bluuebunny/crossref_metadata_2025 huggingface dataset:
Lamellar diffusion during heat treatment in meltcrystallized low‐density polyethylene
Authors: Rueda D. R. , Martinez‐Salazar J. , Calleja F. J. Baltá
Published: April 2003

The annealing behavior of low‐density melt‐crystallized polyethylene is discussed in terms of an unprecedented lamellar diffusion mechanism. For this purpose a combined small‐angle x‐ray diffraction (SAXS) and differential scanning calorimetry (DSC) study has been carried out. The presence of an initial double‐lamellar population is directly evidenced by electron microscopy of freeze‐cut and stained sections. The intercalation of thinner lamellae within the dominant wide‐lamella population gives rise to an x‐ray periodicity of 220 Å (structure I). The independent stacking of thinner lamellae within the material contributes to a second periodicity at 110 Å (structure II). During annealing at successively higher temperatures TA, the low‐molecular‐weight components from the thin lamellae progressively diffuse out of the double population, reinforcing the stacks of thinner lamellae. At the melting temperature of the thinner crystals a complete segregation of these lamellae takes place, and a new periodicity (structure III) corresponding to stacks of collapsed thick lamellae emerges. The periodicity of structure III increases further with TA. The thin lamellae of structure II can be extracted by a solvent, removing the corresponding SAXS peak and DSC maxima. The partial removal of thin lamellae from structure I by means of solvent extraction concurrently yields a decrease of the SAXS period. The present results suggest that molecular segregation of a low‐molecular‐weight fraction, contributing to the population of thinner lamellae, occurs during annealing.
Piezoelectric properties and molecular motion of poly(β‐hydroxybutyrate) films
Authors: Ando Yutaka , Fukada Eiichi
Published: April 2003

Piezoelectric, elastic, and dielectric properties of films of poly(β‐hydroxybutyrate) (PHB), an optically active natural polymer, were measured as functions of frequency and temperature. In mechanical properties, three relaxation processes were observed at 10 Hz: the α dispersion at 130°C, the β dispersion at room temperature, and the γ dispersion at −120°C. It was concluded from x‐ray diffraction and the thermal expansion coefficient that the α dispersion can be ascribed to thermal molecular motions in the crystalline phase, that the β dispersion is the primary dispersion due to the glass transition, and that the γ dispersion is related to local molecular motion of the main chains in the amorphous phase. Piezoelectric relaxations were also observed in these relaxation regions. It is proposed that the high‐temperature process is due to ionic dc conduction. The piezoelectric relaxation at room temperature is ascribed to the increase of piezoelectric activity in the oriented noncrystalline phase, in which the sign of the piezoelectric modulus is opposite to that in the oriented crystalline phase.
Dependence of the elastomeric properties of bimodal networks on the lengths and amounts of the short chains
Authors: Mark J. E. , Tang M.‐Y.
Published: April 2003

Bimodal elastomeric networks were synthesized by tetrafunctionally end‐linking very short and relatively long hydroxyl‐terminated chains of poly(dimethylsiloxane). Decrease in the molecular weight of the short chains (from 880 to 660 to 460 g mol−1) generally results in significant increases in ultimate strength and energy for rupture. Decrease in the number of short chains, however, causes these two quantities to go through a maximum. Too many short chains gives essentially a brittle thermoset, and this precludes any upturn in the modulus from the limited extensibility of the short chains. Having too few short chains makes their limited extensibility irrelevant since the entire macroscopic deformation can then be taken up by the long chains present in the network.
Longitudinal acoustic mode in polymers. VII. Surface structure from swelling studies of freeze‐dried polyethylene single crystals
Authors: Chang Chih , Krimm S.
Published: April 2003

Raman longitudinal acoustic mode (LAM) spectra have been obtained from freeze‐dried polyethylene single‐crystal samples swollen in decalin. The changes in ν(LAM) have been studied as a function of molecular weight, temperature of crystallization, and temperature of measurement. These data, together with knowledge of how terminal “defects” influence ν(LAM) of the trans stems, lead to the conclusion that surface folds and cilia are the components responding to the swelling agent. The analysis also shows what the relative effects of these structures are as a function of molecular weight and crystallization temperature. This study indicates that cilia are primarily responsible for the large increases in x‐ray long period observed for swollen single‐crystal mats.
Interpretation of anomalous sorption kinetics in polymer‐penetrant systems in terms of a time‐dependent solubility coefficient
Authors: Petropoulos J. H.
Published: April 2003

A formulation of the molecular relaxation model of anomalous diffusion in polymers, in terms of a time‐dependent solubility coefficient, which was previously introduced and studied by us, is discussed here in greater detail. A full account of the methods of application of the treatment is given and the prediction of typical absorption and desorption kinetic features characteristic of glassy polymer‐good swelling agent systems, including Case II absorption, is demonstrated.
A quantitative electron microscopic study of the crystallite structure of molecular weight fractions of linear polyethylene
Authors: Voigt‐Martin I. G. , Mandelkern L.
Published: April 2003

