bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid‐state coextrusion of poly(ethylene terephthalate). II. Drawing of semicrystalline PET
Authors: Pereira Jose R. C. , Porter Roger S.
Published: April 2003

The drawing of semicrystalline (33 and 50%) poly(ethylene terephthalate) (PET) films has been studied by solid‐state coextrusion. Because of its brittleness and opacity, isotropic and semicrystalline PET film is of little practical use. Early attempts to cold‐draw crystalline films led to fracture in contrast to deformation of amorphous PET. However, we have succeeded in systematically preparing films with extrusion draw ratios ≤4.4 from semicrystalline PET. In many cases, the properties of the drawn extrudates, as a function of extrusion temperature Text and extrusion draw ratio EDR, were similar to those prepared from amorphous PET. However, some remarkable differences have also been found. In the case of coextrudates prepared from isotropic 50% crystalline PET, we found that the larger the deformation, the lower the apparent resulting crystallinity. In the extreme, a 34% reduction in crystallinity after deformation was observed. For the coextrudates drawn from initially 33% crystalline PET, slightly different behavior occurred. For Text ≤ 90°C, all extrudates showed crystallinities lower than the original isotropic film, with a minimum at EDR = 3; for Text ≥ 110°C, crystallinities were slightly greater than in the original film and increased with EDR. Qualitative measurements of heats of fusion were in agreement with density gradient results for PET crystallinity. In contrast is our previous finding that extrudates from initially amorphous PET always increase in crystallinity with EDR, because of stress‐induced crystallization. The results now suggest that in the Text range investigated, the initial spherulitic structure is at least in part destroyed on drawing. In addition, the percent crystallinity is revealed to be dependent on Text, with lower values at lower temperatures. Mechanical tests show that the extrudates are similar or sometimes higher in tensile modulus when compared to amorphous PET drawn under the same conditions.
The dependence of dielectric response of an elastomer on hydrostatic pressure
Authors: Pae K. D. , Questad D. L.
Published: April 2003

Dielectric methods have been employed to study the high‐pressure behavior of a polyurethane elastomer (Solithane 113) in the vicinity of its α transition. The α‐loss peak is shifted to higher temperatures and broadened somewhat with the application of hydrostatic pressure up to 6.4 kbars. The slope ofTαvs.P, ordTα/dP, obtained at low frequencies was found to be equal todTg/dPobtained by a volumetric method. Moreover, it attained a nonzero limiting value at high pressures for each frequency tested (3—30,000 Hz) and the limiting value itself increased with increasing frequency from 10.5°C/kbar at 3 Hz to 18°C/kbar at 30,000 Hz. The activation enthalpy ΔH* was found to be nearly constant over the pressure range tested, but the activation volume ΔV* decreased with increasing pressure. The relationdTα/dP=T(ΔV*/ΔH*) was shown to hold for the elastomer.
Rheological studies of moderately concentrated polystyrene solutions in the vicinity of the θ temperature. II. Shear‐rate dependence for different thermodynamic conditions
Authors: Ballauff M. , Krämer H. , Wolf B. A.
Published: April 2003

The viscosity data of moderately concentrated polystyrene solutions in trans‐decalin (TD) (θ solvent, θ temperature 21°C) and toluene (TL) (good solvent) reported in Part I are discussed in terms of Graessley's entanglement theory. Under good solvent conditions, Graessley's master curve provides an excellent fit up to high shear rates, whereas in the vicinity of the θ conditions the data have to be modified by a parameter ηfric introduced by Ito and Shishido. The characteristic time of mechanical response to flow of chains approximately given by the shift factor τ0 is found in good solvents to be on the order of the Rouse relaxation time. In poor solvents, close to demixing, τ0 tends to much higher values, indicating a reduced chain mobility. The influence of temperature on the viscosity decreases with increasing shear. The resulting apparent energy of activation of flow shows very small or even negative values at high shear rates. This behavior can be explained by the modified Graessley theory, however, in a quite natural way.
Studies on dilute solutions of rodlike macroions. II. Electrostatic effects
Authors: Cotts P. Metzger , Berry G. C.
Published: April 2003

A group of rodlike polymers soluble only in strong protic acids was studied using light scattering and viscosity techniques. These include poly(1,4‐phenylene benzobisoxazole), poly(1,4‐phenylene benzobisthiazole) and poly(1,4‐phenylene terephthalamide). The solution properties were dependent on the ionic strength of the acid used as solvent. In a low ionic strength acid such as chlorosulfonic acid, the polymer solutions exhibited decreased unpolarized scattering, an extremely small translational diffusion coefficient, and high viscosity. All of these effects could be eliminated by the addition of a salt such as lithium chlorosulfonate, which increased the ionic strength of the solvent. The effects were attributed to a pseudo ordering of the polymer solvent system caused by electrostatic repulsions between protonated polymer chains effective over large distances (ca. 100 Å) in the low ionic strength solvent. This type of ordering is distinct from actual anisotropic phase formation, which occurs at higher concentrations in these systems. Analysis of data at infinite dilution gave a persistence length of at least 45 nm for poly(1,4‐phenylene terephthalamide), larger than previous experimental results, but in accord with recent rotational isomeric state calculations and similar to experimental data for poly(p‐benzamide).
Thermoluminescence from extended‐chain crystals of polyethylene
Authors: Hashimoto Toshimasa , Ogita Kiyoshi , Umemoto Susumu , Sakai Tetsuya
Published: April 2003

