bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on dilute solutions of rodlike macroions. I. Light scattering, densitometry, and cryoscopy
Authors: Lee C. C. , Chu S.‐G. , Berry G. C.
Published: April 2003

Total integrated and photon correlation light scattering have been used to study two samples of poly(1,4‐phenylene‐2,6‐benzobisthiazole) (PBT) representing two methods of precipitation to recover the polymer from the polymerization solvent. Some details of the light‐scattering instrument are given. It is found that the PBT sample is rodlike, with persistence length of at least 50 nm, but that the postpolymerization processing method influences the state of interchain aggregation. The data are augmented by measurements of freezing‐point depression to estimate the degree of protonation of PBT in sulfuric acid, and by measurements of partial specific volume to provide an estimate for the geometric diameter of the chain in solution. The results show a degree of protonation of 2–4 protons per repeating unit, and partial specific volumes that are appreciably smaller than the specific volume determined for the polymers. Similar data and results are reported for poly(1,4‐phenyl‐ene‐2,6‐benzobisoxazole) and poly(1,4‐phenylene terephthalamide).
Polymer single crystals of poly(4‐hydroxybenzoate). I. Morphology
Authors: Lieser G. , Schwarz G. , Kricheldorf H. R.
Published: April 2003

Poly(4‐hydroxybenzoate) was prepared from 4‐acetoxybenzoic acid, 4‐pivaloyloxybenzoic acid, and 4‐trimethylsiloxy benzoyl chloride by condensation without the addition of a catalyst. Although various reaction conditions were used the products were always crystalline. The morphology of the as‐polymerized crystals has been studied by transmission electron microscopy as a function of molecular weight and end‐group type. It was possible to detect morphological features during the course of reaction from oligomers to polymer which enabled us to determine the mechanisms that are likely to control chain growth for different regimes of polymerization kinetics.
Small‐angle x‐ray scattering study of density fluctuation in pressure‐densified polystyrene glasses
Authors: Curro J. J. , Roe Ryong‐Joon
Published: April 2003

Densified polystyrene glasses, prepared by cooling from the liquid state under elevated pressure, were studied by small‐angle x‐ray scattering at ambient pressure. The density fluctuation, determined from the x‐ray data, showed a decrease with increasing pressure up to about 1.5 kbar, and then leveled off to a fairly constant value. The reduction in the density fluctuation produced by the pressure is much greater than the associated decrease in the specific volume. The observed change in density fluctuation is consistent with the view that the density fluctuation in glassy polymers consists of dynamic and quasistatic components and that the first of these can be correlated with the compressibility of the glass. The present data on the density fluctuation, in conjunction with the available data on volume and enthalpy, can be interpreted to mean that in pressure‐densified glasses unfavorable chain configurations are trapped in local energy minima, and the strain energy thus stored can promote segmental motion leading to volume expansion at temperatures far below Tg. Some preliminary evidence indicating the formation of microcavities in these pressure‐densified glasses is also presented.
Microstructure rearrangement during the heat‐treatment of melt‐drawn poly(ethylene terephthalate) fibers
Authors: Gupte K. M. , Motz Heike , Schultz J. M.
Published: April 2003

Melt‐spun poly(ethylene terephthalate) fibers were isothermally heat‐treated at constant length. Microstructural changes occurring during the heat‐treatment were monitored using specific gravity, wide‐angle x‐ray scattering (WAXS), small‐angle x‐ray scattering (SAXS), optical birefringence, and static mechanical testing. Major changes in the density of the most highly oriented fiber examined occurred in times below 100 ms. For less oriented fibers, the time scale for significant density change increases to the 1–10 s range. The course of birefringence increase approximates that of the density. WAXS measurements show that crystallinity develops at essentially constant crystal perfection, but that the orientation of the crystallites first decreases and then increases with time. SAXS results show development of a four‐point pattern, the azimuthal angle of the lobes decreasing with initial orientation, with temperature, and with time. A streak transverse to the fiber axis develops more rapidly than do the lobes. A two‐stage transformation process is envisaged, the first stage being the formation of defective crystal fibrils and the second being internal rearrangement of the fibrils to form more perfect crystallites, separated by more amorphous zones. Changes in the crystallite orientation are related to constraints of the noncrystalline material on the crystallites.
Optimization of permanganic etching of polyethylenes for scanning electron microscopy
Authors: Naylor K. L. , Phillips P. J.
Published: April 2003

The permanganic etching technique has been studied as a function of time, temperature, and concentration for a series of polyethylenes. Kinetic studies show that a film of reaction products builds up on the surface, impeding further etching, an effect which is greatest for the lowest‐crystallinity polymers. SEM studies combined with EDS show that the film contains sulfur, potassium, and some manganese. An artifact is produced by the etching process which is impossible to remove by washing procedures if certain limits of time, temperature, and concentration are exceeded. For lower‐crystallinity polyethylenes multiple etching and washing steps were required for optimal resolution. Plastic deformation during specimen preparation, whether from scratches or freeze fracturing, enhances artifact formation. When appropriate procedures are used virtually artifact‐free surfaces can be produced allowing a combination of permanganic etching and scanning electron microscopy to give a rapid method for detailed morphological characterization of bulk specimens.
Nonlinear viscoelasticity of entangled polymer chains. I. Response of the slip‐link model to elongation strains
Authors: Thirion P. , Tassin J. F.
Published: April 2003

