bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface orientation of polypropylene. I. Theoretical considerations for the application of internal reflection spectroscopy
Authors: Mirabella Francis M.
Published: April 2003

A theoretical consideration of the orientation of the transverse magnetic and the transverse electric polarization vectors of the evanescent field in attenuated total reflection spectroscopy was made. It was demonstrated that near the critical angle of total reflection the transverse magnetic polarization vector approaches a purely normal orientation to the interface between the sample and internal reflection element surfaces, while the transverse electric vector is parallel to this interface. With an appropriate experimental design a set of three orthogonal electric vectors can be obtained for the analysis of surface orientations. A method to obtain high‐quality infrared spectra of polypropylene surfaces at a fraction of a degree above the critical angle was developed using a KRS‐5 internal reflection element specially cut with a 40° entrance aperture. The surface orientation of uniaxially extended polypropylene films was studied by using the proposed experimental design. It was shown that the orientation of the helix axis of the macromolecular chains of polypropylene could be qualitatively detected. A method employing the 841‐ and 809‐cm−1 bands of polypropylene was used to show that the ratio of absorbances of these bands reflects the surface orientation of the uniaxially extended polypropylene films for a set of films extended 0–500%.
Effects of copolymer composition on the formation of ionic species, hydrogen evolution, and free‐radical reaction in γ‐irradiated styrene‐butadiene random and block copolymers
Authors: Basheer Rafil , Dole Malcolm
Published: April 2003

Block and random copolymers of butadiene and styrene as well as polybutadiene and polystyrene homopolymers have been investigated with respect to formation of trapped electrons, contribution of ionic species to crosslinking, and hydrogen gas evolution due to γ radiation. The decay kinetics of the disubstituted benzyl radical has also been studied. The yields of electron trapping G(e−) are measured. The G(e−) increase linearly with increased polystyrene content in block polymers, while in random copolymer a deviation from a linear relation is observed. The contribution of ionic reactions to crosslinking is about 25–35% of the total crosslinking yield. Hydrogen production in block copolymers is approximately a linear function of the weight‐fraction additivity of the yield of hydrogen formation in polystyrene and polybutadiene homopolymers. Energy transfer from butadiene units to styrene units in random copolymers resulted in a deviation from such an additivity relation. The decay of the disubstituted benzyl free radical in block copolymers is a second‐order reaction. In random copolymer, the decay is best interpreted in terms of equation based on a second‐order decay mechanism of a fraction of the free radicals decaying in the presence of other nondecaying free radicals.
Orientation of the boundary faces in nylon‐11 lamellar crystals
Authors: Dosiere M. , Point J. J.
Published: April 2003

A semicrystalline polymer having a large repeat unit, as does nylon‐11, is particularly suitable for seeking correlation between the orientation of the lattice and the basal planes of the lamellar crystals. In filter mats of nylon‐11 single crystals, the basal planes of the lamellae are parallel to (00l) crystallographic planes; the chain axis is tilted with respect to the mat plane. By planar extrusion, bulk double oriented specimens with a nearly single texture can be prepared: the basal planes of the lamellae are parallel to (00l) planes and the chain axis is along the extrusion direction. Doubly oriented samples of nylon‐11 having a double texture have been obtained by unidirectional rolling. In these samples, the chain axes are along the rolling direction; the basal planes of the lamellar crystals are not parallel to (00l) planes. It has been proposed that lamellae consist of blocks of six hydrogen‐bonded planes shifted by one monomer unit. The parallelism between basal planes of lamellae and (00l) planes is obtained again in rolled samples annealled in contact with formic acid. Those annealed samples are similar to filter mats with respect to the orientation of the lamellar basal planes but they remain doubly oriented at the level of the unit cell; they have a long spacing larger than filter mats of single crystals.
An ESR study of the decay reaction of isotactic polypropylene peroxy radicals in air
Authors: Hori Yasuro , Shimada Shigetaka , Kashiwabara Hisatsugu
Published: April 2003

The decay of peroxy radicals trapped in irradiated isotactic polypropylene has been studied by ESR in air at various temperatures between 284 and 309 K. All the ESR spectra obtained at the various reaction stages are shown to be composed of two components arising from a mobile fraction and an immobile fraction. Only the mobile peroxy radicals decay; those belonging to the immobile fraction are stable. Various reaction mechanisms are examined in order to explain the experimental results; it is concluded that the decay reaction is controlled by diffusion of peroxy radicals and that the immobile peroxy radicals play no role in the decay reaction. Intermolecular hydrogen abstraction of the peroxy radicals, rather than intramolecular abstraction, is suggested as the rate‐determining reaction.
Molecular mechanics of photopolymerization of 2,5‐distyrylpyrazine in solid state
Authors: Swiatkiewicz Jacek , Prasad Paras N.
Published: April 2003