Utilizing thin‐section techniques, transmission electron microscope studies were performed on a series of bulk‐crystalized fractions of linear polyethylene covering the range M = 5 × 103−6 × 106. The crystallization conditions were varied from long‐time isothermal to rapid quenching. Quantitative analysis could be carried out on such samples crystallized under controlled conditions. The crystallite thickness distributions and long periods are presented in terms of histograms. From these data the degree of crystallinity can be calculated and was found to compare favorably with that from other methods. The amorphous thickness increases significantly with molecular weight for all modes of crystallization. On the other hand, the crystallite thickness is essentially independent of molecular weight for very rapid crystallization, and shows a complex dependence on chain length for isothermal crystallization. The tilt angle, the angle of inclination of the chain axis with the lamellar basal plane, has also been determined. There is a tendency for this angle to increase with decreasing crystallization temperature. This observation can be related to the crystallization mechanisms.
Molecular aggregation and mechanical properties of Kapton H
Authors: Kochi Masakatsu , Shimada Hiromichi , Kambe Hirotaro
Published: April 2003

Molecular aggregation of Kapton H (KH) was investigated by small‐angle x‐ray scattering (SAXS). Superstructure parameters were estimated using a one‐dimensional model, taking into account that the SAXS from KH is anisotropic out of the film plane. The results show that KH has a two‐phase structure with a volume ratio of the ordered to the less‐ordered phase of about 1:1. The β dispersion in dynamic mechanical properties is reasonably ascribed to oscillations of p‐phenylene groups in the main chain.
Birefringence of amorphous polyoxides: Stress‐optical behavior of poly(3‐methyltetrahydrofuran)
Authors: Saiz Enrique , Tarazona María P. , Riande Evaristo , Guzmán Julio
Published: April 2003

The stress‐optical behavior of an unswollen elastomeric network of poly(3‐methyltetrahydrofuran) was measured for elongation ratios a in the range 1.182–1.549, at several temperatures between 20 and 60°C. No evidence of strain‐induced crystallization was found; moreover, the dependence of birefringence Δn on true stress f/A was linear in the interval of α investigated. Values of Δa ranged from 2.4 to 2.8 in units of 10−24 cm3, in the temperature range studied, with a temperature coefficient 3.1 × 10−3 K−1. Theoretical calculations carried out with the rotational‐isomeric‐state model gave values of Δa noticeably smaller than the experimental results; however, a small increase in the backbone valence angles θ improved the theoretical result of Δa without worsening that of the dipole ratio. Analysis of the Δa results seems to corroborate the conclusion obtained through the study of dipole moments concerning the preference for nucleophilic attack on the less hindered α carbon in the monomer. Theoretical and experimental values of the temperature coefficient of Δa were in clear disagreement; a qualitative explanation for this discrepancy is discussed.
Analysis of the longitudinal acoustic mode in linear aliphatic polyesters
Authors: Chang Chih , Wang Y. K. , Waldman D. A. , Hsu S. L.
Published: April 2003

Two intense modes are observed in the low‐frequency Raman spectra of as‐grown and annealed linear aliphatic polyester single crystals. Our experimental data in conjunction with theoretical normal mode calculations of several model oligomers reveal the two bands observed to be vibrations of the longitudinal acoustic mode type. The unbalanced mass units associated with the ester groups couple the transverse and longitudinal motions, giving rise to the multiple modes.
New treatment of the theory for small‐angle x‐ray scattering with applications to polystyrene crazes
Authors: Tang Ming‐Ya , Fellers John F. , Lin J. S.
Published: April 2003

The phenomenon of surface scattering of electromagnetic waves by single or multiple layers of films is reviewed and a special treatment for the total reflection of x rays is developed. This theory is applied to the analysis of the surface scattering observed in small‐angle x‐ray scattering (SAXS) studies of two‐phase matter in polymers having lamella stacks or a flat interfacial boundary structure. Important features of this vector theory are the ability to calculate the surface scattering invariant, the absolute scattering intensity, and the surface roughness, which gives rise to dispersion of specular reflection from perfectly smooth surfaces. By considering the interfacial surface roughness of polystyrene crazes, the surface scattering spectrum is calculated theoretically and compared with some experimental results. Also the theory is presented in such a way as to compare surface scattering with volume scattering; i.e., both two‐ and three‐dimensional scattering events can be simultaneously treated. This provides a new basis for quantitative analysis of crazes in polystyrene.
Synthesis and conductivity of poly acene quinone radical polymers
Authors: Dunn Lee C. , Ford Warren T. , Hilal Nabil , Vijayakumar Pormimilla S. , Pohl H. A.
Published: April 2003

Polymers with conductivities from 8.6 × 100 to 7.3 × 10−6 (ω cm)−1 at 2–12 kbar were prepared by zinc‐chloride‐catalyzed condensation of polycyclic aromatic hydrocarbons, heterocycles, and quinones with pyromellitic dianhydride, tetrabromophthalic anhydride, and tetrachlorophthalic anhydride at 450°C. These materials are stable in air and exhibit strong electroactive character without addition of oxidizing or reducing agents (dopants).
Rebuttal to “comments on ‘some evidence against the existence of the liquid–liquid transition. IV. The temperature dependence of shear viscosity’”
Authors: Orbon Stephen J. , Plazek Donald J.
Published: April 2003

