bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion and equilibrium swelling of macromolecular networks by their linear homologs
Authors: Gent A. N. , Tobias R. H. 
Published: April 2003

AbstractPolydimethylsiloxane (PDMS) networks having strands of molecular weight in the range 11,000–36,000 have been prepared by endlinking linear PDMS molecules of these molecular weights with a tetrafunctional linking agent. Absorption of a series of homologous linear PDMS molecules by the resulting PDMS networks has been investigated. The diffusion coefficients at 70°C were found to be rather large, 1 × 10−12–6 × 10−12 m2/s, and approximately inversely proportional to the molecular weight of the diffusing liquid, over the range 5000–38,000. The amount of liquid absorbed at equilibrium was relatively small, 10–80%, in good agreement in all cases with an especially simple version of the Flory–Huggins theory when the heat of mixing is made vanishingly small and only entropic terms are retained.
Accordian‐type Laser‐Raman scattering by polymers
Authors: Peterlin Anton 
Published: April 2003

AbstractAll the improvements of the independent‐rod model of longitudinal accordian‐type acoustic mode (LAM) oscillations have assumed that the oscillation energy is retained either on the isolated macromolecule oscillating in a vacuum or in a narrow cylinder containing the straight sections of the macromolecules in the crystal lattice and their straight continuations through the amorphous layers. According to such concepts, concentration of the oscillation energy in gauche defects or amorphous layers occurs, respectively, whenever the axial elastic modulus of the straight sections (crystal lattice) is very much larger than that of the kinked sections (amorphous layers). The effect is enhanced by low crystallinity. Actually such behavior has never been observed. To agree with experimental data the model has to be modified in such a manner that the oscillation amplitude in the amorphous layer steadily decreases with increasing distance from the boundary between the two phases. The necessary large damping of the LAM oscillation in the kinked sections results from true damping in the viscoelastic amorphous component and energy transfer to adjacent chains which turns out to be just as easy as energy conduction along the kinked chain. Such a transfer is equivalent to radiation of the oscillation energy in all directions in the kinked phase. As a consequence of damping, the coupling of chains in adjacent crystals becomes so small that it may be completely neglected. Such a model explains in a satisfactory manner the observed accordion Laser‐Raman spectra of the semicrystalline polymers and the infrared absorption of paraffins in the liquid state.
Morphology and properties of poly(vinyl chloride)–poly(butadiene‐co‐acrylonitrile) blends
Authors: Wang Carl B. , Cooper Stuart L. 
Published: April 2003

AbstractThe objective of this research was to study the structure‐property relationships of two poly(vinyl chloride) (PVC)–poly(butadiene‐co‐acrylonitrile) (BAN) blends which exhibit differences in blend compatibility. Studies were carried out utilizing differential scanning calorimetry, dynamic mechanical testing, stress–strain, transmission electron microscopy (TEM), and infrared dichroism experiments at different temperatures. The BAN 31/PVC (BAN containing 31% acrylonitrile) system is considered to be nearly compatible as evidenced by Tg shifts, stress–strain results, orientation characteristics, and TEM micrographs. Similar experiments indicate that the BAN 44/PVC system is incompatible, and contains a mixed phase of BAN 44‐PVC and a pure BAN 44 phase. The extent of heterogeneity in the compatible BAN 31/PVC system, however, plays an important role in the orientation characteristics of the blends.
Microstructure and unit‐cell orientation in α‐polypropylene
Authors: Lovinger Andrew J. 
Published: April 2003

AbstractThe microstructure of melt‐grown dendritic aggregates of the monoclinic α phase of isotactic polypropylene has been examined by optical microscopy, electron microscopy, and electron diffraction. Whereas the tightly crosshatched structure of such dendrites grown in the usual manner from the melt had not heretofore permitted unequivocal determination of unit‐cell orientation, crystallization on mica at high temperatures eliminates this problem by suppressing branching and allowing lamellae to grow uninterruptedly to many micrometers in length. In this manner, it is shown that the preferred growth direction in single crystals of α‐polypropylene is a*. X‐ray diffraction analysis of unidirectionally crystallized specimens shows that the a* axis becomes radial in spherulites of this polymorph. Implications of this growth axis in terms of the branching model and of the crystallographic identification of the amorphous surfaces are discussed. Addition of large amounts of melt diluents is found to impart a distinct curvature to the dendritic crystals, causing their concave sides to face preferentially toward the centers of the resulting spherulitic aggregates.
Radiation chemistry of polybutadiene and butadiene‐styrene block copolymers. II. Kinetics and mechanisms of free‐radical decay reactions
Authors: Basheer Rafil , Dole Malcolm 
Published: April 2003

