bluuebunny/crossref_metadata_2025 huggingface dataset:
Intersegmental interaction and critical concentrations in PET–HFIP solutions
Authors: Sonnenschein M. F. , Roland C. M.
Published: April 2003

Spectroscopic determinations of the concentrations associated with the onset of intermolecular interaction in solutions of poly(ethylene terephthalate) (PET) are described. The intersegment forces perturb the electronic spectra and induce ground‐state aggregation. These phenomena become observable at different chain densities, reflecting the influence of concentration on the coil dimensions, as well as the dynamical nature of the interactions. An estimate of the equilibrium constant for PET dimer formation in hexafluoroisopropanol is reported.
Self‐diffusion of poly (ethylene oxide) fractions and its influence on the crystalline texture
Authors: Cheng Stephen Z. D. , Barley Jeffrey S. , Von Meerwall Ernst D.
Published: April 2003

Two somewhat separate issues have been delat with: the diffusion coefficients of various poly(ethylene oxide) (PEO) fractions at different temperatures; and morphological observations of spherulitic textures of a PEO mixture containing low‐ and high‐molecular mass components at different supercooling and cooling rates. We found that simultaneous knowledge of diffusion coefficient of PEO fractions and crystal growth rate of the mixture leads to a better description of the crystal growth. As observed, the spherulitic texture of the PEO mixture comprises three texture levels: the spherulite as a whole; the crystalgrowth unit comprised of different number of lamellae in a stack; and the individual lamellar crystal. Under certain crystallization conditions, the thickness of the lamellar stack is on the same order of magnitude as the parameter δ proposed by Keith and Padden.
Step‐strain deformations for viscoelastic fluids: Formulation of a strain‐coupling constitutive equation
Authors: Vrentas J. S. , Venerus D. C. , Vrentas C. M.
Published: April 2003

An integral constitutive equation which includes strain‐coupling effects is proposed. The constitutive equation is more general than the K‐BKZ equation, and it is shown that this equation can explain various important aspects of double‐step stress‐relaxation data.
Light‐scattering studies on solutions of cellulose in the ammonia / ammonium thiocyanate solvent system. II. Quasielastic light‐scattering and liquid crystal study
Authors: De Groot A. W. , Guinnup D. E. , Thiel M. H. , Cuculo J. A.
Published: April 2003

This is the second part of a two–part study of the NH3NH4SCN cellulose solvent system. Quasielastic light scattering was used to determine the diffusion coefficients of cellulose in solution and the effective hydrodynamic radius of the dissolved molecules. Additionally, the system was studied using light microscopy to determine the minimum critical volume fraction or liquid crystal formation. Very little change was found in the diffusion coefficients with change in cellulose concentration indicating little interaction between the chains in solution. Values of 7.69 and 2.66 × 108 cm2/s were measured for samples having a degree of polymerization of 153 and 969. The value of the coefficient relating the hydrodynamic volume to the radius of gyration was found to be in the range of 0.33 to 0.53, indicating an extended coil conformation according to the Kirkwood‐Riseman theory. The minimum critical volume fractions necessary for liquid crystal formation, υ2′ were 0.039, 0.038, and 0.048 for the three solvent compositions studied. The values calculated for υ2′ based on the measured persistence lengths were much larger than the predicted values, indicating strong deviation from theory or possible aggregation in the system.
Percolation effects in degradable polyethylene‐starch blends
Authors: Peanasky J. S. , Long J. M. , Wool R. P.
Published: April 2003

The accessibility of starch in polyethylene starch blends was investigated by computer simulation, percolation theory, and acid hydrolysis experiments. The object of this work was to model the bilateral invasion of microbes in polyethylene‐starch blends as a function of starch concentration (p), and thickness of the material. It was found that computer simulations in three dimensions were in agreement with both percolation theory and the acid digestion experiments. In computer simulation the accessibility is highly dependent on the percolation threshold concentration (pc), which is 31.17%. Similarly, the accessibility of starch is highly dependent on an apparent percolation threshold near 30% by volume or approximately 40% by weight of starch. At p < pc a small amount of starch is removed from the surfaces only, but at p > pc connected pathways existing throughout the bulk of the material facilitate large amounts of starch extraction. The sharpness of the transition at pc increases with the ratio of sample thickness to starch particle size. The results of this work have application to conduction and reacting systems where one component is dispersed in a matrix of the other.
Determination of chain stiffness and polydispersity from static light‐scattering
Authors: Denkinger Peter , Burchard Walther
Published: April 2003