Data on the temperature dependence of viscosity obtained on three different polystyrenes with narrow molecular weight distributions are fitted to the Vogel, Fulcher, Tamman, and Hesse (VTFH) equation as well as to two intersecting Arrhenius lines. Both fits are optimized by means of computer programs. The data were chosen to fit the requirements stated by Boyer. The results of the analyses support the earlier conclusions that temperature‐dependent viscosity data do not indicate the presence of any liquid‐liquid transition TLL above the glass temperature Tg. In addition, evidence is presented which indicates that the viscosity at Tg of high‐molecular‐weight polystyrenes is proportional to the 3.4 power of the molecular weight. Hence Tg is not an isoviscous temperature.
Linear polymers in nonhomogeneous flow fields. II. The cross‐stream migration velocity
Authors: Brunn P. O.
Published: April 2003

The cross‐stream migration velocity v⊥ is that part of the velocity of a particle which has no component in the direction of the undistrubed flow. In order to obtain v⊥ for bead–spring model macromolecules, it is necessary to compute the trace of the matrix product \documentclass{article}\pagestyle{empty}\begin{document}$ \underline \ell \cdot \underline {{\rm \hat C}} $\end{document}, where \documentclass{article}\pagestyle{empty}\begin{document}$ \underline \ell $\end{document} denotes the migration matrix and \documentclass{article}\pagestyle{empty}\begin{document}$ \underline {{\rm \hat C}} $\end{document} is the modified Kramer's matrix. In this paper this is done via an eigenvalue calculation, where the eigenvalues are estimated by using the Rouse eigenfunctions. The results are then checked against the few known exact results and excellent agreement is found. It turns out that v⊥ depends on the third power of the molecular weight for free‐draining polymers. The dependence upon molecular weight becomes weaker with increasing hydrodynamic interaction until, in the nondraining limit, v⊥ ∝ M2.5. A simple yet accurate formula for v⊥ is proposed. In conjunction with the results for D (of Part I), purely rotational flow fields are shown to be characterized by a single parameter, the particle Peclet number Pe. Up to a constant of order one (actually a function of the hydrodynamic interaction parameters h* and h, which can vary only between 0.8 and 2.057), Pe depends only upon D, the mean‐square equilibrium extension R, and q0, the magnitude of the maximum shear rate for the flow.
A simple theoretical study of the dissolution of block copolymer molecules into their own microphases
Authors: Krause Sonja
Published: April 2003

A simple theoretical treatment of microphase separation in block copolymers [S. Krause, Macromolecules, 3, 84 (1970)] has been extended to the case in which individual molecules of the block copolymer may dissolve in one or the other of the microphases. When the free energy driving force for microphase separation is near zero, the minimum free energy state of the system has a relatively high concentration of block copolymer molecules dissolved in one or in both of the microphases, depending partly on the percent composition of the block copolymer. The theoretical predictions are compared with experimental data in the literature.
An analytical solution for diffusion in a shrinking body
Authors: Viollaz Pascual
Published: April 2003

An analytical solution for the equation that describes the mass balance for a solvent diffusing out of a shrinking body gives the variation of the half‐thickness of an infinite slab and its diffusant content as functions of time. This solution is compared with numerical results obtained previously for a slab of finite thickness.
Dependence of degree of crystallinity and melting point on time and temperature of annealing for γ‐irradiated polytetrafluroethylene
Authors: Takenaga Mitsuru , Yamagata Kyozo
Published: April 2003

The annealing behavior of polytetrafluoroethylene (PTFE) irradiated with 1 × 105 R of γ rays has been studied in terms of the degree of crystallinity and the melting temperature. At short annealing times the crystallinity changes rapidly to a level characteristic of the annealing temperature. It seems that the crystallization arises from transport of chain segments in noncrystalline regions. The increase in crystallinity at long times of annealing is linear in the logarithm of time. This process is mostly due to elimination of voids formed during γ irradiation, but it also involves slight lamellar thickening and crystallization to form extended‐chain regions.
Defect morphology in oriented systems
Authors: Meakin Paul , Scalapino D. J.
Published: April 2003

In fibrils composed of highly extended chains, a characteristic clustering of defects into laminae perpendicular to the chain axes is often found. One model suggested to explain this morphology assumes that initially the defects are randomly distributed but that under heat treatment the system undergoes a spinodal phase separation in which the defects cluster to form the laminar structure. Here we report results obtained from numerical simulations which support this picture. We then explore the more general question of the response of such a nonequilibrium system to small imposed patterns. We examine under what conditions the patterns are amplified or attenuated.
Polymer decoration: The orientation of polymer folds as revealed by the crystallization of polymer vapors
Authors: Wittmann J. C. , Lotz B.
Published: April 2003

A new technique of decoration of the fold surface of polymer crystals is described. It is similar in methodology to gold decoration, but makes use of vapors of crystallizable polymers, principally polyethylene, as decorating material. Upon condensation and crystallization, the highly anisometric decorating molecules become oriented parallel to the fold direction. They build up small crystalline lamellae which, seen edge‐on, appear as elongated rods and can be easily observed by conventional transmission electron microscopy. This decoration technique reveals the sectorization of polymer single crystals grown from solution. It can be used to determine the local fold orientation (with a resolution of ca. 10 nm) of polymers crystallized under a wide range of conditions, including crystallization from the bulk. The technique reveals that under all crystallization conditions so far investigated the outermost part of the polymer fold surface is relatively ordered, and the folds and/or loops are, as a rule, oriented nearly parallel to the macroscopic growth front.
Diffusion study of a polymer–diluent system using the optical mass transport method
Authors: Hakemi H. , Krigbaum W. R.
Published: April 2003