The theoretical stress relaxation of polymer melts is derived from a new solution of the response of Doi's slip‐link model in the plateau zone of the rubberlike part of the spectrum. The results of this treatment, based on the application of the statistical theory of elasticity to a virtual transient network of monodisperse entangled chains, are applied to the calculation of stress‐strain relations for uniaxial extension performed at constant strain rate and to that of stress relaxation after such an elongation.
Bisphenol‐A polycarbonate–diluent interactions
Authors: Belfiore L. A. , Cooper S. L.
Published: April 2003

The effect of low‐molecular‐weight miscible additives on the sub‐Tg (β) relaxation process in bisphenol‐A polycarbonate (BPAPC) was studied using high‐resolution carbon‐13 solid‐state NMR. The trend of the spin‐lattice relaxation times T1 at 50 MHz suggests that strong intermolecular interactions occur upon mixing when BPAPC is physically stiffened by the antiplasticizing diluent, diphenylphthalate. The values of 13C T1 at 15 MHz in d‐chloroform solutions for similar BPAPC‐diluent mixtures suggest that diluent effects on the megahertz mobility of the polymer occur exclusively in the solid state. These results are explained using equilibrium thermodynamics, in the Ehrenfest sense, at the second‐order glass transition temperature Tg. Theory predicts that the temperature dependence of the Flory–Huggins interaction parameter ∂χ/∂T changes abruptly as the polymer‐diluent blends are cooled below Tg from the molten state. The difference between ∂χ/∂T in the liquid and glassy states is the major factor which determines the diluent concentration dependence of Tg. A method is developed to estimate the relative magnitudes of χ for polymerdiluent blends in the glassy state.
Hard‐segment domain sizes in MDI/diol polyurethane elastomers
Authors: Blackwell John , Lee Chun Dong
Published: April 2003

Wide‐angle x‐ray line broadening methods have been used to determine the crystallite size and degree of distortion for the crystalline hard domains in MDI/diol polyurethane elastomers. Crystallite widths have been determined from the integral breadths of the 00l reflections following correction for distortions of the second kind according to the method Hosemann for polymers prepared using ethylene glycol, propandiol, butandiol, and hexandiol as the chain extender. These data relate to the width of the crystallites along the chain axis and thus can be interpreted in terms of the morphology of the hard domains. The crystallite sizes increase and the distortions decrease with increasing elongation and annealing time, and the sizes tend toward asymptotic values which correspond approximately to the average lengths of the hard‐segment chains. These results rule out any appreciable folding of the hard‐segment chains and point to a model for the hard domains formed by lateral aggregation of extended hard segments.
Halato‐telechelic polymers. VII. Viscoelastic behavior of α,ω‐divalent cation dicarboxylato polybutadiene
Authors: Broze G. , Jérôme R. , Teyssié Ph. , Marco C.
Published: April 2003

Ba, Ca, Mg, and Zn short‐length carboxylato‐telechelic polybutadienes (M̄n = 4,600) exhibit thermorheological simplicity. A secondary relaxation characteristic of ionic aggregates obeys an Arrhenius type of activation, the energy of which is in inverse proportion to the ionic radius of the cation, whereas the mean size of the ionic aggregates is proportional to it. The glass transition of the carboxy‐telechelic polybutadiene is quite independent of the degree of neutralization and of the subsequent phase separation by the metal cations. The increase in cation size favors the growth of the multiplets into layered structures. Two sets of relaxation times are reported for the smallest alkaline‐earth cation (Be). They suggest the existence of small multiplets unable to grow except into clusters.
An examination of specific interactions of esters and polyesters with chlorinated solvents by infrared and nuclear magnetic resonance spectroscopies
Authors: Garton Andrew , Cousin Patrice , Prud'homme Robert E.
Published: April 2003

Poly(ϵ‐caprolactone) and low‐molecular‐weight esters (methyl acetate and propyl propionate) were dissolved in binary solvent mixtures. The relative ability of the two solvents to associate with the ester group was then determined by examining the equilibrium between the two solvation states of the ester using infrared and nuclear magnetic resonance spectroscopies. The ability of the solvents to associate with the chosen esters was found to be in the sequence α‐hydrogenated chlorocarbons > β‐hydrogenated chlorocarbon > carbon tetrachloride ≈ aliphatic hydrocarbons. The association‐state equilibrium was also shown to be concentration dependent and the polyester was shown to become involved in specific interactions to a lesser degree than the model esters. The relevance of these results to the nature of the specific interactions in polyester/halogenated polymer blends is discussed.
Comparison of the rheological properties of linear and star‐branched polyisoprenes in shear and elongational flows
Authors: Pearson Dale S. , Mueller Susan J. , Fetters Lewis J. , Hadjichristidis N.
Published: April 2003