Thermoluminescence (TL) has been observed in γ‐irradiated extended‐chain crystals of polyethylene above room temperature. The TL curve, which exhibits four peaks at 50, 90, 120, and 140°C, is different from that given by folded‐chain crystals, in both shape and intensity. In particular, a shape, strong glow peak is observed at 140°C, corresponding to the melting temperature of the extended chain crystals. These results are discussed in relation to independent measurements by differential scanning calorimetry and electron spin resonance.
Retardation of spherulitic growth rate in the crystallization of isotactic polystyrene due to the presence of nucleant
Authors: Kennedy M. A. , Turturro G. , Brown G. R. , St‐Pierre L. E.
Published: April 2003

Although the rate of heterogeneous nucleation of crystallization in isotactic polystyrene, as studied by photomicroscopy, is markedly increased by addition of fine‐particle silica, the rate of subsequent radial growth of spherulites formed is diminished. The latter observation is rationalized on the basis of a modified Hoffman–Lauritzen treatment wherein the nucleant is depicted as a quasicrosslink which impedes the transport of polymer segments.
Polymer single crystals of poly(4‐hydroxybenzoate). II. A contribution to crystal structure and polymorphism
Authors: Lieser G.
Published: April 2003

Electron diffraction has been used to investigate the structure of a wide range of as‐polymerized crystals of poly(4‐hydroxybenzoate) [systematic name: poly(1,4‐oxybenzoyl)]. The chemical composition and the degree of polymerization (DP) have been varied and some samples have been thermally treated. At room temperature two crystalline modifications with orthorhombic unit cells coexist. The chains adopt a 21 helical conformation in both forms, but there are differences for oligomer and polymer crystals. Oligomers of low DP have an extended chain‐conformation, whereas in polymers a shortening of the repeat distance along the chain is observed as a function of both the DP and the crystallization conditions. From the most extensive data sets we have derived the lattice parameters a = 7.52, b = 5.70, and c = 12.49 Å for polymer crystals of phase I, and the subcell parameters for oligomer crystals of phase II a = 3.77, b = 11.06, and c = 12.89 Å. Both phases contain two chains per unit cell. In addition to modifications I and II several defect structures exist the unit cells of which contain more than two chains. At temperatures which depend on the degree of polymerization, a phase transition to a third modification takes place. The large difference between the densities of phase III as compared to both phase I and II suggests that torsional degrees of freedom exist in phase III which allow a certain mobility of the phenyl and ester groups. This mobility enables the end groups of adjacent layers in interlamellar regions of oligomer crystals to undergo transesterification reactions and therefore to increase the molecular weight of the samples.
Study of molecular deformation mechanisms in the glassy state. I. Temperature effect on stress‐birefringence and strain‐birefringence responses of poly(methyl methacrylate)
Authors: Hong Su‐Don , Chung Shirley Y. , Fedors Robert F. , Moacanin Jovan
Published: April 2003

In order to gain better understanding of the molecular deformation processes occurring in poly‐(methyl methacrylate), a series of studies was carried out in uniaxial tension on the simultaneous stress and birefringence response in both constant‐strain‐rate and stress relaxation experiments. The former covered the temperature range −120 to 75°C and the latter 0 to 90°C. Three deformation mechanisms, i.e., (i) change in intermolecular distance, (ii) distortion of the conformation of the COOCH3 group from its thermal equilibrium state, and (iii) orientation of main‐chain segments, are invoked to interpret the experimental results. It is concluded that, in the temperature range from −120 to 75°C and possibly at higher temperatures as well, the polymer chains deform in the small‐strain region by an orientation of those chain segments having lower potential‐energy barriers to conformational changes and straining those chain segments having higher potential‐energy barriers. Subsequent chain orientation of the already strained segments occur in the higher strain regions. Changes in intermolecular distances occur over the entire temperature range from −120 to 90°C, but their magnitude decreases gradually as the temperature increases from −40 to 40°C and then decreases sharply for temperatures above 40°C. Strain‐induced distortion of the conformation of the COOCH3 group may involve only rotation of the OCH3 group around the CO bond rather than rotation of the entire ester group itself.
The effect of dye sorption on electromechanical properties in sodium poly(L‐glutamate)
Authors: Ando Yutaka , Kawabata Naruto , Nishida Kenzo
Published: April 2003

Piezoelectric constant, Young's elastic modulus, and dielectric constant of undyed and dyed films of poly(L‐glutamate) were measured at 10 Hz over the temperature range −120 to 120°C. The temperature of the maximum in −d″14 shifts toward higher temperature up to 0.6 mg/g polymer of dye uptake and then shifts toward lower temperature by further dye sorption. The variation of the piezoelectric modulus was interpreted by the change of mobility of impurity ions in the sample.
C‐13 NMR analysis of polystyrene from low‐molecular‐weight model compounds
Authors: Sato Hisaya , Tanaka Yasuyuki , Hatada Koichi
Published: April 2003

