bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of molecular motion of block copolymers in solution by high‐resolution proton magnetic resonance
Authors: Nakamura Kanehiro , Endo Ryuichi , Takeda Masatami
Published: April 2003

Molecular motions of hydrophobic–hydrophilic water‐soluble block copolymers in solution were investigated by high‐resolution proton magnetic resonance (NMR). Samples studied include block copolymers of polystyrene–poly(ethylene oxide), polybutadiene–poly(ethylene oxide), and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide). NMR measurements were carried out varying molecular weight, temperature, and solvent composition. For AB copolymers of polystyrene and poly(ethylene oxide), two peaks caused by the phenyl protons of low‐molecular‐weight (M̄n = 3,300) copolymer were clearly resolved in D2O at 100°C, but the phenyl proton peaks of high‐molecular‐weight (M̄n = 13,500 and 36,000) copolymers were too broad to observe in the same solvent, even at 100°C. It is concluded that polystyrene blocks are more mobile in low‐molecular‐weight copolymer in water than in high‐molecular‐weight copolymer in the same solvent because the molecular weight of the polystyrene block of the low‐molecular‐weight copolymer is itself small. In the mixed solvent D2O and deuterated tetrahydrofuran (THF‐d8), two peaks caused by the phenyl protons of the high‐molecular‐weight (M̄n = 36,000) copolymer were clearly resolved at 67°C. It is thought that the molecular motions of the polystyrene blocks are activated by the interaction between these blocks and THF in the mixed solvent.
A small‐angle x‐ray scattering study of blends of isotactic and atactic polystyrene
Authors: Warner Frank P. , MacKnight William J. , Stein Richard S.
Published: April 2003

Small‐angle x‐ray scattering (SAXS) from blends of isotactic and atactic polystyrene has been studied. Results have been interpreted and compared using the Tsvankin, Vonk, and Hosemann techniques. The studies suggest that segregation of the atactic component occurs during crystallization within the growing spherulite of the isotactic component. However, since the interlamellar distance does not increase with atactic content, segregation is believed to occur with the formation of domains larger than interlamellar but smaller than spherulite size.
Dynamics of macromolecular chains. VII. Nuclear magnetic relaxation of monosubstituted polystyrenes in solution
Authors: Lauprêtre F. , Noël C. , Monnerie L.
Published: April 2003

The 1H spin‐echo and 13C spin–lattice relaxation times have been measured for solutions of polystyrene derivatives: ortho, meta, and para‐halo (F, Cl, Br) and ortho, meta, para, and α‐methyl. Results obtained from these two techniques permit comparison of the intramolecular mobility of these polymers with that of polystyrene. Poly(α‐methylstyrene) does not differ from polystyrene except for a slight slowing of both segmental reorientation and internal phenyl‐group motions and apparent hindrance of the methyl‐group rotation. Segmental reorientation of poly(m‐methylstyrene) is similar to that of polystyrene; rotation of the methyl group is free, while the internal phenyl‐ring process is slower. Poly(p‐methylstyrene) and poly(o‐methylstyrene) also contain freely rotating methyl groups; the intramolecular mobility decreases from the para to the ortho position of the substituent. Finally, in poly(o‐bromostyrene) and poly(o‐chlorostyrene), the internal motion of the phenyl ring is completely overshadowed by the segemental reorientation, which is itself quite reduced.
Strain energy function of styrene butadiene rubber and the effect of temperature
Authors: Glucklich Joseph , Landel Robert F.
Published: April 2003

Biaxial and uniaxial tensile stress relaxation tests were made on square sheet specimens of styrene butadiene rubber (SBR), mounted in a universal biaxial tester within a temperature‐controlled box, with the object of studying the effect of temperature on the strain energy function. The stress relaxation responses, usually for times up to 10 min, were obtained for various degrees of biaxiality, various extension ratios, and various temperatures within the limits of +25 to −45°C. The results indicated that if the Valanis–Landel representation of the strain energy function \documentclass{article}\pagestyle{empty}\begin{document}$ W = \sum\nolimits_{i = 1}^3 {w\left( {\lambda _i } \right)} $\end{document}
is adopted, then time and strain are factorizable over the indicated temperature range, with time and temperature being related in the usual fashion. That is, changing the temperature does not affect the form of w(λi) but only that of G(t/αT), the temperature‐dependent relaxation modulus, aT being the regular Williams–Landel–Ferry (WLF) shift factor. The results verify the Valanis–Landel theory for various combinations of biaxiality
Spectroscopic analysis of electrically polarized polyacrylonitrile
Authors: Stupp S. I. , Carr S. H.
Published: April 2003

