bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigations of a series of PPDI‐based polyurethane block copolymers. II. Annealing effects
Authors: Kazmierczak M. E. , Fornes R. E. , Buchanan D. R. , Gilbert R. D.
Published: April 2003

In a previous study, the morphologies of a group of paraphenylene diisocyanate (PPDI)‐based polyurethane block copolymers were examined. These polyurethanes exhibited a multiphase structure with an interfacial boundary thickness estimated to be on the order of 1 nm and crystallization of the polyoxytetramethylene (POTM) flexible segment. Further studies involving annealing of these polyurethanes are reported here. An annealing time of 4 h was used, and the annealing temperature varied from 125 to 200°C. The samples have been characterized using differential scanning calorimetry (DSC) and with wide‐ and small‐angle x‐ray scattering (WAXS, SAXS) in order to determine the effects of annealing on the microphase structure. Annealing increases the phase separation of the two phases as evidenced by sharper endotherms in DSC thermograms and increased intensities in WAXS diffractometer traces. Annealing also slightly increases the transition zone thickness and long‐period spacing. At the highest annealing temperature in this study, the long‐period spacing increases dramatically due to hard segment domain aggregation.
Miscibility of poly(vinyl chloride) with styrene/acrylonitrile copolymers
Authors: Kim J. H. , Barlow J. W. , Paul D. R.
Published: April 2003

Poly(vinyl chloride) (PVC) is shown to be miscible with styrene/acrylonitrile copolymers (SAN) having AN compositions from 11.5 to 26%. Blend samples were prepared using several methods, including solution casting, melt mixing, and precipitation of solutions by a nonsolvent. It is shown that the blend phase behavior is affected by preparation method due to the solvent effect, or Δχ effect, and lower critical solution temperature (LCST) behavior. The intramolecular repulsion between styrene and acrylonitrile units in SAN is shown to be the cause of miscibility using heats of mixing obtained from low‐molecular‐weight analog compounds. An FTIR analysis supplements the above results.
Interplay of rubber network theory with the damping behavior of crosslinked polyurethanes
Authors: Hur T. , Manson J. A. , Sperling L. H.
Published: April 2003

Network formation (branching) theory was used to examine the relationships between network structure and concomitant sound and vibration damping. For a series of model polyether‐based polyurethane networks with varying stoichiometry and composition, the glass transition temperature Tg, was found to increase with increasing concentration of elastically active network chains, EANCs, as well as the ratio of branch OH group concentration to the total OH group concentration ρ. The values of (tan δ)max, the peak height of tan δ at Tg, linearly decrease with increasing concentration of EANCs, regardless of the ρ values. However, the loss area (LA), equal to the integral of the linear loss modulus‐temperature curve, is independent of the concentration of EANCs and/or ρ. Utilizing group contribution analysis techniques, the value of the main chain ‐O‐ group contribution, LA‐O‐, is 19.1 GPa·K/g, a rather large value. This finding gives insight into why polyether urethanes are preferred for many damping applications.
Short time molecular dynamics simulations: Stressed polyethylene results
Authors: Noid Donald W. , Pfeffer George A.
Published: April 2003

The multiple signal classification method (MUSIC) for frequency estimation is used to compute the spectrum (intensity versus frequency) for stressed polyethylene in a crystal from the time‐dependent structure factor. In this article we demonstrate that MUSIC can accurately determine the frequencies for our model from very short time trajectories and can compute the frequency shifts for various stress perturbations. A preliminary study of the dynamical effects of stress on the fracture of a PE chain showed that at low stress the chain had an irregular period of the end‐to‐end distance (reaction coordinate) oscillation and at higher stress a periodic extension and contraction.
Synthesis and solution properties of comblike poly(mono‐n‐alkyl itaconates). I. Poly(monodecyl itaconate)
Authors: Leon Arturo , Gargallo Ligia , Horta Arturo , Radić Deodato
Published: April 2003

The monoester of itaconic acid with n‐decyl alcohol was prepared and polymerized. The polymer was fractionated and characterized by viscometry, size‐exclusion chromatography (SEC) and light scattering. Some of the common semiempirical relations for flexible and rigid polymers were used in order to obtain the unperturbed dimensions and the conformational parameters. Thermodynamic and dimensional parameters were determined and calculated. The results are compared with those reported previously for similar compounds.
Angular dependence of 1H‐NMR and 2H‐NMR spectra of water absorbed in cellulose film
Authors: Matsumura Kazunori , Hayamizu Kikuko , Yamamoto Osamu
Published: April 2003

1H‐NMR and 2H‐NMR spectra of water (H2O and D2O) absorbed in Visking cellulose tubing have been observed as a function of the angle Θ between the film surface and the magnetic field. 1H‐NMR spectra show broad lines, and the chemical shift and the linewidth depend on Θ. From the angular dependence of the chemical shift, the anisotropic volume diamagnetic susceptibilities of the film are determined, i.e., χ∥ in the direction longitudinal to the tubing (stretched direction) is 0.43 ppm, and χ⊥ in the transverse direction is 0.57 ppm. The different values of χ∥ and χ⊥ afford an evidence of the anisotropy of the film. 2H‐NMR spectra of D2O absorbed in the film show quadrupole splitting which also depends on Θ. The angular dependences of the linewidth (1H‐NMR) and the quadrupole splitting (2H‐NMR) indicate that the HH axes of the water molecules have a tendency to orient in the direction longitudinal to the film surface.
Kinetics of structural relaxation of poly(ethylene terephthalate)
Authors: Avramov I. , Avramova N. , Fakirov S.
Published: April 2003

