bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerization of N‐carboxy–amino acid anhydrides in the solid state. II. Relation between polymerizability and molecular arrangement in L‐leucine NCA and L‐alanine NCA crystals
Authors: Kanazawa Hitoshi , Ohashi Yuji , Sasada Yoshio , Kawai Tohru
Published: April 2003

The polymerizability of N‐carboxy–amino acid anhydrides (NCAs) of L‐leucine and L‐alanine was examined in the solid state and in solution. L‐leucine NCA shows much higher reactivity in the solid state (when immersed in hexane) than in solution (in acetonitrile), but the opposite is true for L‐alanine NCA. However, the two NCAs give similar values of apparent activation energy in each polymerization system. Rather high‐molecular‐weight polypeptides were obtained in the polymerization of L‐leucine NCA in the solid state compared with those obtained in solution, while the molecular weight of polymers obtained from L‐alanine NCA was higher in solution than in the solid state. IR spectra showed that α helices form mainly in the polymerization of both L‐leucine NCA and L‐alanine NCA in the solid state; a small amount of the β structure forms in the latter polymerization. X‐ray diffraction and electron microscopy revealed that L‐leucine NCA polymerizes predominantly along the c axis in the crystal, while the polymer chains grow in random directions in the crystal of L‐alanine NCA. The difference can be explained by the molecular arrangement in the crystal. There are two requirements for high reactivity in the solid state: the five‐membered rings of the monomer must form a layer structure and the polymer must occupy nearly the same space as the reacting monomer.
Bisphenol‐A polycarbonate–poly(butylene terephthalate) transesterification. III. Study of model reactions
Authors: Devaux J. , Godard P. , Mercier J. P.
Published: April 2003

Exchange reactions in molten bisphenol‐A polycarbonate–poly(butylene terephthalate) mixtures are investigated by means of model reactions. Transesterification can result either from direct ester‐ester interchange or via alcoholysis or acidolysis. Among the various reactions investigated, only the PBTP alcoholysis by phenol is not found to occur. Taking into account that bisphenol‐A terephthalate units (A2B1) and butylene carbonate units (A1B2) are formed in equimolecular amounts, it is concluded that direct ester‐ester interchange is the most likely mechanism for PC‐PBTP transesterification.
Bisphenol‐A polycarbonate–poly(butylene terephthalate) transesterification. IV. Kinetics and mechanism of the exchange reaction
Authors: Devaux J. , Godard P. , Mercier J. P.
Published: April 2003

The kinetic aspects of the bisphenol‐A polycarbonate–polybutylene terephthalate exchange reaction are considered as a function of temperature and of the PC/PBTP ratio. The most likely mechanism is a direct reversible ester‐ester interchange reaction catalyzed by titanium residues present in commercial PBTP.
Phase behavior of the quasiternary system N‐methylmorpholine‐N‐oxide, water, and cellulose
Authors: Chanzy H. , Nawrot S. , Peguy A. , Smith P. , Chevalier J.
Published: April 2003

The crystallization and melting behavior of the system N‐methylmorpholine‐N‐oxide (MMNO)–H2O–cellulose has been studied by differential scanning calorimetry, optical and electron microscopy, and x‐ray scattering. The phase diagram of the MMNO–H2O solvent system is reported up to a water content of 28% w/w. MMNO forms two crystalline hydrates, namely a monohydrate (13,3% w/w H2O) and a hydrate comprising five molecules of crystal water per two MMNO molecules (28% w/w H2O), which melts at 78°C and 39°C, respectively. The melting points of the various diluent crystals are strongly depressed in the presence of cellulose. For example, the solvent liquidus curve in the quasibinary system MMNO.1H2O–cellulose can be described very well using the simple Flory–Huggins expression with an interaction parameter χ = −3. Finally, the MMNO‐rich part of the melting point/composition diagram of the quasiternary MMNO–H2O–cellulose system is constructed and discussed.
Dynamics of rodlike polymers in semidilute solutions: Short‐time‐scale motion
Authors: Doi Masao
Published: April 2003

A new kinetic equation which describes the rotational Brownian motion of rodlike polymers in concentrated solution is proposed on the basis of the tube model. The equation takes into account the two types of rotational motion, i.e., (i) the slow diffusion due to the reptation‐rotation process, and (ii) the rapid fluctuation of the polymer inside the tube. This equation explains the recent experimental finding by Mori et al. that the dc component of the dynamic Kerr constant changes sign from positive to negative at high frequency.
The β relaxation behavior of bisphenol‐type resins
Authors: Takahama T. , Geil P. H.
Published: April 2003