AbstractThe decay of free radicals produced in polybutadiene, polystyrene, and block copolymers of butadiene and styrene by γ irradiation at 77 K has been studied at −110°C in the case of polybutadiene and at −95°C for the other samples. The free‐radical decay rate is best interpreted in terms of an equation based on a second‐order decay mechanism of a fraction of the free radicals decaying in the presence of other nondecaying free radicals. Hydrogen gas accelerates the free‐radical decay. Increase of radiation dose increases the fraction of the radicals that decay, while increase of the fraction of styrene segments decreases the decaying fraction. In pure polybutadiene the higher the cis content, the greater fraction of decaying free radicals, but the second‐order decay constant is less in the high‐cis‐content polybutadiene and is also less at the higher dose, probably owing to the hindrance of the radiation‐produced crosslinks on the free‐radical decay. The decrease of the second‐order constant with increase of dose is also true for all the block copolymers studied.
Dynamics of adsorbed polymer chains subjected to flow: The dumbbell model
Authors: Fuller Gerald G. 
Published: April 2003

AbstractThe dumbbell model of an adsorbed polymer segment is analyzed in order to investigate the response of such segments to a velocity gradient imposed at the solid/liquid interface. It is demonstrated that exact expressions for the time‐dependent moments of the distribution function describing the conformation can be obtained. Both a dangling end and an attached loop can be represented and several bulk properties of a polymer film subjected to flow are evaluated.
Properties and chain flexibility of poly(tetrahydro‐4H‐pyranyl‐2‐methacrylate)
Authors: Hadjichristidas Nikos , Mays J. , Vargo R. D. , Fetters L. J. 
Published: April 2003

AbstractThe dilute‐solution properties of six poly(tetrahydro‐4H‐pyranyl‐2‐methacrylate) (PTHPM) fractions covering the molecular weight (Mw) range 4.8 × 104 to 8.4 × 105 (Mw/Mn = 1.2–1.4) were studied in tetrahydrofuran, a good solvent, and in isobutanol, a θ solvent a t 30.5°C as determined by light scattering from the A2 vs. T plot. The unperturbed dimensions were calculated from a low‐angle laser light‐scattering and intrinsic‐viscosity data. The results indicate that PTHPM is less extended chain than poly(cyclohexyl methacrylate) (PCyM). The higher flexibility of PTHPM parallels the lower T, (57°C) of this polymer relative to PCyM (66°C).
Miscible blends prepared from two crystalline polymers
Authors: Aubin Madeleine , Bédard Yves , Morrissette Marie‐France , Prud'homme Robert E. 
Published: April 2003

AbstractDifferential scanning calorimetry was used to determine the miscibility behavior of several polyester/Saran blends, the two polymers forming these blends being semicrystalline. It was found that Saran is miscible with polycaprolactone (PCL), polyvalerolactone, poly(butylene adipate), and poly(hexamethylene sebacate) since a single glass transition temperature Tg was observed at each composition. However, immiscibility was found between Saran and poly(ethylene adipate), poly‐(ethylene succinate), poly(β‐propiolactone), and poly(α‐methyl‐α‐n‐propyl‐β‐propiolactone) since two Tg's were recorded at several compositions. Blends were then obtained containing, over a wide range of composition, a miscible amorphous phase and two different types of crystals. From melting‐point depression data on PCL and Saran crystals, thermodynamic interaction parameters χ were calculated and found to be different for PCL‐rich blends and for Saran‐rich blends. This result suggests a variation of χ with composition. Saran is a polymer which does not contain α‐hydrogens and its miscibility with polyesters may result from a β‐hydrogen bonding interaction or a CO/CCl dipole‐dipole interaction.
Particle morphology in the radiation‐induced heterophase polymerization of vinyl chloride with solvent added in small amounts
Authors: Palma G. , Tavan M. , Carenza M. 
Published: April 2003

