of a molecular network which embraces both crystalline and noncrystalline material is more helpful in understanding the drawing behavior over the whole range of molecular weights.
Crystallization of poly(vinylidene fluoride): Equilibrium melting point and heat of fusion of the α‐polymorph
Authors: Welch Gordon J. , Miller Robert L.
Published: April 2003

Samples of poly(vinylidene fluoride) were crystallized either (a) isothermally at a series of temperatures, or (b) in the presence of varying amounts of diluent (dimethylphthalate or dimethylacetamide). The α‐polymorph was the only crystalline form present in these samples. Melting points of the first series (a) were determined by DSC and of the second (b) by dilatometry. The same equilibrium melting point for the α‐polymorph (178°C) was obtained from analysis of the two sets of data. A value of 1425 cal mole−1 (5.96 kJ mole−1) for the heat of fusion of this polymorph was obtained from analysis of the polymer–diluent melting data. The heat of fusion and the entropy of fusion calculated therefrom correlated well with corresponding values for other fluoroethylene polymers. Thus, the equilibrium melting point and the heat of fusion could be predicted for a fluoropolymer for which data have not yet been reported–poly(trifluoroethylene). The melting point predicted, 222°C, agreed remarkably well with that determined here for an experimental sample, thereby lending support to the empirical correlations. The heat of fusion of poly(trifluoroethylene) is, therefore, expected to be approximately 1300 cal mole−1.
Ionic transport in a sulfonated polystyrene–polyethylene copolymer
Authors: Crowley John L. , Wallace Richard A. , Bube Richard H.
Published: April 2003

The conductivity of a grafted copolymer composed of 21% sulfonated polystyrene and 79% polyethylene has been investigated as a function of temperature and absorbed moisture for membranes containing the monovalent counterions H+, Li+, Na+, K+, Rb+, Cs, and Ag+. The mobility of Ag+ was measured directly in an experiment analogous to that used for the mobility of F‐centers in alkali halides. The mobility and density of free counterions depend on the amount of absorbed water, but only the mobility and not the density of free counterions is a thermally activated process. Current is carried by both intrinsic counterions and, in samples containing absorbed water with greater than 1.5 V applied, by protonic carriers created when the absorbed water is electrolyzed. Thermal depolarization studies indicate that persistent polarization observed is the result of homogeneous volume polarization, due to the orientation of sulfonic acid side groups.
High resolution 1H‐NMR relaxation study of polyisobutylene in solution
Authors: Spěváček J. , Schneider B.
Published: April 2003

From the temperature dependence of integrated intensities and from line widths in high‐resolution 1H‐NMR spectra, the relaxation times T1 and T2 of protons in CH2 and CH3 groups of polyisobutylene in CCl4 solution have been determined. Although the relaxation time T1 of methylene protons is determined mainly by intragroup interactions, intergroup interactions of two methyl groups from each two consecutive monomer units were found to contribute considerably to T1 of methyl protons. The Structure and mobility of polyisobutylene (PIB) molecules in solution is discussed on the basis of the relaxation time data.
Theory of epitaxial crystallization of S2N2 and (SN)x on alkali halide substrates
Authors: Mauritz K. A. , Hopfinger A. J.
Published: April 2003

An initial series of energy calculations is aimed at predicting the epitactic behavior of S2N2 as deposited from the vapor phase upon NaCl‐type alkali halide substrates and preferred orientation of molecular chains in the (SN)x polymerized phase. Although the preferred orientation of a single S2N2 molecule is identical for NaCl and NaF, the energetics of dimer formation on the surface greatly favor use of the latter substrate as a heterogeneous nucleation catalyst. Enhancement of dimer formation on NaF is due to a near match between S2N2–S2N2 equilibrium distance and substrate unit‐cell spacing. Furthermore, the (SN)x chain‐orientation tendency also appears to be a function of alkali halide type. On NaCl, the chain axis lies along the 〈110〉 surface direction above cationic rows, the plane of interatomic bonds being perpendicular to the surface. For NaF the axial direction is 〈100〉 with alignment between rows of alternating charge, with the molecular plane in this case parallel to the substrate surface. From the calculations it appears that primary Coulombic forces are not a significant factor in dictating the epitactic properties of monomer or polymer.
A theory of the stress‐induced crystallization of crosslinked polymeric networks
Authors: Gaylord R. J.
Published: April 2003