Methylene and phenyl C1 carbon signals of polystyrene are assigned on the basis of the signal assignments of styrene oligomers. Polystyrenes prepared with benzoyl peroxide, n‐butyllithium, and trifluoroboron etherate catalysts have random distributions with probabilities of racemic dyads of 0.54, 0.56, and 0.45, respectively.
An inverse gas‐chromatographic study of the interaction of water with some cellulose derivatives
Authors: Aspler J. S. , Gray D. G.
Published: April 2003

The sorption isotherms for water on cellulose triacetate, cellulose acetate (degree of substitution 2.45), cellulose monoacetate (degree of substitution 0.89), and ethyl cellulose were measured by finite‐concentration inverse gas chromatography. The isotherms for cellulose monoacetate were also measured with a vacuum microbalance. Polymer–solvent interaction parameters and partial molar heats of sorption at zero concentration of water were estimated from the extrapolated data, but kinetic effects and isotherm curvature lowered the precision of these results. The water sorption isotherms were examined according to the Zimm cluster theory, and the results were compared to those for cellulose and (hydroxypropyl)cellulose.
Chain orientation in polystyrene/poly(2,6‐dimethyl‐1,4‐phenylene oxide) blends
Authors: Wang L. H. , Porter Roger S.
Published: April 2003

The differential orientation of polymer chains has been measured in polystyrene (PS)/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) compatible blends. Density measurements are reported as a function of binary blend composition at 23°C. Drawing was performed by solid‐state coextrusion. PS/PPO blend compositions of 90/10 and 75/25 were drawn within sandwiches of polyethylene at 145°C and isotactic polypropylene at 155°C, i.e. at ca. 25°C above the glass transition temperatures of the two blends. The change in Fourier‐transform infrared dichroisms on drawing these blends was measured at 906 and 1190 cm−1, corresponding to predominantly PS and PPO, respectively. The orientation of PS and PPO was observed as a function of draw ratio λ in the range 1–5; orientations increased with λ for both PS and PPO in both blends but to different degrees. Both polymers decreased in orientation with increasing PPO content. Annealing with fixed ends showed that the PPO chains disorient more slowly than those of PS. All binary systems were found to be amorphous and compatible.
A 13C NMR study of mesomorphic solutions of poly(p‐phenylene terephthalamide)
Authors: Close L. G. , Fornes R. E. , Gilbert R. D.
Published: April 2003

Solutions of poly(p‐phenylene terephthalamide) in fuming sulfuric acid were characterized by 13C NMR spectroscopy and solution viscosity measurements over the 2–28% w/w concentration range. The spectra showed the presence of two distinct amide carbonyl resonances at low concentration, tentatively assigned to cis and trans conformations. As the concentration increased, additional carbonyl lines were observed along with significant broadening. Peak area measurements showed that only the polymer molecules in the isotropic environments contributed to the 13C NMR spectra and a considerable amount of the polymer remained in the isotropic phase at concentrations previously considered to consist of polymer in highly anisotropic regions. Spin‐lattice relaxation times were measured at six concentrations using the inversion recovery method. The aromatic carbons relaxed at a much faster rate (ca. 0.10 s) than the carbonyls (ca. 0.45 s), but the relaxation rates for both carbons were essentially constant over the concentration range, indicating that the observed isotropic phase is not affected by changes in the macroscopic solution behavior so as to alter spin‐lattice relaxation mechanisms.
Determination of long‐chain branching in model polystyrene samples by the GPC‐sedimentation method
Authors: Tung L. H. , Gatzke A. L.
Published: April 2003

The GPC–sedimentation velocity method proposed earlier for the determination of long‐chain branches was examined quantitatively by using model star‐shaped and comb‐shaped polystyrene samples of known degree of branching. The results showed that separation by sedimentation velocity was more sensitive to branching variations than separation by GPC. The results showed also that at low and moderate levels of branching the GPC–sedimentation velocity method reflected accurately the amounts of branching in the model samples. At high levels of branching, the method underestimated the amount of branching. The discrepancy, however, appears to have been caused by the inadequacy of the theories used in the interpretation of the raw data and not by any inherent problem in the method itself. The relative sensitivities of the GPC‐sedimentation, GPC‐viscosity, and GPC–light scattering methods are discussed.
Thermotropic homopolyesters. III. Preparation and properties of polymers based on 4′‐hydroxyphenyl‐4‐hydroxycinnamate
Authors: Krigbaum W. R. , Ishikawa T. , Watanabe J. , Toriumi H. , Kubota K. , Preston J.
Published: April 2003

