bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rapid stress‐induced crystallization in natural rubber
Authors: Mitchell J. C. , Meier D. J. 
Published: April 2003

AbstractStress‐induced crystallization in a rapidly stretched natural rubber gum vulcanizate has been studied using thermal techniques to follow the development of crystallinity. A special‐purpose analog computer has been assembled and used on‐line to process the thermal and mechanical data obtained in high speed tensile testing. Roughly first‐order room temperature crystallization kinetics curves were obtained having time constants of 50–60 msec in the range of 400–540% extension. While the rate of this rapid, presumably primary crystallization appears rather insensitive to elongation in this limited range, the extent of crystallization at 400 msec increases smoothly from zero at 340% elongation to around 18% at 540% elongation. It is shown that our high‐speed tensile tester can stretch this vulcanizate fast enough that most of the crystallization takes place after extension has been completed. Stress‐strain curves obtained at this high rate are compared with those obtained at lower rates where crystallization takes place during the stretching.
Birefringence of semicrystalline polymeric networks
Authors: Smith K. J. 
Published: April 2003

AbstractA simple theoretical development is proposed to explain the variation of birefringence with degree of crystallization for crosslinked, stretched polymer networks. The model adopted for the calculations is one proposed by Flory in order to calculate the thermodynamic properties of such systems and hence is restricted to the special case of network orientation prior to the onset of crystallization. Our findings are briefly discussed and possible applications of the results are considered.
Birefringence of native cellulosic fibers. I. Untreated cotton and ramie
Authors: Iyer K. R. Krishna , Neelakantan P. , Radhakrishnan T. 
Published: April 2003

AbstractThe Rayleigh‐Gans theory of light scattering by a homogeneous cylinder has been applied to the case of scattering by a pad of fibers immersed in a liquid. The theory enables one to locate precisely the matching wavelength at which the mean refractive index of a sample of optically heterogeneous fibers coincides with that of an immersion medium. Thereby it offers a method of determining the mean refractive index. Besides, it facilitates a quantitative estimation of the variability of refractive index. The new technique has been used to study the birefringence of untreated cotton and ramie. The results are presented and discussed.
Intrinsic viscosity of polymers of low molecular weight
Authors: Bianchi Umberto , Peterlin Anton 
Published: April 2003

AbstractExperimental evidence concerning the dependence of the intrinsic viscosity [η] on molecular weight M in the low molecular weight range (from oligomers to M = 5 × 104) has been collected in a variety of solvents for about ten polymers, i.e., polyethylene, poly(ethylene oxide), poly(propylene oxide), polydimethylsiloxane, polyisobutylene, poly(vinylacetate), poly(methyl methacrylate), polystyrene, poly‐α‐methylstyrene, and some cellulose derivatives. In theta solvents, the constancy of the ratio [η]Θ/M0.5 extends down to values of M much lower than those predicted by current hydrodynamic theories. In good solvents, and on decreasing M, the polymers examined, with the exception of polyethylene and some cellulose derivatives, show a decrease in the exponent a of the Mark‐Houwink equation [η] = KMa. This upward curvature gives rise to the existence of a more or less extended linear region where the equation [η] = K0M0.5 is obeyed. Below the linear range, i.e., for even shorter chains, the exponent a can increase, i.e., polydimethylsiloxane, or decrease below 0.5, i.e., poly(ethylene oxide), depending on the particular chain properties. These different dependences have been discussed in terms of: (a) variations of thermodynamic interactions with molecular weight; (b) variations of conformational characteristics (as for instance the ratio) 〈r02/nl2〉, where 〈r02〉 is the unperturbed mean square end‐to‐end distance and n is the number of bonds each of length l; (c) hydrodynamic properties of short chains.
Multiple melting in nylon 66
Authors: Bell J. P. , Slade P. E. , Dumbleton J. H. 
Published: April 2003