Chain stiffness is often difficult to distinguish from molecular polydisperity. Both effects cause a downturn of the angular dependence at large q2 (q = (4π/λ)sin θ/2) in a Zimm plot. A quick estimation of polydisperity becomes possible from a bending rod (BR) plot in which lim (c → 0) qRθ/Kc is plotted against q(〈S2〉z)1/2 = u. Flexible and semiflexible chains show a maximum whose position is shifted from umax = 1.41 for monodisperse chains towards larger values as polydispersity is increased, while simultaneously, the maximum height is lowered. Stiff chains display a constant plateau at large q, its value is πML where ML is the linear mass density. Using Koyama's theory, the number of Kuhn segments can be determined from the ratio of the maximum height to the plateau height, if the polydispersity index z = (Mw/Mn − 1)−1 is known. Thus, if the weight‐average molecular weight Mw, is known, the contour length Lw, the number of Kuhn segments (Nk)w, the Kuhn segment length lk and the polydispersity of the stiff chains can be determined. The influence of excluded volume is shown to have no effect on this set of data. The reliability of this set can be cross‐checked with the mean‐square radius of gyration 〈s2〉z which can be calculated from the Benoit‐Doty equation for polydisperse chains. Rigid and slightly bending rods exhibit no maximum in the BR plot, and the effect of polydispersity can no longer be distinguished from a slight flexibility if only static scattering techniques are applied.
Phase behavior and gelation of solutions of poly (vinyl alcohol)
Authors: Stoks W. , Berghmans H.
Published: April 2003

The phase behavior of poly (vinyl alcohol) dissolved in ethylene glycol and propylene glycol was studied. On cooling a solution in the low concentration range, solidification results from a combination of a liquid‐liquid demixing and a crystallization or liquid‐solid demixing. This conclusion is based on the results obtained from optical and calorimetric observations and is further supported by the influence of the molecular weight and the solvent quality. It also explains the melting point‐crystallization relationship observed after isothermal crystallization of the polymer in presence of the solvent. The mechanism proposed for the thermoreversible gelation of these solution is confirmed.
Glass transitions in hydrogen‐bonded polymer complexes
Authors: Wang L. F. , Pearce Eli M. , Kwei T. K.
Published: April 2003

Mutual precipitates of poly (N, N‐dimethyl acrylamide) and poly (4‐hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (Tg) temperatures of the precipitates are higher than the weight‐average values. Clear films cast from dimethylformamide solutions have lower Tg values. Complexation also occurred between poly (ethyl oxazoline) and poly (4‐hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4‐hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔCp values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates.
Synthesis and characterization of an amphoteric ion‐exchange membrane
Authors: Elmidaoui Azzeddine , Boutevin Bernard , Belcadi Said , Gavach Claude
Published: April 2003

An amphoteric ion‐exchange membrane was prepared by chemical grafting of acrylic acid and dimethyl amino‐2‐ethyl methacrylate on ozonized polyethylene. The effects of the variation of external pH on the physicochemical properties of this membrane were studied (exchange capacity, electrical resistance, water and electrolyte content, and membrane potential). The determination of the mean activity coefficient of the NaCl in the membrane phase using the Donnan equilibrium equation reveals that this coefficient increases with the NaCl concentration in the external solution. Fundamental electrochemical properties of the amphoteric membrane are discussed on the basis of the variation of the membrane selectivity with the external electrolyte concentrations and the pH. The properties at neutral pH are accounted for by a mutual neutralization of some acidic and basic groups in the membrane phase.
A novel chromatographic method for determining the polydispersity index for polymers with a specified number of functional groups
Authors: Yu Wei‐Ching , Mattice Wayne L.
Published: April 2003

A novel chromatographic method is proposed to determine the polydispersity index, without reference to standards, for polymers that contain a specified number of functional groups. Refractive index and ultraviolet‐visible (or infrared) detectors are employed for detecting the weight and number fractions, respectively, of the sample eluted in size exclusion chromatography (SEC). Pyrene‐labeled polystyrenes were used to demonstrate the validity of this method. The polydispersity index, Mw/Mn, measured by the new method underestimates the true value by 3%, whereas the application of the calibration curve overestimates the polydispersity index of the same sample by 6%. An illustrative SEC model including the effect of diffusion was used to explain the production of errors in different directions by the two methods.
Transport of gases in aromatic polyesters: Correlation with WAXD studies
Authors: Charati S. G. , Houde A. Y. , Kulkarni S. S. , Kulkarni M. G.
Published: April 2003

Polymer packing density can be conveniently measured by either density‐based measurements (direct or estimated free volume) or wide‐angle X‐ray diffraction (WAXD) spectra. Previously reported diffusivity and permeability values for various polyarylates and polyimides are examined on the basis of the packing density measured by these different techniques. It is shown that in these rigid glassy polymers, the mean intersegmental distance, the d‐spacing, obtained from WAXD provides a better measure of the effect of polymer packing on diffusivity than either direct density measurements or estimated free volumes. It has been possible to correlate previously reported diffusivity and sorption data for various polyarylates and polycarbonate on the basis of the WAXD investigation, using the d‐spacing and the amorphous peak width, respectively. The effect of polyarylate structure on d‐spacing has been studied. A series of polyarylates have been synthesized with different substituents on the bridge carbon. In this series the d‐spacing remains constant while the carbonyl group density and the glass transition temperatures are varied. However, small substituents on the aromatic ring cause significant changes in the d‐spacing. These results can be used to tailor polyarylates with desired intersegmental distances and chain flexibility.
Viscoelastic properties of styrene‐co‐methyl methacrylate random copolymers
Authors: Halary J. L. , Oultache A. K. , Louyot J. F. , Jasse B. , Sarraf T. , Muller R.
Published: April 2003