The molecular mechanics of photopolymerization of 2,5‐distyrylpyrazine in the solid‐state α form is investigated by a combination of Raman and electronic spectroscopic techniques. A stepwise photoreaction is used to stabilize an intermediate oligomer structure. For this purpose, the 476.5‐nm argon‐ion laser line is used to convert the monomer to the oligomer. The Raman phonon spectra reveal a homogeneous mechanism, with considerable lattice rearrangement, for the oligomerization process, which is also found to produce lattice strain. Further photoreaction of the oligomer is carried out with light of wavelength ≤400 nm from a 200‐W mercuryxenon lamp as well as with the 355‐ and 417‐nm laser lines from a Nd: Yag laser system. The Raman phonon spectra, monitored during the conversion of the oligomer to the polymer, show that initially the process starts homogeneously, with considerable lattice rearrangment. Then it turns heterogeneous, with a phase separation accompanied by a gradual ordering of the polymer product lattice. The electronic absorption spectra of the monomer are characterized and related to the stepwise photo process discussed above. Although the emission spectra show a monotonic change during the photoreaction, energy transfer from the oligomer to the monomer and from the polymer to the oligomer obscures and quantitative characterization by emission spectroscopy.
The heat of fusion of copolymers of tetrafluoroethylene and hexafluoropropylene
Authors: Starkweather Howard W. , Zoller Paul , Jones Glover A.
Published: April 2003

The Clapeyron equation has been applied to determine the heat of fusion of two copolymers of tetrafluoroethylene and hexafluoropropylene. The values obtained are within experimental uncertainty of that for the homopolymer, PTFE. This study supports the conclusion of earlier workers that the CF3 side groups are included in the crystal lattice. In both PTFE and polyethylene, C1 side groups are included in the crystal but have little if any effect on its density. We believe that the same relationship between the crystallinity and the heat of fusion can be used for both PTFE and copolymers of TFE and HFP.
Giant polarization in stable polymeric dielectrics
Authors: Vijayakumar Pormamilla S. , Pohl Herbert A.
Published: April 2003

Macromolecular solids of highly aromatized structure can exhibit giant polarization. Their structures must be capable of providing long‐range electron orbital delocalization. Intermolecular conformality of the orbitals of these huge molecules can result in ready carrier formation. The ready transport of these electronic holes and electronic carriers as polarons able to range over long molecular domains will then produce the giant polarization characteristic of the nomadic polarization mechanism. Recent developments in the synthesis and characterization of such materials new make available a new and interesting class of very stable organic dielectrics having dielectric constants in excess of 100. A number of such materials are described.
Mechanical relaxation mechanism of epoxide resins cured with acid anhydrides
Authors: Shimbo Masaki , Ochi Mitsukazu , Iesako Hiroshi
Published: April 2003

The mechanism of low‐temperature mechanical relaxation in epoxide resins cured with various acid anhydrides has been investigated by comparing dynamic mechanical properties and chemical structures of these networks. One mechanical relaxation, denoted as the β relaxation, is observed at about −70°C. The β relaxation is affected by the chemical structure of the curing agents, but not by that of the epoxide resins. In addition, the strength of the relaxation increases linearly with increasing concentration of diester linkage introduced in the network by reaction with acid anhydrides. From these results, it is concluded that the β relaxation mechanism of the anhydride‐cured systems involves the motion of diester segments included in the network structures.
Photon correlation spectra of poly(phenylmethyl siloxane) under high pressures
Authors: Fytas George , Dorfmuller Thomas , Chu Benjamin
Published: April 2003

We report polarized photon correlation measurements of bulk poly(phenylmethyl siloxane) (PPMS) with a molecular weight of about 2500 at different pressures from 1 to 1750 bar and temperatures between 269 and 308 K. In the Frequency range accessible by present‐day digital correlators, the time correlation function can measure a slow q2‐dependent diffusional process due to local concentration fluctuations and a fast α‐mode structural relaxation process. The mean characteristic times of the two processes approach each other at low temperatures and high pressures, in contrast to the behavior of the α‐ and β‐relaxation times. We should be cautious in relating the mean characteristic times for the structural relaxation process obtained by different experimental techniques, such as Brillouin scattering and photon correlation spectroscopy, because of the differnces in the probe emphasis and the extremely broad frequency distribution of such relaxation processes.
Effect of interfacial bonding on the strength of adhesion of elastomers. III. Interlinking by molecular entanglements
Authors: Gent A. N. , Tobias R. H.
Published: April 2003

Polydimethylsiloxane (PDMS) networks have been formed by end‐linking linear PDMS molecules. When a second layer is cast on top of a fully gelled lower layer, the new molecules diffuse into the surface of the lower layer and form molecular loops (“entanglements”) in the course of end‐linking with themselves. The two layers are then joined only by these macromolecular loops. Measurements have been made of the work required to separate such layers under threshold conditions, i.e., at low rates, high temperatures, and, in some cases, in the swollen state. Values of the work of detachement have been found to be 15–25 J/m2, generally about one‐half of the work of fracture of the layers themselves, and consistent with the inferred density of interlinking molecular loops at the interface. Values of the work of detachment were higher for higher densities of interlinking, roughly in proportion, and for interlinking molecular strands of higher molecular weight, in accordance with the theory of Lake and Thomas. In the absence of interlinking the work of detachment was extremely small, only about 70 mJ/m2.
Determination of elastic shear constants of polyethylene at room temperature by inelastic neutron scattering
Authors: Heyer D. , Buchenau U. , Stamm M.
Published: April 2003

