bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relation between free radicals and ultraviolet absorption in poly(methyl methacrylate)
Authors: Bosch J. J. Ten , Verhelst W. F. , Chadwick K. H. 
Published: April 2003

AbstractA correlation between the radiation‐induced nine‐line electron spin resonance signal and the unstable component of the optical absorption in the near ultraviolet in poly(methyl methacrylate) is made on the basis of the radiation dose relationship, the dependence of production on irradiation temperature at a constant radiation dose, and on the fading of both signals on oxygen diffusion into the poly(methyl methacrylate) after irradiation. It is concluded that this correlation is applicable only immediately after irradiation and the stability of the initial radical is discussed with respect to the fading results. A process of radical decay and conversion is suggested to account for differences found in the fading characteristics of the two signals.
Thermal degradation of poly‐p‐oxybenzoate under vacuum
Authors: Jellinek H. H. G. , Fujiwara H. 
Published: April 2003

AbstractThe thermal degradation of poly‐p‐oxybenzoate in vacuo as function of temperature has been studied. The energy of activation of the process up to about 30% volatile formation is 59.6 kcal/mole. The degradation is preceded by induction periods, which have been shown to be due to poor heat conductivity of the polymer powder. CO, CO2, phenol, and an unknown compound of molecular weight larger than 200 are the main degradation products found by chromatographic analysis. Infrared spectra of the original polymer, the polymer residue after degradation and of a degradation product solid at room temperature are presented. The possible reactions taking place have been indicated. The heat stability of the polymer in vacuo lies between those of polytetra‐fluoroethylene and polyethylene.
Study of some silver‐thiol complexes and polymers: Stoichiometry and optical effects
Authors: Andersson Lars‐Olov 
Published: April 2003

AbstractThe silver complexes of various thiols of low molecular weight have been studied by amperometric and spectrophotometric titrations. Cysteine and cysteamine form complexes with silver containing up to 1.5 Ag+/—SH. The ligands participating in the binding of silver are the —SH and amino groups.Under some conditions it was found that 1:1 thiol‐silver polymers were formed. These polymers probably have the general structure AgS(R)AgS(R). Some of them were prepared in pure form and subjected to various studies. Molecular weight determinations of the cysteine‐silver and glutathione‐silver polymers yielded values of 4000–7000 daltons. Studies on the UV absorption characteristics revealed that all of the polymers showed some type of regular band pattern. The cysteamine‐silver polymer is able to sensitize photographic emulsions.
ESR study on the photosensitized decomposition of polyethylene
Authors: Takeshita Takuo , Tsuji Kozo , Seiki Toshifumi 
Published: April 2003

AbstractSeveral aromatic compounds were added to low‐density polyethylene to determine their effects on the photodegradation of polyethylene. It was shown that some aromatic compounds indeed sensitize the hydrogen abstraction of the allylic hydrogen of unsaturated groups contained in polyethylene as an improper bond. The mechanism of photosensitization was investigated by an ESR method. It was found that the higher photoexcited triplet state of an aromatic molecule produced by the biphotonic ultraviolet light absorption transfers its excess energy to the unsaturated bond to excite it, and the excited unsaturated group releases its allylic hydrogen atom, giving an allylic radical.
Reaction profiles for kinetic studies of inhomogeneous reactions within solid organic films
Authors: Webb J. R. 
Published: April 2003

AbstractA technique is described whereby an assessment of the extent of reaction at any time and at any selected depth beneath the surface of a solid film is obtained from infrared spectrophotometric data. The resultant reaction profiles can be used to investigate the kinetics in planes normal to the surface. Group concentration–time curves can be constructed for planes at selected depths parallel to the surface and used to assess the kinetics in such planes. As a result it is possible to study realistically reactions which do not occur homogeneously throughout a solid, e.g., those effected by oxidation, irradiation, plasma treatment, etc.
Kinetics of donor–acceptor complex polymerization. III. Assessment of some approximations in the kinetics
Authors: Rybicky J. , Tanner J. , Funt B. L. 
Published: April 2003