A non‐Gaussian theory of the stress‐induced crystallization of polymeric networks is presented. It is predicted that for uniaxial extension of crosslinked polyethylene, a perfectly oriented, extended‐chain crystal is formed initially, changing to one‐fold crystal oriented perpendicular to the stretch direction at low extension and to a two‐fold crystal having nearly perfect orientation at high extension. The stress is predicted to decay initially and then to rise as the network chains switch from an extended‐ to a folded‐chain morphology, the rise being delayed and finally suppressed by additional crosslinking. The final, equilibrium birefringence is calculated and found to be negative at low extension and positive at high extension. The initial rate of crystallization is calculated using irreversible thermodynamics and is found to increase with extension and decrease with increasing crosslinking and temperature. All of the theoretical predictions are in qualitative agreement with experiment.
Poly(styrene sulfonic acid)–poly(vinylidene fluoride) interpolymer ion‐exchange membranes. I. Preparation and characterization
Authors: Gryte Carl C. , Gregor Harry P.
Published: April 2003

Highly porous interpolymer ion‐exchange membranes have been prepared from poly(styrene sulfonic acid), PSSA and poly(vinylidene fluoride) PVdF using a casting solvent of dimethylformamide and hexamethylphosphoramide. The membranes have been characterized by their water content, concentration potential, ionic conductivity, and their hydraulic permeability. An estimation of the porosity of the membranes has been made from the relative conductance of the potassium and the tetrabutylammonium ions in the film. This porosity has been compared with that derived from a consideration of the water flux through a Poiseuille‐type pore.
Effect of solvent on depolarized light scattering in dilute polymer solutions
Authors: Fortelny I.
Published: April 2003

An optical model of a system in which both polymer segments and solvent molecules are described as point dipoles has been used to calculate the intensity of light depolarized in scattering. The final expression consists of six terms, the physical meaning of which is briefly discussed. An approximation procedure has been worked out for the calculation of two interaction terms due to deviations of the local field in solution from the Lorentz–Lorenz field; the terms have been calculated for simple models of flexible and rigid molecules. Their dependence on molecular weight appears to be approximately the same as the intrinsic anisotropy of the polymer molecule; their contribution is nonzero even for a solvent isorefractive with the polymer.
Crystallization and melting of polyethylene under high pressure. III. Mixed crystallization of two kinds of extended‐chain crystals
Authors: Maeda Yoji , Kanetsuna Hisaaki
Published: April 2003

Thermal behaviors of extended‐chain crystals of polyethylene formed during various crystallization processes and conditions under about 5000kg/cm2 were studied by high‐pressure dilatometry and differential scanning calorimetry. The experiments indicate that by isothermal crystallization at small undercoolings for prolonged periods, the products show two endothermic peaks in the melting region of the usual extended‐chain crystals. This means of the presence of a bimodal lamellar thickness distribution in the extended‐chain crystals. A phase diagram has been made for pressures up to 5000 kg/cm2. The experimental results confirm the existence of two kinds of extended‐chain crystals, i.e., ordinary extended‐chain and highly extended‐chain crystals, as suggested previously by the authors.
On the modulus of particulate‐filled composites: Application of van der Poel's equation
Authors: Dickie Ray A.
Published: April 2003

Application of the van der Poel equation (as recently corrected and simplified by Smith) to modulus‐composition data on polymer composites is discussed. The van der Poel equation is in good agreement with experimental results on systems for which the ratio of filler to matrix modulus is either much less than or, if the filler particles are large enough, much greater than unity. For these systems, it is shown that the van der Poel equation is essentially equivalent to an empirically modified form of the Kerner equation. Discrepancies between the van der Poel equation and experimental modulus values for the remaining systems are analyzed in terms of an effective volume fraction veff. A functional form for veff found to be in agreement with experimental results on several systems is: veff = vf + k′(vf/d)2/3 where vf is filler volume fraction, d is filler particle size, and k′ is an empirical parameter. For the systems studied, k′ ranges between 0.28 and 1 μm2/3.
Craze initiation of glassy polymers under the action of crazing agent
Authors: Kitagawa M.
Published: April 2003

This paper deals with the formation of crazes that may be caused by an external load on glassy polymers wetted with kerosene. First, the orientation of crazes has been determined when applying a uniaxial tension to a specimen of cold‐rolled polyvinyl chloride sheet at various angles to the rolling direction. The critical stress for craze initiation in poly(methyl methacrylate) and polyvinyl chloride rods has been investigated under combined tension–torsion loading. It is shown that: (1) in an anisotropic, as well as an isotropic polymer, the direction of crazes is perpendicular to that of the maximum strain calculated by taking into account the internal stress due to rolling; and (2) under the action of a crazing agent, crazing may occur even under the pure torsional load, i.e., in the absence of dilatational stress.
Characterization of polystyrene networks by small‐angle neutron scattering
Authors: Benoit H. , Decker D. , Duplessix R. , Picot C. , Rempp P. , Cotton J. P. , Farnoux B. , Jannink G. , Ober R.
Published: April 2003