Electrically polarized and unpolarized films of polyacrylonitrile (PAN) have been investigated by both infrared attenuated total reflection (ATR) and thermally stimulated discharge (TSD). ATR analysis of PAN films has been aimed at explaining the molecular origin of thermally stimulated currents, and consequently that of phenomena contributing to electrical polarization in this material. Preferred orientation of nitrile dipoles along the thickness direction (applied electric field direction) has been detected by ATR in both polarized and unpolarized films. It is suggested that dipolar alignment in unpolarized solvent‐cast films could result from internal electric fields associated with space charges. The observed orientational anisotropy is found to disappear gradually as films (both polarized and unpolarized) are heated from ambient temperature to 100°C and rotational motion in the backbone is thermally activated. TSD currents observed in this thermal range are thus associated with randomization of molecular dipoles. TSD currents observed above 100°C are suggested to originate from drift of space charges, since both an isotropic orientation of dipoles and onset of considerable diffusion are detected by ATR in this temperature range. PAN films polarized by high‐intensity electric fields (5 × 105Vcm−1, as opposed to 5 × 104Vcm−1) are found to retain orientational anisotropy above 100°C, and this is believed to be associated with a structural rearrangement induced by electrical polarization.
Polarized Raman studies of crystalline and amorphous orientation in polyethylene
Authors: Maxfield J. , Stein R. S. , Chen M. C.
Published: April 2003

Polarized Raman intensities have been obtained from thin films of oriented low‐density polyethylene (PE) immersed in silicone oil to minimize surface scattering. Studies were made using the 1170 cm−1 crystalline band and the 1081 cm−1 amorphous band, and from these the orientation averages 〈cos2 θ〉 and 〈cos4 θ〉 were calculated. These were found to compare favorably with the values of 〈cos2 θ〉 for the polymer chain in the crystalline and amorphous phases obtained from measurements of infrared dichroism. Both orientation averages could be theoretically fitted by using reasonable parameters.
Structure of the quenched form of polypropylene
Authors: McAllister P. B. , Carter T. J. , Hinde R. M.
Published: April 2003

X‐ray diffraction has been used to further investigate the quenched form of polypropylene. The diffractometer traces were analyzed by a mathematical peak separation procedure which assumed a combined Cauchy and Gaussian shape for the peaks. The results confirmed that the quenched form contains about 60% of amorphous polypropylene. In the remainder, the x‐ray diffraction peak positions indicate that the chain helices are arranged in a square array and a cubic or tetragonal symmetry is proposed for this phase. The shape of the x‐ray diffractometer peaks indicates a degree of strain in the structure. Crystallite sizes, determined from peak breadths, have been estimated as approximately 30 Å.
Dynamic mechanical and dielectric properties of phosphonylated polypentenamers and their hydrogenated derivatives
Authors: Rahrig D. , Azuma C. , MacKnight W. J.
Published: April 2003

Dynamic mechanical and dielectric properties of substituted polypentenamers with phosphonate side groups and their hydrogenated derivatives have been studied. Methyl esters, acids, and salts were investigated at two concentrations, 6.5 and 11.1 mole percent. In the unhydrogenated derivatives, one principal relaxation, labeled β, is observed mechanically in the temperature range from −160 to 100°C. This β relaxation arises from micro‐Brownian segmental motion accompanying the glass transition. Its temperature is substantially affected by the substituent concentration while its breadth is affected by the chemical nature of the substituent. An extended “rubbery plateau” region exists in the acid and salt derivatives. The dielectric results generally reinforce the mechanical assignments. In the hydrogenated derivatives, three relaxations labeled α, β, and γ in order of decreasing temperature occur mechanically in this temperature range. The temperatures at which the α and β relaxations occur depend greatly on the chemical nature of the substituents, the substituent concentration, and the thermal history of the sample; while the γ relaxation appears to be independent of these variables. Suggested assignments for the relaxations observed in these polymers, based on the dual glass transition theory of Boyer for semicrystalline polymers, have been proposed. The dielectric results are consistent with the proposed assignments.
On a nonexponential transformation equation for spherulitic crystallization
Authors: Hay J. N. , Przekop Z. J.
Published: April 2003

An equation has been derived for the development of crystallinity from heterogeneously nucleated spherulites which impinge with a small number of neighboring but randomly centered spherulites. The crystallization‐time dependence calculated from the equation conforms to an Avrami equation with initial fractional values for the n exponent, and the equation appears to be a better fit of the initial time dependence of the crystallization of polyethylene than the Avrami equation itself. It appears to account satisfactorily for the observation of fractional n values in the analysis of the crystallization curves of this polymer. The derivation of the equation only accounts for the impingement of spherulites in pairs and does not allow for multiple impingements. This limits its fit to less than the total primary crystallization. The effect on nonrandom centering of spherulites is discussed.
Vapor sorption isotherms for benzene and n‐hepatane with poly(styrene‐co‐butadiene)
Authors: Yen L. Y. , Eichinger B. E.
Published: April 2003

Vapor sorption measurements of Flory–Huggins interaction parameters χ for three poly(styrene‐co‐butadiene) + solvent systems at 25°C are reported. For Philprene 1502 + benzene: χ = 0.379–0.297 v22; for Philprene 1502 + n‐heptane: χ = 0.595 + 0.030 v2 for Solprene 1204 + benzene: χ = 0.516–0.026 v2. The volume for fractions of polymer v2 range from ca. 0.4 to 0.9.
Observation of preferred (epitaxial) orientation relationships between polyethylene crystals
Authors: Miles M. , Gleiter H.
Published: April 2003

Preferred orientations have been observed for polyethylene single crystals deposited at room temperature on a clean polyethlene substrate crystal or a polyethylene substrate crystal coated with silicone oil (but not with a carbon layer). The observed angular relationships can be explained in terms of a network of interfacial dislocations, the cores of which lie in the fold regions between the crystals, and the long‐range strain fields extend into the lattices of both crystals. The interfacial dislocations seem likely to result from the plugging of cilia from one crystal into another.
Epitaxial growth of low molecular weight polypropylene from vapor phase
Authors: Ashida Michio , Ueda Yasukiyo , Watanabe Teizo
Published: April 2003