Viscoelastic properties of styrene‐co‐methyl methacrylate random copolymers have been determined over a temperature range covering the glass transition, the rubbery plateau, and the terminal zone and compared with polystyrene and polymethyl methacrylate homopolymers. Nonlinear behavior was observed in the variations of most of the physical and rheological characteristics with the methyl methacrylate content in the copolymer. Results are interpreted in terms of the rupture of polar‐polar intermolecular interactions between ester groups due to the presence of styrene units.
The kinetics of flow‐induced crystallization from solution
Authors: McHugh A. J. , Spevacek J. A.
Published: April 2003

In situ birefringence measurements of the seeded growth in a tubular flow geometry of 0.01 wt% solution of a polyethylene fraction in xylene have been used to determine the flowinduced crystallization kinetics as a function of temperature and flow rate. In contrast to earlier reports on higher molecular weight polyethylene and polypropylene systems, orientational properties of the crystallized fibers do not show a clear correlation with growth conditions (i.e., temperature and flow rate). The combined kinetic data from these experiments and our earlier studies of higher molecular weight polyethylene—xylene and polypropylene—tetralin systems are analyzed in terms of a modified from of the Avrami equation which provides a basis for separately correlating temperature and flow rate effects. The observed temperature dependency of the crystallization process can be interpreted in terms of nucleation and growth models while the flow rate dependency can be interpreted on the basis of entanglement formation arguments. Results showing liquid phase precursor formation in an atactic polystyrene system are also presented to further document the liquidphase separation which can be induced in polymers under flow.
A dual‐mode interpretation of spin relaxation for 13CO2 sorbed in polycarbonate
Authors: Cain E. J. , Wen W.‐Y. , Jones A. A. , Inglefield P. T. , Cauley B. J. , Bendler J. T.
Published: April 2003

Carbon‐13 spin‐lattice relaxation, spin‐spin relaxation and nuclear Overhauser enhancements (NOE) are reported for 13CO2 sorbed in glassy polycarbonate. These spin relaxation parameters were determined as a function of temperature and Larmor frequency. A quantitative interpretation is presented based on a two‐site, rapid exchange model. The model is related to the dual‐mode model developed to interpret sorption and permeability data for gases sorbed in glassy polymers. This model proposes the existence of two types of sorbed gas molecules: dissolved molecules and Langmuir sorbed molecules. The nuclear magnetic resonance (NMR) interpretation supports the conceptual features of the dualmode model. Gas molecules in the dissolved site have rotational, collisional, and translational dynamics typical of low molecular liquids. Langmuir sorbed gas molecules have much slower rotational and translational motions. The activation energy for motions in the dissolved site is about 1 kJ while the activation energy for the Langmuir site is about 10 kJ. The relative values of these activation energies are again consistent with the dual‐mode picture. The translational diffusion constants determined from the NMR data range from 10−7 to 10−13 cm2 s−1 and are consistent with the apparent diffusion constant from permeability measurements of 3x10−8 cm2 s−1. A relation between the permeability value and the NMR values is available from a theoretical description of the dualmode model in terms of a random walk on a lattice containing two sites.
Measurement of molecular transport in poly(vinyl chloride) by the step response technique
Authors: Wachi S. , Yates J. G.
Published: April 2003

Sorption and diffusion of methane and 1‐butene in poly(vinyl chloride) (PVC) powder have been investigated by the step‐response method using gas chromatography. The sorption equilibrium constant of 1‐butene was lower than that of chlorine, despite the higher critical temperature of 1‐butene, while the sorption of methane was negligibly small at temperatures much higher than critical. The diffusivity of 1‐butene in PVC showed a discontinuous dependence on temperature at the glass transition point, suggesting that the micro‐Brownian motion of the polymer chain enhances the diffusivity at the higher temperature. Below the glass transition temperature, the diffusivity of 1‐butene in PVC showed a lower value than has been measured for other smaller molecules such as chlorine and hydrogen chloride.
Measurement of thermal diffusivity of filler‐polymide composites by flash radiometry
Authors: Tsutsumi Naoto , Takeuchi Norihito , Kiyotsukuri Tsuyoshi
Published: April 2003

Thermal diffusivity D of filler‐polyimide composites was investigated using flash radiometry. The fillers used were: diamond, alumina, boron nitride, aluminium nitride, silicon carbide, and silicon carbide whiskers, Composite films were prepared by casting a polyamic acid solution with dispersed filler on a glass plate and then annealing. The effects of filler type, size, content, and shape on D were studied. D increased with increasing average filler particle diameter and filler content. For the composite filled with fine Al2O3 whose average particle diameter is about 0.2 μm, aggregates of filler were observed with dimensions up to a few microns. The formation of thermal paths through this aggregate enhances thermal diffusion. For the composites filled with high thermal conductivity filler such as BN and AIN, there was a strong increase in D above a filler content of 20 vol %. D was ten times larger than that of unfilled polyimide when the BN content was 54 vol %. D of the SiC‐whisker composite increased strongly up to a filler content of 18 vol %. Above this content D significantly decreased, probably because of interconnected voids formed by mold shrinkage.
Relaxations in thermosets. X. Analysis of dipolar relaxations in DGEBA‐based thermosets during isothermal cure
Authors: Mangion Michel B. M. , Joharis G. P.
Published: April 2003

Dielectric properties measured during isothermal curing of DGEBA‐based thermosets using a mixture of aromatic amines as curing agent are analyzed. The evolution of the dielectric features of thermosets during curing and after a time when their dc conductivity has reached a negligibly small value are phenomenologically similar to the dielectric features of physically and chemically stable dipolar liquids and solids observed with increasing frequency or decreasing temperature. This equivalence is a consequence of the invariance of the dynamic behavior of dielectric susceptibility with respect to either the frequency of measurement or the relaxation time of the substance and demonstrates that crosslinking of a thermoset causes its relaxation time to increase monotonically.