The β relaxation of a phenoxy resin and a number of related uncured and cured bisphenol‐type epoxide resins was studied using a torsion pendulum. Two molecular mechanisms are proposed to contribute to the β relaxation in the range from −55 to −80°C. One is the motion of the hydroxyether group and the other is related to motions of the crosslink itself. The β‐relaxation peak temperature was found to increase with the concentration of hydroxyether groups in the matrix. Motion of the crosslinks in the matrix gives rise to a contribution to the β peak at −80°C. In addition, motion of the diphenyl propane group is proposed to result in a relaxation process at ca. −110°C.
Aging of piezoelectricity in poly(vinylidene fluoride)
Authors: Kolbeck A. G.
Published: April 2003

This report describes isothermal aging of piezoelectricity in poly(vinylidene fluoride) (PVDF) based on long‐term heat treatments between 40 and 160°C. The results demonstrate that no piezoelectric decay occurs below about 60°C, that between 60 and 160°C the aging behavior follows logarithmic kinetics, and that aging is linearly dependent on temperature. Both uniaxial and biaxial PVDF show similar trends, but piezoelectric decay is more rapid for uniaxial film. Decay of permanent poling‐induced polarization is identified as the likeliest cause of piezoelectric aging, and piezoelectric decay is found to be associated with long‐range annealing effects which also produce macroscopic shrinkage of the PVDF film.
An unusual fatigue crack‐tip plastic zone: The epsilon plastic zone of polycarbonate
Authors: Takemori Michael T. , Matsumoto Dean S.
Published: April 2003

Polycarbonate exhibits an extraordinary crack‐tip plastic zone under certain fatigue loading conditions. During discontinuous growth (multiple load cycles per crack jump), the plastic zone consists of a leading craze and a pair of sharply delineated shear bands, which together look like the Greek letter epsilon. The kinetics of the development of the epsilon plastic zone and the nature of the transition from discontinuous growth to a shear fatigue fracture mode are discussed.
Tensile strength of filled polymers
Authors: Chow T. S.
Published: April 2003

A model is developed to predict the ultimate tensile strength of a particulate‐filled polymer which depends not only on the volume fraction of the filler and the elastic moduli of the two material phases, but also on the shape, size, and interfacial adhesion between the filler particle and the matrix. The effects of these parameters have been examined and attempts have been made to compare them with those available in the literature. Considering the complexity of fracture, the theoretical prediction is in reasonably good agreement with published experimental data.
End effects for a rodlike polyelectrolyte molecule in salt solution
Authors: Katoh T. , Ohtsuki T.
Published: April 2003

Electrostatic potentials around a single rodlike polyelectrolyte molecule are calculated by solving the nonlinear Poisson–Boltzmann equation numerically in the presence of externally added salt. The polyion is regarded as a cylinder with a finite length whose side surface is uniformly charged and end surfaces uncharged. The calculations show that the distance to which end effects extend is about half the Debye screening length and is almost independent of the surface charge density and concentration of added salt. For a long polyion whose length is much greater than the Debye length, the end effects can be neglected even for a polyelectrolyte with high surface charges, whereas they play an important role for a short polyion with a length of the same order as the Debye length. In addition, a strong charge condensation is found in the direction of the axis of the cylinder for a long polyion.
Effects of carbon filler on sorption and diffusion of gases through rubbery materials
Authors: Tanioka Akihiko , Oobayashi Atsushi , Kageyama Yuji , Miyasaka Keizo , Ishikawa Kinzo
Published: April 2003

Effects of carbon filler on the sorption and diffusion of carbon dioxide in natural rubber and in styrene‐butadiene rubber have been studied. Sorption isotherms conform to Henry's law in unfilled rubber and to Langmuir's law in carbon black. The isotherms in filled rubber exhibit a combination of the two sorption modes. The Henry's law solubility parameter kD increases with carbon filler content; the Langmuir saturation constant C′A initially is constant with filler level, but then decreases abruptly when carbon particles begin to aggregate. The diffusion coefficient decreases with increasing filler content, presumably owing to geometric effects and to polymer chain immobilization in the interfacial regions.
Light‐scattering studies of phase‐demixing of polystyrene/poly(o‐chlorostyrene) blends
Authors: Gilmer John , Goldstein Niel , Stein Richard S.
Published: April 2003