AbstractEither of the two endothermic melting peaks found by differential thermal analysis of nylon 66 may be converted to the other by appropriate choice of annealing conditions. The two peaks are considered due to the melting of two morphological species, forms I and II. Form I is relatively fixed in melting temperature, while the form II melting temperature varies with annealing conditions and can be either above or below form I. The two forms can be distinguished by whether or not the conversion I → II takes place; if the sample is in form II no change in the thermogram is observed under suitable conversion conditions. The conversion of form I to form II also takes place during cold drawing. It has been previously shown that form I results from rapid cooling from the melt, and form II results from slow cooling. Form I appears to be kinetically favored, while form II is thermodynamically preferred. The variability in the form II melting point is attributed to variable crystal size and/or perfection.
β Relaxations in polyethylenes and their anisotropy
Authors: Stachurski Z. H. , Ward I. M. 
Published: April 2003

AbstractMeasurements have been made of the anisotropy of viscoelastic behavior in specially oriented sheets of low‐density polyethylene. The results for the cold‐drawn sheets show a β relaxation process of very characteristic anisotropy. The annealed sheets show two relaxations in this region of temperature. The lower relaxation (about −10°C) is identified as an interlamellar shear process. The higher relaxation (about 70°C) has a very similar anisotropy to the β relaxation in cold‐drawn samples. Isotropic sheets of low‐density polyethylene have been also investigated. Two β relaxations are found in these materials.
Diffusion in polymer–solvent systems. A study of numerical methods of simulation
Authors: Riek Raymond F. , McAvoy Thomas J. , Chappelear David C. 
Published: April 2003

AbstractFickian and non‐Fickian diffusion into polymer‐solvent systems were simulated on both analog and digital computers. Methods were evaluated to solve the descriptive nonlinear ordinary and partial differential equations. Analog methods published previously have been expanded. It was shown that discrete time solutions are superior to discrete distance solutions for partial differential equations, as hardware requirements are small. Also, accuracy problems on some of the smaller installations can be reduced by reverse time integration. For highly nonlinear equations, analog methods are superior to digital in stability and effort required. Digital solutions can be require extensive preliminary work to define computation parameters. However, the errors introduced by the finite difference equations are small in moderately nonlinear equations and much more accurate solutions are possible. Generalized solutions for polymer‐solvent diffusion with exponential concentration dependence are presented for the Fickian cases. Also, typical solutions are demonstrated for all known types of non‐Fickian diffusion.
Equation for the interfacial tension between demixed polymer solutions
Authors: Vrij A. 
Published: April 2003

AbstractThe theory of Cahn and Hilliard is used to derive an equation for the interfacial tension (free energy) between some demixed polymer solutions, applying a simple solution model treated by Debye in his theory of light scattering near the critical solution temperature. For a (symmetrical) system containing two polymers in a common solvent it is found that the interfacial tension is given by σ = (l/12½)Ωφp 2σr, where l is the Debye l parameter for the range of molecular interaction—here equal to (2S2)½, where (S2)½ is the radius of gyration of both polymers, Ω is a heat of mixing parameter for polymer‐polymer interaction, φp is the total volume fraction of polymer and σr is a function of the ratio of temperature and critical solution temperature. The equation is in qualitative agreement with experiments of Langhammer and Nestler.
Annealing of polybutene‐1 single crystals
Authors: Woodward A. E. , Morrow D. R. 
Published: April 2003

AbstractThe effects of thermal treatment in the 70–90°C. region on polybutene‐1 crystals, prepared by precipitation from dilute pentyl acetate solutions and with lath, hexagonal, and square morphologies, have been studied by using electron microscopy. The stability of polybutene‐1 crystals to thermal treatment increases in the order: lath < hexagonal < square. Elucidation of the crystallographic directions in unheated lath crystals with respect to the overall morphology was carried out; evidence for restricted folding in these crystals is discussed.
Solution properties of polystyrene–polybutadiene block copolymers
Authors: Utracki Lechoslaw A. , Simha Robert , Fetters Lewis J. 
Published: April 2003