Low‐molecular‐weight 4′‐acetoxyphenyl‐4‐acetoxyoinnamate, as well as several polyesters synthesized from this monomer and aliphatic dibasic acids, exhibit thermotropic nematic phases. DSC heating curves for all of the polymers exhibit multiple transitions. The amount of crystallinity of these polymers at room temperature is small and the degree of order along the chain axis in the crystalline phase is poor. For the lower homologues the nematic phase exists over a broad temperature range of approximately 100°C. The polyester from chiral (+)‐3‐methyl adipate forms a thermotropic cholesteric phase. Both the diacetoxy monomer and azelate polymers of low molecular weight adopt the homeotropic texture on glass slides, but with increasing molecular weight the planar texture becomes preferred. Investigation of the effects of electric fields in the conduction regime upon the nematic phase of the diacetoxy monomer revealed that Williams domains are formed only with difficulty. In most cases, a stationary pattern appeared instead. At higher voltage the dynamic scattering mode (DSM) was obtained, and above this a field‐induced transition to the isotropic phase. The azelate polyesters exhibited Williams domains and the DSM in the conduction regime. The formation time for Williams domains was fairly short for polymers having ηinh < 0.44 dL/g, but increased to 80 min when ηinh = 0.68 dL/g. The DSM was only observed for polymers having ηinh < 0.61 dL/g. For these polymers the critical frequency separating the conduction and dielectric regimes exhibits a stronger temperature dependence than that of low‐molecular‐weight nematogens. A new instability pattern is reported for the azelate polyesters in the dielectric regime.
Pressure dependence of the viscosity of dilute polystyrene solutions in toluene
Authors: Claesson Stig , McAtee James L. , Ali Sabz
Published: April 2003

The effect of pressure on the viscosity of dilute solutions of anionically polymerized polystyrene (M̄w = 209,000; Mw/Mn = 1.12) in toluene has been studied at different temperatures and concentrations using a falling‐body viscometer. Measurements were performed in the concentration range from 0.0025 to 0.02 g/mL and at temperatures from 25 to 45°C under pressure up to 1057 bars. The viscosity coefficient η increases exponentially with pressure at a given temperature and concentration, while the apparent volume of activation V‡ decreases with increasing temperature. The hypothesis that the pressure dependence of η is given by the pressure dependence of the activation energy holds true under the prevailing thermodynamic conditions. Log η increases linearly with increasing concentration at a given pressure. Intrinsic viscosity increases with increasing pressure, whereas the Huggins constant decreases.
Light‐scattering photography of polymers near the glass transition
Authors: Carroll P. J. , Patterson G. D. , Cullerton S. A.
Published: April 2003

Laser light scattered from a block of polystyrene is observed to have a pattern of bright and dark regions called speckle. We observe that the speckle pattern has a lifetime consistent with that of the average relaxation lifetime 〈τ〉 of the intensity fluctuations of the medium as determined by photon correlation spectroscopy. In order to study the pattern of the scattered light, a series of photographs was taken at a variety of exposure times. For each series, the value of the average relaxation lifetime is defined by the temperature and pressure of the polystyrene sample. When the value of 〈τ〉 is short relative to the exposure time, the photograph displays only a random pattern of exposed grains. This is due to the large number of fluctuations that have occurred during the exposure time with random phases relative to one another. As the average relaxation time is increased at a constant exposure time, the speckle pattern appears when the value of 〈τ〉 becomes comparable to the exposure time. The phenomenon of laser speckle allows the time scale of the slowly relaxing fluctuations near the glass transition to be visualized. A digitized series of such pictures could be analyzed to obtain the average relaxation time for the fluctuations, just as in normal photon correlation spectroscopy where the intensity of one coherence area is measured as a function of time.
Photon correlation spectroscopy of polymers in the glassy state
Authors: Patterson G. D. , Carroll P. J.
Published: April 2003

Photon correlation spectroscopy has proven to be a very useful technique for studying slowly relaxing density and optical anisotropy fluctuations in bulk polymers near the glass transition. When some of the fluctuations achieve relaxation times much longer than the typical averaging time for the intensity autocorrelation function (104 s), the result must be treated in the partially heterodyned limit. Also, when the sample is near the glass transition but not at equilibrium the correlation function is not stationary in time because the system is relaxing as a whole toward the equilibrium state. The above effects are discussed theoretically and demonstrated experimentally in polystyrene as a function of temperature and pressure. Light scattering with coherent excitation also fluctuates in space as well as in time (as shown in the accompanying paper). The consequences of this effect are discussed. When most of the intensity is associated with fluctuations whose relaxation times are very long in polystyrene, there is still a broad relaxation function evident. This is characteristic of a secondary relaxation process.
An analysis of the reflective component of small‐angle X‐ray scattering patterns from crazed polystyrene
Authors: Westbrook P. A. , Fellers J. F. , Cakmak M. , Lin J. S. , Hendricks R. W.
Published: April 2003

An investigation of the reflective component of small‐angle x‐ray scattering patterns of polystyrene crazes is performed. It is shown that the strong streak parallel to the tensile axis consists predominantly of reflected radiation, while the remaining pattern is composed entirely of diffracted radiation. X‐ray reflection off unparallel regions of crazes is discussed and the nature of the reflection is also considered in terms of collimation quality. An analysis methodology based on craze tip angular distribution is proposed.
The use of model networks with reptating chains to study extraction efficiencies
Authors: Mark J. E. , Zhang Z.‐M.
Published: April 2003