It is shown that the stretched exponential relaxation function formalism satisfactorily describes the dielectric results and that the value of its distribution parameter initially decreases and, after gelation, reaches a constant value, which we denote γ, in the latter part of the cure. The value of the curing parameter, γ, which lies between 0.2 and 0.4, monotonically decreases with increasing curing temperature and tends to a limiting value characteristic of a thermoset at higher temperatures. This is in contrast with the increase found in the corresponding representation in the Kohlrausch‐Williams‐Watts parameter β with increasing temperature. The curing time dependence of the dipolar relaxation time ι has been determined and found to have the shape of an elongated S, with a well‐defined point of inflexion, as ι increases during the cure, from a value characteristic of a liquid to an ultimate value characteristic of a glass.
The equation of state of solid and molten poly (butylene terephthalate) to 300°C and 200 MPa
Authors: Fakhreddine Youssef A. , Zoller Paul
Published: April 2003

The volumetric behavior of poly (butylene terephthalate) (PBT) was studied from 30 to 303°C and pressures from atmospheric to 200 MPa. The pressure‐volume‐tempreature (PVT) data show behavior typical of other semicrystalline materials. The empirical Tait equation was used to fit the measured volumes in the solid and melt regions. The maximum deviations between the Tait fits and the measured volumes were 0.001 and 0.002 cm3/g in the semicrystalline and melt regions, respectively. The theoretical equation of Simha‐Somcynsky was used to represent the PVT behavior of this material in the equilibrium melt. Fitting the theory to the data involves a determination of the reducing parameters of the theory. We find P* = 1139 MPa, V* = 0.7838 cm3/g, and T* = 11133 K. From these parameters we calculate that the chemical repeat unit of PBT has 6.37 external degrees of freedom, in comparison with 4.97 degrees of freedom to the closely related poly(ethylene terephthalate), with two less (CH2) units in the backbone. The difference of 1.4 degrees of freedom may be compared with the 0.88 degrees of freedom of the polyethylene (C2H4) repeat unit itself.
The structure and properties of drawn blends of poly (vinylidene fluoride) and poly (methyl methacrylate)
Authors: Gallagher G. A. , Jakeways R. , Ward I. M.
Published: April 2003

A blend consisting of equal proportions of poly (vinylidene fluoride) and poly (methyl methacrylate) has been prepared and drawn to draw ratios up to 7. The mechanical properties and the structure and morphology of the samples have been measured, the latter using differential scanning calorimetry, optical microscopy, and various x‐ray techniques. A structural model is proposed for the drawn materials which accounts for the mechanical properties and for the response of the crystalline regions of the material to an applied stress.
Transport properties of a side‐chain liquid‐crystalline polymer. Poly(4‐acryloyloxy biphenyl)
Authors: Vittoria V. , Russo R. , De Candia F. , Magagnini P. L. , Bresci B.
Published: April 2003

The transport properties of a side‐chain liquid‐crystalline polymer forming a smectic A phase have been investigated using dichloromethane as a permeant. Samples differing in the isotropization enthaoly were analyzed. A. Correlation between this thermal parameter and sorption has been found, while the diffusion coefficient is substantially the same in all samples. The results obtained can be explained in terms of a biphasis model in which a disordered permeable phase is present within the liquid‐crystalline phase, which is impermeable to the diffusant molecules.
Modified fuoss–kirkwood distribution function for interpretation of asymmetric nmr relaxation curves. I
Authors: Schneider Horst
Published: April 2003

Interpretation of asymmetric representations of nuclear magnetic resonance (NMR) relaxation times versus reciprocal temperature requires a distribution function of correlation times that describes any relation between the slopes in the high‐ and low‐temperature regions. Although it can be shown that the Havriliak–Negami function fulfills this condition after slight modification, a more useful function (a generalization of the Fuoss—Kirkwood distribution) is introduced and discussed in detail. This new function allows for description of curves of different symmetry by an expression similar to that for a single correlation time and gives a simple rough estimation of the distribution parameters, as well as more exact computer fitting. This interpretative discussion of NMR relaxation data is purely phenomenological and has no direct connection with molecular properties.
A calorimetric investigation on high molecular weight polyethylene reactor powders
Authors: Ottani Stefano , Porter Roger S.
Published: April 2003