The rheological properties of narrow‐molecular‐weight‐distribution linear and star‐branched polyisoprenes have been determined using both shearing and stretching deformations. At all strain rates studied the tensile stress measured under transient and steady‐state conditions did not increase above the linear viscoelastic value. The absence of an enhanced tensile stress for the branched polymer is in contrast to what is observed for branched low‐density polyethylene. An explanation for the difference is proposed. Additional remarks are made about the broad distribution of relaxation times observed for star‐branched polyisoprenes and about the approach to steady state in constant‐strain‐rate and constant‐stress tests.
Carbon‐13 NMR of polyethylenes: Correlation of the crystalline component T1 with structure
Authors: Axelson D. E. , Mandelkern L. , Popli R. , Mathieu P.
Published: April 2003

The carbon‐13 spin‐lattice relaxation times T1 of the crystalline portion of a set of polyethylenes have been studied. Chain structure and crystallization conditions have been varied over the widest possible extremes so that large differences are developed in the level of crystallinity, the supermolecular structure, and the crystallite thickness. Concomitantly, the observed crystalline T1 values cover the extraordinarily wide range of about 40–4500 s. They bear a one‐to‐one relation with the crystallite thickness, which is found to be the key structural variable determining this property. A correlation with the temperature for the α‐transition can be established, which implies a similar type of segmental motions for the two phenomena. Major changes in the interfacial structure can also have a drastic influence on the value for the crystalline T1. Analysis of the magnetization decay curve also allows for a quantitative determination of the degree of crystallinity, which is found to be in excellent agreement with the corresponding value found from Raman spectroscopy.
A kinetic analysis of the gauche‐trans isomerization in semicrystalline poly(ethylene terephthalate)
Authors: Lin Shaow‐Burn , Koenig Jack L.
Published: April 2003

A series of kinetic measurements using FT‐IR have been carried out in order to clarify the mechanism of the gauche‐trans isomerization process and the time‐temperature‐transformation relationships in poly(ethylene terephthalate). Two‐stage isomerization isotherms are distinguished on the logarithmic scale of annealing time: a primary transformation stage with an activation energy of 40 kcal/mol characterized by a sigmoidal curve, followed by a linear secondary process. The activation energies of the secondary transformation obey an equation of the Arrhenius type InaT = B(1/T − 1/Tm) where 160 < T < 260°C ≈ Tm and can be used to describe the effects of annealing time and temperature on the isomerization process of PET in the secondary transformation region. On the basis of these analyses, the morphology and microstructure of PET in these temperature regimes of the isomerization process are proposed.
Epitaxial crystallization of polymers onto benzoic acid: Polyethylene and paraffins, aliphatic polyesters, and polyamides
Authors: Wittmann J. C. , Hodge A. M. , Lotz B.
Published: April 2003

Epitaxial crystallization of polyethylene, n‐paraffins, aliphatic polyesters, and various polyamides has been achieved on benzoic acid crystal substrates, specifically on their (001) crystals faces, which are made up of the aromatic rings. The epitaxial relationship is very similar for all polymers investigated: it is characterized by a unique chain orientation (parallel to the b axis of the substrate) and a plane of contact which is either the b‐c, plane of polyethylene, or crystallographically similar ones for polyesters, or the plane of the hydrogen‐bonded sheet for polyamides. Since benzoic acid is structurally similar to its alkali‐metal salts, it is inferred that the nucleating efficiency of the latter toward chemically different but structurally similar polymers may well rest on an epitaxial relationship. Finally, the highly oriented morphology made it possible, for some polyesters with a monoclinic cell, to determine the angle between the chain axis and the Z axis of the optical indicatrix, a quantity not measured so far in polymers.
The crystallite orientation distribution functions of deformed polytetrafluoroethylene: Multiple‐pulse 19F NMR spectroscopy
Authors: Brandolini Anita J. , Alvey Mark D. , Dybowski Cecil
Published: April 2003

A moment analysis of dipolar‐decoupled 19F NMR spectra of deformed polytetrafluoroethylene leads to an expansion which approximates the crystallite orientation distribution function. The resulting distributions are then interpreted in terms of this polymer's known mechanical properties, and an attempt is made to model these functions.
The production and properties of poly(vinylidene fluoride) rods oriented by drawing through a conical die
Authors: Richardson A. , Hope P. S. , Ward I. M.
Published: April 2003

Highly oriented poly(vinylidene fluoride) rods have been produced by drawing isotropic polymer through a conical die. A range of oriented products was obtained, depending on the drawing temperature and the deformation ratio achieved. At low draw temperatures the draw ratio and final modulus are comparatively low, but a high Form I crystal content is obtained. At high draw temperatures the Form I content varies greatly with draw ratio, reaching high values at large draw ratios, where the highest‐modulus samples were obtained.
Line broadening in the 13C NMR spectra of bulk polymers above Tg
Authors: Komoroski Richard A.
Published: April 2003