Polypropylene was evaporated on the (001) cleavage faces of alkali halide single crystals, NaCl, KCl, KBr, and KI, under a vacuum of 10−5 torr. Films evaporated on the substrate were found to be composed of low molecular weight polypropylene with a narrow molecular weight distribution. The polypropylene film evaporated on the substrate maintained at 100°C, was composed of rod‐like crystals of α form, the (010) plane of which was parallel to the (001) plane of alkali halide and their long axes were oriented in the (110) direction of the substrate. When the substrate was kept above 150°C, the film included three crystalline forms, α, γ, and δ forms. Fiber‐like crystals of the α form lay parallel to the (110) direction of NaCl. In the initial stage of growth, lamellar crystals were observed in the film. The lamellar (001) plane lay flat in the film and branching occurred on the (010) lateral faces. Both the γ‐form and the (predominately) new δ‐form crystals were observed in the same area of the film prepared at temperatures above 150°C.
Selective degradation of nylon 6,6. II. Application of the degradation technique to commercially drawn fibers
Authors: Bell James P. , Hughes Alfred J.
Published: April 2003

Treatement with hydrazine was used to investigate the crystalline morophology of commercially drawn nylon 6,6 fibers. Electron microscopic investigation revealed a stacked lamellar structure for the debris of a highly oriented, rapidly drawn fiber. However, the high molecular weight range of the gel permeation chromatogram of this same oriented fiber indicated the presence of high molecular weight material. This is thought to be due to the production of rod‐like, partially extended regions during drawing.
Crystal and amorphous orientation behavior of poly(chlorotrifluoroethylene) films in relation to crystalline superstructure
Authors: Hashimoto Takeji , Kawasaki Hiroshi , Kawai Hiromichi
Published: April 2003

The relationship between the crystalline superstructure of polymer films and molecular orientation was studied in cold‐drawn poly(chlorotrifluoroethylene) films by wide‐angle x‐ray diffraction, birefringence, and depolarized light scattering. By changing crystallization conditions, specimens with almost identical crystallinity but different crystalline superstructures were obtained; i.e., (1) a structure having a random array of crystallites, (2) a superstructure having a rod‐like orientation correlation of the chains (a prespherulitic and sheaf‐like superstructure), and (3) spherulitic superstructure. Upon stretching of specimens, crystallites initially randomly arranged orient with their chain axes along the stretching direction in accord with simple affine deformation. The amorphous chains also orient along the stretching direction. The orientation behavior of the specimens having the rod‐like superstructure is similar to that of the specimens with a random array of crystallites, indicating that the interaction between the crystallites in the superstructure is relatively weak. The molecular orientation behavior of the spherulitic specimens, however, strongly deviates from simple affine deformation owing to strong interaction of the crystallites in the spherulites. The deviation can be interpreted in terms of spherulite deformation and of internal reorientation of chains within deformed spherulites.
Equilibrium melting parameters of poly(ethylene terephthalate)
Authors: Mehta Aspy , Gaur Umesh , Wunderlich Bernhard
Published: April 2003

The equilibrium melting temperature, volume, and enthalpy and entropy changes on melting of poly(ethylene terephthalate) have been analyzed and heats of fusion have been newly measured with an automated scanning calorimeter to yield the following data: 553°K, 16.9 cm3/mole, 2.69 kJ/mole, and 48.6 J/deg/mole, respectively. A more detailed discussion of annealed samples obtained from etched starting materials shows that the density of the noncrystalline regions may be variable.
Nonstationary diffusion of polystyrenes through a cellophane membrane
Authors: Hoogervorst C. J. P. , Smit J. A. M. , Staverman A. J.
Published: April 2003

Diffusion of five polystyrene fractions at various concentrations in toluene through cellophane membranes has been observed. The results have been used to calculate friction coefficients between solvent and solute, and between solute and membrane. The calculation requires measurement of the diffusion coefficient and the reflection coefficient of the solute, of the permeability for the solvent, of the pore volume of the membrane, and of the partition coefficient of the solute between membrane and solvent. By comparing the friction coefficient between solvent and solute in the membrane with this coefficient in free solution, the tortuosity factor and the pore diameter of the membrane can be estimated. The dependence of the friction coefficients on molecular weight M2 of the solute is determined. For large values of M2, the friction between solute and solvent is the determining factor. The friction coefficient between solute and solvent increases more strongly with M2 in the membrane than in free solution owing to an entrance effect for the permeating solute at the interface.
Collapse of pyramidal polyethylene crystals
Authors: White J. R.
Published: April 2003

An assessment of the possible collapse mechanisms for solution‐grown pyramidal polymer crystals is made, taking into account electron microscope observations and the mechanics of the loading situation. That comprehensive collapse always occurs is shown not to be as self‐evident as is normally assumed, even though the more exacting criteria for its establishment are indeed usually met. Bending of lamellar crystals is found to account for many observations, although an alternative means of tilting molecular chains, the “differential shear tilt model” is also considered.
Analysis of the effect of interfacial slippage on the elastic moduli of a particle‐filled polymer
Authors: Takahashi Kiyohisa , Ikeda Masahiko , Harakawa Kazuhisa , Tanaka Kenji , Sakai Tetsuya
Published: April 2003