AbstractInvestigations were carried out on the polymer particle morphology obtained in the early stages of radiation‐induced bulk polymerization of vinyl chloride with solvent added in small amounts over the temperature range of −10 to 70°C under quiescent conditions. At low temperatures, when the polymerization is carried out in the absence of solvent, there is flocculation of irregular aggregates of two types depending on polymerization conditions: (i) small primary particles that remain finely dispersed and (ii) large flocs that undergo rapid sedimentation. By addition of increasing amounts of solvent a gradual change towards single small spherical particles that remain finely dispersed is obtained. With more than 3% w/w THF, spherical particles in latexlike dispersions are obtained in polymerizations at −10 and 22.8°C, and show a small change in size with increasing amounts of THF. In the high‐temperature range, 50–70°C, where spherical particles can be obtained in the absence of solvent, no significant changes are produced by addition of THF. The results are discussed in the terms of a marked increase in particle plasticization by the solvent, enabling the coalescence of flocculated particles of small size to occur also in polymerization at low temperature.
Fourier‐transform infrared study of coextrusion‐drawn poly(ethylene terephthalate)
Authors: Ito Masayoshi , Pereira Jose R. C. , Hsu Shaw Ling , Porter Roger S. 
Published: April 2003

AbstractThe effects of initial morphology and extrusion temperature on the orientational anisotropy and conformational changes on coextrusion drawing of poly(ethylene terephthalate) (PET) have been determined by Fourier‐transform polarized infrared spectroscopy. The samples were drawn from both amorphous and semicrystalline (50%) PET at 50 and 90°C. A strong influence of coextrusion drawing temperature was observed for overall chain orientation evaluated from the dichroic ratio of the 795‐cm−1 band for the samples prepared from the amorphous state: this dependence was less prominent in samples drawn from the semicrystalline state. Under the same drawing conditions, the dichroic ratio for the 973‐cm−1 trans band for samples prepared from the amorphous state was higher than from the semicrystalline state. Furthermore, in all samples, the relative intensity of this band was almost proportional to the degree of crystallinity. In all samples, the gauche content, evaluated from the 896‐cm−1 band, decreased with increasing draw ratio. However, the dichroic ratio of this band was near unity regardless of draw ratio, initial morphology, or extrusion temperature. From these results it is considered that all gauche units in the amorphous phase are almost isotropic in the extrusion‐drawn samples with overall orientation arising largely from the crystalline chains possessing totally the trans conformation (973 cm−1) in its content. In order to evaluate the deformation mechanism of the coextrusion drawing method, the relationship between the bulk and film surface orientation is also reported.
A model for predicting solvent self‐diffusion coefficients in nonglassy polymer/solvent solutions
Authors: Paul C. W. 
Published: April 2003

AbstractCohen‐Turnbull diffusion theory is used to develop a model for predicting solvent self‐diffusion coefficients D1 in nonglassy polymer/solvent solutions. Polymer molecules are envisioned as hindering solvent mobility by reducing the average free volume per unit mass in the system and through the lower mobility of polymer segments relative to solvent molecules. The concentration dependence of D1 predicted by the model is in reasonable agreement with data for the solvents heptane, hexadecane, benzene, cyclohexane, and decalin in polyisobutylene (PIB), and for toluene in polystyrene, poly(methyl mothacrylate), and PIB. Although none of the data is for high concentrations of polymer (volume fractions ϕ≥0.9) it is anticipated the model will be less representative in this regime where the assumptions in its development are unsure. The model also demonstrates the correct temperature and concentration dependence of the apparent activation energy for diffusion. The only experimental data needed to use the model are the viscosity and critical volume of the pure solvent, and the specific volume of both the solvent and mixture. No binary transport data are required.
Tests of a “free‐volume” model of gas permeation through polymer membranes. I. Pure CO2, CH4, C2H4, and C3H8 in polyethylene
Authors: Stern S. A. , Kulkarni S. S. , Frisch H. L. 
Published: April 2003