AbstractDilute solution viscosity and osmotic pressure measurements were performed on polystyrene (PS), polybutadiene (PB), polystyrene–polybutadiene (SB) diblock and polystyrene–polybutadiene (SBS) triblock copolymers. Anionic polymerization was used in such a way that the molecular weight of the PS block was kept constant (ca. 10 000), while the molecular weight of the PB block varied from 18000 to 450000. The measurements were carried out at a fixed temperature of 34.20°C in three solvents, namely toluene, a good solvent for PS as well as for PB, dioxane, which is a good solvent for PS and almost a theta solvent for PB, and cyclohexane, which is nearly a theta solvent for PS and a good solvent for PB. The compositions of SB and SBS, as derived from kinetic data agree with ultraviolet measurements in CHCl3 solutions. The viscosity and osmotic pressure results indicate that the properties of SB and SBS are similar. Their intrinsic viscosities and second virial coefficients can be calculated from their chemical compositions, molecular weight, properties of parent polymers, and values of the interaction parameter \documentclass{article}\pagestyle{empty}\begin{document}$\bar \beta _{{\rm SB}}$\end{document} between styrene and butadiene units, for molecular weights not exceeding approximately 105. The magnitude of \documentclass{article}\pagestyle{empty}\begin{document}$\bar \beta _{{\rm SB}} $\end{document} varies with the solvent. The results suggest that the domains of the PS and PB blocks overlap to a great extent.
La luminescence différée du styrène en solution vitreuse dans le méthylcyclohexane
Authors: Hayashi K. , Déroulède A. , Kieffer F. 
Published: April 2003

AbstractThe trapping of electrons and styrene cations and anions has been studied in a methylcyclohexane glass by the techniques of deferred luminescence. Radiothermoluminescence curves consist of two peaks, at 90 and 95°K, in this matrix. The second peak increases linearly with styrene concentration up to 2 × 10−2M when it reaches a constant value, whereas the first peak increases from 10−4 to 10−3M and then decreases at higher concentrations and is not discernible at concentrations above 10−2M. We propose two mechanisms which are qualitatively consistent with this behavior and are based essentially on the recombination of styrene cations with thermally detrapped electrons in the first peak and with anions in the second peak. Photothermoluminescence (i.e., thermoluminescence after photoionization with ultraviolet light) similarly consists of the 90 and 95°K peaks for a 10−3M solution and of the 95° peak alone for a 10−d M solution.Radiophotoluminescence excitation spectra at 77°K, corresponding to absorption spectra of trapped electrons and styrene anions, show that anions are the predominant negative species in 10−2 molar solution, and trapped electrons in 10−3 molar solution. Spectral analysis of radiothermoluminescenece shows the presence of two emission bands, one of which is identical with styrene fluorescence excited by the 254 Nm mercury line (λmax = 292, 302, 307, and 317 Nm). The other band has three fairly poorly resolved maxima at 474, 486 and 496 nm and seems to correspond to the fluorescence of C6H5ĊH‐CH3 radicals formed during radiolysis.
Polymerization of aromatic nuclei. XIV. Polymerization of toluene with aluminum chloride–cupric chloride
Authors: Kovacic Peter , Ramsey J. S. 
Published: April 2003

AbstractThe polymerization of toluene with aluminum chloride and cupric chloride was performed in carbon disulfide and in a neat system. The solvent reaction produced an insoluble, light‐brown product which did not melt below 350°C. In the neat system, polymerization was much more vigorous, yielding a dark, purple‐brown solid with mp ∼250°C and molecular weight of 634. Infrared, NMR, and ultraviolet spectroscopy, along with elemental analysis and oxidative degradation, indicated that the backbone chain contains o‐polyphenylene units with the methyl group situated in the 4‐position. Some p‐polyphenylene structures may also be present. Evidence for small amounts of benzyl and polynuclear moieties was obtained. The mechanistic aspects are discussed. Our principal conclusions concerning oligomer structure are in disagreement with those of Kuwata.
Effect of a trifluoromethyl group on the polymerizability of α‐olefins by transition metal catalysts
Authors: Overberger C. G. , Khattab G. 
Published: April 2003