An attempt was made to study the effect of interfacial slippage on the filler reinforcement based on the boundary condition that the constituents of a particle‐filled composite can slip relative to each other, but no cavities are formed at the interfaces. The elastic field satisfying these conditions is derived using the linear theory of elasticity and the effective elastic moduli of the composite are calculated. The following assumptions are made: (1) Filler particles are spherical, (2) fillers are completely dispersed, and (3) the volume fraction of fillers is sufficiently small that the interaction among fillers may be neglected. The expression for the shear modulus of the composite μ**, which is derived here, is consistent with the viscosity of a suspension which has been derived by Oldroyd. Experiments who that the increase of Young's modulus by glass beads (GB) is lower in polystyrene (PS) than in epoxy resin (Ep). The reinforcement in Ep‐GB systems can be estimated by the well known formula derived assuming perfect adhesion. However, the reinforcement in PS‐GB systems is in rather good agreement with the formula derived here assuming interfacial slippage.
Study of latex film structure by radiothermoluminescence
Authors: Zlatkevich L. , Shepelev M.
Published: April 2003

Radiothermoluminescence has been used to show that the surface of latex globules in nonvulcanized latex films contain segments which become mobile at a temperature 20°K below that observed in bulk polymer. Vulcanization in latex films takes place mainly on the surfaces of the latex globules; vulcanized latex films are microheterogeneous systems.
Association of stereoregular poly(methyl methacrylates) in dilute solution. Proton NMR study
Authors: Spéváček J.
Published: April 2003

By measurement of integrated intensities of high‐resolution proton nuclear magnetic resonance (NMR) bands, associated structures of isotactic (i) and syndiotactic (s) poly(methyl methacrylate) (PMMA) in dilute toluene‐d8 and dimethylformamide‐d7 solutions were detected and characterized. In 1% (w/v) solutions of highly stereoregular s‐PMMA in toluene‐d8 at 27°C, 76% of the monomer units are present in the form of compact aggregates. Consequences of this finding for the polymerization of methyl methacrylate in toluene in the presence of s‐PMMA are discussed.
An endochronic prediction of the variability in fracture times of polymers
Authors: Valanis K. C. , Yilmazer Ulku
Published: April 2003

A theory of variability in lifetimes of identical polymer specimens under identical test conditions is formulated, using the theory of fracture of amorphous crosslinked polymers developed previously by the authors. Variability in fracture times follows from the assumption that the critical number Ncr of bonds that must fail in order to cause fracture of a specimen varies from specimen to specimen. A plausible physical explanation for the variation in Ncr may well lie in the variability of the spatial distribution of weak local regions. The scale of locality may vary from molecular to grosser dimensions. The theory is applied to styrene–butadiene rubber (SBR) under creep conditions and fares well in its prediction of observed results. Most notably, it predicts that the shape of the distribution curve of the observed lifetimes remains invariant with changes in the levels of stress and temperature and that the effects of these manifest themselves through shifts of the curve on the logarithmic time axis. The theory also predicts correctly that the fracture process is accelerated if the creep test is interrupted by unloading–reloading cycles at high strain rates. This last result is shown to be a direct consequence of the concept of “the endochronic time to fracture,” previously introduced by the first author.
Microvoid formation during deformation of high‐impact polystyrene
Authors: Steger T. R. , Nielsen L. E.
Published: April 2003

Small‐angle x‐ray scattering (SAXS) has been used to study the formation of microvoids in polymers which craze or stress‐whiten extensively. Specimens are subjected to a stepwise uniaxial strain, with scattering curves being obtained at each step. The increase in scattering intensity upon crazing is attributed to the formation of microvoids, and the relative size, shape, and concentration of the scattering elements are determined by a Porod analysis of the SAXS curves. The major portion of our work has been on high‐impact polystyrene which shows a large increase in SAXS intensity as crazing occurs. We are able to follow the changes in void size and concentration during craze initiation and growth. Effects of temperature, molecular orientation, and matrix molecular weight have also been studied. The results add to the information on craze growth and microstructure known from electron microscopy and dilatometry. In addition, a qualitative physical model for microvoid nucleation is proposed, and the implications for toughness are discussed.
Dielectric properties of maleic acid–ethylene copolymer in salt‐free aqueous solutions
Authors: Paoletti S. , Van Der Touw F. , Mandel M.
Published: April 2003

The dielectric behavior of maleic acid–ethylene copolymer solutions has been investigated at different polymer concentrations and two degrees of neutralization α′. It is shown that this behavior is analogous to that of ordinary polyacids. Also the experimental data can be explained in terms of the van der Touw–Mandel theory, but at low α′ a possible contribution from motion of negative charges (in turn related to bound proton fluctuations) has to be taken into account. The dielectric results suggest that the formation of intramolecular hydrogen bonds has an influence on the change of the average dimensions of the chain with increasing α′. This seems to be confirmed by viscosity data.
Solubility of carbon dioxide in cellulose acetate at elevated pressures
Authors: Stern S. A. , De Meringo A. H.
Published: April 2003