The effects of magic‐angle sample spinning (MAS), high‐power decoupling, and resonance frequency on the 13C NMR linewidths of bulk polyisobutylene and bulk trans‐polybutadiene are examined. The 13C linewidths increase with resonance frequency, are unaffected by high‐power decoupling, and are reduced to different extents by MAS. The dominant contribution of the natural linewidth of the polyisobutylene lines is confirmed. The two carbons of trans‐polybutadiene have approximately equal linewidths under all conditions, a result that eliminates residual chemical shift anisotropy as a major contributor to the linewidths. The large reduction of the trans‐polybutadiene linewidths with MAS, coupled with the above result, suggests that microscopic variation of magnetic susceptibility is the major factor for this semicrystalline polymer. Cross‐polarized 13C spectra of trans‐polybutadiene were obtained with and without MAS. With MAS, resonances due to the crystalline and amorphous components were resolved. The principal components of the chemical shift tensor of the vinylene carbons were obtained from the spectrum without MAS.
Studies of TSD of polyethylene electrets by a differential technique
Authors: Reboul Jean‐Pierre , Toureille Alain
Published: April 2003

The determination of charge storage and charge decay processes in polyethylene electrets by means of TSD techniques alone seems to be limited by deficiencies in resolving power and reproducibility. Therefore, in the present work, we describe a new differential technique which cancels the effects of parasitic currents and improves the reproducibility of the measurements. The dependence of the shape of thermograms on experimental poling conditions has been studied. The comparison of discharge currents from the differential technique and from the usual one has also been found to be an interesting means of investigating the charge decay processes.
Fourier‐transform infrared study of polystyrene/poly(vinyl methyl ether) blends
Authors: Garcia Dana
Published: April 2003

Fourier‐transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends are presented. Both compatible (one‐phase) and phase‐separated blends were studied. In the case of compatible PS/PVME blends, there is strong evidence for molecular interactions. The interaction spectrum was obtained by digital subtraction techniques. In contrast, no interaction is detected for the phase‐separated blends. In view of these results, molecular interactions must play a role in the compatibility of the two polymers. The merits of factor analysis and least‐squares fit methods, as pertaining to our data, are also discussed.
NMR study of the tie‐chain length distribution in oriented polymers
Authors: Zhizhenkov V. V. , Egorov E. A.
Published: April 2003

Wide‐line NMR has been used in an investigation of noncrystalline (amorphous) regions in oriented semicrystalline polymers. Nylon 6 was chosen as a model material. The tie‐chain length distribution function, the fraction of tie chains in the total number of chains in the crystallite cross section, and the relative number of taut tie chains have been determined. The data on the tie‐chain length distribution are used in discussing specific features of vitrification of the amorphous regions in oriented polymers and in prediction macroscopic mechanical properties.
Application of the transverse differential swelling stress model to the interpretation of case II diffusion kinetics
Authors: Petropoulos J. H.
Published: April 2003

Attention is called to an early observation of Case II diffusion kinetics during penetration of a liquid into a uniaxially prestretched polymer film along the axis of stretching. Application of a previously developed transverse differential swelling stress model to these experimental conditions is described. It is shown that the model can predict Case II diffusion kinetics in a physically meaningful manner and will also explain the transition of the kinetics of the above system into normal or hindered diffusion regimes as either the degree of stretching or its direction relative to that of penetration is changed.
Effect of diluents on poly(vinyl acetate) dynamics
Authors: Blum Frank D. , Dickson Jane E. , Miller Wilmer G.
Published: April 2003

The effect of diluents and temperature on segmental motion in poly(vinyl acetate) was investigated by both NMR and ESR spectroscopy. Three classes of diluents were studied: chloroform, a thermodynamically good solvent; water, a poor solvent which slightly swells the polymer and lowers its glass transition temperature; and decane, a nonsolvent so poor it does not appear to swell the polymer nor lower the calorimetric glass transition temperature. At all temperatures investigated each type of diluent increased the segmental motion of the polymer over that of the bulk sample. Under the conditions studied, 13C and 2H NMR and nitroxide spin‐label ESR data gave similar views of segmental motion of the polymer, indicating that in this amorphous polymer the segmental motion of the polymer may be safely inferred from spin‐label data.
Transport of hydrogen and carbon monoxide in highly crosslinked poly(propylene glycol) networks
Authors: Andrady A. L. , Sefcik M. D.
Published: April 2003

Previous interpretations of gas transport data in crosslinked networks have been hindered by an inability to accurately control and evaluate the network parameters. We have recently prepared a series of model networks by reacting poly(propylene glycol) with a triisocyanate crosslinking agent. The poly(propylene glycol)s had narrow molecular weight distributions and average molecular weights between 425 and 3000, so the resulting networks had uniform average molecular weights between crosslinks. Hydrogen and carbon monoxide permeabilities in membranes formed from these networks increase with decreasing crosslink density. These results indicate increased cooperative molecular motions in the networks with longer average chain lengths between crosslinks. Increasing the average molecular weight between crosslinks also reduces the discrimination between these two gases so that the separation factors decrease. For networks prepared from mixtures of poly(propylene glycol)s with different molecular weights the gas permeabilities (but not the separation factors) depend on the molecular weight distribution.
Chlorination mechanism of polyethylene crystals
Authors: Chang B. H. , Siegmann A. , Hiltner A.
Published: April 2003