The results of an experimental study of the kinetics of structural relaxation of amorphous poly(ethylene terephthalate) are reported. Samples were prepared by ultraquenching the melt on rotating stainless‐steel discs. Two types of measurements by differential scanning calorimetry were made: (1) the dependence of the “fictive” (or “structural”) temperature Tf(q−) introduced by Tool, on the cooling rate q− and (2) the dependence of the glass transition temperature Tg on the heating rate q+. In this way the value x = 0.47 was obtained for the dimensionless parameter proposed by Narayanaswamy.
Effect of molecular weight distribution on the structure and mechanical properties of ultradrawn, ultrahigh‐molecular‐weight polyethylene cast from solution. I. Thermoluminescence and NMR
Authors: Bao Liu Liang , Murakami Noriko , Sumita Masao , Miyasaka Keizo
Published: April 2003

Ultradrawing of ultrahigh‐molecular‐weight polyethylene (UHMW‐PE) films produced by gelation/crystallization from solution was investigated using thermoluminescence (TL), DSC, and pulsed NMR. The TL from an x‐irradiated UHMW‐PE gel film is considerably affected by ultradrawing. The TL glow peak is correlated with the αc dispersion of the crystalline phase in the UHMW‐PE gel film. The TL integrated intensity is weak for folded‐chain crystals but strong for extended‐chain crystals. An extra higher TL peak, observed for samples drawn 150x, is related to the appearance of some highly extended tie‐chains in the interfacial region in the process of ultradrawing. On the basis of the above observations, the effects of molecular weight distribution on the morphology of UHMW‐PE gel film are examined. It is concluded that B‐PE (Broad MWD) having a broader MWD has better drawability than N‐PE; but at a given draw ratio, higher modulus and tensile strength are realized for N‐PE (Narrow MWD).
Effect of molecular weight distribution on the structure and mechanical properties of ultradrawn, ultrahigh‐molecular‐weight polyethylene cast from solution. II. Drawability and mechanical properties
Authors: Bao Liu Liang , Murakami Noriko , Sumita Masao , Miyasaka Keizo
Published: April 2003

The effect of molecular weight distribution (MWD) on the ultradrawability and mechanical properties of solution‐cast films of ultrahigh‐molecular‐weight polyethylene (UHMW‐PE) has been investigated using tensile and dynamic mechanical measurements. The MWD has a marked effect on ultradrawability and thus on the ultimate mechanical properties such as the tensile modulus. It is proposed that UHMW‐PE with a narrow MWD(N‐PE) attains the ultimate structure at a lower draw ratio than UHMW‐PE with a broad MWD(B‐PE) because of the existence in the latter of less fully extended intercrystalline tie chains. It is found that, at the same drawing temperature (100°C), N‐PE shows a higher modulus than B‐PE at draw ratios up to 150 x, which is assumed to be the ultimate value for N‐PE.
Role of orientation in kinetics of nucleation and growth of crystals in polymers
Authors: Desai Prashant , Abhiraman A. S.
Published: April 2003

A theoretical framework is provided for generalizing the inferences drawn from the results of earlier experimental studies of kinetics of crystallization in oriented poly(ethylene terephthalate). The framework is obtained by combining extensions of classical nucleation theories in polymers3,4 and a theory of crystal growth with anisotropic incorporation of segments into growing crystals.15 It is shown that, while a very strong dependence of rate of primary nucleation on orientation does exist, there is a only a much weaker dependence of rate of crystal growth on the orientation of the crystallizing polymer. The theoretical formulation provided here would allow qualitative estimates for comparison with experiments.
Coagulation studies for cellulose in the ammonia/ammonium thiocyanate (NH3/NH4SCN) direct solvent system
Authors: Liu Cheng‐kung , Cuculo John A. , Smith Brent
Published: April 2003

An extensive study of the coagulation of cellulose from cellulose/ammonia/ammonium thiocyanate solutions is presented. The effect of major variables upon the coagulation process for cellulose solutions is reported. Microscopic observations of the moving boundary associated with the coagulation were performed on gelled cellulose solutions to determine the coagulation rate as a function of molecular volumes of coagulant, bath temperatures, bath compositions, and cellulose concentrations. The data were analyzed by means of a one‐dimensional linear diffusion model based on Fick's law, thereby depicting the mechanism of the coagulation process, and obtaining the diffusion coefficients of mobile components involved in the coagulation.
The hard‐sphere model for linear and regular star polybutadienes
Authors: Roovers J. , Martin J. E.
Published: April 2003

The dilute solution properties of linear, 18‐arm, and 270‐arm star polybutadienes have been studied in a theta solvent and in a good solvent. Values of the radius of gyration RG, the second virial coefficient A2, the intrinsic viscosity [η], and the diffusion coefficient D0 have been measured for each polymer. The ratios RT/RG, RV/RG, and RH/RG for each type of polymer are used to compare the four dilute solution properties. RT is termed the “thermodynamic radius.” It is the radius of the hard sphere with the same excluded volume as the polymer coil. RT is calculated from A2 by RT = (3A2M2/16ηNA)1/3. RV and RH are equivalent hard spheres defined for the intrinsic viscosity and translational diffusion coefficient, respectively. RT/RG, RV/RG, and RH/RG increase from about 0.7 for linear polymer coils as the number of arms in the star increases. Values of the ratios for the 18‐arm stars are less than the value for the hard‐sphere, but the values of the ratios of the 270‐arm stars are equal to the hard‐sphere limit within experimental error.
Adhesion through molecular entanglements in polymer interfaces
Authors: Raghava Ram S. , Smith Ronald W.
Published: April 2003