The solubility of carbon dioxide in symmetric (dense) cellulose 2.4‐acetate has been measured at temperatures from 0 to 70°C and pressures up to 45 atm. The polymer samples were prepared by slowly drying asymmetric reverse osmosis membranes. The solubility isotherms can be described satisfactorily up to 60°C by the “dual‐sorption” model for glassy polymers. The model cannot represent the experimental data above 60°C, possibly because of a second‐order transition in the polymer between 60 and 70°C. An analysis of the dual‐sorption parameters and of the heats of solution and “hole filling” suggests that the polymer samples contained a relatively large volume of microcavities. Gas solution appears to occur predominantly in microcavities, a large fraction of the penetrant moleculers being immobilized or partially immobilized. The solubilities obtained in this work are compared with similar data computed from time‐lag measurements of other investigators, and the validity of the dual‐sorption model is examined for the present case.
Thermodynamic properties of phenol–formaldehyde resin
Authors: Harwood C. , Wostenholm G. H. , Yates B. , Badami D. V.
Published: April 2003

Characterization measurements of a commercial phenol‐formaldehyde resin prepared from constituents including phenol and formaldehyde in the molar ratio 1:1.33 are reported. The measurements consist of (1) the linear thermal expansion coefficient between approximately 85 and 270°K; (2) the specific heat capacity between approximately 6 and 100°K; (3) the Young's modulus at room temperature. A critical examination of the data reveals that: (1) the vibrational behavior is predominantly that of a three‐dimensional assembly; (2) as far as data available from other sources permit an assessment to be made, the principle of additivity appears to be applicable to the specific heat capacity between approximately 50 and 100°K; and (3) the data lie near the limit of an empirical relationship observed between the Young's modulus and linear thermal expansion coefficient of other polymers.
Morphology and rheology of peel of model adhesives
Authors: Parsons W. F. , Faust M. A. , Brady L. E.
Published: April 2003

The morphology of surfaces produced during peel experiments was studied to increase the understanding of peel phenomena. Thin films of polystyrenes of narrow molecular‐weight distribution and a polydisperse polyester on flexible supports were peeled from rigid substrates at temperatures above their glass transitions with equipment that also permitted quenching and preservation of the peeled surfaces which then could be studied by scanning electron microscopy. The results show many types of cavitation including foams and the coalescence of cavities to form fibers. Cavitation occurred throughout and beyond the region of transition from cohesive to interfacial failure where peel force decreased abruptly; however, cavity growth was abruptly restricted as the failure mode changed. The master curves and shift factors obtained in this work provided strong evidence that the quenching used to preserve the peeled surfaces did not introduce large perturbations in the results. The reason was that failure occurred at or close to the heated substrate.
Effect of ozone on creep of vulcanizates
Authors: Metherell C.
Published: April 2003

In‐service secondary creep rates of natural rubber (NR) vulcanizates at ambient temperature are known to be low. However, in tests on thin strips of NR vulcanizates in tension, secondary creep at rates of up to 120%/week were observed. From an examination of the effect of antioxidants, antiozonants, waxes, and specimen thickness it was shown that the anomalous creep was due to ozone attack on the vulcanizate, which only becomes serious in tests on thin strips in tension.
Fourier transform infrared studies on the thermal degradation of polyacrylonitrile
Authors: Coleman M. M. , Petcavich R. J.
Published: April 2003

Fourier transform infrared studies of the thermal degradation of polyacrylonitrile (PAN) conducted at 200°C in air and under reduced pressure are presented. The spectra are markedly superior to those published previously. A mechanism consistent with the infrared results obtained under reduced pressure is advanced, and assignments for the infrared bands occuring in the spectrum of both the reduced pressure and air degraded PAN are given.
Solid‐state polymerization of a diacetylene crystal: Thermal, ultraviolet, and γ‐ray polymerization of 2,4‐hexadiyne‐1,6‐diol bis‐(p‐toluene sulfonate)
Authors: Chance R. R. , Patel G. N.
Published: April 2003

Results are presented for the thermal, ultraviolet, and γ‐ray polymerization of 2,4‐hexadiyne‐1,6‐diol bis‐(p‐toluene sulfonate) (PTS). Monomer extraction is used to obtain polymer conversion‐vs.‐time curves at 30, 50, and 80°C. In agreement with previous work over a narrower temperature range, the curves all display a dramatic autocatalytic effect with an onset at about 10% conversion to polymer. Although the polymerization rate undergoes a 200‐fold change over this temperature range, the shape of the conversion curves does not change. These data yield an activation energy (E) of 22.2 ± 0.4 kcal/mole when interpreted in terms of the time required to reach 50% polymer. An annealing technique is used to provide a closer look at the autocatalytic region. In that case, E = 22.5 ± 0.8 kcal/mole is determined from measurements of the time required to go from 10 to 50% polymer at temperatures ranging from 23 to 80°C (a 500‐fold change in rate). Thermal polymerization rates measured in the low‐conversion limit using a spectroscopic method based on diffuse reflectance yield E = 22.8 ± 0.6 kcal/mole. Thus E is independent of polymer conversion and the autocatalytic effect can be best understood as arising from a large increase in the propagation length of the polymer chains. The autocatalytic effect is shown to be present in both UV and γ‐ray polymerization. In the case of γ‐ray polymerization, conversion‐vs.‐time and spectroscopic measurements are consistent with inhomogeneities in the polymer concentration caused by particle tracks. Activation energies for UV and γ‐ray polymerization are quite low (2‐3 kcal/mole) and confirm that the chain initiation event makes the major energetic contribution to E. The polymerization mechanism is discussed in detail. The photopolymerization experiments can be consistently interpreted with a model based on the triplet excited state of the diacetylene monomer as the chain initiation species.
Epitaxial crystallization of polyesters on inorganic and organic substrates
Authors: Rickert S. E. , Baer E. , Wittmann J. C. , Kovacs A. J.
Published: April 2003