AbstractThe mathematical solution of the equations derived from a kinetic scheme previously developed for donor–acceptor complex polymerization was based on steady‐state conditions and the applicability of initial concentration conditions over a range of conversion. These assumptions are scrutinized and tested by computer simulation and by the exact differential equations utilizing Runge‐Kutta method. The analysis shows that for case I conditions of low concentration of complexing‐agent, the degree of conversion is not critical and that the previous approximate solutions are valid. The steady‐state and non‐steady‐state conditions are compared, and the range of validity of the assumptions is established. The approximate solutions are found inapplicable in the instances of non‐steady‐state conditions coupled with a low concentration of either monomer.
Ethylene polymerization with supported bis(triphenylsilyl) chromate catalysts
Authors: Carrick Wayne L. , Turbett Robert J. , Karol Frederick J. , Karapinka George L. , Fox Adrian S. , Johnson Robert N. 
Published: April 2003

AbstractBis(triphenylsilyl) chromate is an active catalyst for ethylene polymerization without further treatment or additives. Catalytic activity is markedly increased when the compound is deposited on silica–alumina and is further increased if it is deposited on silica and then treated with an aluminum alkyl. Polymer molecular weight can be controlled by reaction temperature, hydrogen addition, support type, and reducing agent structure to give polymers ranging in melt index from essentially zero to > 100. In the supported catalysts the bis(triphenylsilyl) chromate appears to be bound to the support and to undergo a reduction step either by reaction with ethylene or with aluminum alkyl prior to polymerization. The active site is envisioned as chromium alkyl, bound to the support, with propagation occurring by insertion of the monomer into a CrC bond. Chain termination is by chain transfer to monomer.
Long branching in poly(vinyl acetate) and poly(vinyl alcohol). II. Polymerization of vinyl acetate in the presence of crosslinked poly(vinyl alcohol)
Authors: Nozakura Shun‐Ichi , Morishima Yotaro , Murahashi Shunsuke 
Published: April 2003

AbstractIt is a common view that poly(vinyl acetate) has many branches at the acetyl side group, but that the corresponding poly(vinyl alcohol) has little branching. In order to study the branching in poly(vinyl acetate) and poly(vinyl alcohol) which is formed by chain transfer to polymer, the polymerization of 14C‐labeled vinyl acetate in the presence of crosslinked poly(vinyl acetate), which was able to be decrosslinked to give soluble polymers, was investigated at 60°C and 0°C. This system made it possible to separate as well as to distinguish the graft polymer from the newly polymerized homopolymer. Furthermore, the degree of grafting onto the acetoxymethyl group and onto the main chain were estimated. It became clear that, in the polymerization of vinyl acetate, chain transfer to the polymer main chain takes place about 2.4 times as frequently at 60°C as that to the acetoxy group and about 4.8 times as frequently at 0°C.
Investigation into the mechanism of tack of rubbers
Authors: Bauer R. F. 
Published: April 2003

AbstractThe tack of cis‐polybutadiene was measured by means of a Skewis tackmeter, and the results, which showed considerable variability, could be represented by a double exponential cumulative distribution function of Gumbel. It was concluded that there exists a linear relationship between the applied forces (contact and break) and the time that these forces are applied in the tack test. The mechanism of tack is considered in terms of two distinct processes: (a) the development of a bond and (b) the strength of the bond thus formed. The latter is rationalized by applying Eyring's absolute rate theory. A simple equation is derived which predicts an inverse linear relation between the breaking time and breaking force, which is in agreement with the experiment. The theory also suggests that the area of actual interpenetration of polymer interfaces depends largely on the contact pressure, whereas the depth of penetration appears to depend to a similar degree on both contact pressure and contact time.
Structure of ethylene–chlorotrifluoroethylene copolymers
Authors: Sibilia John P. , Roldan Luis G. , Chandrasekaran Swayambu 
Published: April 2003