The phase separation of blends of polystyrene and poly(o‐chlorostyrene) has been studied by observing the changing small‐angle light‐scattering profile with time. As a blend is heated to a temperature at which it undergoes phase separation, a light‐scattering maximum is observed which grows in intensity and moves to smaller angles with time. This maximum is associated with a characteristic spacing which increases at a rate which becomes greater at higher temperature or with lower molecular weight. This spacing varies with a power of time as might be expected for domain growth occurring by a viscous flow mechanism. The integrated scattering intensity (invariant) is found to increase initially with time and then remain constant, as is characteristic of phase separation followed by phase ripening.
Spectroscopic characterization of the rotational conformations in the disordered phase of poly(ethylene terephthalate)
Authors: Lin Shaow‐Burn , Koenig Jack L.
Published: April 2003

Recently developed data processing techniques have been applied to determine the complete spectra of the trans and gauche isomers of PET and to use these spectra to determine the conformational composition of PET samples isothermally crystallized from the glassy state between 75 and 240°C. A linear correlation was found between normalized absorbance of conformational bands and density measurements, with the trans bands showing a positive slope and the gauche bands a negative slope. Extrapolation of the results from trans bands to zero percent of trans yields the density of the pure gauche isomer, 1.326 ± 0.002 g/cm3. Similarly, from the gauche bands the density of 100% crystalline trans is found to be 1.510 ± 0.014 g/cm3. Meanwhile, the density of the amorphous trans is calculated to be 1.430 ± 0.003 g/cm3. From these values and the combined density and infrared measurements, the content of trans isomers in the amorphous phase is calculated. It is found that the content of amorphous trans is a function of both annealing temperature and time. It is observed that the amorphous trans content decreases as the crystalline trans content increases. At high crystallinity, the amorphous trans content approaches zero. These amorphous trans isomers are associated with the extended units making up the interlamellar links. The loss of these extended trans interlamellar links is reflected in the mechanical properties of PET.
Quantitative analysis of polymers by attenuated total reflectance fourier‐transform infrared spectroscopy: Vinyl acetate and methyl content of polyethylenes
Authors: Mirabella Francis M.
Published: April 2003

A comparison was made between the transmission and attenuated total reflectance (ATR) infrared spectroscopic techniques for the determination of the vinyl acetate content of poly(ethylene–vinyl acetate) copolymers and methyl content of polyethylene. It was demonstrated that the transmission and ATR calibration curves for ratios of absorbances of bands with maxima at very similar wavelength were coincident, while those for ratios of absorbances of bands with maxima at significantly dissimilar wavelength were shifted apart. The explanation of this behavior is based on the wavelength dependence of the interaction of the IR radiation in ATR, compared to the wavelength independence of the interaction in transmission IR. The effect of polarized radiation was investigated in each type of analysis with the ATR technique. It was found that essentially the same results were obtained with the IR radiation polarized at 0° or 90°, relative to the plane of incidence, as compared to spectra obtained with unpolarized radiation. However, larger scatter was observed with polarized radiation. The effect of clamping pressure was also investigated. It was found that a minimum clamping torque of 5 in. lb is necessary to assure good physical contact in ATR work.
Diffusion and equilibrium swelling of macromolecular networks by their linear homologs
Authors: Gent A. N. , Tobias R. H.
Published: April 2003

Polydimethylsiloxane (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

All 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

The 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

The 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

The 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

The 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

The 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

Differential 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

Investigations 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

The 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

Cohen‐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

Permeability 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

Bounds 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

The 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

Methylol 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

When 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

13C 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

The 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

The 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

The 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.
Impact fracture mechanisms in polymer blends: Rubber‐toughened nylon
Authors: Wu Souheng
Published: April 2003

The impact fracture mechanisms of rubber‐toughened nylon are analyzed by measuring the energy dissipated in several different processes during notched fracture. An energy balance is thus established for the impact fracture. The stress‐whitened zone is shown to be the energy dissipation zone, having an energy dissipation density of 5.30 cal/g. About 25% (i.e., 1.44 cal/g) of the impact energy is dissipated by matrix crazing. About 75% (i.e., 3.86 cal/g) is dissipated as heat by matrix yielding, causing a temperature rise of 9.1 °C in the energy dissipation zone. Surface energy storage on the fracture surfaces is negligible (i.e., 1.45 × 10−5 cal/g). During matrix yielding, about 12% of α‐triclinic nylon crystals is transformed into pseudohexagonal crystals.
Raman scattering from the longitudinal acoustic mode of oligo‐oxyethylene
Authors: Viras K. , Teo H. H. , Marshall A. , Domszy R. C. , King T. A. , Booth C.
Published: April 2003