AbstractSeveral α‐olefins containing the trifluoromethyl group were prepared and characterized. 4,4,4‐Trifluoro‐1‐butene, 3‐trifluoromethyl‐1‐butene, 5,5,5‐trifluoro‐1‐pentene, and 4‐trifluoromethyl‐1‐pentene were homopolymerized with VCl3–Al(i‐Bu)3 catalyst. The trifluorobutenes gave low‐melting polymers with low fluorine contents. Polymers obtained from the trifluoropentenes were soluble having moderately high intrinsic viscosities. Copolymerizations of these monomers with their nonfluorinated homologs by the same catalyst system indicated low reactivities of the fluoromonomers. Nuclear magnetic resonance spectra of the fluorinated and nonfluorinated monomers and their respective spectroscopic studies with the catalyst (C5H5)2TiCl2–Al(CH3)3 indicated an electron deficiency of the vinyl group of the fluorobutenes. This was related to the inductive effect of the trifluoromethyl group. The inductive effect of this group was absent in the fluoropentenes and the nonfluorinated monomers. The electron‐deficient vinyl group of the fluorobutenes apparently did not allow these monomers to coordinate with the active sites of the catalyst. Polymerization studies of the nonfluorinated monomers, 1‐butene, 3‐methyl‐1‐butene, 1‐pentane, and 4‐methyl‐1‐pentene, with the catalyst VCl3–Al(Bu)3, were performed in the presence of compounds containing the trifluoromethyl group. Results indicated that this group did not retard the rate of polymerization of these monomers. Evidence is presented to show that a catalytic amount of benzotrifluoride enhanced the rate of polymerization of α‐olefins, particularly that of sterically hindered monomers such as 3‐methyl‐1‐butene.
Tri‐o‐tolylphosphine: A rapid photopolymerization initiator
Authors: Eldred Roger J. 
Published: April 2003

AbstractThe rate of tri‐o‐tolyphosphine‐initiated photopolymerization of methyl methacrylate was found to be significantly higher than that for the triphenylphosphine initiated polymerization. The mechanism was shown to be dependent upon the concentration of the initiator. At low concentrations (10−4 mole/l.), an activated complex is the initiating species, while at higher concentrations (above 10−2 mole/l.) homolytic cleavage of the phosphorus–carbon bond is the radical source. Steric inhibition of resonance is advanced as an explanation for the enhanced activity of tri‐o‐tolylphosphine over triphenylphosphine.
γ‐Ray‐induced terpolymerization of carbon monoxide, aziridines, and cyclic ethers
Authors: Kagiya Tsutomu , Kondo Masatsune , Maruta Isao , Fukui Kenichi 
Published: April 2003

AbstractThe terpolymerization of carbon monoxide, aziridines, and cyclic ethers was carried out by γ‐irradiation. A partially crystalline solid copolymer was obtained. The infrared spectrum of the copolymer obtained indicated characteristic peaks due to the secondary amide and ester groups. The results of elementry analysis, infrared spectra, and x‐ray diffraction of the copolymer showed that terpolymerization of carbon monoxide, aziridine, and cyclic ether took place by γ‐irradiation. 2‐Vinyl‐1,3‐dioxolane was polymerized in the system of carbon monoxide and ethylenimine to give a solid polymer. The infrared spectrum showed characteristics of the secondary amide and dioxolane ring, while no absorption due to carbonyl group of ester was observed. The infrared spectra and results of elementary analysis confirmed that the terpolymerization of carbon monoxide–ethylenimine–2‐vinyl‐1,3‐dioxolane occurred.
The high‐temperature degradation of poly(2,6‐dimethyl‐1,4‐phenylene ether)
Authors: Factor A. 
Published: April 2003

AbstractThe thermal degradation of poly(2,6‐dimethyl‐1,4‐phenylene ether) has been investigated to 1000°C in an inert atmosphere. X‐ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were employed to study the physical changes in the polymer, and vapor‐phase chromatography, infrared spectroscopy, and mass spectrometric thermal analysis were used to elucidate the chemical aspects of the degradation process. It was found that degradation occurs in two steps: (1) a rapid exothermic process occurs between 430 and 500°C, leading to the evolution of phenolic products, water, and a black, highly crosslinked residue, and (2) a slower, char‐forming process occurs above 500°C, characterized by the evolution of methane, carbon monoxide, and hydrogen. The chars formed in process 2 were found by x‐ray analysis to be amorphous. The infrared spectrum of a sample heated to 510°C is nearly identical with that of the starting polymer, indicating that oxidative reactions are not important in the first process. The data for the low‐temperature process are consistent with a thermal degradation scheme based on the radical‐redistribution reaction of polyphenylene ethers and/or the degradation of o‐benzylphenols formed by the thermal rearrangement of o‐methyl diphenyl ethers. The char‐forming process is best explained by simultaneous operation of the Szwarc mechanism of toluene pyrolysis, producing hydrogen and methane and reactions that cleave the aromatic rings and produce carbon monoxide.
Isolation and identification of the linear and cyclic oligomers of poly(ethylene terephthalate) and the mechanism of cyclic oligomer formation
Authors: Peebles L. H. , Huffman M. W. , Ablett C. T. 
Published: April 2003