Thermotropic polymers and low‐molecular‐weight mesogens share many common textural features. This circumstance is exploited to determine diffusion coefficents in a system consisting of a cholesteric polymer and a low‐molecular‐weight nematogen using the recently developed optical mass transport method. The self‐diffusion coefficient and its concentration dependence were determined by using a distance–time approach, whereas the time dependence of the mutual diffusion coefficient was evaluated by a conventional concentration–distance analysis of the diffusion profile. Comparison with literature data indicates satisfactory agreement. The coefficient of the scaling law relating the self‐diffusion coefficient and concentration is in accord with the value predicted by de Gennes for semidilute polymer solutions.
Molecular orientation in stretched poly(vinyl alcohol). I. NMR anisotropy and birefringence
Authors: Spegt P. , Meurer B. , Hornick C. , Weill G.
Published: April 2003

The second and fourth moments of the proton resonance line in stretched poly(vinyl alcohol) samples have been measured by a pulse technique. Their anisotropy has been analyzed at different elongation ratios λ. The use of the second and fourth moments gives an interesting cross‐check on the reliability of the results. Despite the fact that the lattice sums required for absolute determination of the orientation cannot be calculated, coefficients related to the second and fourth moments of the orientation distribution function can be compared to the prediction of the quasiaffine orientation scheme for the crystalline phase and to the experimental values of the birefringence as a function of λ. It is shown that NMR clearly detects the onset of the orientation of the amorphous chains above λ ≈ 4.
Numerical study of the phase behavior of rods in solution: Warner–Flory model with polydisperse system of rods
Authors: Moscicki J. K.
Published: April 2003

Phase equilibria of polydisperse rods in solution are studied in terms of the Warner–Flory model. Numerical calculations are made with a Gaussian‐like asymmetric distribution of rod lengths. The aim of these studies is to investigate (i) the dependence of the phase diagram on the shape of the polydispersity distribution function and (ii) the isotropic–anisotropic phase separation within the coexistence range. It is shown that, as a consequence of polydispersity, even for a narrow distribution, the phase diagram is very simple, with only one type of anisotropic phase present. However, within the biphasic range, the properties of the anisotropic phase vary significantly with temperature. At high temperatures, they are essentially governed by steric effects and at low temperatures by both steric effects and soft anisotropic interactions between the rods.
Crystallization of bisphenol‐A polycarbonate induced by organic salts: Chemical modification of the polymer. II. Model reactions
Authors: Bailly Ch. , Legras R. , Mercier J. P.
Published: April 2003

In the presence of sodium o‐chlorobenzoate, bisphenol‐A diphenylcarbonate (BADPC) undergoes complex chemical modifications from 170°C. Reaction between BADPC and minute amounts of salt produces sodium phenoxide end groups which undergo a fast exchange reaction with the carbonate groups of BADPC. In a closed system, an equilibrium molecular weight distribution is progressively attained which agrees fairly well with the one predicted from a simple model based on Bernoulli statistics. In an open system, the equilibrium is continuously displaced by the evaporation of volatile diphenyl carbonate. This leads to a steady increase of the molecular weight.
Fourier‐transform infrared investigation of conformational changes occurring at the yield point in uniaxially drawn atactic polystyrene
Authors: Theodorou M. , Jasse B. , Monnerie L.
Published: April 2003

Fourier‐transform infrared measurements on atactic polystyrene have been made during application of strain. On passing through the yield point, spectra indicate an increase of the amount of the higher‐energy gauche conformation corresponding to the conformational distribution observed at 30°C above the glass transition. The trans conformation recovers after yield. The results are in agreement with the theory of Robertson but do not allow the validity of his model to be unambiguously established.
Hydrogen bonding in nylon 66 and model compounds
Authors: Garcia Dana , Starkweather Howard W.
Published: April 2003

Fourier‐transform infrared spectroscopy was used to study the hydrogen bond‐breaking process in nylon 66 and two model compounds. The resulting enthalpy and entropy values indicated that while there is no interaction between adjacent amide groups in the polymer chain, there is, nevertheless, a substantial cooperative effect in the transverse hydrogen bond direction. We have also established that any analysis of hydrogen bond breaking in semicrystalline polymers (i.e., nylon 66) below the melting point should include a crystallinity correction factor. Extrapolation of our data above the melting point of nylon 66 yielded a 26% retention of hydrogen bonding.
Copolyesters exhibiting a thermotropic cholesteric phase
Authors: Watanabe J. , Krigbaum W. R.
Published: April 2003