A new chlorination mechanism has been suggested for polyethylene crystals. Based on electron microsocopy and infrared spectroscopy of chlorinated high‐density polyethylene single crystals, it is proposed that beyond the initial chlorination of the lamellae surfaces, which accounts for only 2‐3% chlorine uptake, the reaction proceeds through the lamellar side faces from the periphery inward. Thus at intermediate degrees of chlorination two major phases coexist: the undamaged interior regions of the lamellae and the surrounding chlorinated material. This mechanism differs from that of oxidative degradation, and also from the generally Accepted mechanism of chlorination. Rather than proceeding through the reacted fold surface into the crystalline core, it is proposed that the direction of chemical attack is prependicular to that suggested previously. This mechanism probably describes any chemically nondestructive attack on the crystalline regions of polymers in general.
Formation, structure, and elasticity of loosely crosslinked epoxy‐amine networks. II. Mechanical and optical properties
Authors: Ilavský M. , Bogdanova L. M. , Dušek K.
Published: April 2003

The mechanical and optical behavior in the dry and swollen states of loosely crosslinked epoxy networks prepared from the diglycidyl ether of bisphenol A, phenylglycidyl ether, and 4,4′‐diaminodiphenylmethane was investigated, and the weight fraction of sol in the networks was determined. The crosslinking density was controlled by an excess of diamine and by the fraction of monoepoxide. The reaction proceeded to almost full conversion of epoxy groups. With increasing content of monoepoxide or with increasing excess of diamine, the main transition region is shifted to lower temperatures. The dependence of the viscoelastic modulus on temperature and the optical behavior indicate that the networks are homogeneous. In all cases, the sol fraction is adequately described by the theory of branching processes (cf. Part I). The equilibrium modulus related to the dry state is the same irrespective of whether it is obtained by measurements in the dry or swollen state. The mechanical behavior in the rubbery state can be described by the theory of phantom networks with fully suppressed fluctuations of crosslinking (front factor A = 1) or by the theory of phantom networks with fully released fluctuations of crosslinks (front factor) A = fe−2/fe] and contribution of trapped entanglements of the Langley‐Graessley type (cf. Part I). In the analysis of the equilibrium behavior, it is advantegeous to use the plot of superimposed dependences of Ge on the gel fraction, which considerably reduces the effect of experimental inaccuracy in determination of composition and degree of conversion.
Far‐infrared and x‐ray studies on poled semicrystalline poly(vinylidene fluoride)
Authors: Latour M. , Dorra H. Abo , Galigné J. L.
Published: April 2003

Far‐infrared (FIR) Fourier‐transform transmission spectra and x‐ray diagrams of poly(vinylidene fluoride) films are examined in terms of poling‐field action on the crystalline phase (α and β forms) and on the amorphous phase. We show that the poling field induces an increase of crystallinity in the α phase as well as in the β phase, and for the latter an orientation of dipoles in the field direction. For samples containing a mixture of phases α and β we note an α to β phase transition, a rotation of the dipoles in the β phase, and an increase of the crystallinity of the sample. Part of the β phase is generated from the amorphous phase.
The thermodynamic properties of polytetrafluoroethylene
Authors: Fai Lau Suk , Suzuki Hidematsu , Wunderlich Bernhard
Published: April 2003

Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ3 of 54 K, and θ1 of 250 K, and a full set of group vibrations. Cv to Cp conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10−3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔCp of 9.4 J/K mol. The room‐temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high‐temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.
Dynamic mechanical studies of α and β relaxations of polyethylenes
Authors: Popli R. , Glotin M. , Mandelkern L. , Benson R. S.
Published: April 2003

The α and β relaxations of a variety of polyethylenes have been extensively studied using lowfrequency dynamic mechanical methods. The main focus of this work has been both the control and the quantitative measurement of the key structural factors that describe semicrystalline polymer systems. The structural factors that have been examined in detail include the level of crystallinity, the crystallite thickness, the interfacial content, and the supermolecular structure. Consequently a variety of other types of supplementary measurements were made to accomplish the necessary characterization. The location of the α transition is found to depend primarily on the crystallite thickness. There also is the distinct possibility that the interfacial structure exerts an important influence. The level of crystallinity and the supermolecular structure do not play a significant role in the location of Tα. A strong correlation is found with the carbon‐13 NMR crystalline T1, which is reported in a separate paper. From analysis of the influence of the different structural factors on the β transition, it is concluded that this transition results from the relaxation of chain units which are located in the interfacial region. The elusiveness of this transition and the contradictory reports that have existed in the literature are given a ready explanation. The enhancement of this transition by branching and copolymerization follows naturally as does its invariance with counit content.
Isothermal melting behavior of poly(L‐lactic acid)
Authors: Kishore K. , Vasanthakumari R. , Pennings A. J.
Published: April 2003