AbstractPermeability coefficients have been measured for CO2, CH4, C2H4, and C3H8 in polyethylene membranes at temperatures of 5, 20, and 35°C and at applied gas pressures of up to 30 atm. The temperature and pressure dependence of the permeability coefficients was represented satisfactorily by an extension of Fujita's free‐volume model of diffusion of small molecules in polymers. The results of the present steady‐state permeability measurements provide further support for the conclusion reached from previous unsteady‐state diffusivity measurements that Fujita's model is applicable to the transport of small molecules, such as CO2, CH4, C2H4, and C3H8, in polyethylene. It was previously thought that this model is applicable only to the transport of larger molecules, such as of organic vapors, in polymers.
The mechanical moduli of lamellar semicrystalline polymers
Authors: Boyd Richard H. 
Published: April 2003

AbstractBounds on the elastic constants are derived for semicrystalline polymers whose local morphology is lamellar. Local response matrices (stiffness and compliance) are formulated in three dimensions that simultaneously incorporate uniform in‐plane strain and additive forces from layer to layer of crystalline and amorphous phases and uniform stress and additive displacements normal to the lamellar surfaces. Spatial averaging of the stiffness and compliance matrices under the assumption of axially symmetric orientation gives the upper and lower bounds on the longitudinal and transverse tensile moduli and the axial and transverse shear moduli as functions of the separate phase elastic constants, the volume percent crystallinity, and the moments of the orientation 〈cos2θ〉 and 〈cos4θ〉. The bounds are much tighter than the Voight upper and Reuss lower bounds that do not recognize phase geometry. Using the known crystal elastic constants of polyethylene, sample calculations on isotropic unoriented materials show that the divergence of bounds at high crystallinity necessitated by the extreme crystal anisotropy shows up only at very high crystallinity. At low temperature the bounds are tight enough to specify G1, the amorphous modulus, from the measured G and the known crystal elastic constants. At higher temperatures and lower G, the bounds are not tight enough for this purpose but the shear modulus versus crystallinity and temperature data are well fitted by the lamellar lower bound using a temperature‐dependent, crystallinity‐independent G1.
The dielectric constant of lamellar semicrystalline polymers
Authors: Boyd Richard H. 
Published: April 2003

AbstractThe problem of representing the dielectric constant of semicrystalline polymers in terms of the dielectric constants and volume fractions of the constitutent crystalline and amorphous phases is considered. For locally lamellar morphology, bounds based on uniform electric and displacement fields are derived. The equations also include the degree of crystal orientation as a parameter. For unoriented polymers the bounds are considerably tighter than the Hashin–Shtrikman bounds, the latter being the best possible without knowledge of phase geometries. The bounds presented here are sufficiently tight to represent the dielectric constant with practical accuracy for a number of examples of semicrystalline polymers. A treatment is also given of the dielectric constant where the lamellar morphology is further specified as being organized into spherulite‐like structures. These bounds are somewhat tighter than the lamellar bounds.
Anisotropic solutions of methylol cellulose
Authors: Patton Penelope A. , Gilbert Richard D. 
Published: April 2003

AbstractMethylol cellulose solutions in dimethylsulfoxide exhibit a viscosity maximum at 18% w/v followed by a minimum at 20%, as is characteristic of lyotropic liquid crystals. The biphasic solutions exhibit areas of clear and cloudy appearance. The latter are birefringent. The highly anisotropic solutions are uniformly briefringent and in the 25–33% w/v concentration region they are brightly colored. The optical rotations of the mesomorphic phases are high, indicating a cholesteric structure. The sign of the optical rotation depends on the solution concentration and at high concentrations (25+% w/v) varies with the area of the solution viewed.
The influence of low‐temperature crystallization on the tensile elastic modulus of natural rubber
Authors: Stevenson A. 
Published: April 2003

AbstractWhen natural rubber crystallizes at low temperatures, there is an increase in elastic modulus of up to two orders of magnitude. This phenomenon has been studied at various temperatures in the range 0 to −55°C for samples held at tensile strains of up to 500%. There is an induction period associated with the nucleation of crystallites, before any increase in modulus is observed. The induction period increases with decreasing strain and passes through a minimum with increasing temperature at −25°C. The growth rate subsequent to nucleation is successfully described in terms of Avrami‐type rate relationships. The Avrami rate coefficient is independent of temperature and follows a simple exponential function of strain. The equilibrium extent of the modulus increase has also been studied by means of experiments of up to three months' duration. The equilibrium modulus increases with decreasing temperature—as predicted by Flory's thermodynamic theory.
13C NMR analysis of propylene‐butylene copolymers by a reaction probability model
Authors: Cheng H. N. 
Published: April 2003