Reactor powders of high‐ and ultrahigh‐molecular weight polyethylene have been investigated. Two different Ziegler‐Natta synthesis processes were used: polymerization in a slurry and in the gas phase. Synthesis temperature range was 30–85°C. Monoclinic crystals were identified in samples synthesized at 30°C. Investigations of thermal parameters were carried out by differential scanning calorimetry. A range of heating rates (0.4–10.0°C/min) was used to obtain information on sample reorganization on heating. The corresponding melt‐crystallized samples were scanned and their thermal parameters were compared with those obtained from the original nascent powders. Percent crystallinity and average lamellar thickness, computed by the Thompson‐Gibbs equation, were found to be controlled by conditions of synthesis. For reactor powders, the fraction of crystallinity is found to be insensitive to synthesis temperature. Crystallinity is controlled mainly by the synthesis process type: slurry or gas phase. Lamellar thickness was found to decrease as synthesis temperature was increased. This trend is the opposite of what is obtained on melt crystallization and can be interpreted on the basis of Lauritzen and Hoffman's theory of crystal growth. Nascent reactor powders give experimental support for the dependence of lamellar thickness on crystallization temperature that follows the pattern described in the theory at high undercooling. The influence of molecular weight on crystallinity and lamellar thickness of both nascent powders and melt‐crystallized samples was also studied. Catalyst and synthesis conditions were found to control crystallinity and crystallite dimensions of the reactor powders. Thus, polyethylenes suitable for a specific purpose can be obtained directly on synthesis.
On orientational and distortional contributions to birefringence
Authors: Heymans Nicole
Published: April 2003

A model for the effect of orientation dependence of polarizability anisotropy on birefringence is given and compared with literature data. If this dependence arises through bond angle distortion, the model shows a significant contribution to birefringence but a very small contribution to strain, accounting satisfactorily for differences in birefringence between hot‐drawn and cold‐drawn samples, for discrepancies between measurements of orientation obtained by different experimental methods and for previous observations on orientational behavior of preorientated polycarbonate at low additional strain.
Sub‐TG relaxations in LiClO4‐poly (propylene glycol)‐2000 solutions
Authors: Sidebottom D. L. , Johari G. P.
Published: April 2003

The dielectric permittivity and loss of LiClO4 solutions in poly (propylene glycol (PPG)), molecular weight 2000, have been measured over a concentration range up to a ratio of Li+ to oxygen atoms in PPG of 33.3:100, between 77 and 350 K. The data have been analyzed in both the permittivity and electrical modulus formalisms. Addition of LiClO4 to poly (propylene glycol) first increases the height of the β‐relaxation peak, and ultimately a second sub‐Tg relaxation peak at a higher temperature emerges. This is in addition to the β‐relaxation peak due to the reorientation of PPG dipoles, whose strength decreases from that in pure PPG‐2000. For a fixed temperature, the dc conductivity initially decreases with increasing Li+ concentration up to 20 Li+ per 100 O atoms and thereafter increases. This concentration corresponds to that at which the Tg of the solution reaches its limiting value of ca. 310 K. It is concluded that the formation of ion pairs causes a second and slower sub‐Tg relaxation process and that the increase in the efficiency of chain packing reduces the strength of the β‐relaxation of the polymer.
Calorimetric study of the room‐temperature transitions of polytetrafluoroethylene: The influence of thermal history
Authors: Villani Vincenzo , Pucciariello Rachele , Ajroldi Giuseppe
Published: April 2003

The trend of the room‐temperature transitions of native polytetrafluoroethylene versus annealing temperature has been studied. A method of deconvolution for the calorimetric curves Cp(T), based on Pearson VII type functions and the Marquardt's nonlinear leastsquares method, allowed the evaluation of the temperatures and of the heat of each transition. Annealing at 330°C determines the loss of the crystalline fraction responsible of the lowest room‐temperature transition. An interpretation of the lowest room‐temperature transition is suggested.
The combined effects of evaporation and quench steps on asymmetric membrane formation by phase inversion
Authors: Tsay C. S. , McHugh A. J.
Published: April 2003

An analysis of the effects of combined evaporation and quench periods on the formation of asymmetric membranes by the phase inversion technique is presented. The model for the evaporation period assumes binary diffusion and includes composition dependence in the mutual diffusion coefficient and free convection mass transfer in the gas phase. The quench period model includes the use of 4 composition‐dependent diffusion coefficients and incorporates a modified from of the interface jump mass balance which enables efficient numerical analysis of composition gradients in the film at the beginning of the quench period. Results for the effects of evaporation‐period variable, including: evaporation time, initial cast film thickness, casting surface dimension, and vapor‐phase composition, clearly indicate that significant effects of the evaporation period on membrane structure formation and its reproducibility occur within 20 seconds.
Toward a quantitative theory of the rheology of concentrated solutions of stiff polymers
Authors: Larson R. G. , Mead D. W.
Published: April 2003

Predictions of the rheological properties of concentrated isotropic solutions of stiff polymers are made that improve on those obtained with the approximate Doi theory. Predictions of the shear‐rate and concentration dependence of the viscosity η and the first and second normal stress differences N1 and N2 that avoid the closure approximations of Doi are obtained by using a Galerkin numerical solution for the orientation distribution function. The predictions for η and N1, though they neglect the effects of polydispersity in molecular weight, are shown to be in quantative agreement with recent measurements on solutions of poly‐γ‐benzyl‐L‐glutamate (PBLG). The polydispersities of a series of commercial PBLG and PBDG samples are measured by gel permeation chromatography, and found to be broad. An attempt is made to account for the effects of polydispersity on the linear viscoelastic storage and loss moduli for PBLG solutions by using the Marrucci–Grizzuti extension of the Doi theory. The attempt fails. The most probable explanation for the failure is that the rotary diffusive motions of the shorter molecules in the mixture are drastically slowed by the matrix of surrounding longer molecules.
The influence of chain structure on the equilibrium melting temperature of poly(vinylidene fluoride)
Authors: Nandi A. K. , Mandelkern L.
Published: April 2003