Polystyrene networks prepared by anionic polymerization have been characterized by small‐angle neutron scattering. Two kinds of systems have been examined:

(A) networks with labelled branch points allowing characterization of the spatial distribution of crosslinking points; (B) networks containing a low proportion of chains labelled with perdeuterated polystyrene in order to characterize the conformation of individual elastic chains of the polymeric network. The dependence of the results on swelling and uniaxial extension is discussed.
Environmental effects on the mechanical properties of reconstituted collagen hollow fiber membranes
Authors: Viswanadham R. K. , Agrawal Dinesh C. , Kramer Edward J.
Published: April 2003

The lateral swelling, changes in length and tensile stress–strain curve of reconstituted collagen hollow fibers, crosslinked with uv irradiation, were measured as a function of the pH and ionic strength of their aqueous environment. From pH 5 to pH 10 the lateral swelling and length are constant; at lower and higher pH the lateral swelling increases rapidly while the fiber shrinks in length. Corresponding to these changes, a pronounced toe develops in the stress–strain curve and extends to a higher strain in more acid (or basic) media. This toe is attributed to the straightening of a microcrimp in the collagen fibrils; the microcrimp is accentuated by the repulsion between the charged fibrils in acid or basic media. Direct small‐angle x‐ray evidence of these microcrimp structure changes at low pH is presented. Increasing the ionic strength of an acid solution by adding NaCl decreases the lateral swelling, increases the length, and decreases the extent of the toe on the stress–strain curve. These changes result from an increased screening of the charge on neighboring fibrils at higher ionic strengths thus decreasing the repulsion between fibrils and the resulting microcrimp. Although the zigzag elastica model of the crimp developed by Diamant et al. [Proc. Roy. Soc., Ser. B, 180, 293 (1972)] provides a good empirical fit to the stress–strain data, it is shown to be inappropriate where the crimp results from repulsive forces between fibrils. A new model taking these forces into account is developed and is shown to be in reasonable agreement with the experimental results.
Effects of diluent on molecular motion and glass transitions in polymers. II. The system polyvinylchloride–tetrahydrofuran
Authors: Adachi Keiichiro , Ishida Yoichi
Published: April 2003

Dielectric measurements, differential thermal analyses, and density measurements are reported on concentrated solutions of polyvinylchloride in tetrahydrofuran. The relaxation processes observed between 80 and 400°K have been classified into four types. From the analysis of experimental data, the primary process at the highest temperature and the process at the lowest temperature are assigned, respectively, to segmental motion of the polymer and motion of the solvent. Activation plots for the primary process conform to the Vogel–Tamman equation. The dielectric glass‐transition temperature T'g (defined as the temperature at which the dielectric relaxation time is 100 sec) determined with this equation agrees well with the glass‐transition temperature Tg from thermal analysis. Therefore, Tg can be represented by an expression of the form

The parameters of the Vogel–Tamman equation A and B are nearly independent of concentration, whereas To depends strongly on concentration. The dipole moment per monomeric unit calculated from the experimental data changes with concentration and exhibits steep increments around 30% and 90% by weight. The width of the distribution of the relaxation time also increases with the concentration. The results were compared with those for the system polystyrene–toluene studies in the same way.
Dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains
Authors: Riande E.
Published: April 2003

The mean‐square dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains have been determined from dielectric constant measurements on dilute solutions of the polymers in benzene. The values obtained are in good agreement with those predccted using the rotational isomeric state models for these chains. In addition, the unperturbed dimensions of poly(hexamethylene oxide) have been calculated as a function of molecular weight, using the isomeric state theory.
Mechanical relaxations in some ionene polymers. II. Influence of counterions and absorbed water
Authors: Tsutsui Tetsuo , Tanaka Ryuichi , Tanaka Takehide
Published: April 2003