This paper examines the role of polymer interdiffusion or interpenetration along and across a boundary of two compatible but dissimilar polymers in controlling interfacial adhesion in the interface region (interphase). The effect of interphase adhesion on the mechanical properties as well as the deformation and fracture behavior of sandwich laminates of poly(methylmethacrylate) (PMMA) and poly(vinylidene) fluoride (PVF2) have been studied. The interphase has been characterized using microscopy (optical, transmission, and scanning electron), dynamic mechanical spectroscopy, and x‐ray microanalysis. Conditions of multiple crazing/fracture in the brittle phase (PMMA) and shear yielding in the ductile phase (PVF2) are discussed. Scanning electron micrographs confirm these deformation modes in PMMA‐PVF2 sandwich composite laminates.
Miscibility of poly(ethylene oxide) with poly(N‐vinyl pyrrolidone): DMTA and DTA studies
Authors: Cesteros Luis C. , Quintana JosÉ R. , Fernández JosÉ A. , Katime Issa A.
Published: April 2003

Dynamic mechanical thermal analysis and calorimetric studies are reported on blends of poly(ethylene oxide) (PEO) with poly(N‐vinyl pyrrolidone) (PVP) between 80% and 40% PEO. DMTA curves show a peak corresponding to a phase of pure PEO and another peak which can be attributed to blended material. The calorimetric analysis shows an appreciable melting point depression and a marked decrease in the crystallization rate as the PVP content increases. The melting point depression follows the Nishi‐Wang equation, giving an interaction parameter of −0.50. These studies suggest the existence of microphases in the blend.
Cold crystallization and thermal shrinkage of uniaxially drawn poly(ethylene 2,6‐naphthalate) by solid‐state coextrusion
Authors: Ghanem Antoine Michel , Porter Roger S.
Published: April 2003

Solid‐state coextrusion has been used to prepare uniaxially drawn films from isotropic poly(ethylene 2,6‐naphthalate) (PEN) of a minimum degree of crystallinity (ca. 5%) both below and above its glass transition temperature Tg. The onset of cold crystallization (Tc) of the drawn films has been studied as a function of the extrusion temperature (ET) and the draw ratio (EDR). It has been shown that Tc decreases markedly on draw, as much as 95°C, and, at constant draw ratio Tc goes through a minimum in the Tg region. For undrawn PEN, annealing below 153°C has no significant effect on Tc. To evaluate the crystallization rate constant (k) and the activation energy (Ea) of the drawn specimens, a nonisothermal DSC procedure has been used. With increasing EDR, k increases markedly and Ea goes down over threefold compared with the undrawn polymer. At high ET, strain‐induced crystallization has also been shown to play an important role in lowering Ea for cold crystallization. Thermal shrinkage above Tm indicates a high elastic recovery, underlining the efficiency of deformation, ca. 93%, achieved by solid‐state coextrusion.
Effects of fiber orientation on the stress distribution in model composites
Authors: Fan Cun F. , Hsu Shaw L.
Published: April 2003

A Raman‐mechanical technique was used to study the relationship between stress distribution and fiber orientation in model composites. Our experimental data generally were consistent with most simplistic mechanical models. A more complete analysis, using the Eshelby equivalent inclusion method, fitted our experimental data exceptionally well. For large applied strains, compressive failure occurred for fibers which were oriented at high angles relative to the draw direction. This occurred because of the lateral shrinkage associated with the matrix when the sample was stretched. The effect of fiber end geometry on the stress distribution for these misaligned fibers was the same as observed earlier. Tapered‐end fibers generally carried loads more efficiently in composites than blunt‐end fibers.
Dielectric properties of complex zn(II) salts of ethylene‐methacrylic acid copolymer with n‐hexylamine
Authors: Yano Shinichi , Yamamoto Hitoshi , Tadano Kenji , Hirasawa Eisaku
Published: April 2003

This article describes dielectric properties of complex Zn(II) salts of ethylene‐methacrylic acid copolymer (5.4 mol% methacrylic acid) with n‐hexylamine. In all samples, the β′ relaxation near 340 K and γ relaxation near 170 K are observed. These are assigned, respectively, to micro‐Brownian molecular motion of long segments above Tg and to local molecular motion of short segments below Tg. The dielectric results indicate that ionic clusters are not formed in these systems.
Tracing the spontaneous mixing and mobility of miscible polymer blends using differential scanning calorimetry [Cellulose acetate‐poly(styrenephosphonate ester)]
Authors: Sun J. , Frisch H. L. , Cabasso I.
Published: April 2003