The elastic shear constants of both the amorphous and crystalline regions of polyethylene have been measured at room temperature. A newly developed method is used which allows the determination of elastic constants from the coherent inelastic neutron scattering of polycrystals. A deuterated and partially oriented sample is investigated on a triple‐axis spectrometer and a time‐of‐flight instrument. The elastic constants of the crystalline regions of polyethylene are c44 = 2.1 ± 0.3, c55 = 2.2 ± 0.3, c66 = 1.8 ± 0.2, and c′ = 1/4(c11 + c22 − 2c12) = 0.92 GPa. The shear modulus of the amorphous regions is obtained as G = 0.55 ± 0.03 GPa. In connection with other experimental results the elastic constant matrix is given and compared with theoretical estimates. With simple models, macroscopic moduli are calculated which are in good agreement with published experimental data.
Transient and steady rheology of polydisperse entangled melts. Predictions of a kinetic network model and data comparisons
Authors: Liu Tony Y. , Soong David S. , Williams Michael C.
Published: April 2003

The kinetic network (KN) model discussed previously in the context of monodisperse and bimodal polymer systems is extended to polymers of arbitrary molecular weight distribution. A generalization is proposed for the flow‐dependent entanglement loss term in the structure equation, replacing the shear rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} by a new variable \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \Gamma $\end{document} which reduces to\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} for simple shear and is more appropriate for elongational and other flows. New data are obtained on shear stress transients of many kinds, using a recently developed parallel‐plate rheometer. These data and others on steady and transient flows of well‐characterized polydisperse polymers in shear and in elongation are used to demonstrate that the KN model predictions are valid. Comparisons with predictions for monodisperse polymers having the same as Mw polydisperse systems show that transient behavior—especially stress overshoot—is particularly sensitive to details of the molecular weight distribution. Further possible improvements in the theory are suggested, and the relationship of the KN model to other recent network models is discussed. The KN model has greater data fitting capabilities, with fewer parameters, than any other model available at present.
High‐modulus polydiacetylene single‐crystal fibers
Authors: Galiotis C. , Read R. T. , Yeung P. H. J. , Young R. J. , Chalmers I. F. , Bloor D.
Published: April 2003

The relationship between structure and mechanical properties of polydiactetylene single‐crystal fibers has been studied in detail. It is shown by transmission electron microscopy that the fibers have a high degree of internal perfection, with the polymer molecules aligned parallel to the fiber axes. The fibers of the dicarbazolyl derivative investigated were found to have a Young's modulus of 45 GPa and fracture strengths of up to 1.5 GPa, the strengths being controlled by defects such as surface steps. It is shown that the stiffness of the polymer backbone is similar to that of polyethylene, and the theoretical strength of the polydiacetylene singlecrystal fibers is determined to be about 3 GPa, corresponding to a fracture strain of between 6 and 8% and a force required to break molecules to the order of 3 nN. The derivative studied is also found to have good thermal stability, not degrading below 300°C, and excellent creep resistance up to at least 100°C. The possibility of using the single‐crystal fibers in composites is also discussed.
The heat of fusion of 66 nylon
Authors: Starkweather Howard W. , Zoller Paul , Jones Glover A.
Published: April 2003

The heat of fusion ΔHf of 66 nylon has been determined by use of the Clapeyron equation. Measurements of ΔHf and the unit‐cell parameters on molding pellets show that this material contains the α2 crystal phase, which is less dense than the α1 phase obtained by crystallization from solution. The value of ΔHf‐45–46 cal/g, is in good agreement with earlier reports.
Tearing of unvulcanized natural rubber
Authors: Kadir A. , Thomas A. G.
Published: April 2003

The tear behavior of unvulcanized natural rubber has been studied by using established techniques normally adopted for the study of vulcanized rubbers. Unvulcanized rubber has been found to tear in a relatively steady manner, in contrast to the stick‐slip tear behavior of the vulcanized rubber, the tearing energy being dependent on the rate of tearing. Crystallization seems to be an important factor in determining the tear behavior since it has not been found possible to tear unvulcanized SBR under the same conditions. The effect of the pronounced imperfect elastic nature of the material was studied under conditions where the driving force for tearing was solely governed by the rate of release of elastic energy. Under such conditions, it has been found that the tearing energy is determined not by the strain energy required to stretch the material but by the energy which can be recovered on retraction. The set developed in the test piece, due to imperfect elasticity, has also to be taken into account.
On the CO2 permeation of uniaxially drawn polymers
Authors: Wang L. H. , Proter Roger S.
Published: April 2003

The CO2 permeation coefficient and the difficient were measured using the permeation time‐lag method for films of atactic polystyrene and high‐density polyethylene, each as a function of uniaxial draw ratio. The reduction of permeability with draw ratio is observed for polystyrene and for polyethylene. In the latter it is associated with an increase in crystallinity. In both cases the premeability decreases and the solubility constant remains unchanged. The reduction of permeability is thus caused only by the reduction in diffusion of CO2 in the drawn polymers. The mechainism is different for the two polymers, as is confirmed by measurements of birefringence, glass transition temperature, and crystallinity.
Hydrodynamic radius and intrinsic viscosity of polystyrene in the crossover region from θ to good‐solvent conditions
Authors: Varma Brijesh Kumar , Fujita Yutaka , Takahashi Masato , Nose Takuhei
Published: April 2003