Three poly(vinylidene fluoride) whole polymers were fractionated according to their head‐to‐head concentrations. Their melting temperatures and fusion properties were studied. Although small but significant differences were found among the fractions obtained from a given parent polymer, a wide range in chain compositions was not obtained. The equilibrium melting temperatures were determined by extrapolating the dependence of the observed melting temperature on the crystallization temperature. A critical analysis is given of this extrapolation method as applied to poly(vinylidene fluoride) and the results are compared with literature reports. The problems involved in explaining the dependence of the equilibrium melting temperatures on the structural irregularities of the chain are given. Possible reasons for the relatively high level of crystallinity that is observed, for what is essentially a copolymer, are also discussed.
Diffusion of polymer molecules into polymer networks: Effect of stresses and contraints
Authors: Gent A. N. , Liu Ginger L.
Published: April 2003

Fine threads of cis‐1, 4‐polyisoprene, diameter ca. 50 μm, were prepared by drawing from solution and drying. They were crosslinked by reaction with H2S and SO2 and then swollen with linear cis‐polyisoprene liquids of varied molecular weight Ms, from 1,000 to 24,000 g/mol. Diffusion coefficients were determined from the initial rate of uptake, for both unrestrained and stretched threads. They were found to be in good agreement for stretches of up to about 300%. On the other hand, the equilibrium uptake increased markedly (> 100%) over this range of strain, similar to the increase in swelling observed with low‐molecular‐weight liquids. Values of diffusion coefficient were also obtained from the rate of deswelling upon release of swollen threads from tension, and from the rate of uptake of polymer liquids by a thin coating of crosslinked polymer, bonded onto glass fibers. Satisfactory agreement was obtained in all cases. A number of simple experiments thus give similar values for the diffusion coefficient of polymer liquids in lightly crosslinked polymer networks, in the range 10−13−10−16 m2/s, depending upon the molecular weight Ms of the polymer liquid approximately weight as M−2s. The amount of liquid absorbed was strongly dependent on its molecular weight, Ms, the degree of crosslinking of the host material, and applied stresses or constraints.
A model for dynamic relaxations in amorphous polymers. II. Extensions and generalizations of formalism and application to poly(methacrylates)
Authors: Bicerano Jozef
Published: April 2003

Extensions and generalizations of a new model for the dynamic relaxations in amorphous polymers, and its application to the poly(methacrylates), will be presented. The sizes of moving subunits will be extrapolated for the β and γ relaxations in several poly(methacrylates), by working backward from the relaxation temperatures (Tr) observed at frequencies of 1 to 100 Hz to subunits giving Tcs comparable to those Trs. A general form will be proposed for activation energy distributions; and used to derive relaxation time distributions satisfying the experimental trends. The good agreement between the calculated Tc and the Tr observed dynamically at frequencies of 1 to 100 Hz will be shown to result from the nature of these distributions. The loss peak observed at very low temperatures by isochronal sweeps at very low frequencies is therefore caused by the dissipation of applied energy in localized domains. At sweep frequencies of 1 to 100 Hz, Tr ≈ Tc, and energy dissipation begins to take place over regions spanning the entire polymer. This delocalization of the energy dissipation is relevant to the effects of molecular level factors on many mechanical and thermodynamic properties of amorphous polymers. The effects of activation entropy and of dynamic excess entropy will be shown to be small in magnitude but important in terms of fully understanding relaxation behavior. Physical aging will be shown to result in a slight increase in the calculated characteristic temperatures. Finally, it will be shown that the relaxation behavior of the moduli and the compliances share some important common features with many other physical phenomena of seemingly very different nature.
Supramolecular structure investigation of poly(γ‐benzyl, α‐l‐glutamate)‐benzyl alcohol system by static light scattering
Authors: Shukla Premal , Muthukumar M.
Published: April 2003

The cholesteric mesophase of the PBLG‐BA system in concentrated solutions and in the gel phase has been investigated by static laser light scattering. The observed ‘distortion’ of the patterns in terms of their dependence on the azimuthal angle was studied. Effect of form‐optical rotation on the pattern is discussed. The manner of distortion in the Hv pattern determines the sense of cholesteric twisting. The observed scattering patterns are analogous to those obtained by previous investigators in other solvents. Quantitative measurements of the intensity as a function of scattering vector provide information on the sense and pitch of the cholesteric twisting, as a function of temperature and concentration. Optical microscopy studies reveal onset and build‐up of the cholesteric structure. Optical rotation and differential scanning calorimetry (DSC) studies support the conclusions obtained from light‐scattering experiments.
Short‐range order in miscible polymer blends: A monte carlo study
Authors: Cifra P. , Karasz F. E. , Macknight W. J.
Published: April 2003