AbstractChromatographic techniques are described which can be used to isolate and identify the linear and the cyclic oligomers of poly(ethylene terephthalate). Extraction of the oligomers from high molecular weight polymer produces at least eight different cyclic species, some of which are isolated and identified.The cyclic dimer, the cyclic trimer, and the cyclic tetramer of poly(ethylene terephthalate) have also been prepared by acid chloride esterification and transesterification. Similar materials can be isolated from the ethylene glycol distillate obtained from the polymer melt. The mechanism of cyclic oligomer formation has been studied by determining the rate of formation of the cyclic oligomers during polymerization and during melt extrusion of polyesters which did not initially contain cyclic oligomers. The rate of formation depends upon the concentration of hydroxyl groups; hence, the cyclic oligomers are formed by transesterification from the chain ends or cyclodepolymerization. Therefore oligomers are inevitably produced during polymerization.
Copolymerization of some epoxides by coordination‐type catalysts
Authors: Price Charles C. , Brecker Lawrence R. 
Published: April 2003

AbstractCopolymerizations of tritiated phenyl glycidyl ether with p‐ and m‐methoxy, p‐methyl, and p‐chloro analogs, as well as with propylene oxide and epichlorohydrin are reported. The relative reactivities indicate greater Lewis acid character for triethylaluminum–water than for diethyl‐zinc–water or ferric chloride–propylene oxide catalyst systems. The copolymerization of the PGE analogs is promoted by electron‐donor groups and retarded by electron‐withdrawing groups.
Preparation and properties of isomeric polyphenylacetylenes
Authors: Kern R. J. 
Published: April 2003

AbstractPolyphenylacetylenes were prepared using ferric acetylacetonate and (i‐Bu)2AlH, RhCl[(C6H5)3P]3 and thermal initiation. Color, infrared spectra, softening temperatures, ultraviolet fluorescence, solubility, and crystallinity are described. A method is presented for assigning to these three macromolecular species predominantly cis, trans, and cis–trans copolymer structures, respectively. The dominantly cis polymer is believed to form in a transoid conformation which can easily be transformed to a more helical arrangement which exhibits a degree of crystallinity. Pyridine promotes the isomerization of cis to trans structure. The rhodium phosphine is thought to effect chain growth by repeated additions of the acetylenic CH of monomer across a terminal triple bond. Phenylacetylene thus behaves as a bifunctional molecule in this system. Color, polymer conformation, and crystallinity appear to be strongly interrelated.
Generation of free radicals at subzero temperatures. III. Polyamine–hydroperoxide–iron system
Authors: Minato Hiroshi , Hisada Ryuki 
Published: April 2003

AbstractThe mechanism of the reaction of tetraethylenepentamine (TEPA) with cumene hydroperoxide (CHP) and iron ions was investigated. It was found that (1) TEPA did not reduce Fe(III); (2) TEPA was consumed by this reaction; (3) both Fe(II) and Fe(III) were effective for this reaction. It was shown that though the OO bond of a hydroperoxide could be cleaved only at elevated temperatures, it could be easily cleaved by the reaction with the iron–TEPA complex. The function of this iron–TEPA complex is discussed.
Polyaddition reaction of biscarbodiimides. II. Synthesis of polyguanidines by polyaddition reaction of biscarbodiimides with diamines
Authors: Iwakura Yoshio , Noguchi Kohji 
Published: April 2003

AbstractA series of polyguanidines was prepared by the polyaddition reaction of biscarbodiimides with diamines. The polyaddition reaction was carried out in solution. The polymers thus obtained had intrinsic viscosities up to 0.84 and molecular weights up to 15000. The structure of the polymers was identified by comparison of their infrared spectra with those of model compounds, elementary analysis, and a study of the reaction conditions. Thermogravimetric study indicated that the polyguanidines decomposed over 170°C under nitrogen. The polyguanidines were highly resistant to hydrolytic degradation by strong acid or alkali. The polyguanidines had basic groups and formed stable hydrochloric salts when they were treated with hydrochloric acid.