A method in which the dissolution of a miscible polymer pair is traced in a differential scanning calorimetry cell is described. The polymer blend is initially prepared as an heterogeneous system with microdomains of one component embedded in the continuous matrix of the second polymer. Annealing the system in the DSC cell above the glass‐transition temperature causes a spontaneous mixing of the polymer pair which can be observed by the progressive shift of the Tgs of both components until they merge. The time scale for dissolution and aspects of mass‐transport phenomenon are thus determined for the specific blend, cellulose acetate‐poly(styronephosphonate ester). Rather sharp progressive shifts of the Tgs are shown to prevail without significant broadening of the transition curve (ΔTg). Mass‐transport analyses supported by electron microscopy observation of the blend, before and after annealing, suggest that the domain sizes remain nearly unchanged and the physicochemical makeup of the phase boundary interfaces determines the time scale of dissolution in the system. A model from which mean‐value diffusion coefficients are calculated for both components at different annealing temperatures is reported.
Halato‐telechelic polymers. XIV. Solution behavior of α, ω‐divalent transition metal dicarboxylato polybutadiene
Authors: Horrion J. , Jérôme R. , Teyssié Ph.
Published: April 2003

A procedure is described which allows α,ω‐dicarboxylic acid polybutadiene to be end‐neutralized using a stoichiometric amount of a transition metal acetate. In a nonpolar solvent, the solution viscosity of this new class of carboxylato telechelic polymers depends on the neutralization degree of the acid end groups in such a way that the progress of the neutralization may be compared with that of a polycondensation reaction. In contrast to Cu(II), the Zn, Ni, Co, and Mn carboxylate endgroups promote very early gelation of toluene solutions when the polymer concentration increases. The particular behavior of Cu(II) can only be explained by a difference in the coordination number compared with the other elements of the first transition series. The dependence of the solution viscosity on the atomic number of the element cannot be completely accounted for so far. Nevertheless, an electrostatic association of the cupric carboxylate end groups can be disregarded, since the solution viscosity is independent of the polarity of the solvent in the range of 2.28–7.28 D.
Kinetically stable structures in the nonlinear theory of spinodal decomposition
Authors: Mitlin V. S. , Manevich L. I.
Published: April 2003

A nonlinear diffusion equation is used to study the spinodal decomposition of binary polymer mixtures. The structure of steady‐state solutions is analyzed. The free energy of the system for the solutions is shown to be a nonincreasing time function. The solution with the minimum free energy is the only stable solution and corresponds to complete phase separation in the system. A numerical analysis shows that transition to complete equilibrium takes place through a succession of fast concentration structure changes interspersed by periods in which the process is abruptly showed down. The free energy of the system is almost constant in the kinetically stable periods. All these facts indicate a relaxation process of an absolutely new type. Slow variables are introduced to describe the spinodal decomposition in macroscopic regions. These variables govern the spatial transformation of the forms and sizes of microphases. The perturbation theory is used to derive the equations for slow variables. The final relations of the simplest type give an exponential time dependence of the average size of a microphase. The problem of a contact of two pure components that are not compatible in the entire composition range is set.
Raman longitudinal acoustic mode (LAM) studies of folded‐chain morphology in poly(ethylene oxide) (PEO). I. Normal mode analysis of LAM of a helical‐chain oligomer of PEO
Authors: Song Kigook , Krimm Samuel
Published: April 2003

Normal mode analyses were done for the exact structures of model oligomers of PEO to investigate the longitudinal acoustic mode (LAM) in this helical polymer. It quickly became apparent that it is impossible to reproduce observed LAM frequencies without incorporating explicit interchain interactions. We have developed a force field that includes interchain interactions through an atom‐atom potential and have shown that this force field reproduces very well the observed LAM frequencies of helical‐chain oligomers of PEO. This result indicates that the LAM of helical chains is much more sensitive to intermolecular interactions than that of planar zigzag chains.
Raman longitudinal acoustic mode (LAM) studies of folded‐chain morphology in poly(ethylene oxide) (PEO). II. Normal mode analysis of folded‐chain structures of PEO
Authors: Song Kigook , Krimm Samuel
Published: April 2003

Normal mode calculations were carried out on model folded‐chain molecules to determine the effect of a fold on the LAM of PEO. The presence of a chain fold results in a decrease in the LAM frequency and intensity, the change in frequency being very much smaller than the change in intensity. End interactions do not seem to have much effect on the LAM when a fold is present at the chain ends. The effective chain length for determining the LAM frequency was found to be that part of the chain experiencing interchain interactions.
Relaxations of thermosets. III. Sub‐Tg dielectric relaxations of bisphenol‐A–based epoxide cured with different cross‐linking agents
Authors: Mangion M. B. M. , Johari G. P.
Published: April 2003

The sub‐Tg relaxations of bisphenol‐A–based thermosets cured with diaminodiphenyl methane and diaminodiphenyl sulfone have been studied by dielectric measurements over the frequency range 12 Hz to 200 kHz from their ungelled or “least” cured states to their fully cured states. Both thermosets show two relaxation processes, γ and β, as the temperature is increased toward their Tgs. In the ungelled states, the γ process is more prominent than the β process. As curing proceeds, the strength of the γ process decreases and reaches a limiting value, while that of the β process initially increases, reaches a maximum value, and then decreases. An increase in the chain iength and the number of crosslinks increases the number of ‐OH dipoles and/or degree of their motions in local regions of the network matrix. This is partly caused by the decreasing efficiency of segmental packing as the curing proceeds. The sub‐Tg relaxations become increasingly more, separated from the α relaxation during curing. Physical aging causes a decrease in the strength of the β relaxation of the thermosets as a result of the collapse of loosely packed regions of low cross‐linking density, and this decrease competes against an increase caused by further crosslinking during the “post‐cure” process.
Scaling tests of late stages of spinodal decomposition in PC/PMMA blends
Authors: Kyu Thein , Saldanha Jeanne M.
Published: April 2003