Mesomorphic copolymers were synthesized by incorporating varying ratios of azelaic acid and (+)‐3‐methyl adipic acid into copolyesters based upon 4,4′‐dihydroxybiphenyl. Introduction of the phenylene (+)‐3‐methyl adipate unit broadens the temperature range of the nematic phase of the azelate homopolymer and, at the same time, produces a chiral nematic (cholesteric) mesophase which exhibits various iridescent colors. Circular dichroism measurements were used to determine the pitch of the cholesteric liquid crystals. The pitch decreased gradually with increasing temperature, and the inverse pitch increased in direct proportion to the molar content of the units containing (+)‐3‐methyl adipate. The twisted cholesteric structure could be conserved by quenching to produce films with various colors at room temperature. Annealing these films at a temperature immediately below that of the crystal–mesophase transition improved the regularity of the cholesteric structure.
Rheo‐optical studies of concentrated polystyrene solutions subjected to transient simple shear flow
Authors: Zebrowski Beth E. , Fuller Gerald G.
Published: April 2003

Concentrated polystyrene solutions were investigated on the inception and cessation of simple shear flow by means of the technique of two‐color flow birefringence. Both monodisperse solutions of various molecular weights and bimodal mixtures were studied. The molecular weight affected both the amount of overshoot in the birefringence and the response time on the inception of shear flow. Large overshoots in birefringence, up to 250%, and undershoot in the orientation angle were observed. The shear stress and the first normal stress difference were calculated by using the stress–optical rule. The amount of strain at the peaks in the stress growth curves are presented along with the steady‐state viscosity and primary normal stress coefficient. The experimental results are compared qualitatively with theoretical predictions of various molecular models.
Bead–spring model for adsorbed polymer chains in shear flow: Hydrodynamic interaction
Authors: Goh C. J. , Phan‐Thien N. , Atkinson J. D.
Published: April 2003

We consider the hydrodynamic interaction between two absorbed polymer chains in a simple shear flow, each modeled by a bead connected to the wall by a linear spring. It is concluded that hydrodynamic interaction between the beads or between the beads and the wall cannot be responsible for the experimentally observed increase in hydrodynamic thickness.
Monte Carlo simulation of the crystal structure of the low‐temperature phase of polytetrafluoroethylene
Authors: Yamamoto Takashi
Published: April 2003

An energy analysis based on molecular field theory and Monte Carlo simulation is carried out for the crystal structure of the low‐temperature phase of polytetrafluoroethylene (PTFE). PTFE molecules in right‐handed and left‐handed 13/6 helical conformation are assumed to be packed in a hexagonal array, with each molecule having 13 possible orientations around the chain axis. Interactions between nearest‐neighbor chains are calculated from van der Waals interactions between nonbonded C‐C, C‐F, and F‐F atom pairs. First, an approximate molecular field calculation is made of the critical fluctuation of the chain orientation at the order–disorder transition point. This suggests that the low‐temperature phase has two chain stems in the unit cell. The Monte Carlo calculation, similar to that used for spin systems, is then applied to the equilibrium packing mode in the low‐temperature phase. A crystal structure containing two chain stems in the unit cell is again obtained. A large amount of disorder in the chain orientation is indicated and is believed to be essential in the PTFE crystal.
Comparative study of dielectric, mechanical, and nuclear magnetic relaxations in linear polyethylene. II. Relaxation spectroscopy of the α, β, and γ loss bands with special emphasis on fine structure
Authors: Kakizaki Maeko , Kakudate Takuo , Hideshima Teruo
Published: April 2003

Dielectric, mechanical, and NMR retardation (correlation) spectra for relaxations in linear polyethylene were calculated in normalized form and intercompared. For each of the two local‐mode relaxations in the γ region, called γ1 and γ2, these spectra are found to be in excellent agreement. For the α region, the spectra for two mechanical processes, called α1 and α2, two NMR processes, called α′ and α, and one dielectric process α were calculated. Excellent agreement is found between the spectra for the dielectric α and NMR α′ processes and also spectra for the mechanical α2 and NMR α processes, due to molecular motion in the interior of crystals. However, the spectrum for the mechanical α1 process is different from that for the dielectric α and NMR α′ processes, though the activation energy for the first process is almost the same as for the other two. This behavior is interpreted on the assumption that the dielectric α and NMR α′ processes are caused by molecular motion in lamellar surface layers while the mechanical α1 process is due to grain‐boundary slip with viscous resistance of the surface layers in the boundaries. The shapes of the spectra, including the spectrum for the β process, are not affected by diluent.
Coherent elastic scattering of a reptating chain in a melt during transient relaxation
Authors: Boue F. , Osaki K. , Ball R. C.
Published: April 2003

We calculate the elastic scattering of a long chain in a polymer melt during the process of relaxation after a sudden deformation, i.e., the return to equilibrium with time, while the deformed shape is maintained. The scattering thus depends on the duration t of the relaxation, as well as on the scattering vector, and is a physical quantity characteristic of the dynamics of long chains. The reptation model of de Gennes is used as developed for deformed melts by Doi and Edwards: the chain is confined by other chains in a tube, from which disengagement by the ends is the only way of renewing its configuration. The tube diameter is taken as a parameter. We give both an analytic form and numerical evaluations. On comparison with calculations based on the Rouse model, in which the chain is assumed to be free in a viscous medium, it is seen that the experimental data (given elsewhere) should enable one to distinguish between the two models.
Quantitative aspects of internal reflection spectroscopy: Polymer surface composition measurement
Authors: Mirabella Francis M.
Published: April 2003