It is possible to prepare “model” elastomeric networks having known values of the molecular weight Mc between crosslinks by endlinking functionally terminated polymer chains having number‐average molecular weights Mn equal to the desired values of Mc. If chains having chemically inert groups at both ends are intentionally included during the preparation of such a system, they will remain unattached, merely reptating through the subsequently formed network structure. This technique was used to prepare a series of tetrafunctional polydimethylsiloxane (PDMS) networks having essentially the same degree of crosslinking (10−3Mc = 11.3 g mol−1) and constant amount of diluent in the form of unattached PDMS chains having molecular weights of 10−3Md = 26.4, 18.6, 15.8, 9.8, 6.7, 1.2, and 0.70 g mol−1. Because of the very high mobility of PDMS, it was also possible to introduce essentially the same amount of the same diluents into already formed PDMS networks having the same Mc. Extractions carried out using tetrahydrofuran at room temperature showed that the diluent (“sol fraction”) introduced by swelling the network is more easily removed than that present during the endlinking, possibly because of less convoluted arrangements within the network structure. Chains with the largest values of Md which were present during the endlinking were found to be very difficult to remove entirely. It is therefore extremely important to carry out exhaustive extractions to obtain reliable values of network sol fractions, particularly when such data are to be used to estimate extents of reaction in the preparation of end‐linked elastomers.
A fluorescence polarization study of the effect of matrix molecular weight on the relaxation of a labeled molecule in a stretched polymer melt
Authors: Tassin J. F. , Monnerie L.
Published: April 2003

Fluorescence polarization has been used to measure the orientation during stretching of a polystyrene chain embedded in a matrix of narrow‐dispersion polystyrene chains of a different molecular weight and labeled by an anthracene group covalently bound at the middle of a chain. Strong coupling between the relaxation of the labeled chain and the matrix chains is evidenced, the orientation of the labeled chain being partially governed by the molecular weight of the matrix. This behavior is interpreted qualitatively on the basis of a molecular model showing that the relaxation of a polymer chain is strongly affected by the entanglements acting on the chain, the number of which is also related to the motion of the surroundings. Good agreement is found between experimental data and the behavior predicted by the model.
Polymer–polymer interaction parameters of polystyrene and polybutadiene from studies in solutions of toluene or tetrahydrofuran
Authors: Narasimhan Venkataraman , Huang Robert Y. M. , Burns Charles M.
Published: April 2003

Equations used for the determination of polymer–polymer interaction parameters for narrow molecular weight distribution polymers which have undergone phase separation in solutions are discussed. Binodals with tie lines and plait points are presented for ternary systems polystyrene‐polybutadiene‐toluene and polystyrene‐polybutadiene‐tetrahydrofuran. Typical interaction parameters determined from the experimental data for the polystyrene‐polybutadiene systems are presented.
Cage effects in recombination of allyl radicals in irradiated polyethylene. II. Cumulative reaction rates and decay kinetic processes
Authors: Hwang Lian‐Pin
Published: April 2003

Hwang and Cheng have studied the recombination reaction of allyl radicals in irradiated polyethylene by including the effects of (i) diffusion of macroradicals by jumps of finite size in the crystalline phase and (ii) a caging reaction with a finite rate in the disordered region. In this work their results are used to analyze cumulative reaction rate data on the decay of allyl radicals in extended‐chain and Marlex film polyethylene. The kinetic parameters obtained show the effects of reaction temperature, irradiation dose, and morphological differences.
ESR study of the diacetylene polymer 4BCMU
Authors: Freitas J. A. , Greenbaum S. G.
Published: April 2003

Electron Spin Resonance (ESR) measurements of the polydiacetylene 4BCMU in the solid‐state indicate the presence of a thermally activated paramagnetic center with g ≈ 2.002 and first‐derivative peak‐to‐peak linewidth of ≈ 17G. An abrupt and irreversible decrease in ESR signal intensity is observed at ca. 400 K, and appears to be associated with the solid‐state planar‐nonplanar conformational transformation manifested by an irreversible color change from metallic brown to red.
The effect of temperature on the infrared spectra of poly(ethylene terephthalate)
Authors: Lin Shaow‐Burn , Koenig Jack L.
Published: April 2003

Reversible and irreversible spectral changes are observed on heating of solvent‐cast films of poly(ethylene terephthalate) (PET) between 30 and 230°C. The irreversible changes are due to the gauche‐trans isomerization of the ethylene glycol segments and the corresponding changes in the symmetry and resonance characteristics of the aromatic rings. On the other hand, there are thermally reversible spectral changes. These reversible effects are primarily observed for the modes of the aromatic ring and the trans ethylene glycol segment. These reversible spectral changes include intensity variations and frequency shifts and are found to be linearly dependent on the measurement temperature. These reversible changes arise from changes in intermolecular and intramolecular forces as the temperature changes.
Nonlinear viscoelasticity of entangled polymer chains. II. Comparison of the slip‐link model with stress measurements at constant rate of elongation on narrow‐distribution polystyrenes
Authors: Tassin J. F. , Thirion P. , Monnerie L.
Published: April 2003

Stress measurements have been performed at constant‐strain‐rate stretching of narrow distribution polystyrenes with various molecular weights elongated up to 300% at about 30°C above the glass transition temperature. The experimental stress‐strain curves are compared with those calculated on the basis of a new treatment of Doi's molecular model (Part I). Satisfactory agreement is obtained, leading to a rather precise estimate of the equilibration time. The latter has a theoretical dependence on the square of molecular weight.
A flow visualization technique for the determination of velocity profiles in dies with circular cross sections
Authors: Crater Davis H. , Cuculo John A.
Published: April 2003