The radius of gyration Rg, the hydrodynamic radius Rh, and the intrinsic viscosity [η] have been measured for polystyrene in cyclohexane (at the θ temperature and 44.5°C), 2‐butanone (at 30°C), and toluene (at 30°C) in the molecular weight range 2.38 × 105 ≤ Mw ≤ 5.47 × 106 to elucidate the excluded‐volume effects on dynamical behavior in dilute polymer solutions in the crossover region from θ to good‐solvent conditions. The results are compared with theoretical predictions of current thermal blob theories and the Pade approximant theory of Tanaka. It is found that the ratio of Rh/Rg decreases with an increase in the excluded‐volume effect, following the prediction of the simple blob theory, but that its magnitude is about 15% higher than the theoretical value. Experimental variation of [η] with Rh and/or Rg lies in between predictions of the scaling law and the Pade approximant. The concentration dependence of the diffusion coefficient is also compared with predictions of current theories.
Miscible blends of amorphous polymers
Authors: Tremblay C. , Prud'homme R. E.
Published: April 2003

Thirty‐five polymethacrylate/chlorinated polymer blends were investigated by differential scanning calorimetry. Poly(ethyl), poly(n‐propyl), poly(n‐butyl), and poly(n‐amyl methacrylate)s were found to be miscible with poly(vinyl chloride) (PVC), chlorinated PVC, and Saran, but immiscible with a chlorinated polyethylene containing 48% chlorine. Poly(methyl) (PMMA), poly(n‐hexyl) (PHMA), and poly(n‐lauryl methacrylate)s were found to be immiscible with the same chlorinated polymers, except the PMMA/PVC, PMMA/Saran, and PHMA/Saran blends, which were miscible. A high chlorine content of the chlorinated polymer and an optimum CH2/COO ratio of the polymethacrylate are required to obtain miscibility. However, poly(methyl), poly(ethyl), poly(n‐butyl), and poly(n‐octadecyl acrylate)s were found to be immiscible with the same chlorinated polymers, except with Saran, indicating a much greater miscibility of the polymethacrylates with the chlorinated polymers as compared with the polyacrylates.
The role of molecular diffusion in the adhesion of elastomers
Authors: Ellul M. D. , Gent A. N.
Published: April 2003

Butyl rubber (polyisobutylene‐co‐isoprene) mixed with polyisobutylene was crosslinked to yield elastomeric macromolecular networks containing dissolved linear macromolecules. Adhesion of these materials to themselves (self‐adhesion) and to an inert substrate was investigated over a wide range of peel rates and test temperatures. Greatly enhanced self‐adhesion was found when linear polyisobutylene molecules of high molecular weight were present, but the strength of adhesion to a rigid inert substrate was hardly affected. The enhancement of self‐adhesion is attributed to interdiffusion of polyisobutylene molecules. It was greatest at intermediate peel rates and temperatures, becoming insignificant at extremely low rates, probably because the diffusing species can then migrate readily, and at high effective rates of peel when the polymer approaches the glassy state and the strength of adhesion is high in all cases. A transition to somewhat lower levels of adhesion at relatively high rates of peel is tentatively ascribed to the onset of molecular fracture in place of pullout. The presence of large amounts of low‐molecular‐weight polyisobutylene (M̄v = 50,000 g/mol) increased the level of self‐adhesion and of adhesion to an inert substrate to a similar degree, over a broad range of peel rates. This effect is attributed primarily to enhanced viscous losses in the elastomeric layer during separation. Application of these results to crack and weld‐line healing in glassy plastics is discussed.
Magic‐angle 13C‐NMR of cured and degraded acrylic copolymer/melamine formaldehyde coatings
Authors: Bauer D. R. , Dickie R. A. , Koenig J. L.
Published: April 2003

Magic‐angle carbon‐13 NMR has been used to probe the structure and dynamics of acrylic copolymer melamine formaldehyde crosslinked coatings. Changes in chemical composition that occur in conventional accelerated weathering tests were found to be dominated by hydrolysis of acrylic‐melamine crosslinks and subsequent formation of melamine‐melamine crosslinks. Evidence for photo‐oxidation was also observed. These results are in substantial agreement with infrared measurements also made on these coatings. Gated high‐power decoupling experiments were used to determine relative mobilities of the different carbon resonances as a function of acrylic copolymer composition and as a function of degradation. It was found that motion of the side‐chain carbons on the acrylic copolymer was not sensitive either to the chemical composition of the coating or to the extent of degradation. Mobilities of the main‐chain carbons of the acrylic copolymer decrease with increasing glass transition temperature of the acrylic copolymer. For acrylic copolymers containing styrene, it is found that the main‐chain carbon mobilities decrease with weathering. The melamine triazine ring becomes very rigid after degradation consistent with the formation of short melamine‐melamine crosslinks.
Regularities in x‐ray scattering patterns from amorphous polymers
Authors: Miller Robert L. , Boyer Raymond F.
Published: April 2003

It is known that the x‐ray scattering pattern of an amorphous polymer may contain one or more halos corresponding to van der Waals spacings or larger. In this work we found that (i) the halo positions (and equivalent Bragg spacings) vary systematically with the cross‐sectional area of the polymer chain in the crystal and (ii) there are at least two families of such halos with spacings larger than that of van der Waals contacts of atoms. From the wide variety and nature of the polymers considered, this behavior is believed to be representative of the amorphous state existing in polymeric samples. This work indicates that there is a degree of packing regularity in amorphous polymers that should be considered in models and theories of polymer chain conformation.
Chemical healing in poly(ethylene terephthalate)
Authors: Fakirov S.
Published: April 2003