The use of band‐ratioing techniques in internal reflection spectroscopy (IRS) for a wide variety of polymer surface composition and orientation measurements is discussed. It is shown that quantitative data can be obtained under a wide range of experimental conditions. The effects of variations in sample contact, internal reflection element, and angle of incidence are considered in detail. The applicability and limitations of calibration procedures for the determination of surface composition under various experimental conditions are considered. The requirements for obtaining quantitative results by IRS are shown to be far more lenient than is typically assumed.
Fracto‐emission from filled and unfilled polybutadiene
Authors: Dickinson J. T. , Jensen L. C.
Published: April 2003

We further examine the mechanisms involved in the emission of electrons and positive ions from polybutadiene accompanying fracture. Experimental evidence is given in support of a previously presented model involving a microdischarge accompanying fracture which excites the fracture surfaces by particle bombardment. Calculations of the time dependence for the emission from such excitations for both isothermal and thermal stimulation from a simple trap model are presented. We conclude that both filled and unfilled polybutadiene are experiencing the same excitations except at a considerably reduced intensity for the unfilled material.
Influence of tacticity on Tβ, Tg, and TLL in poly(methyl methacrylate)s by the method of thermally stimulated current (TSC)
Authors: Gourari A. , Bendaoud Mohamed , Lacabanne Colette , Boyer Raymond F.
Published: April 2003

The thermally stimulated‐current method (TSC) has been employed to determine the temperatures and intensities of Tβ, Tg, and T > Tg for pure isotactic, pure syndiotactic, and five atactic specimens with syndiotactic triad content from 49.5 to 75%; Tg was found to increase linearly with syndiotactic triad content as Tg (°C) = 48.0 + 0.856 (% syn), with R2 = 0.970 standard error 5.6°C; Tg for the syndiotactic specimen is 136.6°C measured, 133.6°C calculated. Several atactic specimens exhibit a second glass temperature 15 to 35 K above the regression line ascribed to some pure syndio content, and/or some isotactic–syndiotactic stereocomplexes. All specimens exhibited the liquid–liquid or TLL transition (relaxation) which increases linearly with 100‐% isotactic triad content. Isotactic PMMA shows a T′LL relaxation 50 K above TLL. The Tg and TLL values obtained correlate extremely well with values from differential scanning calorimetry (DSC) determined in a separate study, as well as with most literature data. Intensities of Tg and TLL by TSC are greatest for isotactic, next for syndiotactic, with a broad, low minimum for atactic materials. The intensity of a β relaxation increases slowly from isotactic to syndiotactic. The TLL found by TSC compares well with literature values for isotactic PMMA obtained by several methods, and TLL in the atactic region compares well with literature values for atactic material. The ratio TLL/Tg ranges from 1.09 to 1.20 with no dependence on tacticity. Tg follows simple Arrhenius behavior with enthalpies of activation about one‐half of the values normally calculated from dielectric and mechanical loss. The frequency dependences of TLL and T′LL follow a Vogel–WLF relationship with temperature. The origin of TLL is discussed in terms of the Frenkel hypothesis of segment–segment interaction. Evidence for TLL and TLL from a variety of methods indicates that these two temperatures are not artifacts of the TSC method.
Effect of molecular weight on the refractive index increments of polystyrene, poly(ethylene glycol), poly(propylene glycol), and poly(dichlorophenylene oxide) in solution
Authors: Binboga Nevin , Kisakürek Duygu , Baysal Bahattin M.
Published: April 2003

The variation of refractive index increments with molecular weight has been studied using solutions of polystyrene (2.2 × 103 < Mw < 1.8 × 106), poly(ethylene glycol) (1.0 × 103 < Mw < 2.0 × 104), and poly(dichlorophenylene oxide) (3.3 × 103 < Mw < 4.8 × 105) in toluene and poly(propylene glycol) (1.2 × 103 < Mw < 4.0 × 103) in benzene. The refractive index increments of polyglycols containing aliphatic ether moieties are negative in these solvents. However, poly(dichlorophenylene oxide) polymers, which contain aromatic ether moieties, give positive values. Linear and branched halogenated poly(phenylene oxide)s show an asymptotic approach of the refractive index increment to the same limiting value, but the approach is more rapid for the branched polymer.
Lattice imaging of radiation‐sensitive polymer crystals
Authors: Tsuji Masaki , Roy Saroj K. , St. John Manley R.
Published: April 2003

The total end‐point dose (i.e., the electron irradiation dose necessary for complete destruction of the crystal lattice) was measured at 120 kV and room temperature for poly(ethylene oxide), polyethylene, isotactic polystyrene (i‐PS), poly(p‐xylylene), ramie and bacterial cellulose, and lobster chitin. On the basis of the results obtained, the possibility of lattice imaging of polymer crystals is discussed. As reported in an earlier preliminary paper, 1.1‐ and 0.55‐nm lattice fringes were resolved in i‐PS single crystals by using a conventional transmission electron microscope equipped with a device for low‐dose imaging. In this paper, the detailed procedure for lattice imaging of i‐PS crystals is described and various features of the lattice images are discussed.
The bulk viscoelastic properties of poly(styrene‐co‐sodium styrene‐p‐carboxylate)
Authors: Brockman N. L. , Eisenberg A.
Published: April 2003