A unique retainer/transparent quartz die assembly was designed and fabricated to fit on a melt extruder. It permitted visualization of polymer flow behavior during melt spinning. Tracer particles were mixed with polymer chips prior to extrusion. A laser beam was directed through a lens system and used to illuminate the tracer particles in the melt only in a thin, vertical cross section of the transparent quartz die. Streak photography was used to determine the cross‐sectional velocity distribution of the melt as it passed through the die.
Matrix polymerization on polycationic backbones: A continuous method for following the polymerization kinetics
Authors: Blumstein A. , Milas M. , Ozcayir Y. , Bellantoni E.
Published: April 2003

A novel method of following polymerization kinetics in dilute solutions of ionic monomers is described. The method, based on conductimetry, is very well adapted to follow polymerization of ionic species in very dilute solutions, in micellar solutions, or at interfaces, i.e., in all systems in which the polymerization process involves a shift in ionic equilibria. The method is applied to matrix polymerization of p‐styrene sulfonate–(2,2,2)4‐ionene complex and yields results in full agreement with the standard spectroscopic method frequently used in such systems. The conversion curves obtained by conductimetry are satisfactorily explained by Manning's ion condensation model and are in agreement with a previously proposed mechanism, based on ion condensation theory, for matrix polymerization of ionized monomers on polyelectrolytes.
A visualization study of poly(ethylene terephthalate) flow using potential chain‐ordering die geometries
Authors: Crater Davis H. , Cuculo John A.
Published: April 2003

Streak‐photographic and stress birefringence techniques were used to analyze the flow of poly(ethylene terephthalate) through potential chain‐ordering die geometries. The streak photographs were used to determine velocity distributions and streamlines in various convergent dies. The different contours were seen to have a significant effect on the polymer streamlines and velocity distributions. The measured velocities were used to develop empirical equations, specific for each geometry, which relate velocity to position within the die and to throughput rate. Flow birefringence was used to determine the extent of molecular ordering. The optimum chain‐ordering die geometry was determined to be one which included a rapid initial decrease in cross‐sectional area. Birefringence was also used to monitor polymer flow instability. An unusual mechanism for instability was observed at intermediate throughput rates.
Effect of copolymerization and heat treatment on the structure and x‐ray diffraction of polyacrylonitrile
Authors: Gupta A. K. , Singhal R. P.
Published: April 2003

Wide‐angle x‐ray diffraction studies are reported on polyacrylonitrile (PAN) (homopolymer powder and fiber samples) and its random copolymers with methyl methacrylate (MMA) and methacrylonitrile (MAN). A new method of determination of degree of order which involves resolution of the individual maxima in the diffraction pattern is described and compared with the methods used in the literature. Comparison of the results on untreated fibers with those on untreated homopolymer powder samples, and the effect of heat treatment, suggest the molecular rod conformation of the PAN molecules in the amorphous phase. Heat treatment or the orientation induces a parallel alignment of the molecular rods in the amorphous phase, similar to the cyrstalline structure of PAN. Copolymerization with both the comonomers MMA and MAN produces qualitatively similar effect on the structure of PAN, which depends on the comonomer content. Below a critical comonomer content c* (c* = 12 mol % for MMA and 25 mol % for MAN comonomer), the crystalline lattice remains that characteristic of PAN, whereas above the critical comonomer content some modification in the crystalline lattice is apparent.
Fourier‐transform infrared study of conformational changes in plasticized poly(vinyl chloride)
Authors: Theodorou M. , Jasse B.
Published: April 2003

Fourier‐transform infrared spectroscopy has been used for the detection of conformational changes induced by plasticization in atactic poly(vinyl chloride) (PVC). The amount of short trans syndiotactic sequences decrease upon plasticization. This change depends on the amount and kind of plasticizer. Difference spectra emphasize changes in the distribution of gauche defects in the chains as a function of temperature in plasticized PVC films.
Thermodynamic properties of a small droplet of water around an ion in a compressible matrix
Authors: Dreyfus Bernard
Published: April 2003

A model is presented for the adsorption of water by ions in a deformable matrix. Only two opposing “effects” are included. The first is the mechanical resistance of the matrix to deformation which is treated within the framework of linear elasticity extended to the case of large deformations. The other effect is of electrical origin which is shown to be much more important than the purely entropic osmotic pressure. In the model only one immobile ion located at the center of a spherical droplet of water is considered. It is shown that the result does not significantly depend upon the dielectric constant of water, provided it is much larger than that of the matrix. The thermodynamic relations reveal that in fact most of the properties of the system depend mostly on the dielectric and elastic coefficients of the matrix. This simplified model should be considered as a guide for the understanding of the behavior of such systems rather than as a precise description of real materials. Some quantitative comparisons are made with a few experimental results.
X‐ray structure analysis of poly[di‐(3,4‐dimethylphenoxy)phosphazene]
Authors: Burkhart Craig W. , Gillette Paul C. , Lando Jerome B. , Beres John J.
Published: April 2003