A series of low‐molecular‐weight linear polyesters were epitaxially crystallized from dilute solution and the melt on a variety of organic and inorganic substrates. The rod‐like polyester crystals which were formed assumed general orientations in alignment with substrate geometry. This yielded monodirectional orientation of these crystals on one of the organic substrates, and bidirectional orientation on the other surfaces. Heterogeneous nucleation on the organic substrates, trioxane and naphthalene, induced the growth of much larger epitaxial crystals than have previously been observed on inorganic substrates. Those polyesters, with a high percentage of methylene units per chain repeat, crystallized in an unusual polymorphic form when in contact with the organic substrates. Polymorphic transformation to the normal form was not possible under thermal treatment or with increased crystal thickness. The expected relationship between dipolar alignment in the polymer crystal and this polymorphism was established.
Observations on the dielectric anisotropy of solutions of flexible polymers in flow
Authors: Block H. , Ions W. D. , Walker S. M.
Published: April 2003

Measurements of the increase in the relative permittivity for solutions of polystyrenes, poly(p‐ethoxystyrene), poly(methyl methacrylate), and poly(N‐vinyl carbazole) when subjected to shear gradients are reported. The influences of such factors as shear rate, concentration, viscosity, solvent permittivity, polymer dipole moment, and polymer molecular weight on the phenomenon are described. An empirical correlation for the diverse data obtained with polystyrenes and poly(p‐ethoxystyrene) has been established, but this relation does not entirely match the theoretically predicted effects. We discuss the various physical processes which may have an influence on the observed phenomenon.
Properties of polyethylene modified with phosphonate side groups. II. Dynamic mechanical behavior
Authors: Weiss R. A. , Lenz R. W. , Macknight W. J.
Published: April 2003

The viscoelastic behavior of phosphonate derivatives of phosphonylated low‐density polyethylene (LDPE) was studied by dynamic mechanical techniques. The polymers investigated contained from 0.2 to 9.1 phosphonate groups per 100 carbon atoms and included the dimethyl phosphonate derivative and two derivatives for which the phosphonate ester group was an oligomer of poly(ethylene oxide) (PEO). The temperature dependences of the storage and loss moduli of the dimethyl phosphonate derivatives were qualitatively similar to those of LDPE. At low phosphonate concentrations, the α, β, and γ dispersion regions characteristic of PE were observed, while at concentrations greater than 0.5 pendent groups per 100 carbons atoms, only the β and α relaxations could be discerned. At low degrees of substitution, the temperature of the β relaxation Tβ decreased from that of PE, but above a degree of substitution of 0.1, Tβ increased. This behavior was attributed to the competing influences of steric effects which tend to decrease Tβ and dipolar interactions between the phosphonate groups which increase Tβ. For the phosphonate containing PEO, a new dispersion region designated as the β′ relaxation was observed as a low‐temperature shoulder of the β relaxation. The temperature of the β′ loss was consistent with Tg(U) of the PEO oligomers as determined by differential scanning calorimetry, and it is suggested that the β′‐loss process results from the relaxation of PEO domains which constitute a discrete phase within the PE matrix.
Raman spectroscopic method for determining the crystallinity of polyethylene
Authors: Strobl G. R. , Hagedorn W.
Published: April 2003

The Raman spectrum of partially crystalline polyethylene can be described as a superposition of three components, which originate from the orthorhombic crystalline phase, a meltlike amorphous phase, and a disordered phase of anisotropic nature, where chains are stretched but have lost their lateral order. The mass fractions involved in the three phases can be derived directly from the integral intensities of characteristic bands without an additional calibration procedure. A comparison of the results obtained for a variety of samples shows agreement with the crystallinities derived from the density, and the small‐angle and wide‐angle x‐ray diagrams. Data indicate that the disordered anisotropic phase is located at a transition zone between crystalline and amorphous layers. Application of the method in a temperature‐dependence experiment permits a detailed examination of partial melting.
Growth kinetics of solvent crazes in glassy polymers
Authors: Kramer Edward J. , Bubeck Robert A.
Published: April 2003