The effect of up to 7.82 mol % ionic groups on the stress relaxation and dynamic mechanical (torsion pendulum) properties of poly(styrene‐co‐sodium styrene‐p‐carboxylate) was studied. The results obtained were compared with those reported elsewhere for polymers containing the same ionic groups at a different position on the polystyrene backbone (styrene‐sodium methacrylate copolymers) and with polymers containing different ionic groups at the same position (styrene‐sodium styrene‐p‐sulfonate copolymers). The results of these comparisons showed that positioning of ionic groups affects the size of ionic aggregates formed, while their type dictates the strength of the forces within the aggegrates.
Predicting glass transition temperatures of linear polymers, random copolymers, and cured reactive oligomers from chemical structure
Authors: Wiff D. R. , Altieri M. S. , Goldfarb I. J.
Published: April 2003

A reliable semiempirical method for predicting glass transition tempertures of linear polymers, random copolymers, and selected crosslinked networks from knowledge of only their chemical structure is presented. For cases in which new moieties not in the database are encountered, a scaling technique of similar moiety contributions has proven successful. The basic database was composed of 178 linear homopolymers ranging from aliphatic to aromatic heterocyclic polymers and 12 random copolymers. The crosslinked networks investigated in this study involved only diacetylene end‐group reactions.
Orientation behavior of high‐modulus polyoxymethylene produced by microwave heating drawing
Authors: Takeuchi Y. , Yamamoto F. , Nakagawa K. , Yamakawa S.
Published: April 2003

The orientation behavior of high‐modulus polyoxymethylene tapes produced by tensile drawing with microwave heating has been investigated over the draw ratio range 10–29. Young's modulus E increases monotonically with draw ratio λ and reaches 55 GPa. The volume fraction of taut tie molecules (TTMs) in the amorphous phase has been estimated by using a Takayanagi model for oriented tapes. The increase in E at draw ratios of less than 10 is mainly due to the increase in crystalline orientation (crystalline orientation function, 0.00 → 0.99). The increase in E at draw ratios of more than 10 is due to the increase both in crystallinity (volume‐fraction crystallinity, 0.84 → 0.95) and in TTM (TTM fraction, 0.14 → 0.40). The maximum Young's modulus obtainable by this method of drawing is estimated to be ca. 72 GPa from the relation between 1/E and 1/λ2.
Picosecond relaxations in hydrated polyamide‐6 observed by millimeter‐wave spectroscopy
Authors: Nie C. S. , Kremer F. , Poglitsch A. , Bechtold G. , Genzel L.
Published: April 2003

Absorption measurements at millimeter‐wave frequencies (50–151 GHz) are reported for dried and hydrated polyamide‐6. The measurements were extended over the temperature range from liquid helium to room temperature using the oversized‐cavity technique. For dried polyamide‐6 (water content ≤ 0.5% w/w), a nearly linear increase with frequency and an exponential increase with temperature of the absorption coefficient is found between 50 and 300 K. This frequency and temperature dependence is described by relaxation processes in asymmetric double‐well potentials. The observed relaxation times are on a picosecond time scale, thus suggesting an assignment to the NH…OC hydrogen bonds and the adjacent peptide unit (OCNH). Hydration results in an increase of the absorption over the whole temperature and frequency range. This is attributed to the fact that the water of hydration is adsorbed in the neighborhood of the hydrogen bonds and changes their dynamical properties. This interpretation is supported by IR‐spectroscopic measurements of the shift of amide I and amide II after hydration.
Rheological properties of rodlike polymers in solution. 2. Linear and nonlinear transient behavior
Authors: Venkatraman S. , Berry G. C. , Einaga Y.
Published: April 2003

Rheological and rheo‐optical studies are reported for isotropic solutions of the mesogenic rodlike polymer poly(1,4‐phenylene‐2,6‐benzobisthiazole) (PBT). Several PBT samples were used with average contour lengths from 95 to 135 nm. Concentrations were varied over a range just below the concentration Cc for the formation of an ordered (nematic) state. The predictions of a single‐integral constitutive equation of the BKZ type utilizing experimental estimates of the distribution of discrete relaxation times is compared with experimental data on the steady‐state viscosity ηκ, the recoverable compliance function Rκ, and the steady‐state flow birefringence as functions of the shear rate κ, with satisfactory results. The relaxation of the shear stress and the flow birefringence on cessation of steady‐state flow at shear rate κ are also compared with the single‐integral constitutive equation, and it is found that in the nonlinear response range the data can be superposed over a wide range in κ. The overall behavior is qualitatively similar to that for flexible chains, which can also be fitted by the single‐integral constitutive equations over similar ranges of η0R0κ, with η0 and R0 the limiting values of ηk and Rκ for small κ. Of course, the dependence of η0 and R0 on concentration and molecular weight differs markedly for rodlike and flexible‐chain polymers.
Crystallographic changes in cryogenically pulverized polymers
Authors: Lovinger Andrew J. , Belfiore Laurence A. , Bowmer Trevor N.
Published: April 2003