The isothermal melting behavior of poly(L‐lactic acid) spherulites has been studied in order to understand the mechanism of melting using hot‐stage microscopy. When the periphery of the spherulite melts or shrinks, the central portion undergoes thickening as a result of which the melting or shrinking rate is not linear. Annealing studies at 448 K reveal that there is an increase in melting temperature and heat of fusion with annealing time, suggesting an increase in lamellar thickness. The high activation energy (828 kJ/mol) obtained in this investigation suggests the highly complex nature of the melting process wherein both melting and thickening occur.
The effects of morphology on 1H NMR spectra and relaxation in semicrystalline polyolefins
Authors: Packer K. J. , Pope J. M. , Yeung R. R. , Cudby M. E. A.
Published: April 2003

A brief résumé is given of the role of structural heterogeneity, magnetic dipolar couplings, molecular structure, and molecular motion in determining the 1H NMR spectra and relaxation properties of heterogeneous solids such as semicrystalline polymers. Measurements of 1H spin‐lattice relaxation in laboratory (T1) and rotating frames (T) are reported for a number of solid polyolefin samples. These include solution‐crystallized and melt‐crystallized polyethylene, annealed and quenched isotactic polypropene, and isotactic polybut‐1‐ene. In addition, broad‐line 1H spectra, both normal and partially (T) relaxed, are reported for these materials as well as a number of pulsed NMR experiments having the philosophy of the so‐called Goldman–Shen experiment. Spin‐lattice relaxation (T1) for all samples is a single exponential process, whereas rotating‐frame relaxation comprises three exponential processes both on‐resonance (θ = 90°) and off‐resonance at the magic angle (θ = 54.7°), with the latter generally being much slower. The spectra show clearly the existence of components having differing degrees of mobility and, with the exception of the solution‐crystallized polyethylene, the partially (T) relaxed spectra indicate a correlation between breadth of resonance line and magnitude of T1ρ. The Goldman–Shen‐type experiments indicate a spin‐diffusional transport of magnetization between the different spectral and (T) components. A computer program has been used to simulate the NMR behavior of a three‐region system comprising repeating units of infinite lamellae of different widths, each region having different intrinsic relaxation times and spin diffusion coefficients. The results demonstrate that the observed 1H NMR behavior of these samples can be interpreted in terms of this model and that, inter alia, the long‐time T behavior reflects, qualitatively, the time taken for magnetization to diffuse a distance of the order of the dimensions of the region to which it corresponds.
Correction factors for sizing weakly anisotropic transparent fibers using light scattering
Authors: Sharma S. K. , Somerford D. J.
Published: April 2003

Correction factors defined as the ratio of the true size parameter and the size parameter deduced from Fraunhofer diffraction theory are presented for weakly anisotropic transparent fibers. These correction factors enable the Fraunhofer diffraction approximation to be used for sizing weakly anisotropic fibers from light‐scattering measurements. Fibers in the diameter range 4–50 μm and refractive index range 1.45–1.56 are considered. It is shown that for fibers having birefringence −0.005 ≤ Δm ≤ 0.01, the diameters may be obtained to within 9% accuracy if the fiber diameter lies between 4 and 50 μm.
Polypropylene spherulite morphology and growth rate changes in blends with low‐density polyethylene
Authors: Galeski A. , Pracella M. , Martuscelli E.
Published: April 2003

Morphological studies of isotactic polypropylene/low‐density polyethlene blends revealed that the shape, size, and orientation of LDPE occlusions remain undisturbed during the crystallization of IPP spherulites. On the other hand, LDPE occlusions introduce large changes in the internal structure of IPP spherulites. It was found that many new boundaries similar to those between spherulites are fromed when the crystallizing front passes the LDPE occlusion. Dead‐ended boundaries with soft LDPE occlusions at the ends give rise to an improvement of the impact properties. It was shown that LDPE obstacles do not influence significantly the IPP spherulite growth rate in thin films or in the bulk.
Theory of the rod‐to‐coil transition in polydiacetylene
Authors: Berlinsky A. J. , Wudl F. , Lim K. C. , Fincher C. R. , Heeger A. J.
Published: April 2003

A theory is proposed for the rod to coil transition in polydiacetylene 4BCMU and related polymers which is based on the hypothesis that the high‐temperature (yellow) phase consists predominantly of the cis structure, while the low‐temperature (red) phase is trans. Because the occurrence of a cis‐trans interface is energetically costly, the correlation length for either isomer remains long and the transition is sharp, much like the helix‐coil transition in the theory of Zimm and Bragg. The transition is driven by the higher entropy of the cis isomer, which is free to coil, unlike the trans or butatriene forms. The theory gives excellent agreement with optical absorption measurements and is consistent with all other experimental data for this system.
Effects of polymer chain disentanglement on NMR properties. II. 13C magnetic relaxation in polystyrene
Authors: Cohen‐Addad J. P. , Feio G.
Published: April 2003