The kinetics of craze growth from sharp cracks in polystyrene (PS) and poly(methyl methacrylate) (PMMA) in contact with liquid methanol were measured with time‐lapse photography as a function of the stress intensity factor KI. At high KI the craze length in both systems increases as √t if the sides of the craze are protected from methanol and as t if they are not, where t is the elapsed time after loading. If such a side‐protected craze is dried under load and then methanol is reintroduced to the crack tip, the methanol front advances with the same kinetics as the original craze growth. This experiment Proves that solvent crazing velocities are limited by the hydrodynamic transport of solvent through the porous craze structure under a capillary pressure driving force (which can be as high as 100 atm). An improved model of fluid flow through the craze is developed and shown to predict craze growth kinetics in good agreement with those observed. The hydraulic permeability of methanol crazes in PS was found to be independent of craze length at small craze length and to be independent of KI except at very low KI. Although increases in molecular weight in the range Mw = 200,000 to Mw = 670,000 do not markedly affect the crazing kinetics, they greatly increase the time to fracture of the craze.
Ion‐aggregation and thermal expansion in styrene‐based ionomers
Authors: Eisenberg A. , Trepman E.
Published: April 2003

The linear thermal‐expansion coefficients (α) of styrene–sodium methacrylate copolymers were studied as a function of the concentration of sodium methacrylate comonomer. Over the concentration range studied (0.61–9.0 mole % sodium methacrylate), the expansion coefficients of the glass αg and of the liquid αl were independent of ion concentration. Average values for these quantities were αg = (6.9 ± 0.9) × 10−5 deg−1 and αl = (16.0 ± 2.0) × 10−5 deg−1. When samples of concentrations above 6 mole % were heated from room temperature, a low value for the liquid‐expansion coefficient αl was observed in the first runs. This quantity had an average value of (12.0 ± 1.9) × 10−5 deg−1. Heating of the 6.5 mole % sample from room temperature followed by cycling from the glass transition temperature Tg to successively higher temperatures resulted in a gradual increase in liquid‐expansion coefficient. The results are consistent with the hypothesis of the existence of various types of ionic aggregates in these polymers, with the state of aggregation changing at approximately (5–6) % of ions. Experimental Tg values, which increase with ion concentration over the entire range, are consistent with the results of previous studies.
The structure and properties of oriented fibers of poly(pentamethylene terephthalate). I. Synthesis of polymer and preparation of two different crystalline phases
Authors: Hall I. H. , Pass M. G. , Rammo N. N.
Published: April 2003

The synthesis of poly(pentamethylene terephthalate) and its subsequent drawing into highly oriented fiber has proved difficult for two reasons. First, it was difficult to produce polymers of sufficiently high molecular weight to withstand subsequent drawing; and second, because of the slow rate of crystallization of the material, the spun fiber coalesced on the windup bobbin, becoming useless for drawing. Methods are described which overcome these difficulties. Two crystalline phases of the oriented fiber have been discovered. The α form is obtained by annealing under zero or small tension and has a crystallographic repeat along the fiber axis of 24.7 Å compared with a chemical repeat of 14.5 Å. There are evidently two monomers per crystallographic repeat, each appreciably contracted. The β form is obtained by annealing either under high tension or at constant extended length, but in the relaxed fiber it always exists in mixture with the α form. Its crystallographic repeat is 28.2 Å, and so again consists of two monomers; but their conformation is more highly extended than that of the α form. An α‐form fiber will transform reversibly to the β form under the influence of mechanical stress.
Structural relaxation in poly(vinyl acetate)
Authors: Sasabe Hiroyuki , Moynihan Cornelius T.
Published: April 2003

Structural relaxation in poly(vinyl acetate) (PVAc) in and slightly above the glass‐transition region has been studied by monitoring the time dependence of enthalpy using differential scanning calorimetry and the frequency dependence of electric polarization by dielectric loss measurements. The results have been analyzed to yield the kinetic parameters characterizing the structural relaxation and are compared with similar analyses of previously published shear compliance and volume relaxation experiments. Relaxation of enthalpy, electric polarization, volume, and shear stress in PVAc all appear to be characterized by somewhat different relaxation times. The difference between the volume and enthalpy relaxation times, coupled with the fact that PVAc exhibits a Prigogine–Defay ratio greater than unity, is evidence for a previously proposed connection between the thermodynamics and kinetics of structural relaxation in terms of an order parameter model.
Time‐resolved fluorescence spectroscopy of polystyrene and poly(1‐vinylnaphthalene)
Authors: Ghiggino K. P. , Wright R. D. , Phillips D.
Published: April 2003

An apparatus is described which enables the rapid recording of time‐resolved emission spectra on a nanosecond time scale. The instrument permits detailed study of the time‐dependent photo‐physical processes occurring in many polymer systems. The technique has been used to investigate the kinetics of excimer formation in methylene chloride solutions of polystyrene and poly(1‐vinyl‐naphthalene). Unambiguous evidence for excimer dissociation is observed in poly(1‐vinylnaphthalene) but the process appears unimportant in solutions of polystyrene.
Study of the molecular motions of polyethylene by line‐shape analysis of broad‐line proton NMR spectra
Authors: Bergmann Klaus
Published: April 2003