Cryogenic pulverization of polymers in liquid nitrogen results in a variety of physical and chemical changes, of which crystallographic transformations are among the earliest. These have been investigated in detail for isotactic polystyrene using x‐ray and calorimetric techniques. Amorphization was found to occur rapidly, but with concomitant decreases in crystallite sizes of only a limited extent. These changes can to a large degree be reversed upon annealing at high temperature. Similar behavior is seen also in other polymers possessing stronger intermolecular cohesion, such as polyesters and polyamides. In polymers susceptible to mechanically induced phase transformations, cryogenic pulverization causes polymorphic changes en route to amorphization: these include formation of the monoclinic phase in polyethylene and of the β phase in poly(vinylidene fluoride). Based on these results, a model is proposed for the mechanism of pulverization that incorporates both thermal and mechanical effects; this model suggests a two‐phase structure of the pulverized, particles, consisting of an amorphous skin that surrounds a damaged crystalline core.
Small‐angle polarized light scattering by spherulites
Authors: Champion J. V. , Killey A. , Meeten G. H.
Published: April 2003

The light‐scattering matrix for a three‐dimensional spherulite is derived within the Ray‐leigh‐Gans‐Debye light‐scattering approximation. New expressions for the polarized, small‐angle light‐scattering intensities IVV and IVH are derived from the scattering matrix. These expressions are compared with the IVV and IVH expressions derived for a spherulite by Stein and Rhodes. For the case of a weakly anisotropic spherulite having an average refractive index mismatch with its surroundings, the two sets of expressions predict different IVV and IVH intensities. In particular, our expressions show that the IVVand IVH patterns usually attributed to the spherulitic anisotropy and crystallinity are also predicted for an isotropic sphere. This is in accord with recent experiments.
Study of poly[bis(p‐toluene sulfonate) diacetylene] films prepared by a modification of the Langmuir–Blodgett technique
Authors: McCaffrey Robert R. , Prasad Paras N. , Fornalik Mark , Baier Robert
Published: April 2003

Coherent this films of poly[bis(p‐toluene sulfonate) diacetylene] were successfully formed by modified Langmuir–Blodgett techniques using two methods: (i) Photopolymerization of the monomer film at the gas/liquid interface and then transfer to a solid substrate, and (ii) transfer of the monomer film to the solid substrate and subsequent photopolymerization on the substrate itself. The films thus obtained were characterized by traditional force–area isotherms while on pure water subphases. Segments were transferred at either 1 or 10 dyn/cm surface pressure, in different stages of photopolymerization, to glass or germanium substrates. The films on the substrate were characterized by the methods of multiple attenuated‐internal‐reflection infrared spectroscopy, ellipsometry, contact‐potential measurement, and laser Raman spectroscopy. Our results show that the films are multimolecular and about 100 Å thick. Of special interest were the observation of significant anisotropy of oriented dipoles and the ability to obtain excellent spectral data for these very thin oriented films. Raman spectroscopic features are similar to those observed for the bulk polymer, even in the low‐frequency region. Polarized Raman spectroscopy confirmed the presence of local anisotropy in these films.
Unit‐cell dilation in model ethylene copolymers
Authors: Marks B. S. , Carr S. H.
Published: April 2003

Single crystals of model ethylene copolymers have been grown in dilute solution. The effects of narrow molecular weith distribution (MWD) and a perfectly random distribution of ethyl branches (ca. 17 per 1000 main‐chain carbon atoms) on the unit cell of this ethylene copolymer analog were examined. X‐ray diffraction on dried powder samples revealed expansions of up to 1.5% in a and 0.5% in b. a increased as a mild function of molecular weight; the dependence of b on MW was not as clearly defined. Electron diffraction studies on isolated suspensiongrown single crystals yielded lattice parameters much more strongly expanded. The large expansion in the basal plane of the unit cell is hypothesized to be accompanied by a fore‐shortening of the projected c‐axis distance. This is accomplished by and orthorhombic‐to‐hexagonal polymorphic transformation in which the chains are hypothesized to adopt a disordered helical conformation. The driving force for this transformation is electron irradiation damage of the single‐crystal specimens. The rapidity of the transformation is believed to be due to the model polyethylene crystals being in a higher‐energy, defect‐containing condition prior to irradiation.
Relationship between the functional group concentrations and the infrared reflection–absorbance of polyacrylonitrile films
Authors: Sergides C. A. , Chughtai A. R. , Smith D. M. , Schissel P.
Published: April 2003

The optical constants n and k of polyacrylonitrile (PAN) were determined in the infrared region 3100–700 cm−1 by using theoretical calculations and experimental reflectance spectra. Tests of the validity of the results obtained showed excellent agreement between the measured and the predicted k values. One k value was determined experimentally (k = 0.6155 at V = 2285 cm−1) and showed excellent agreement with that calculated theoretically (k = 0.6153). The p‐polarized light was found to be more sensitive than the s‐polarized light to the absorbance of PAN films at 77° incidence angle. This sensitivity increased rapidly with p‐polarized light for film less than 0.5 μm thick. From the optical constants obtained for p‐polarized light at 77° angle of incidence, the sensitivity of the infrared reflection‐absorbance (IR‐RA) measurements to changes in the functional group concentrations in PAN films was determined for film thicknesses in the region 0.01‐10.0 μm. The IR‐RA measurements of the CN group and the skeletal mode were for a PAN film thickness of about 0.1 μm.