Time‐resolved light scattering studies were undertaken to elucidate the kinetics of phase separation in polycarbonate (PC)/polymethyl methacrylate (PMMA) blends. The 40:60 PC/PMMA blend undergoes thermally induced phase separation through spinodal decomposition. Temperature jump experiments were carried out from a single‐phase to a two‐phase temperature region. The general trend of spinodal decomposition in this blend system is nonlinear in character and obeys the power laws. The time evolution of scattering curves was analyzed in accordance with dynamical scaling laws for self‐similarity and the shape of scaled structure functions.
Permeation of pure carbon dioxide and methane and binary mixtures through cellulose acetate membranes
Authors: Sada E. , Kumazawa H. , Xu P. , Wang S.‐T.
Published: April 2003

Steady‐state permeation rates for pure CO2 and CH4 and their binary mixtures through homogeneous dense cellulose triacetate membranes have been measured at three temperatures between 20 and 40°C and pressures up to 2.8 MPa. The pressure dependence of the mean permeability coefficient for CO2 can be described by the total immobilization model in conjunction with a modified free‐volume model. No appreciable pressure dependence of the permeability coefficient for CH4 is observed, while the permeability coefficients for CH4 in binary mixture of CO2 and CH4 depend on applied gas pressure. The pressure dependences of the mean permeability coefficients for the components in the binary mixture are discussed in terms of the above mobility model. Membrane plasticization induced by CO2 affects permeation by both gases.
Thermal response and structure of PET fibers
Authors: Hristov H. A. , Schultz J. M.
Published: April 2003

The structure and the thermal response of polyethylene terephthalate (PET) fibers, melt‐spun at speeds of 3 to 6 km/min, are investigated in the temperature region 0–200'C. Differential scanning calorimetry thermograms, and radial distribution functions from wide‐angle x‐ray scattering are used. Interpretation of multiple glass transition and crystallization peaks and of the range of structural coherence is interpreted in terms of a nonhomogeneous molecular arrangement for fibers melt‐spun at intermediate spinning speeds. A three‐phase model of the molecular structure of these fibers is used to explain the results. An important feature of the model is the existence of a threadlike, interconnected, highly oriented noncrystalline phase, coexisting with a more unoriented amorphous phase. The model can qualitatively explain a number of experimental observations.
Phase dominance, multiple glass transitions, and apparent activation energies in some poly (styrene‐co‐alkali methacrylate) ionomers
Authors: Hird B. , Eisenberg A.
Published: April 2003

The high‐temperature dispersions occurring in some poly (styrene‐co‐alkali methacrylate) ionomers are investigated by dynamic mechanical thermal analysis as a function of ion content. The heights and areas of the loss modulus peaks associated with these dispersions suggest that the ionic “cluster” phase becomes the dominant and perhaps even continuous phase above an ion concentration of ca. 6 mol %. Apparent activation energies of these high‐temperature transitions support the phase‐separated cluster model and indicate that the dispersions are true glass transitions.
An optical study of phase transitions of poly (ethylene terephthalate‐co‐p‐hydroxybenzoic acid) liquid crystal
Authors: Sun Tong , Bhattacharya Subrata K. , Lenz Robert W. , Porter Roger S.
Published: April 2003

The copolyester containing 40 mol % ethylene terephthalate (PET) and 60 mol % p‐hydroxybenzoate (HB) units has been reported by several investigators to be biphasic in the solid and the liquid states. The reported thermal transitions in the two phases, however, are in part contradictory, perhaps partly due to different polymerization conditions. The present work is a study of the transitions in each of the two phases of this copolyester by polarized light microscopy and by light transmission measurements. By light transmission measurements, the two phases were found to have two different glass transition temperatures for the onset of segmental motion, consistent with two assignable temperatures (T.). Cold crystallization and melting in each of the two different phases was also detected. The results help clarify the nature of transitions and agree with the results of dynamic mechanical analysis on the same thermotropic liquid crystalline copolyester.
Preparation and thermal characterization of the glass transition temperatures of sulfonated polystyrene‐metal ionomers
Authors: Yang Sen , Sun Kang , Risen William M.
Published: April 2003

The glass transition temperatures and heat capacity changes in the transition region are reported for six sulfonated linear polystyrenes in the hydrogen form, H‐SPS, in the 3.4–20.1 mol % sulfonation range and 76 metal SPS ionomers in the 3.4–12.8 mol % range. The metals are those which interact predominantly ionically and include +1, +2, and +3 ions of the alkali metal, alkaline earth, and rare earth (lanthanide) series. The results show the effect of H2O or coordinating ligands on glass transition temperatures (Tg) and the importance of eliminating it to obtaining reproducible values for Tg and ΔCp. The Tg values of dry M‐SPS ionomers depend only on the sulfonation level despite wide variation in metal ion charge and size. The variation of ΔCp with sulfonation level is interpreted as showing that at high levels a few unsulfonated styrene units adjacent to sulfonated ones are constrained, presumably by clustering, from participation in the polystyrene‐like cooperative rearrangements in the transition region.
Computer simulation of laser backscattering from fiber surfaces
Authors: Luo Cheng , Bresee Randall R.
Published: April 2003