Local ordering in miscible binary polymer blends with strong attractive interactions between the two types of chains was investigated by computer simulation of allowable conformations on an incompressible cubic lattice. A tendency toward maximum ordering (in which chains pack in alternate parallel rows) is shown by the calculation of pair correlations and in “snapshots” of the mixtures. A specific directional interaction is not necessarily required for ordering. A comparison of these results with those recently obtained using mean‐field theory is presented. The heat capacity of mixing was also calculated and found to be positive, with a value close to that reported experimentally.
Effect of polymer binding on the spectroscopic properties of stilbene‐based fluorescent dyes
Authors: Smit K. J. , Ghiggino K. P.
Published: April 2003

Studies utilizing absorption and emission spectrophotometry have been carried out to observe the effect of various polymer substrates on the spectral characteristics of several stilbene‐based fluorescent dyes. Poly(vinyl alcohol), cellulose acetate, cellulose fiber, and bovine serum albumin were used as substrates for two common fluorescent whitening agents and for two model compounds. Binding of these molecules to polymers leads to a marked red shift in the absorption spectra and an increase in vibrational structure. These effects are attributed to an increase in molecular planarity induced by the polymer environment. For the case of bovine serum albumin, it is concluded that the dye molecules bind to the protein largely through electrostatic interaction involving the dye sulfonate groups. The spectral characteristics of the dye molecules on wool fibers are interpreted in light of these results.
Comparison of x‐ray diffraction and thermal analysis methods for assessing order in poly(vinyl chloride)
Authors: Dawson P. C. , Gilbert M. , Maddams W. F.
Published: April 2003

Thermal analysis and wide‐angle x‐ray diffraction were used to assess the crystallinity for a series of poly(vinyl chloride) (PVC) samples, and the use of two complementary techniques was found beneficial. Two polymers were studied; a commercial suspension grade PVC, and an experimental grade of higher syndiotacticity. Both were examined as powders, and after processing. All samples were also examined after heat treatment at various temperatures between 100 and 175°C. Annealing the suspension grade of PVC appeared to cause a small change in total crystallinity, but little change in crystallite size. When the low temperature powder was annealed, some increase in crystallinity was detected. However, when this polymer was milled, there was a significant increase in crystallite size, and crystallinity seemed to increase further. Particularly noticeable was the increase in the amount of high melting crystallites.
Phase separation in mixtures of poly(ethylene glycol monomethylether) and poly(propylene glycol) oligomers
Authors: Takahashi H. , Kyu T. , Tran‐Cong Q. , Yano O. , Soen T.
Published: April 2003

Time‐resolved light scattering was employed to investigate kinetics of phase separation in mixtures of poly (ethylene glycol monomethylether) (PEGE)/poly (propylene glycol) (PPG) oligomers. Phase diagrams for PEGE/PPG of varying molecular weights were established by means of cold point measurements. The oligomer mixtures reveal an upper critical solution temperature (UCST). Several temperature quench experiments were carried out with a 60/40 PEGE/PPG blend by rapidly quenching from a single phase (69°C) to two‐phase temperatures (66–61°C) at 1°C intervals. As is typical for oligomer mixtures, the early stage of spinodal decomposition (SD) was not detected. The kinetics of phase decomposition was found to be dominated by the late stage of SD. Time‐evolution of scattering intensity was analyzed in accordance with nonlinear and dynamical scaling theories. The time dependence of the peak intensity Im and the corresponding peak wavenumber qm was found to follow the power‐law {Im(t)˜ tα, qm(t)˜ t‐β} with the values of α = 3 ± 0.3 and β = 1 ± 0.2, which are very close to the values predicted by Siggia. This process has been attributed to a coarsening mechanism driven by surface tension. In the temporal scaling analysis, the structure function reveals university with time, suggesting self‐similarity. Phase separation dynamics in 60/40 PEGE/PPG resembles the behavior predicted for off‐critical mixtures.
Low‐frequency Raman spectra of odd α,ω‐disubstituted n‐alkanes
Authors: Viras Fotini , Viras Kyriakos , Campbell Carl , King Terence A. , Booth Colin
Published: April 2003

Low‐Frequency Raman spectra of odd α,ω‐dibromo‐ and α,ω‐dihydroxy‐n‐alkanes were recorded. The longitudinal acoustic mode (LAM‐1) frequencies were assigned by references to the published results for n‐alkanes and even α,ω‐disubstituted n‐alkanes and also by taking account of the effects of end intermolecular forces and end‐group masses by use of the chain model of Minoni and Zerbi.
Study of phase separation in polyurethane using paramagnetic labels. Effect of soft segment molecular weight, structure, and thermal history
Authors: Chen Wen‐Pin , Kenney Donald J. , Frisch Kurt C. , Wong Shaio‐Wen , Moore Ralph
Published: April 2003