The crystal structure of oriented poly[di‐(3,4‐dimethylphenoxy) phosphazene] (PDMP) was determined by x‐ray diffraction. Unit‐cell parameters were found to be a = 15.85, b = 19.43, and c = 9.85 Å. The unit cell is metrically orthorhombic with monoclinic space group P21. There were 48 refinable diffraction spots in the observed reciprocal lattice region, of which 28 were observed and 20 were unobserved. A refined model yielded the following residuals: R(obs) = 0.162 and 0.138. It was shown that a two‐chain unit cell with a [T3C]2 (trans, trans, trans, cis, trans, trans, trans, cis) backbone conformation was the correct structure. The dimethylphenoxy side groups were arranged in nearly parallel planes, slightly off‐normal to the fiber c axis. The polymer chains are extremely tightly packed and contain close but reasonable steric contacts.
Modeling the structure of chain‐molecule liquids: A computer simulation of the n‐alkanes C8–C30
Authors: Avitabile G. , Tuzi A.
Published: April 2003

Computer models of a series of liquid n‐alkanes were generated, allowing for continuous variation of torsion angles and of atomic positions. Torsional and intramolecular and intermolecular non‐bonded potentials were introduced. Calculated fractions of gauche bonds are slightly higher than those calculated from a rotational isomeric state model. Calculated radial distribution functions exhibit peaks in good agreement with experimental data. No directional correlation between chains is found, except at very short distances. Calculated end‐to‐end distances and radii of gyration indicate random coil conformations. These results are unaffected by extension of the range of interaction to the attractive region and by variations of temperature and density.
Particle morphology of self‐hydrolyzed acrylate polymer colloids: A 13C NMR and DSC study
Authors: Tarcha P. J. , Fitch R. M. , Dumais J. J. , Jelinski L. W.
Published: April 2003

Methyl acrylate polymer colloids can be hydrolyzed self‐catalytically by bound strong acid surface groups derived from the polymerization initiator. The kinetics of hydrolysis were earlier shown to be apparently pseudo‐zeroth‐order for any given latex, and first order with respect to surface strong acid concentration. A surface reaction zone model was proposed to explain the kinetics. This model leads to the prediction that the polymer particles will possess a core‐shell morphology after some hydrolysis has occurred. This study employs 13C NMR spectroscopy to investigate the particle morphology in the wet latex, a new application for this method. The temperature dependence of the 13C NMR integrated intensities at various levels of hydrolysis provides strong evidence that the particles do possess core‐shell morphology, and that the shell is composed of PAA/PMA copolymer. This shell is swollen and plasticized by water, resulting in greatly enhanced segmental mobility of the polymer chains as evidenced by marked narrowing of the NMR lines. Thermal measurements alone cannot distinguish particle morphology because PMA appears to be somewhat compatible with its partially hydrolyzed analog at the temperatures of measurement.
Tube relaxation: A necessary concept in the dynamics of strained polymers
Authors: Viovy J. L. , Monnerie L. , Tassin J. F.
Published: April 2003

A theory for the relaxation of large strains in polymer melts is outlined. It is based on the Doi–Edwards slip‐link model and the new concept of tube relaxation. Self‐consistency makes this concept necessary when polymer melts are concerned. The discrepancy with previous non‐self‐consistent theories is not negligible and should be easy to observe experimentally. Special attention is given to the overall size and to the mean orientation of a labeled N‐chain in a step‐strained melt of P‐chains. Using semiquantitative arguments, we predict different regimes depending on the respective values of N and P, and propose approximate evolution equations for each case. These equations may be used to design and interpret a variety of fluorescence, infrared, or NMR polarization measurements, as well as small‐angle neutron scattering experiments.
Dynamic relaxation behavior of copolymers of n‐butyl methacrylate with n‐butyl acrylate and of 2‐hydroxyethyl methacrylate with ethyl acrylate, n‐butyl acrylate, and dodecyl methacrylate
Authors: Kolařík Jan
Published: April 2003

The effect of the α‐methyl group on the mobility of the main and side chains of methacrylateacrylate copolymers has been investigated. Poly(ethyl acrylate) shows a small secondary loss maximum (attributed to the rotation of COOR side chains) at 145 K, while in the case of poly(n‐butyl acrylate) this relaxation process is smeared out or possibly absent. On the contrary, poly(n‐butyl methacrylate) and poly(2‐hydroxyethyl methacrylate) exhibit secondary relaxations at about 278 and 301 K, respectively. From the dynamic mechanical response spectra of methacrylate‐acrylate copolymers one can see that the removal of the α‐methyl group causes a qualitative change in the molecular mechanism of the secondary relaxation, presumably as a consequence of the different participation of the main chains. The existing data, however, are insufficient to quantify these differences. The low‐temperature relaxation attributed to internal motion within the side groups is not distinctly affected by the presence of α‐methyl groups. If both components of the copolymer display the low‐temperature relaxation (above 77 K), the loss maxima preserve their identity to a large extent. The effect of copolymer composition on the main (glass) transition temperature has been described by means of a one‐parameter equation.
Study of light‐scattering changes induced in tRNA solutions by a strong optical field of picosecond pulses
Authors: Dobek A. , Deprez J.
Published: April 2003