Low‐frequency Raman spectra are reported for monodisperse oligo‐oxyethylenes with hydroxy and alkoxy end groups. Assignments are made to the longitudinal acoustic modes. The results are modeled by a rod with a longitudinal modulus E ≥ 2.2 × 1010 N m−2 and perturbing forces as large as (alkoxy‐ended oligomers) or larger than (hydroxy‐ended oligomers) those suggested for the n‐alkanes.
The swelling interface number as a criterion for prediction of diffusional solute release mechanisms in swellable polymers
Authors: Peppas Nikolaos A. , Franson Nancy M.
Published: April 2003

When a glassy polymer containing a uniformly dispersed solute is brought in contact with a penetrant, solute diffusion will be associated with the transport mechanism and penetration velocity of the penetrant in the polymer. Analysis and prediction of mechanisms of diffusional solute release may be obtained through a new dimensionless number, the swelling interface number, Sw, which compares the relative mobilities of the penetrant and the solute in the presence of macromolecular relaxations in the polymer. It is shown that a sufficient and necessary criterion for time‐independent diffusional solute release rates from these swellable systems is that the Sw be smaller than 10−2. The swelling interface number Sw may be related to easily determined structural and thermodynamic parameters of the solute/polymer/penetrant system. Preliminary experimental results of dynamic water swelling of poly(2‐hydroxyethyl methacrylate‐co‐methyl methacrylate) and diffusional release of theophylline from initially glassy copolymers show that decreasing values of Sw are related to increased pseudo‐case‐II transport kinetics of the solute.
An investigation of the compatibility and morphology of semicrystalline poly(ε‐caprolactone)–poly(vinyl chloride) blends
Authors: Russell T. P. , Stein R. S.
Published: April 2003

Blends of poly(ε‐caprolactone) (PCL) and poly(vinyl chloride) (PVC) were investigated at concentrations of PCL greater than 50 wt % using purified materials. For these concentrations, PCL partially crystallizes with degrees of crystallinity ranging from 50% for pure PCL to < 10% for the 50% mixture. Small‐angle x‐ray scattering was used to characterize the resultant morphologies. Model calculations for the interference functions and for the integrated scattering indicate that PVC is incorporated between the PCL lamellae and that the two polymers form a homogeneous mixture in the amorphous phase. These results were compared to previous results on the same system using the identical technique. Purification of the two homopolymers proved to play a critical role in the overall mixing characteristics of PVC and PCL
Time‐dependent reactivity of species trapped in polymer matrices: Decay of allyl radicals in irradiated polyethylene
Authors: Płonka Andrzej
Published: April 2003

Using a time‐dependent rate constant of the form k(t) = Btα−1 it is possible to describe adequately the time‐dependent reactivity of species trapped in polymer matrices. The constant 0 < α ≤ 1 characterizes the initial distribution of species: the smaller the numerical value of α the wider is the distribution related to the kinetic curve by inverse Laplace transformation. Data of Auerbach and Sanders and of Patel et al. on allyl radical decay in irradiated polyethylene are discussed.
Diffusivity of gases and main‐chain cooperative motions in plasticized poly(vinyl chloride)
Authors: Sefcik M. D. , Schaefer Jacob , May F. L. , Raucher Daniel , Dub S. M.
Published: April 2003

Permeability and time‐lag measurements for H2 and CO in poly(vinyl chloride) (PVC) plasticized with tricresyl phosphate show that the apparent diffusion coefficients at first decrease as the plas‐ticizer concentration is increased. The diffusion coefficients then increase as the additive concentration is raised above 15 wt %. These changes in the apparent diffusion coefficients can be related to the behavior of a variety of mechanical properties and are attributed to antiplasticization and plasticization effects of low and high concentrations of tricresyl phosphate, respectively. The antiplasticization‐plasticization effects reflect altered molecular motions of the polymer. Carbon‐13 NMR rotating‐frame relaxation rate measurements show directly that the cooperative main‐chain molecular motions of PVC are reduced when the additive acts as an antiplasticizer and are increased when the polymer is plasticized. Both the apparent diffusion coefficient and the rotating‐frame relaxation rate have a similar dependence on additive concentration. An application of the molecular theory of diffusion of Pace and Datyner accounts qualitatively for the way in which additives alter the average chain interaction energy, cooperative polymer main‐chain motions, and the diffusion coefficients of gaseous penetrants.
Mesomorphic solutions of cellulose triacetate in trifluoroacetic acid halogenated solvent mixtures: Phase separations and factors affecting the cholesteric pitch
Authors: Patel D. L. , Gilbert R. D.
Published: April 2003