Abstract13C NMR spectra of propylene‐1‐butene copolymers have been studied at 90.55 MHz. At this high field, many lines previously not resolvable were found to be sensitive to comonomer sequence distribution; these microstructures have been fully assigned. Each NMR spectrum was analyzed by a reaction probability model. Information available includes polymer composition, comonomer sequence distribution, and Markovian reaction probabilities. The use of this model reduces errors in the determination of sequence distribution and furthermore enables the product r1r2 of the reactivity ratios to be determined for the copolymer/catalyst system.
Thermal annealing of doubly oriented nylon 11 in contact with formic acid
Authors: Dosière M. , Point J. J. 
Published: April 2003

AbstractThe most striking feature of the mechanism of thermal annealing of doubly oriented samples of low‐density polyethylene (LDPE) and probably of high‐density polyethylene (HDPE) is a progressive tilt of lamellar crystals around their crystallographic b axis. Such a rotation does not occur on thermal annealing in doubly oriented nylons. However, this rotation mechanism occurs during the thermal annealing of doubly oriented samples of nylon 11 in contact with a solvent below its dissolution temperature. As for oriented samples of polyethylene (PE), a correlation between the changes of macroscopic dimensions and long spacing obtained from the small‐angle x‐ray pattern is difficult to establish. In doubly oriented samples of nylon 11, the basal faces of the lamellar crystals are parallel to the a axis of the unit cell. Nevertheless, simple Miller indices cannot be assigned to the basal planes of the lamellae. On thermal annealing in formic acid, the basal planes of the lamellar crystals are, in some cases, parallel to (00l) planes. Annealing in formic acid at room temperature induces a phase transition: the chain c axis remains oriented along the rolling direction and the (00l) planes become parallel to the limiting planes of the lamellar crystals. Bulk doubly oriented samples of nylon 11 annealed in formic acid just below the “dissolution temperature” have the same texture of orientation as filter mats of single crystals grown from dilute solution; moreover, as these bulk specimens remain doubly oriented, they can be used for further physicochemical investigations. The usual interpretation of the small‐angle x‐ray pattern is also discussed on the basis of the results reported in this paper.
Thermal expansion of oriented poly(methyl methacrylate)
Authors: Wang Li‐Hui , Choy C. L. , Porter Roger S. 
Published: April 2003

AbstractThe thermal expansivities along (α∥) and perpendicular (α⊥) to the draw direction of poly(methyl methacrylate) (PMMA) with extrusion draw ratios 1 ≤ λ ≤ 4 have been measured between 150 and 298 K. As λ was increased from 1 to 4, α∥ decreased 2–3 times, whereas α⊥ increased only 20–35%. The orientation function f calculated from thermal expansivity using the aggregate model is found to change linearly with birefringence, indicating that each property provides a sensitive measure of molecular orientation. For PMMA, however, only thermal expansivity can give an absolute f, with results at 150 K in reasonable agreement with previous studies using other techniques. At higher temperature, i.e., above ambient, PMMA side‐group motions are excited, expanding volume, and calculations based on the aggregate model may not be valid.
Explanation for the 3.4‐power law for viscosity of polymeric liquids on the basis of the tube model
Authors: Doi Masao 
Published: April 2003

AbstractThe viscosity η0(M) of polymeric liquids of molecular weight M is calculated on the basis of the tube model formulated by Doi and Edwards (ref. 3). The contour length fluctuation of polymers along the tube, which was neglected in ref. 3, is now explicitly taken into account. The result is

equation image

where Mc = 2Me, and Me is the molecular weight between the entanglement points. This result is numerically close to the empirical 3.4‐power law, η0(M) = η0(Mc)(M/Mc)3.4, for 10Mc ≲ M ≲ 100Mc but approaches the result in ref. 3 for very high molecular weight. We thus conclude that the 3.4‐power law is actually an approximate expression for the real curve which slowly approaches the asymptotic form calculated in ref. 3.