A new molecular mechanism for the healing phenomenon in semicrystalline linear polycondensates (healing resulting from chemical reactions between macromolecules located in the interfacial surface) is demonstrated. Strips of commercial poly(ethylene terephthalate) are annealed at 258°C in order to avoid melt sticking. Two such strips are partially overlapped, pressed, and heated in a vacuum at 240°C for 10, 20, 30, and 100 h. By measuring the stress at break outside the contact area and the debonding shear stress the critical overlapping length is computed. It is concluded that transreaction contributes more than solid‐state post‐condensation to chemical healing.
Preparation, fractionation, and dilute‐solution behavior of ABA poly(methyl methacrylate‐b‐α‐methylstyrene) block copolymers
Authors: Corner T. , Peaker F. W.
Published: April 2003

The preparation by anionic polymerization of six ABA poly(methyl methacrylate‐b‐α‐methylstyrene) block copolymers and of sixteen poly(α‐methylstyrene)s is described. The block copolymers, of similar molecular weight but with different chemical compositions, were fractionated by preparative gel permeation chromatography and their behavior in dilute solution was investigated using viscometry. The results obtained indicate that the intramolecular phase separation does not occur under the conditions utilized, the block copolymers assuming randomcoil configurations in all of the copolymer/solvent systems studied. Consequently the block copolymer molecules are more expanded than homopolymers of the same molecular weight. The series of poly(α‐methylstyrene)s covered the molecular weight range 2.7 × 103–1.3 × 106and enabled the determination of Mark–Houwink–Sakurada constants for poly(α‐methylstyrene) in the solvents chosen for the block copolymer studies.
Small‐angle polarized light scattering from amorphous spheres
Authors: Meeten G. H. , Navard P.
Published: April 2003

Small‐angle light‐scattering measurements have been made using micron‐diameter isotropic and spherical polymer latex particles placed between crossed polarizers. Four‐leaf clover patterns are obtained, reminiscent of those commonly found for spherical birefringent scatterers. The experimental results compare closely with predictions of Mie scattering theory for isotropic spheres.
The effect of crosslinking on the reactivity of free radicals in isotactic polypropylene
Authors: Klimová Marta , Tin̆O Jozef , Borsig Eberhard , Ambrovic̆ Peter
Published: April 2003

Isotactic polypropylene of various degrees of crosslinking was prepared using high concentrations of dicumyl peroxide as the crosslinking agent. Free radicals were generated by γ irradiation of crosslinked iso‐PP with a dose of 2.4 Mrad. It was found that the rate constant for free‐radical decay is independent of crosslinking in the temperature range from −30 to +20°C. The result is discussed from the point of view of degradation processes taking place simultaneously with crosslinking of iso‐PP.
Relaxation by reptation and tube enlargement: A model for polydisperse polymers
Authors: Marrucci G.
Published: April 2003

Modern theories of the dynamics of concentrated polymeric liquids have not yet accounted for the effects of polydispersity to a sufficient extent. In order to approach quantitatively the problem of polydispersity, a model is proposed here which is based on the concept that the “tube” of constraints around a chain enlarges as the relaxation proceeds. Predictions of linear viscoelasticity obtained with this model compare favorably with experimental results on homopolymeric blends reported in the literature. However, the theory is limited to the case of very long chains and it embodies an arbitrary, if plausible, closure assumption in the self‐consistency scheme. Thus, quantitative agreement remains incomplete.
Effects of solvent goodness and polymer concentration on rejection of polystyrene from small pores
Authors: Long T. D. , Anderson J. L.
Published: April 2003

Solutions of polystyrene of molecular weight 4.5 × 106 and 8.4 × 106 in mixed solvents of carbon tetrachloride/methanol were filtered through track‐etched mica membranes at low membrane velocities. The unperturbed hydrodynamic radius of the polymer was always larger than the pore radius. The reflection coefficient σ, defined as the fraction of polymer held back by the membrane, was determined from material balances as a function of solvent flow rate per pore q, volume percent CCl4 of the solvent, and polymer concentration C0. In the dilute region (C0 < C*) σ was found to depend primarily on q and was essentially independent of chain size (or solvent goodness), molecular weight, and pore radius. In the semidilute region (C0 > C*) σ decreased significantly as C0 was increased.
Crystal structure of poly(γ‐methyl L‐glutamate) at high temperature
Authors: Sasaki Shintaro , Uematsu Ichitaro
Published: April 2003

A unique crystal structure of the α‐helical form of poly(γ‐methyl L‐glutamate) appearing above 170°C is analyzed by x‐ray diffraction. At room temperature, the unit cell determined for a well‐annealed sample is hexagonal with dimension a = 11.82 Å and contains one α helix with pitch P = 5.42 Å and unit height p = 1.493 Å. This form is reversibly transformed at about 170°C into a modification characterized by a trigonal unit cell (a = 21.27 Å) having three times the cross section of the single‐chain unit cell and containing three α helices with P = 5.50 Å and p = 1.504 Å. In a narrow temperature range below 180°C, the three chains in the unit cell are not interrelated by any crystallographic symmetry element, but they are reasonably associated with one another so that all helices are surrounded by other helices in the same way. The axial and azimuthal displacements between neighboring chains are expressed by z = ±4p/3 and ϕ = ± (2π/3)(4p/P − 1), respectively. The segmental main‐chain motion, which becomes appreciable above 150°C, is composed of screw‐type motion along the α‐helix fold and correlated P/3 axial jumps. The relation between the structural transition and thermal motion is discussed.
Free‐volume theories for self‐diffusion in polymer–solvent systems. I. Conceptual differences in theories
Authors: Vrentas J. S. , Duda J. L. , Ling H.‐C.
Published: April 2003