Six 6,10‐ionenes with different counterions were prepared by ion exchange reactions in aqueous solutions. The counterions were Br, I, CIO4, BF4, SCN, and B(C6H5)4. The dynamic mechanical properties of these polymers were investigated by use of a torsional braid analyser. Three relaxations α (25–140°C), β (−30–0°C), and γ (−140–120°C) were observed at the frequencies of 0.3–0.8 Hz. The temperature of the α and β relaxations were largely dependent on the size of counterions, but those of the γ relaxations had little variation. The effects of electrostatic forces in the polymers on each relaxation was discussed. The influence of absorbed water on the α, β, and γ relaxations was examined. The absorbed water in the polymers greatly depressed the temperature of the α relaxations and this phenomenon was interpreted to be the result of the specific hydration on ionic portions.
Rapid small‐angle and wide‐angle x‐ray studies of crystallization behavior in polymers
Authors: Schultz J. M.
Published: April 2003

Small‐angle and wide‐angle x‐ray scattering measurements, using a position‐sensitive detector, were made during melt‐crystallization of linear polyethylenes and PEO–PS–PEO triblock copolymer. The scattering measurements indicated that the triblock copolymer grew by the enlargement of regions in which lamellae are regularly stacked. During primary crystallization at higher temperatures similar behavior is observed in two linear polyethylenes. At lower temperatures, changes in the shape of small‐angle scattering curves during the primary stage of crystallization indicate that amorphous gaps within the lamellar stacking become filled in. During secondary crystallization at higher temperatures new crystallites appear to grow between those formed in the primary stage. Concurrent decrease of the overall scattered intensity leads to the conclusion that secondary crystallization has two components: crystallization of new lamellae behind the spherulite growth front and the thickening of existing lamellae.
The effects of cyclic loading on polymers in a glassy state
Authors: Bouda V. , Zilvar V. , Staverman A. J.
Published: April 2003

The effects of cyclic loading on several physical properties of some polymers have been investigated. The results indicate that internal damping, shear modulus, heat capacity, and density of poly(methyl methacrylate) and alkali‐polymerized polyamide 6 in the glassy state undergo changes during cyclic loading well before the appearance of crazes. It is suggested that cyclic loading induces a nonuniform volume contraction in the structure of the material.
Photon correlation spectroscopy of crosslinked polystyrene networks in the swollen state: Influence of macromolecular polydispersity
Authors: Munch J. P. , Candau S. , Hild G.
Published: April 2003

We report measurements of the correlation function of light scattered from thermally excited longitudinal fluctuations in crosslinked polystyrene networks at equilibrium. In order to investigate the influence of the polydispersity of linear chain elements between successive branch points, we synthesized a network by means of anionic block copolymerization, using a mixture of two “precursor” polystyrenes of different molecular weights to initiate polymerization of a small amount of divinyl‐benzene (DVB). The correlation function for fluctuations having a wave vector K, has the form of an exponential decay, exp (−Γ). The decay rate is given by Γ = D′K2, where D′ represents the diffusion constant of longitudinal modes of the network. We also present measurements of the correlation function of light scattered from gels prepared by anionic block copolymerization of styrene and DVB with only one “precursor” polystyrene and by a free‐radical process. In the latter case, the gels should have a wide distribution of linear chain lengths between branch points.
Processing of semicrystalline polymers by high‐stress extrusion
Authors: Kolbeck A. G. , Uhlmann D. R.
Published: April 2003

A study has been conducted on the solid‐state extrusion of three semicrystalline polymers:poly‐propylene (PP), poly(vinylidene fluoride) (PVDF), and high‐density polyethylene (HDPE). HDPE has been extruded in continuous lengths with area reductions up to 25× at temperatures substantially below the melting region. Such extrusion has been identified as a solid‐state process, since measurements of the temperature of the polymer during extrusion indicate the absence of significant heating due to deformation. In contrast, continuous lengths of PP and PVDF could not be obtained substantially below their melting temperatures, indicating that crystallization during extrusion is an important process for these polymers. Under severe extrusion conditions (low temperatures, high area reductions. etc.), all three polymers failed within the tapered region of the extrusion die. Two modes of failure have been identified, brittle fracture and, surprisingly, necking. Grid‐line distortion patterns and a highly simplified upper‐bound plasticity analysis both indicate that shear deformations are a major factor during high‐stress extrusion.
Dielectric loss of polyethylene below 4.2°K arising from proton tunneling
Authors: Yano Okimichi , Saiki Koichiro , Tarucha Seigo , Wada Yasaku
Published: April 2003