The transverse magnetic relaxation of 13Cα nuclei has been studied in concentrated solutions of polystyrene. The magnetic relaxation rate was measured as a function of molecular weight at several temperatures (313,318, and 323 K) and at several concentrations (0.53, 0.43, and 0.34 g/cm3). The spin‐system response of these nuclei in natural abundance exhibits a characteristic evolution from pseudosolid properties to liquidlike one, induced by decreasing the molecular weight of polymer molecules. This evolution is analogous to that already observed in protons attached to polyisobutylene or polydimethylsiloxane chains; it is assumed to be induced by an increase of the disentanglement rate of polymer chains. The spin‐system response may be considered as reflecting single‐chain magnetic properties, because of the low concentration of 13CCα nuclei, although all chains are in dynamic interaction with one another. The NMR disentanglement transition is interpreted in terms of a two‐step motional averaging effect involving submolecules. A numerical analysis of NMR properties is given using a model of polymer chain relaxation based on a multiple‐mode relaxation process, characterized by (i)a terminal relaxation time τv1 depending upon M3, the molecular weight, and approximately proportional to the polymer concentration C (like the reptation time); (ii)a relaxation‐time spectrum analogous to a Rouse spectrum; (iii)a terminal relaxation time τv1 = 2.5 × 10−2s for M = 2.5 × 105, C = 0.53 g/cm3 in carbon tetrachloride at 313 K.
Molecular parameters for the prediction of polyurethane structures
Authors: Blackwell J. , Quay J. R. , Nagarajan M. R. , Born L. , Hespe H.
Published: April 2003

Recent efforts to determine the structures of poly(MDI/diol) hard segments in polyurethane elastomers have relied on the structures determined by single‐crystal x‐ray methods for diphenylmethane urethane model compounds. We have surveyed the structure of six model compounds, and have derived average values for the bond lengths, bond angles, and bond torsion angles for use in future analyses. The applicability of these averages to polymer structures is discussed, and the data are used to derive models for the poly(MDI‐butanediol) chain which are found to be consistent with the fiber repeat determine by x‐ray methods.
An analysis of the crystallization behavior of poly(ethylene oxide)/poly(methyl methacrylate) blends by spectroscopic and calorimetric techniques
Authors: Li X. , Hsu S. L.
Published: April 2003

Infrared spectra in conjunction with calorimetric measurements have been used to follow the crystallization process and microstructural changes of poly(ethylene oxide) (PEO) in poly(ethylene oxide) and poly(methyl methacrylate) (PMMA) blends. We have given particular attention to compositions containing low PEO concentrations. The crystallization behavior and the resultant microstructures of PEO are strongly perturbed by the presence of PMMA. In addition, we found phase separation and trans sequences of PEO to be present, especially at low PEO concentrations.
Solid‐state extrusion of chain‐extended polyethylene
Authors: Chuah Hoe Hin , Porter Roger S.
Published: April 2003

Billets of chain‐extended polyethylene were prepared from Alathon 7050 (Mw 59,000, Mn 19,000) in an Instron capillary rheometer by crystallization at a constant pressure of 460 MPa, at a series of teimperatures from 198 to 221°C corresponding to varying degrees of undercooling. This gives chain‐extended morphologies with a range of crystallinites and lamellar thicknesses. The billets were then solid‐state extruded at 100°C through a conical die with 20° entrance angle up to an extrusion draw ration 23.4. Thermal behavior was studied with differential scanning calorimetry. The orientation function measured by wide‐angle x‐ray diffraction showed higher orientation function measured by wide‐angle x‐ray diffraction showed higher orientation at equivalent draw ratio when the initial billets were crystallized at lower temperatures. Drawing efficiency, defined as the ratio of molecular draw ratio (from shrinkage) to extrusion draw ratio correspondingly increases, reaching a maximum of 0.71 in our solid‐state extrusion. These studies show that highly chain‐extended polyethylene, i.e., with few chain entanglements, draws poorly. Drawability was improved by increasing chain entanglements by lowering the crystallization temperature. Electron micrographs of fracture surface replicas of extrudates revealed the coexistence of undeformed, tilted, partially drawn lamellae and fibrillar structure consistent with the cahange of morphologies in Peterlin's model of plastic deformation.
The sectioning of randomly branched filamentous structures
Authors: Sellen D. B.
Published: April 2003

A theorectical analysis is given of the two‐dimensional picture observed when a three‐dimensional randomly branched fibrous structure is sectioned. The model adopted consists of randomly oriented, interconnected straight rods having either the same length or a defined distribution of lengths. Expressions are derived for the total number of fragments observed and their total apparant length per unit area projected in the plane of the section, together with the distribution function of the projectd lengths. However, the expression derived for the total projected length per unit area, one‐fourth πtρl, where t is the section thickness and ρl the fiber length per unit volume in the three‐dimensional stucture, is, however, independent of the above model. The theory is discussed in terms of electron microscopy which has been carried out by other workers on agarose gels.
Low‐temperature dielectric relaxation in poly(4,4′‐oxydiphenylene pyromellitimide)
Authors: Iida K. , Nakamura S. , Sawa G. , Waki M. , Ieda M.
Published: April 2003

The effect of end groups on the low‐temperature dielectric relaxation in poly(4,4′‐oxydiphenylene pyromellitimide) has been studied using three kinds of samples with different content of anhydride end groups. The magnitude of the dielectric loss peak, designated here the V peak, which appears near −40°C at 1 kHz, depends on the content of anhydride end groups. If a sample with few anhydride end groups is allowed to absorb water, a loss peak appears near the temperature region of the V peak, but it disappears after subsequent heating. In contrast, a sample having a larger amount of anhydride end groups exhibits a large V peak which remains even after further heating. We conclude that the Oportion of the anhydride end groups is responsible for the V peak, though there may be an additional contribution from absorbed water.
Dielectric relaxation studies of some linear crosslinked and branched polymers
Authors: Aras Leyla , Baysal Bahattin M.
Published: April 2003