The application of laser backscattering to fiber surface characterization was studied theoretically. Computer simulations were employed to investigate the theoretical influence of root‐mean‐square fiber surface roughness, fiber cross‐sectional shape, fiber diameter, and surface asperity shape on scattering patterns. Results from this work indicate that laser backscattering may be useful for obtaining fiber structural information in a variety of applications.
Experimental studies of fiber surface roughness characterization by laser backscattering
Authors: Luo Cheng , Bresee Randall R.
Published: April 2003

The application of laser backscattering to the characterization of fiber surface roughness was studied experimentally using instruments based on optical Fourier transforms. Applications included comparing surface roughness of various fibers, measuring the effect of fiber delustering with TiO2 and detecting surface crystallization. The optical transform method was found to be a simple means of providing nonintrusive, real‐time measurements of fiber surface structure.
Stress relaxation in stretched networks immersed in solvent
Authors: Ozkul M. H. , Onaran K. , Erman B.
Published: April 2003

Stress relaxation in swollen polybutadiene networks is studied. The networks, which are immersed in solvent at equilibrium, are uniaxially stretched suddenly and the relaxation of the force required to keep them at constant length is monitored. The observed relaxation is predominantly due to the diffusion of solvent into the stretched networks. Measurements are made at different extensions and temperatures. The degree of swelling of the networks is calculated as a function of the observed force by adopting the phantom network model of rubber elasticity. The relationship between the diffusion of solvent into the networks and stress relaxation is given. The variation of the degree of swelling with time is used to calculate the coefficients of diffusion for n‐hexane and dodecane in polybutadiene.
Static small‐angle x‐ray scattering study of polymer deformation
Authors: Young P. , Stein R. S. , Kyu T. , Lin J. S.
Published: April 2003

The small‐angle x‐ray scattering (SAXS) approach has been employed in an effort to understand the deformation mechanism of semicrystalline polymers in terms of submicroscopic structure of lamellae. Isotropic melt‐pressed polyethylenes of low, medium, and high densities (LDPE, MDPE, and HDPE, respectively) having spherulitic texture were investigated by SAXS for various Static elongations between 10% and 40%. The SAXS isointensity contours of the deformed polymers are anisotropic (elliptical) with the long axis perpendicular to the stretching direction. Slice averages at various azimuthal angles between 0° and 90° reveal distinct SAXS peaks with respect to scattering angle. The peak position of SAXS profile characterizes the long period or lamellar spacing, while integrated intensity distribution is relevant to lamellar orientation. At low elongations, there is an increase in intensity at both azimuthal angles of 0° and 90°, suggesting that excess scattering arises during deformation, probably associated with lamellar untwisting process. Lamellar orientation distribution and second‐order orientation are defined to account for the lamellar orientation process. Experimental results are compared with Kratky's floating rod model coupled with Stein's lamellar untwisting model. The lamellar orientation closely follows the affine deformation scheme, while the lamellar spacing deviates appreciably from it, particularly at large elongations.
Stability of spherulite growth rate
Authors: Pawlak A. , Galeski A.
Published: April 2003

Spherulite growth rates in thin films of isotactic polypropylene, poly (methylene oxide), and poly (ethylene adipate) have been studied by light microscopy. The growth rate of the parts of spherulites formed from pockets of occluded melt is decreased drastically. The decrease is associated with the negative pressure buildup inside the pockets due to the density change as the melt is converted to spherulites. Material subjected to negative pressure shows a higher melting point of 3–4'C if the pressure is released prior to melting. Slight periodic changes of the growth rate were detected during crystallization of banded spherulites. No changes in growth rate were observed for two spherulites about to impinge or for spherulites growing near a solid obstacle.
X‐ray diffraction of gelatin fibers in the dry and swollen states
Authors: Pezron I. , Djabourov M. , Bosio L. , Leblond J.
Published: April 2003

The aim of this x‐ray diffraction investigation is to establish a comparison between the structure of collagen and that of gelatin gels. The gelatin gels are drawn into fibers, which are dried before use. The xray scattering patterns of the gelatin fibers show a close analogy with collagen, which provides evidence for the presence of bundles of triple helices in the dried, oriented gels. The mechanisms of swelling of the gelatin fibers are identified by investigating the humidity‐sensitive position of the equatorial spots related to the side‐by‐side distance D of the triple helices. The distance D increases continuously as more water is added to the fibers; this is accompanied by a progressive loss of orientation of the triple helices with respect to the fiber axis. The temperature dependence of the x‐ray patterns is also investigated. We discuss the implications of this study for understanding the gelation mechanisms and the structure of gelatin gels. Comparisons are made with other physical gels.
Gel permeation chromatograph interface to collect solvent‐free polymer fractions for composition drift analysis
Authors: Dekmezian A. H. , Morioka T. , Camp C. E.
Published: April 2003