The dielectric loss of high‐density polyethylene (HDPE: melt‐crystallized films and single‐crystal mats), low‐density polyethylene (LDPE), and copolymers of ethylene and vinyl alcohol (PEVA) was measured at 1.5 to 4.2°K in the frequency range from 10 Hz to 10 kHz. Results for HDPE show dispersion curves almost corresponding to a single relaxation and are interpreted in terms of phonon‐assisted tunneling of the protons of hydroxyl groups which are accidentally attached to tertiary carbons (carbons with a short branch). Dispersion curves for LDPE and PEVA are quite broad, indicating a wide distribution of relaxation times. The loss level of PEVA passes through a maximum at 7.5% vinyl alcohol, suggesting that interaction between a couple of neighboring hydroxyl groups depresses the loss. A potential calculation for the rotation of a hydroxyl group in the orthorhombic lattice of polyethylene yielded a double‐minimum potential for the tunneling when the lattice is assumed to have a distortion which is acceptable from x‐ray analysis. The potential quantitatively explains the observed values of relaxation time and relaxation strength of HDPE. The concentration of hydroxyl groups in HDPE, which varies among the samples, is estimated to be of the order of 1016 cm−3.
On‐line viscometry combined with gel permeation chromatography. II. Application to branched polymers
Authors: Park Won S. , Graessley William W.
Published: April 2003

Gel permeation chromatography (GPC) combined with on‐line flow time measurements have been applied to the analysis of branching in polymers. Three sets of branched polymers were examined: polybutadienes lightly crosslinked by high energy radiation, a styrene‐divinyl benzene copolymer and several of its fractions, and polyvinyl acetates branched by polymer transfer reactions during polymerization. The reduction in intrinsic viscosity due to branching was determined for each GPC fraction of the polybutadiene samples. The branching frequency in these fractions was known from other information, so the results were used to establish a relationship between viscosity ratio G and the theoretical size ratio g. This relationship was then used to calculate the distribution of branching and Mw in the styrene copolymers and the polyvinyl acetates. The results were compared with independent information on these polymers. The agreement was generally good.
Raman depolarization measurements over the entire miscible range for polystyrene–cyclohexane and polydimethylsiloxane–benzene solutions: Determination of upper theta temperatures
Authors: Thornley P. W. , Shepherd I. W.
Published: April 2003

Raman depolarization ratio measurements (ρ) have been made for 20% polydimethylsiloxane (PDMS) solutions in benzene and 10% Polystyrene (PS) solutions in cyclohexane over the temperature range 20 > T > 200°C. The bands studied were the 2907 cm−1 methyl stretch in PDMS and the 1002 cm−1 ring breathing mode in PS. The measured ρ are related to rotational isomeric state populations and a qualitative picture of the polymer conformation changes over much of their miscible ranges is described. Measurements of ρ for PDMS gum over the temperature ranges 20 < T < 200°C have been obtained and the upper theta temperature has been determined to be 171 ± 3°C for PDMS/benzene. Quantitative information about the variation of the polymer solvent interaction parameter χ can in principle be obtained.
Solubilities of volatile solutes in poly(vinyl acetate) from 125 to 200°C
Authors: Liu D. D. , Prausnitz J. M.
Published: April 2003

Gas‐liquid chromatography (GLC) was used to measure Henry's law constants for ethylene, ethane, carbon dioxide, sulfur dioxide, methyl chloride, vinyl acetate, isopropyl alcohol, methyl ethyl ketone, and acetone in liquid poly(vinyl acetate) in the region 125 to 200°C. Retention‐time differences were measured relative to nitrogen and corrections for nitrogen's finite solubility were applied; these corrections are significant when measuring the solubilities of sparingly soluble solutes by the GLC method. The effect of GLC column diameter is discussed.
The concentration and pressure dependence of the diffusion of dichlorodifluoromethane in poly(dimethyl siloxane)
Authors: Assink Roger A.
Published: April 2003

The diffusion of dichlorodifluoromethane in poly(dimethyl siloxane) as a function of concentration and pressure was measured by nuclear magnetic resonance (NMR) pulsed‐field‐gradient techniques. The pressure dependence of diffusion could be treated phenomenologically by an activation volume description where the activation volume of 20.9 cm3/mol is only a fraction of the penetrant's molar volume. A free‐volume theory, modified to include the effects of pressure, was used to analyze both the pressure and concentration dependence of diffusion. The functional form of the equation was obeyed very well although it was necessary to assume that the fractional freevolume of penetrant was more than twice its expected value. This discrepancy was interpreted to mean that the motions of the penetrant molecules are weakly coupled to the polymer lattice.