Cellulose triacetate (CTA) forms cholesteric mesophases in trifluoroacetic acetic acid (TFA) and mixtures of TFA and CH2Cl2, 1,2‐dichloroethane (1,2‐DCE), and CHCl3. Cholesteric pitches and solution flow times indicate that the order of solvent powers is TFA‐CH2Cl2> TFA‐1,2‐DCE > TFA > TFA‐CHCl3, which is the order of decreasing acidity of the solvent systems. With TFA‐CH2Cl2as solvent, the one‐fourth power of the pitch varies inversely with the CTA concentration, and increases linearly with temperature. The pitch increases exponentially with time and increases faster the more acidic the solvent. In a magnetic field a cholesteric to nematic transition occurs. A minimum in solution viscosity occurs at 34% w/v of CH2Cl2for solutions in TFA‐CH2Cl2. The miscibility gap as a function of molecular weight depends on the solvent composition and is smaller the higher the acidity of the solvent. Agreement between the experimentally observedAandBpoints and the theoretical points is better for the Khokhlov and Semenov theory for semiflexible chains than for the original Flory theory or the Flory‐Ronca modification.
Molecular orientation of spider silks in the natural and supercontracted states
Authors: Fornes R. E. , Work R. W. , Morosoff N.
Published: April 2003

Two theoretical models are presented to predict average molecular orientation properties of spider silk which has unknown molecular orientation and chemical structure. Birefringence and elongation (or shrinkage) data are required for two distinct lengths of a sample in order to fit the data. The first model is based on the assumptions that each molecule behaves as the average and that the deformations are affine. The second model is based on a random distribution of the molecules as the fiber is first formed and that the molecular deformations are affine when the fiber is elongated to any length. Data were taken from spider silks in the natural state and in a shrunken state (due to water). The second model gives a much better fit of the data. The models are applicable to other systems.
Scattering from copolymer solutions at finite concentration
Authors: Benmouna M. , Benoit H.
Published: April 2003

We consider the variation of the coherent elastic scattering structure factor S(q) with momentum transfer q for a solution of block copolymers at finite concentration. We introduce the effect of concentration using a generalization of Zimm's model to copolymers which enables us to express intermolecular scattering functions in terms of intramolecular form factors only. We show that the shape of the scattering curve is very sensitive to the polymer concentration as well as to the contrast factors, the relative composition of co units, and the second virial coefficients characterizing constituents of the copolymer. In particular, we show that the scattering curve develops a maximum at low q for certain values of these parameters. We also discuss the variation of the apparent radius of gyration with polymer concentration.
Localized volume deficiencies as an effect of spherulite growth. II. The three‐dimensional case
Authors: Gałeski A. , Piórkowska E.
Published: April 2003

As in the two‐dimensional case, the density change due to crystallization leads to a buildup of internal strain in some regions of a polymer melt occluded by growing spherulites. The occluded parts of the sample are called “weak spots.” Computer simulation of spherulite growth in bulk samples shows that the largest weak spots have the size of an average spherulite. The total volumes of weak spots are 0.47, 0.094, and 0.119% of the sample for athermal, thermal, and mixed primary nucleation, respectively. The weak spots in the bulk material exhibit distance correlation. Within weak spots, internal strain is released (Raman spectroscopy), and holes develop. Polypropylene bulk spherulite samples contain holes distinctly visible under a microscope with infrared optics and illumination. The number of visible holes is in agreement with the computer prediction. The increase of impact strength with decreasing spherulite size is explained in terms of changes in the number and size of weak spots.
Effect of amorphous sequences on the longitudinal acoustic modes in partially crystalline polymers. I. Transfer matrix method
Authors: Strobl G. R.
Published: April 2003

A novel theoretical scheme is developed which enables the determination of the LAM‐like vibrations of polymer chains made up of crystalline and amorphous parts as they occur in partially crystalline structures. The boundary conditions effective at the junction points are formulated in terms of the compliances of the associated amorphous sequences. These compliances can be derived from their eigenfrequencies and eigenvectors in a disconnected state. The treatment uses a matrix formalism which can be extended to include bending and torsional motions in a general state of vibration of the crystalline stem. A first numerical example demonstrates that the LA mode of a crystalline stem can be strongly perturbed by the coupling to the adjacent amorphous sequences. Interpretation of frequencies and line shapes of observed LA modes should always include these coupling effects; their neglect can lead to considerable errors.