Dielectric loss measurements are reported for polystyrene, crosslinked polystyrene, polyacrylamide, branched polyacrylamide, and poly(methyl methacrylate) at 1 and 10 kHz f over the temperature range −85 to +100°C. Crosslinking and branching have a pronounced effect on the dielectric relaxation spectra of polymers. The methods of preparation of these polymers and their viscosity molecular weight data are also reported.
Miscibility of poly(vinyl chloride) with ethyl acrylate 4‐vinyl pyridine copolymers
Authors: Clas S.‐D. , Eisenberg A.
Published: April 2003

Blends (50:50, w:w) of poly(vinyl chloride) (PVC) and poly(ethyl acrylate‐co‐4‐vinyl pyridine) (PEA–4‐VP) of different 4‐VP contents (2–14 mol %) were prepared. These were found to be partially miscible as evidenced by the presence of a single, through broad, tangent δ peak obtained from torsion pendulum experiments. Several possible types of interactions which might exist between PVC and PEA‐4‐VP, such as ion‐dipole, crosslinking, charge transfer, hydrogen bonding, and dipole–dipole interactions, were explored. From ultraviolet, conductance, infrared, and solubility studies, it was shown that hydrogen bonding or dipole–dipole (or possibly a combination of the two) interactions were the most likely in this system. These interactions have been suggested previously for other systems by various investigators.
Continuous measurement of dynamic tensile mechanical properties in polymer solids over a wide range of frequencies. III. Effect of absorbed water on nylon 6 at 23°c
Authors: Yokouchi Mitsuru
Published: April 2003

The dynamic tensile mechanical properties (E′, E″, and tanδ) of nylon 6 have been studied over the frequency range 10−25−102 Hz and water content up to 12.6 wt % at a constant temperature of 23°C. From the dispersion maps in the coordinates of frequency and water content, the relaxation behavior can be classified into three regions of water content: (A) dry to 2 wt %, (B) 2‐5 wt % and (C) 5 wt % to wet. For region B, it is found that the logarithmic frequency shift Δ logfα/Δx of the α dispersion per 1 wt % change of water content is 1.7. Taking into consideration that the change of glass transition temperature per 1 wt % change of water content Δ Tg/Δx is 3.7°C (according to Kettle), we find Δ logfα/ΔTg = 0.5. For regions A and C, such an evaluation cannot be made. The effect of absorbed water on the dynamic mechanical properties at 23°C is discussed in terms of two kinds of processes: (a) formation of water‐amide hydrogen bonds with free amide groups and (b) scission of amide‐amide hydrogen bonds.
Properties and chain flexibility of poly(dl‐isobornyl methacrylate)
Authors: Hadjichristidis Nikos , Mays Jimmy , Ferry William , Fetters L. J.
Published: April 2003

The glass transition temperature and characteristic ratio of poly(dl‐isobornyl methacrylate) have been determined. The results indicate that in the case of certain polymethacrylates the chain flexibility depends mostly on the bulkiness of the side group, while the glass transition temperatures depend mostly on side‐group rigidity.
Kinetics of photoinitiated free‐radical polymerization
Authors: Shultz A. R. , Joshi M. G.
Published: April 2003

Analytical expressions describing the kinetics of photoinitiated free‐radical polymerization are derived for a variety of conditions. The effect of the exponential attenuation of intensity of light in the direction of incidence in the system is carefully accounted for in each case. An attempt is made to include the depletion of initiator due to its photolysis in the kinetic scheme. The marked difference between the polymerization kinetics in well‐stirred and unstirred systems is shown by comparing them under limiting conditions. The variation of this difference with the optical density of the system is illustrated graphically. The influence of light absorption by components other than the photoinitiator (e.g., solvent, monomer) is examined. The order of the polymerization reaction with respect to initiator as determined by conventional kinetic experiments depends on the amount of light absorbed by components of the system other than the photoinitiator.
Phase segregation kinetics in segmented linear polyurethanes: Relations between equilibrium time and chain mobility and between equilibrium degree of segregation and interaction parameter
Authors: Camberlin Yves , Pascault Jean Pierre
Published: April 2003

The kinetics of phase segregation of segmented linear polyurethanes, from a homogeneous single‐phase system into a two‐phase one, have been studied by measuring the heat capacity change at the glass transition of the soft phase. The extent of phase segregation at equilibrium is a linear function of the Flory–Huggins interaction parameter χ. For χ lower than about 3, no segregation can take place. This value, higher than expected theoretically, indicates forced compatibility due to chemical links between soft and hard blocks of the segmented polyurethanes. The time required to attain equilibrium is not a function of thermodynamic parameters but of the chain mobility. A linear relation is proposed between the logarithm of equilibrium time and the viscosity of the pure soft phase.