An interface is described that is capable of stripping solvent from polymer solutions emerging from an interfaced high‐temperature gel permeation chromatograph. The chemical composition of each solvent‐free polymer fraction is then determined using Fourier transform infrared (FTIR) or other techniques to obtain the composition drift (CD) pattern of the polymer (i.e., variation of chemical composition as a function of molecular weight). The interface consists of a vacuum oven into which an ultrasonic nebulizer and a stepper motor have been incorporated. The stepper motor drives a fraction collector, equipped with a set of KBr plates, onto which the nebulized polymer solution is sprayed. The temperature and pressure of the interface are maintained so as to strip the solvent from the chromatographic effluent as it impinges on the collector substrates. The technique, which had been applied to the % ethylene CD of ethylene‐propylene rubbers, is employed in the analysis of a block copolymer reaction product. In the example given, the CD pattern of the reaction product generated is simulated along with the observed molecular weight distribution pattern to arrive at the approximate composition of the reaction product. For many applications, this approach eliminates the need to carry out tedious solvent/nonsolvent fractionations commonly employed in the characterization of the compositional heterogeneities in block copolymer reaction products.
The mechanical properties of random copolymers of ethylene: Force‐elongation relations
Authors: Peacock A. J. , Mandelkern L.
Published: April 2003

Utilizing a newly developed apparatus, force‐length measurements were performed on a series of unfractionated random ethylene copolymers having different counit types and a wide composition range. By controling crystallization conditions, crystallinity levels could be varied over wide extremes and a complete repetoire of superstructures was developed. Emphasis was on key mechanical properties such as the initial modulus, yield stress, and the ultimate properties of draw ratio at break and tensile stress. Except for the ethylene‐methacrylic acid copolymers, which behaved in a unique manner, the properties were found to be independent of the chemical nature of the counit and the particular supermolecular structure that was developed. The initial modulus and the yield stress were found to be very dependent on the crystallinity and phase structure. On the other hand, except for the decrease at low counit content, the draw ratio at break was found to be invariant with counit type, crystallinity level, supermolecular structure, and molecular weight. The results are discussed in terms of the molecular constitution of the copolymer and the structure in the crystalline state.
Nonlinear constitutive equation for polyethylene under combined tension and torsion
Authors: Kitagawa Masayoshi , Takagi Hideyuki
Published: April 2003

In order to investigate a viscoelastic‐plastic nonlinear constitutive equation for polymer solids, combined tension and torsion tests were performed using polyethylene (PE) hollow cylinders. The experimental data were compared with the numerical results derived from a multiaxial constitutive equation developed from the uniaxial one proposed by Krempl. It is shown that the proposed theory fairly well describes the stress–strain curves of PE up to relatively high strain ranges not only in simple torsion, but also under combined tension–torsion, provided that the current strain is not below the maximum previous strain.
Small‐angle x‐ray scattering in “bottlebrush” ionomers
Authors: Wollmann D. , Williams C. E. , Eisenberg A.
Published: April 2003

Block copolymers consisting of long styrene midblocks and much shorter 4‐vinyl pyridine end‐blocks were quaternized with n‐iodo alkanes (2 ≤ n ≤ 10) to give block ionomers of a novel architecture. The name “bottlebrush” seems appropriate for these materials. A preliminary investigation of the morphology of these systems, prepared by in situ quaternization, is reported here. The morphology is dependent on both the length of the iodo alkane and the relative sizes of the blocks. Even with identical sample histories, two distinct morphologies are seen. One of these is characterized by a single broad SAXS peak, while the other shows a much narrower peak and higher‐order features. The latter morphology is associated with the higher ionic to nonionic ratios and long side chains.
The dependence of butyl branch density on slow crack growth in polyethylene: Kinetics
Authors: Huang Yan‐Ling , Brown Norman
Published: April 2003

When the density of n‐butyl branches in an ethylene–hexene copolymer increases from 0 to 4.6 butyls/1000 C, the rate of slow crack growth decreases by a factor of 104 . The activation energy for the process is nearly independent of branch density and is about 120 kJ/mol. It is the number of tie molecules and whether they are pinned that control the rate of crack growth which involves the disentanglement of the fibrils in the craze. Branching increases the number of tie molecules by decreasing the lamella thickness, while the branches pin some of the tie molecules to prevent them from sliding through the crystal or other points of entanglement.
Zone drawing and mechanical relaxation of poly(vinylidene fluoride)
Authors: Grubb David T. , Rich Kearney F.
Published: April 2003

Poly(vinylidene fluoride), PVF2, has been zone drawn to extensions up to 7 times. Well oriented β phase tapes are produced when the draw neck moved out of the hot zone, at extensions over six times and zone temperatures =<155°C. Other conditions give α phase tapes. The dynamic mechanical spectra of highly drawn PVF2 is exactly the same for both phases, with Tg at −25°C and a sharp rise in tan δ at 50°C. Isotropic α and β phase sheets gave different mechanical spectra, but with similar features at different strengths. As the isotropic sheets were prepared in very different ways, no specific features of the spectra could be assigned to the different phases.
Sorption and transport of pure gases in random styrene/methyl methacrylate copolymers
Authors: Raymond P. C. , Paul D. R.
Published: April 2003