Conceptual differences in two recent versions of the free‐volume theory for self‐diffusion in polymer–solvent systems are identified and discussed. The validity of the assumptions of these two theories is tested using experimental data. In all cases, the experimental evidence favors the Vrentas–Duda free‐volume theory over the Paul version of this theory.
Free‐volume theories for self‐diffusion in polymer–solvent systems. II. Predictive capabilities
Authors: Vrentas J. S. , Duda J. L. , Ling H.‐C. , Hou A.‐C.
Published: April 2003

The predictive and correlative capabilities of two recent versions of the free‐volume theory for self‐diffusion in polymer–solvent systems are examined by comparisons with experimental data. Neither the Vrentas–Duda free‐volume theory nor the Paul version generally provides satisfactory predictions for the temperature and concentration variations of solvent self‐diffusion coefficients. However, the Vrentas–Duda theory does provide good correlations of solvent self‐diffusion data, and, furthermore, this theory can provide good predictions if a small amount of solvent self‐diffusion data is used to help estimate the parameters of the theory. New diffusivity and equilibrium data were collected for the toluene‐PVAc system to provide a broader database for evaluation of the self‐diffusion theories.
Morphology of poly(phthalocyaninatogermoxane) crystals
Authors: Zhou X. , Marks T. J. , Carr S. H.
Published: April 2003

The morphology of fully and partially polymerized poly(phthalocyaninatogermoxane), [Ge(Pc)O]n, crystals was studied by both scanning and transmission electron microscopy. It was found that the morphological units are lath‐like crystals which aggregate into particles. Generally speaking, the thickness, width, and length of the laths are in the range of 1000–2000 Å, 2000–10,000 Å, and 1–5 μm, respectively. Each lath may possess a mosaic substructure. Selected‐area electron diffraction patterns indicate that the rigid, extended [Ge(Pc)O]n chains are parallel to the large surface of the lath, and in most crystals the chains lie parallel to the lengthwise direction of the lath. However, in several cases, the chain orientation is at an angle of about 60° with respect to the long edge of the lath. The electron diffraction results are in accord with a tetragonal crystal structure (P4/m).
Crystallization of bisphenol‐A polycarbonate induced by organic salts: Chemical modification of the polymer. I. Model reactions
Authors: Bailly Ch. , Daumerie M. , Legras R. , Mercier J. P.
Published: April 2003

The chemical modifications induced in diphenyl carbonate (DPC) by sodium arylcarboxylates between 200 and 250°C were studied to model the behavior of bisphenol‐A polycarbonate – salt systems. Reaction between the salt and DPC produces sodium phenoxide, the phenyl arylcarboxylate corresponding to the salt, and carbon dioxide. The two latter compounds probably result from the decarboxylation of an unstable intermediate compound, viz., a mixed carboxylic carbonic anhydride. CO2 and sodium phenoxide act as catalysts transforming DPC into phenyl salicylate via the formation of a small amount of sodium salicylate. Electrophilic acylation of sodium phenoxide by DPC is another possible but minor source of phenyl salicylate. Above 250°C, phenyl salicylate becomes unstable and pyrolyzes into o‐phenoxybenzoic acid, which is immedicately esterified in the presence of DPC into phenyl o‐phenoxybenzoate. In DPC + sodium o‐chlorobenzoate systems, reaction between phenyl o‐chlorobenzoate and sodium phenoxide is another source of phenyl o‐phenoxybenzoate.
Carbon‐13 NMR relaxation and transitions in polymers
Authors: Dekmezian A. , Axelson D. E. , Dechter J. J. , Borah B. , Mandelkern L.
Published: April 2003

High‐resolution proton‐decoupled carbon‐13 nuclear magnetic resonance relaxation parameters have been obtained as a function of temperature for a set of completely amorphous polymers, semicrystalline polymers, and a series of ethylene–vinyl acetate copolymers. With these samples the nature of the glass temperature, other postulated amorphous transitions, and the β transition were investigated. For the completely amorphous polymers, the average correlation times depend on temperature according to the Williams–Landel–Ferry relation. Spectral collapse occurs at temperatures whose ratio to Tg is in the range 1.2–1.4 and corresponds to a correlation time of about 10−7s. The loss of resolvable spectra is demonstrated to be a consequence of experimental methods and is not due to the occurrence of another amorphous transition. Both the methylene and methine carbons can be resolved for the ethylenevinyl acetate copolymers. Although the correlation time for the methylene carbon is continuous and resolvable through the β transition region, the methine branch‐point resonance is lost. The implication of these results to the molecular nature of the β transition is discussed.
NMR self‐diffusion study of polyethylene and paraffin melts
Authors: Zupancic I. , Lahajnar G. , Blinc R. , Reneker D. H. , Vanderhart D. L.
Published: April 2003

The self‐diffusion coefficient D of paraffin and polyethylene melts—covering the range between N = 19 and 103 where N is the number of monomeric units—was measured by the pulsed‐magnetic‐field‐gradient NMR method for diffusion times between 3 ms and 1 s. For the paraffins, D is proportional to N−2 though the molecular weights are smaller than the critical molecular weight for entanglement. In polyethylene, melts a strong dependence of the diffusion coefficient on the diffusion time is observed, whereas no such dependence is found in paraffin melts. A mathematical formalism for describing spin‐echo attenuation in terms of a velocity autocorrelation function is shown to yield qualitative agreement with the experimental results.
Rheo‐optical Fourier‐transform infrared spectroscopy of polymers. VII. Uniaxial deformation of heat‐set poly‐(ethylene terephthalate) film
Authors: Gupta V. B. , Ramesh C. , Siesler H. W.
Published: April 2003