Changes in the light‐scattering components (λ = 0.53 μm) induced by a strong picosecond optical field (λ = 1.06 μm) applied to macromolecular transfer ribonucleic acid (tRNA) solutions were studied. Two beams were polarized vertically, and the intensity of the vertical and horizontal components of the light (λ = 0.53 μm) scattered at an angle of 90° were measured. The electric field of the strong 30‐ps laser pulse was 5.0 × 103 esu cgs. The experimentally determined changes allowed for calculation of the mean third‐order optical polarizability c, and its anisotropy δc. The measurements were performed in three different solutions: salt free, with magnesium ions, and without magnesium ions. Changes in tRNA structure reflected in changes of nonlinear light scattering, third‐order optical polarizability, and its anisotropy were observed.
The solid‐state polymerization and physical properties of bis(ethyl urethane) of 2,4‐hexadiyne‐1,6‐diol. II. Resonance Raman spectroscopy
Authors: Galiotis C. , Young R. J. , Batchelder D. N.
Published: April 2003

Resonance Raman spectroscopy has been used to measure the frequencies of the vibrational modes of the polymer backbone of fully and partially polymerized crystals of an ethyl urethane diacetylene. The data have assisted in the assignment of crystallographic structures to the different modifications of the crystals. Effective interatomic force constants have been derived and used to estimate the Young's modulus. For fully polymerized crystals a value of approximately 76 GPa was found. The dependence of the frequencies on elastic tensile strain parallel to the polymer chain direction was determined. By comparing the strain dependence of frequencies of partially polymerized singlecrystal fibers with those expected for model composites, it was concluded that the polymer chains in thermally polymerized crystals are considerably longer than in those polymerized using γ rays.
Flow characteristics of poly(ethylene terephthalate) deduced from pressure drop measurements
Authors: Crater Davis H. , Cuculo John A.
Published: April 2003

A unique capillary die was designed which made possible the measurement of extrusion pressure at various locations along the capillary length. Entrance pressure drops, exit pressures, and other rheological characteristics were determined for the flow of poly(ethylene terephthalate) through this extrusion apparatus. The effect of die entrance angle, extrusion temperature, throughput rate and polymer molecular weight were considered. Two samples differing in molecular weight exhibited power‐law behavior at shear rates below 1000s−1. The entrance pressure drops and exit pressures were observed to increase with increasing molecular weight; furthermore, at a specific temperature, both‐increased with increasing shear rate. The values for entrance pressure drop obtained using Bagley analysis were consistently higher than those obtained from direct measurements.
Thermal effects on liquid‐crystalline order in polymers with mesogenic side groups
Authors: Shilov V. V. , Tsukruk V. V. , Lipatov Yu. S.
Published: April 2003

X‐ray studies on polymers with phenyl benzoate side groups separated from the main chain by spacer groups of various lengths have been performed. It was found that the dimensions of liquid‐crystalline regions are 15–20 nm, and they contain four to six close‐packed layers. Thermal changes in x‐ray scattering are associated with the variation of sizes and concentration of liquid‐crystalline regions determined by the mobility of the main chain.
Morphological and structural changes in a copolymer of glycolide and lactide occurring as a result of hydrolysis
Authors: Fredericks Robert J. , Melveger Alvin J. , Dolegiewitz Lawrence J.
Published: April 2003

The changes in the structure and morphology of a random copolymer containing 92 mol % glycolide units and 8 mol % lactide units as a function of in vitro hydrolysis have been studied. A number of techniques, such as wide‐angle x‐ray diffraction, small‐angle x‐ray scattering, density measurements, infrared spectroscopy, and viscometry were employed in this study. The results showed that the hydrolytic attack was initiated in the amorphous areas of the polymer. After 28 days in the in vitro medium most of the amorphous areas had been chemically converted to lower‐molecular‐weight species such as oligomers of poly(glycolide‐co‐lactide). These low‐molecular‐weight species become water solble and are removed rapidly after day 28. Thus the fiber takes on a Swiss cheese character as the amorphous matter is hydrolyzed and eventually dissolved. As hydrolysis proceeds further, the crystalline areas of the polymer are attacked and eventually removed from the fiber by solubilization. The resulting voids in the fiber are eventually filled by a “collapse” of the structure. The role of the amorphous areas of the polymer in controlling the tensile strength of the suture is discussed.
A far‐infrared study of ionic interactions in poly(styrene sulfonic acid) ionomers
Authors: Mattera Vincent D. , Risen William M.
Published: April 2003

The far‐infrared spectra of poly(styrene sulfonic acid) (PSSA) ionomer films containing alkaline and alkaline earth ions have been studied, and strong, broad bands, whose frequencies are cation dependent, have been observed and assigned to cation motion. The force field elements for cations vibrating at sulfonate‐containing sites have been obtained for different models of the cation‐motion vibration. The effects of hydration, dehydration, and thermal annealing are discussed in light of ion clustering in these materials.
Studies on molecular motion of polysaccharides in the solid state by broad‐line nuclear magnetic resonance
Authors: Nishinari Katsuyoshi , Tsutsumi Akihiro
Published: April 2003

Broad‐line NMR measurements have been carried out on solid amylose, pullulan, and dextran in order to shed light upon the relations between different modes of linkage of glucose residues and physical properties. Rotation of the methylol group attached to the C5 atom around the C5C6 linkage and the libration of glucose residues around the α‐1,6 linkage are suggested as the origins of the observed decrease of the second moment with increasing temperature.