Previous work has shown that permeability coefficients for CO2 can increase with pressure for poly(methyl methacrylate) (PMMA); whereas, those for polystyrene decrease slightly as found for many glassy polymers. This response is attributed to a greater propensity for PMMA to be plasticized by CO2. This issue is considered in detail here by examining the behavior of a series of random styrene/methyl methacrylate copolymers in order to learn how the plasticization response varies with MMA content. At low pressure, the sorption and transport of CO2 and other gases in these copolymers depend on copolymer composition in ways expected from simple theories for multicomponent polymers. The change in CO2 permeability coefficient upon pressurization from 1 to 20 atm ranged from –6% for polystyrene to +57% for poly (methyl methacrylate). Furthermore, upon holding at 20 atm of CO2 driving pressure, there was a significant increase in the CO2 permeability coefficient with time for PMMA; whereas this conditioning effect was much smaller for polystyrene. Conditioning and plasticization effects seem to be related to the same molecular causes. The responses change progressively for the copolymers but not directly in proportion to MMA content. The greater effects of CO2 for PMMA are, to a significant extent, but not entirely, due to its much higher level of CO2 sorption compared with that of polystyrene. The results are discussed in terms of relevant theories.
Sorption and transport of pure C02 and CH4 in miscible bisphenol chloral polycarbonate/poly (methyl methacrylate) blends
Authors: Raymond P. C. , Paul D. R.
Published: April 2003

Sorption and permeation behavior of CO2 and CH4 was examined in detail for a series of miscible blends based on bischloral polycarbonate (BCPC) and poly (methyl methacrylate) (PMMA). The former pure polymer exhibits decreases in the permeability coefficients for both CO2 and CH4 as the upstream driving pressure increased as predicted by the dual‐mode sorption model. On the other hand, PMMA shows a decrease for CH4 but an increase for CO2. The latter is attributed to plasticization by this more soluble gas. The blends show intermediate behavior. CO2 permeation was examined on pressurization, at constant pressure for two weeks, and then on depressurization. The pattern of behavior progressively deviated between that of BCPC and PMMA as the MMA content of the blends was varied. These trends were contrasted with those previously described for a series of styrene/methyl methacrylate copolymers. Some differences in behavior between the blends and the copolymers were noted when compared at constant MMA content. These results have important ramifications for the design and selection of polymers for membranes to separate the CO2/CH4 gas pair.
Fragmentation of polycarbonate macroinitiators in solution and in the bulk state
Authors: Kuhn K. J. , Hellmann G. P.
Published: April 2003

The diphenylethane initiator 3,4‐diethyl‐3,4‐(p‐methoxyphenyl)‐hexane (T–OCH3) was synthesized. By cocondensation of bisphenol A or C and the bisphenol derivative (“T”) of T–OCH3 with phosgene, polycarbonate macroinitiators PC(TxA1‐x) and PC(TxC1‐x) with different compositions x were made. The thermal fragmentation of T–OCH3 and the copolycarbonates was investigated with and without a radical scavenger both in solution and in the bulk state. The primary dissociation of T–OCH3 is a monomolecular Arrhenius process with a characteristic temperature of T* (τ = 1h) = 140°C (τ: average life time of the intact molecule). When the radicals are not intercepted, the dissociation is excessively reverted by radical recombination, which raises T* to T* = 163°C. The reaction ends then exclusively in radical disproportionation. The chain fragmentation of the copolycarbonates is of the type of a random decondensation. The counits CT dissociate in solution almost exactly like T–OCH3. In the highly viscous bulk state, the reaction proceeds in matrix cages, which have a stabilizing effect, so that T* is increased to T* = 170°C. These copolycarbonates are model polymers for a novel method to study the hitherto unmeasurably slow chain diffusion processes in polymers near the glass transition temperature.
X‐ray modulus and strain distribution in single fibers of polyethylene
Authors: Prasad Keshav , Grubb David T.
Published: April 2003

Synchrotron x‐ray radiation was used to study structural changes during deformation of a single high‐modulus, high‐strength fiber of polyethylene (Spectra 1000, Allied Corp.) 20–40 μm in diameter. The high brightness of the synchrotron beam allowed x‐ray diffraction patterns to be obtained from 0.5 μg fiber samples in ca. 1 min. The (002) chain axis reflection shifted and broadened when the fiber was loaded in tension. When a model of crystals and disordered material in series was used for the fiber, the measured lattice strain at stresses up to 1 GPa gave a crystal modulus of 250 GPa. At stresses above 1 GPa the (002) reflection no longer shifted with increasing load. A noncrystalline part of the material deforms and takes up the load; this effect has been observed by Raman spectroscopy. The (002) peak also broadens under stress. When fiber bundles were used as samples, broadening could be due to uneven loading of fibers, but with a single fiber sample, one can be sure that the loading at the fiber level is uniform. Broadening of the (002) reflection then indicates inhomogeneities within the fiber. Deconvolution with the line profile of the fiber at zero stress should give the distribution of crystal strains. The strain distributions are symmetric and during loading the full width at half maximum (fwhm) is approximately equal to the mean strain. With an assumed constant crystal modulus this describes the stress distribution as extending from zero to twice the mean stress.
Thermal expansion of oriented liquid crystal copolyesters
Authors: Green D. I. , Orchard G. A. J. , Davies G. R. , Ward I. M.
Published: April 2003

The axial thermal expansion coefficients of a series of highly oriented thermotropic liquid crystal copolyesters with random phenylene‐naphthalene main‐chain sequences are reported. In common with many other highly oriented polymers the values are negative. Generally, there are two transitions in the slope of the expansion‐temperature curves. The positions of these transitions are correlated with high activation energy relaxations in the mechanical spectra. Comparison of the thermal expansion properties determined by x‐ray and macroscopic techniques on two of the samples reveals little difference between the bulk material and a unit with a segmental length of ten monomers.