Poly(ethylene terephthalate) (PET) film was uniaxially stretched to a draw ratio of 2.5. Two samples were prepared from this oriented film by heat‐setting it at 493 K while free to relax and when held at constant length. The structural changes occurring during uniaxial elongation up to fracture of these two oriented crystalline samples and their stress–strain characteristics were simultaneously monitored by rapid‐scanning Fourier‐transform infrared (FTIR) spectroscopy. In the free‐annealed sample, the orientation of the molecules in the amorphous phase shows a gradual improvement throughout the test, while chain unfolding occurs above 20% strain. This indicates that the predominant mechanism of deformation in this sample could be chain uncoiling in the amorphous phase followed by longitudinal slip processes within the sample. In the taut‐annealed sample, chain unfolding occurs at low strains accompanied by slight improvements in amorphous and crystalline orientation. Thus, in this sample longitudinal slip would appear to be the main deformation mechanism. The results of the FTIR measurements are discussed with reference to the dependence of the deformation mechanisms on the initial structure of the samples.
High‐resolution solid‐state 13C‐NMR spectroscopy of cellulose nitrates
Authors: Patterson P. M. , Patterson D. J. , Blackwell J. , Koenig J. L. , Jamieson A. M. , Carignan Y. P. , Turngren Edward V.
Published: April 2003

Solid‐state 13C‐NMR spectroscopy has been used to investigate the structure of cellulose nitrates prepared from cotton linters. The solid‐state technique has the advantage that the entire range of substitution can be studied, which is not possible at present by solution methods. The spectra change progressively with increasing degree of substitution (DOS = 3 for cellulose trinitrate), and can be used to quantify the extent of substitution at C6, C2, and C3. Progressive nitration leads to elimination of the original C6 resonances of native cellulose by DOS = 1.39. The first nitration of C6 occurs in the amorphous regions, and this is complete by DOS = 0.50. Substitution at C6 is accompanied by decrystallization, as indicated by the decrease in the resonance assigned to crystalline C4, which also disappears at DOS = 1.39. A new resonance assigned to C1 appears at DOS = 0.28 at 101 ppm; the original C1 resonance for cellulose declines steadily and disappears by DOS = 2.65. This change is assigned to nitration of C2, based on the published solution spectra. Finally, development of intensity at 82 ppm at DOS = 1.83 is assigned to the effect of nitration at C3. There is no indication of any rearrangement of the unsubstituted regions analogous to those that occur on Mercerization of native cellulose.
Macromolecular pair correlation functions from fluorescence depolarization experiments
Authors: Fredrickson Glenn H. , Andersen Hans C. , Frank Curtis W.
Published: April 2003

Depolarization of fluorescence resulting from the transport of electronic excitations in chromophore‐containing polymers is investigated as a technique for detecting deviations from ideal‐chain statistics. An approximate expression for the fluorescence anisotropy that depends only on the pair correlation function of chromophore labels is presented. This approximation is shown to be accurate for particular cases of long‐range correlations, short‐range correlations, and no correlations among chromophore positions. The formalism allows fluorescence depolarization experiments to be used as a probe of macromolecular pair correlation functions.
Low‐frequency excitations in amorphous poly(vinyl acetate)
Authors: Viras F. , Viras K. G. , King T. A.
Published: April 2003

Raman‐active modes have been detected in amorphous poly(vinyl acetate) in the frequency region 20–160 cm−1. The low‐frequency spectrum appears as a broad band for all three molecular weights examined. Spectra were recorded at two temperatures, 293 and 77 K, and found to show similar characteristics at both temperatures. The presence in solid amorphous polymers of broad structureless bands in general and their significance are discussed.
Structural studies on the polymorphism of nylon 3
Authors: Mun̄oz‐Guerra Sebastian , Fernandez‐Santin Jose Maria , Rodriguez‐Galan Alfonso , Subirana Juan A.
Published: April 2003

The structure and morphology of crystalline nylon 3 [poly(β‐alanine)] have been studied by electron microscopy and x‐ray diffraction. Two clearly defined forms are detected. Form I appears as spherulites made up of ribbonlike lamellae upon crystallization at high temperature from a solution in phenol–butanediol‐1,4. They have monoclinic unit cell with a = 9.60 Å, c = 8.96 Å, and β = 122.5°. The hydrogen‐bonded planes run parallel to the long dimension of the crystals. Form II is observed when the samples are prepared from formic acid solution at room temperature. A second type of spherulite with a microfibrillar structure is formed in this case. The isolated crystalline structures obtained from Form II appear to grow along the intersheet direction rather than along the hydrogen bond direction, which constitutes anomalous behaviour. Our results for this second form are consistent with an orthorhombic lattice with a = 9.56 Å and c = 7.56 Å. No clear information is obtained on the b dimension of the unit cell (chain axis) in either case. We assume a value of 4.78 Å, which corresponds to fully extended chains. The two forms coexist in films prepared from a formic acid–water solution as well as in samples recovered immediately after polymerization.
Comparative study of dielectric, mechanical, and nuclear magnetic relaxations of linear polyethylene. I. Broad‐line NMR investigation of the fine structure of the α and γ loss bands observed by dielectric and mechanical measurements
Authors: Kakudate Takuo , Kakizaki Maeko , Hideshima Teruo
Published: April 2003