The broad‐line proton NMR spectra of polyethylene are separated into three components (broad, medium, and narrow) corresponding to the crystalline and two kinds of amorphous protons, respectively. All amorphous protons are found to be mobile above 210°K. The unusually low molecular mobility in the amorphous regions of polyethylene compared to purely amorphous and other partially crystalline polymers is considered to be adequately described by the network model of Edwards and De Gennes. In this model the chain motions are anisotropic and restricted to small tubular volumes. The medium and the narrow component are believed to result from two different modes of chain motion within these tubes, depending on the free volume available. Two motions in the crystalline regions are observed. One at temperatures below 110°K involves 2%–5% of the protons, depending on the crystallinity of the material, and the other beginning at 290°K involves all crystalline protons (α‐process). Coupling of the amorphous and crystalline motions is found above 290°K. Several line shapes have been tested as representations of the three components. Of these the low‐temperature spectrum, the Gauss–Lorentz product curve, and the Lorentz curve proved to be the most suitable shapes for the broad, medium, and narrow component, respectively. Using these line shapes, the best fit of the experimental spectra and the expected agreement of the broad and the crystalline fraction are obtained over a very broad temperature range. Above 310°K the low‐temperature spectrum must be replaced by the convolution of a Gauss curve and a rectangular function to take into account the line‐shape transition of the α‐process. The modulation broadening of all components is considered, and this allows line‐shape analysis close to the melting point.
An approximate method of determination of birefringence of circular fibers from intensity distribution of backscattered light
Authors: Holoubek Jaroslav
Published: April 2003

A method proposed for determination of high birefringence values of circular fibers is based on an analysis of the intensity of backscattered light for two orthogonal polarization directions of the incident light. The method has been used in the determination of birefringence of nylon 6‐6 fiber from a circular photographic recording of scattered light. The values thus obtained are compared with those obtained by polarized light microscopy.
The effect of pressure on the volume and the dielectric relaxation of linear polyethylene
Authors: Sayre John A. , Swanson Stephen R. , Boyd Richard H.
Published: April 2003

The effects of pressure on the α (ca. 70°C, 1 kHz) and γ (ca. −100°C, 1 kHz) relaxations of linear polyethylene were studied dielectrically between 0 and 4 kbar. Equation of state (PVT) data were also determined in the range of interest of these relaxations. The sample was rendered dielectrically active through oxidation (0.8 C0 per 1000 CH2). The α process (which occurs in the crystalline fraction) could be studied over a much wider temperature range than heretofore possible due to the effect of pressure in increasing the melting point. Examination of relaxation strength from 50 to 150°C showed that there must be two crystalline relaxation processes: the well‐known α relaxation plus a competing one. The α relaxation is believed to be due to a chain twist–rotation–translation mechanism that results in rotation–translation of an entire chain in the crystal. The relaxation strength of the α process decreases and therefore indicates the presence of a second (faster and not directly observed) process that increases in intensity with increasing temperature. It is postulated that the second process is due to motion of defects that become more numerous through thermal injection at higher temperatures. Analysis of the relaxation data along with the PVT data allowed the constant volume activation energy for the α relaxation to be determined. It was found to be 19.4 ± 0.5 kcal/mole. The constant volume activation energy is important in modeling calculations of the crystal motions and is significantly smaller than the atmospheric constant pressure activation energy of 24.9 kcal/mole. The effect of pressure on the activation parameters and shape of the γ process was also determined. There has been controversy over whether the γ process occurs only in the amorphous fraction or in both the amorphous and crystalline phases. Since the two phases have quite different compressibilities, increasing the pressure should change the shape of the loss curves (versus frequency and temperature) if the process occurs in both phases. The shape (but not location) of the loss curves was found to be remarkably independent of pressure. This finding strengthens the view that the γ process is entirely amorphous in origin.
An ESR study of polymer‐Cu(II) complexes in poly(vinyl alcohol), polyacrylamide, and poly(vinyl pyrrolidone) films
Authors: Sumita Osao , Fukuda Atsuo , Kuze Eiichi
Published: April 2003

Optical and ESR spectra of polymer‐Cu(II) complexes in polymer films have been studied. The dependence on F1 = [Cu2+]/[MU] and F2 = [OH−]/[Cu2+], where [MU] is the molar concentration of monomeric units of the polymer, has been obtained. Optical spectra and potentiometric titration curves in solution have also been studied. There exists a buffer region 0 ≲ F2 ≲ 2. Optical spectra in films are slightly different from those in solutions. At least five different ESR signals, designated as A, B, C or D, and E, have been found in poly(vinyl alcohol)‐Cu(II). These signals appear successively with increasing F2. Assignments are proposed as follows. Signal A (F2 ≈ 0), also found in poly(acrylamide)‐Cu(II) and poly(vinyl pyrrolidone)‐Cu(II), is due to a single Cu(II) coordinated with two water molecules and chelated with two oxygens or nitrogens attached to the polymer. A chain of Cu(II) ions singly and double bridged with OH− ions is responsible for the B signal (F2 ≈ 1). The C and D signals (F2 ≈ 2) appear to be caused, respectively, by a dimeric Cu(II) complex singly or doubly bridged with OH− ions. The E signal (F2 ≈ 7) appears to be due to a monomeric Cu(II) complex, different from that responsible for the A signal.
Crystallization and melting of aqueous gelatin
Authors: Godard P. , Biebuyck J. J. , Daumerie M. , Naveau H. , Mercier J. P.
Published: April 2003

Gelation and melting of aqueous gelatin were investigated by differential scanning calorimetry. This phenomenon can be analyzed as a conventional crystallization process assuming predetermined primary nucleation and unidirectional growth. The results were interpreted in terms of the fringed micelle model. Calculated values of the diameter of the renatured collagen fibril were found in excellent agreement with those determined previously by electron microscopy.