The morphology of segmented polyurethane (PU) elastomers was studied by means of ESR at various temperatures ranging from 100K‐450K. The PU's were based on 4,4'‐diphenylmethane diisocyanate (MDI), poly (oxytetramethylene) glycols (PTMO) and hydroxyl‐terminated random compolymers of tetrahydrofuran and 3‐methyl‐tetrahydrofuran (THF/Me‐THF). Purified 1,4‐butanediol (BD) was used as a chain extender. The nitroxide probe, 4‐hydroxy‐2‐2',6‐6'‐tetramethylpiperidine‐1‐oxyl (TEMPOL), was used to label the polyurethanes by reaction with an NCO group of MDI. Analysis of the electron spin resonance (ESR) spectra suggested that the label situates at heterogeneous sites, which means that a two‐phase domain is present. The morphologies at 300K and 400K were compared. It was found from ESR spectra that polyurethanes made from soft segments having higher MW exhibited greater phase separation at 300K than their corresponding elastomers made from lower MW soft segments. However, at 400K the more isotropic ESR spectra for the PUs containing higher MW soft segments suggested that the PUs were more mobile than their analogs having lower MW soft segments. The introduction of 3‐methyl side groups decreased the phase mixing at 400K due to steric hindrance.
Rheology of polystyrene/poly(vinyl methyl ether)blends near the phase transition
Authors: Ajji A. , Choplin L. , Prud'Homme R. E.
Published: April 2003

Mixtures are expected to show anomalous behavior in their viscoelastic properties close to a critical point. In this study, the reheological behavior of blends of polystyrene and poly (vinyl methyl ether) below, close to, and above the phase separation temperature Ts was investigated. Rheological measurements were carried out at three different compositions in the melt. Below and far from Ts, a satisfactory superposition of the storage and loss moduli G' and G″ was observed at all temperatures and frequencies. Close to Ts deviations were observed for G' at low frequencies (the so‐called terminal zone). Above Ts G″ values was still observed over the whole range of frequencies and temperatures. The deviations observed for G' near Ts can be interpreted as due to the presence of significant concentration fluctuations. Plots of log (G'/G″2) as a function of temperature were shown to be sensitive to this anomalous behavior.
Miscibility of poly(ϵ‐caprolactone) and of poly(styrene‐co‐acrylonitrile) with poly(styrene‐co‐acrylic acid)
Authors: Ho Jo Won , Gyun Kim Hong
Published: April 2003

The miscibility of poly (ϵ‐caprolactone) (PCL) with poly (styrene‐co‐acrylic acid) (SAA) and of poly (styrene‐co‐acrylonitrile) (SAN) with SAA was examined as a function of the comonomer composition in the copolymers. For PCL/SAA blends it was found that PCL is miscible with SAA within a specific range of copolymer compositions. Segmental interaction energy densities were evaluated by analysis of the equilibrium melting point depression and application of a binary interaction model. The results suggest that the intramolecular repulsion in SAA copolymer plays an important role in inducing the miscibility. Additionally, the critical AA content in SAA for the blend to be homogeneous was predicted by correlating the segmental interaction energy densities with the binary interaction model. For SAN/SAA blends, it was also found that SAA is miscible with SAN within a specific range of copolymer compositions. From the binary interaction model, segmental interaction energy denisties between different monomer units were estimated from the miscibility map and were found to be positive for all pairs, indicating that the miscibility of the blends is due to the strong repulsion in the SAA copolymers.
Determination of molecular weights and Mark–Houwink constants for soluble electronically conducting polymers
Authors: Holdcroft Steven
Published: April 2003

Intrinsic viscosities and gel permeation chromatography data were used to evaluate the Mark–Houwink constants of the soluble electronically conducting polymer, poly(3‐hexylthiophene) (P3HT):K and a are 2.28 × 10‐3 cm3/g and 0.96, respectively, in tetrahydrofuran (THF) at 25°C. Mark–Houwink constants were used to calibrate gel permeation chromatography (GPC) columns for P3HT. Number‐average molecular weights of P3HT determined with modified calibration curves agreed well with those determined by an absolute method, embulliometry. Molecular weights estimated using unmodified polystyrene calibration procedures were significantly larger than true values.
Low‐frequency raman‐active modes in methoxy‐ended and hydroxy‐ended oligo(oxyethylene)s
Authors: Campbell Carl , Viras Kyriakos , Booth Colin
Published: April 2003

Low‐frequency Raman spectra were recorded for α‐methyl, ω‐methoxy‐oligo(oxyethylene)s, C1EmC1 with m in the range 4–25 (i.e., 15–78 atoms). Longitudinal acoustical mode (LAM‐1) frequencies were identified and compared with those determined previously for α‐hydro, ω‐hydroxy‐oligo (oxyethylene)s. Nonlinear relationships between LAM‐1 frequency and reciprocal chain length were explained as an effect of intermolecular end forces.
Study of solid‐state polymerization by positron lifetime measurements
Authors: Millán Sonia , Sánchez Victor , Fucugauchi Luz Alicia , Ito Yasuo , Tabata Yoneho
Published: April 2003

The positron lifetime measurement technique was applied to analyze the structural changes occurring in solid‐state polymerization of acrylamide and trioxane. Positronium (Ps) parameters, τ2 and I2, which show a marked change as a function of the γ‐ray irradiation dose, signaled the presence of three clearly defined stages in the polymerization process: initiation, propagation, and saturation. The initial increase in τ2, may very well be the result of efficient trapping of Ps in vacancies created around the polymer nuclei. The complicated behavior of I2 may be explained as a chemical reaction between Ps precursors and the radiolysis products of this polymerization process.