Detailed investigation of the linewidth, second moment, and mobile fraction by straightline decomposition of NMR spectra of linear polyethylene from ca. −160 to ca. 100°C reveals five molecular processes denoted γ1, γ2, β, α′, and α. Relaxation maps show that the γ1, γ2, and β processes correspond to the dielectric and mechanical relaxations given the same names, while the α and α′ processes correspond respectively to the mechanical α2 process due to molecular motion in the interior of crystals and to the dielectric α process. Close relations are found between the mass fractions of protons for the γ1 and β processes and also between those for the γ2 and α′ processes. From the effects of diluent on these processes and the annealing‐time dependence of mass fractions of protons, the γ1, and β processes are attributed to two modes of molecular motion in an interlamellar amorphous region, while the γ2 and α′ processes are attributed to motions in the lamellar surface layers. The surface‐layer thickness obtained by applying the two‐phase model for the data on mobile fraction agrees quite well with that reported in the literature. The Bergmann–Nawotki three‐component analysis of NMR spectra and symmetric‐line decomposition for determining mobile fraction are shown to be unsuitable for studying the fine structure of the α and γ loss bands.
Effect of polydispersity on the cloud‐point curves of polymer mixtures
Authors: Roe Ryong‐Joon , Lu Learong
Published: April 2003

A method is presented for the calculation of cloud‐point curves of polymer–polymer mixtures when the polymers involved are polydisperse. The method is based on the Flory–Huggins free energy of mixing with a concentration‐independent χ parameter. Numerical results are given for cases in which the molecular weight distributions are represented by the Schulz–Flory type. When the two polymers have similar average molecular weights and polydispersities, the cloud‐point curves become flatter as the polydispersity increases. When the two polymers have similar average molecular weights but differ in polydispersity, the cloud‐point curves become more skewed as the difference in the polydispersity increases. The results point out that, if the polydispersity effect is not properly accounted for, the value of χ deduced from experimental cloud points is liable to be in error, especially with regard to its temperature coefficient and its concentration dependence.
Influence of the interphase on block copolymer thermodynamics: Extension of the leary model
Authors: Henderson Clayton P. , Williams Michael C.
Published: April 2003

The Leary–Williams model for the microphase thermodynamics of triblock ABA copolymers has been modified to accommodate deviations from homogeneous random‐coil configurations in the B‐chain dimensions as well as in those of the A chains, and has also been extended to cover the case of diblock AB copolymers. Only planar morphology is considered, but qualitative conclusions reported herein are expected to hold for other morphologies as well. The focus is on interphase thickness ΔT, with predictions made also for separation temperatureTsand planar repeat distanceD. Results are presented as systematic functions of copolymer composition (0 ≤ ϕA≤ 1), total molar volume (25,000 ≤Ṽ≤ 4 × 106cm3/g mol), block architecture (AB vs. ABA), temperature (298, 373 K), and for five different interphase composition profiles. In most cases, A represents a polystyrene block and B a butadiene block in these calculations. Predictions for ΔTincrease with temperature and depend on architecture, profile, andṼ; comparisons with data are close, in the range 15–30Å. It is shown thatTsdepends strongly on profile choice and ϕA, reaching a maximum in the ϕAmidrange but always with ϕA> 0.5. The major parameter influencingD(at constantṼ) is architecture, withD(SB) ≈ 2D(SBS), andD(Ṽ) varies fromD∝Ṽ0.75at lowṼtoD∝Ṽ0.5at highṼ.
Stress‐optical behavior of poly(cis/trans‐1, 4‐cyclohexane dimethanol‐alt‐formaldehyde) (PCDO) networks
Authors: Riande E. , Guzman J. , Saiz E. , Tarazona M. P.
Published: April 2003

Two samples of poly(cis/trans‐1,4‐cyclohexane dimethanol‐alt‐formaldehyde), having fractions of trans configuration of cyclohexylene rings Ft = 0.1 and 0.7, were synthesized by polycondensation of the appropriate mixtures of glycols with paraformaldehyde. These two samples were crosslinked by a chemical reaction using 2,4‐bis(p‐isocyanatebenzyl) phenylisocyanate as the crosslinking agent. The stress‐optical behavior of the resulting networks was studied at several temperatures in the range 10–80°C. The values of the optical configuration parameter Δα were 9.9 and 7.2 in units of 10−24 cm3 for Ft = 0.7 and 0.1, respectively. The temperature coefficient of this quantity was roughly zero. Theoretical analysis, performed using the rotational isomeric state model, proved that the only parameters that have an appreciable effect on the calculated values of Δα are those concerning the cyclohexane ring (i.e., Ft and the optical parameter ΓCC = ΔαCC − 2ΔαCH). Conformational energies, geometrical parameters, and contributions to the optical anisotropies from the oxymethylene oxide have no noticeable effect on the value of Δα calculated for the polymer. In fact, values of Δα calculated for the polymer at Ft = 0 and 1 are very close to those obtained, respectively, for cis and trans cyclohexane dimethylene. The theoretical values of Δα are roughly one order of magnitude lower than the experimental results; however, the theory reproduces satisfactorily both the variation of Δα with Ft and its temperature coefficient.