AbstractThe structures of copolymers of ethylene and chlorotrifluoroethylene have been studied by infrared, nuclear magnetic resonance, and x‐ray diffraction techniques. Copolymers varying in ethylene composition from 80 to 50 mole‐% were prepared at a number of different temperatures with a peroxide catalyst system. Compositions of 50/50 mole ratio were found to be semicrystalline and to have melting points as high as 241°C. These materials were found to be copolymers with a high degree of one‐to‐one alternation. They were similar in structure to 1:1 copolymers which had been reported previously by other workers who used a triethylboron catalyst system. The x‐ray evidence indicated that the copolymers prepared with the peroxide catalysts were not stereoregular. A hexagonal unit cell with a theoretical density of 1.70 g/cc was determined for the alternating one‐to‐one copolymer by x‐ray techniques. A value of 262°C was determined for the melting point of the theoretical 100% alternating one‐to‐one copolymer. Values of ΔHƒ = 4500 cal/mole and ΔSƒ = 8.4 cal/deg‐mole were also calculated for the alternating 1:1 copolymer. The preferred conformation of the material appears to be a “kinked” structure with the crystalline phase having ethylene units in one chain lining up opposite chlorotrifluoroethylene units in the adjacent chain. Polar association which can occur between fluorine and hydrogen atoms in this arrangement may account in part for the relatively high melting point of the alternating one‐to‐one copolymers.
EPR studies of mechanically induced bond rupture in elastomers
Authors: Devries K. L. , Roylance D. K. , Williams M. L. 
Published: April 2003

AbstractElectron paramagnetic resonance (EPR) spectroscopy was used to compute the surface bond rupture density in polyurethane and to determine the phase experiencing fracture in styrene‐butadiene block copolymers when these elastomers are subjected to mechanical degradation by grinding. The polyurethane grinding was done at temperatures above and below the glass transition Tg; 0.155 × 1013 radicals/cm2 of fracture surface area were formed above the Tg and 4.42 × 1013 radicals/cm2 for grinding below the Tg. These values are essentially equal to those found earlier for spherulitic polymers. In all cases the fracture appears able to progress along preferential paths so as to rupture significantly fewer molecular chains than one would expect on the basis of calculations of the number of chains passing through each square centimeter of cross section. Comparison of EPR spectra formed by grinding styrene‐butadiene copolymer with those of styrene and butadiene above indicated that at cryogenic temperature, the fracture in the copolymer takes place in the butadiene phase.
Particle size analysis of polymer latexes by light scattering. V. The significance of an assumed distribution in the analysis of angular scattering data
Authors: Wallace T. P. , Kratohvil J. P. 
Published: April 2003

AbstractIn the analysis of light scattering data from polymer latex systems or other systems of spherical particles, it is necessary to assume a particle size distribution function. Theoretical angular scattering functions based on the assumed distribution and representing a wide range of size distribution parameters are compared to experimental data in order to obtain a best fit. In previous work, it has been shown that as the polydispersity increases beyond certain limits the uncertainty in the assignment of the size distribution parameters (i.e., the best fit) increases. This report is concerned with the analysis of angular scattering from unimodal systems and simulated cases where theoretical scattering functions for wide, negatively skewed distributions are used as “experimental data,” are analyzed by utilizing four different distribution functions. These functions represent different degrees of skewness and include negatively, positively, and normally skewed distributions. The results from the use of the various distribution functions are discussed with respect to the uncertainly in the assignment of distribution parameters resulting from the loss of structure in the angular scattering pattern due to increased polydispersity. Scattering data from the bimodal distribution are analyzed by assuming a unimodel distribution, and the consequences of this assumption are assessed.
Hydration‐dependent enthalpy changes in the helix–coil transition in tendon
Authors: Delisi Charles , Shamos Morris H. 
Published: April 2003

AbstractThe shrinkage phenomenon in bovine achilles heel tendon was studied calorimetrically as a function of water content of the tendon. The transition temperature was found to increase from 67°C to 98°C as the water content decreased from 53% by weight to 26% by weight. The enthalpy change was found to increase with increasing percentages of water. The data is interpreted by considering the possibility of water binding to the polar sites on the solute molecule which become free after the transition. A calculation is carried out in which the melting shifts are taken to be related to the free energy of binding. The increase in enthalpy with an increase in water content is shown to have a semiquantitative interpretation in terms of the structural aspects of water.
X‐ray diffraction relaxation of polyethylene
Authors: Oda T. , Stein R. S. 
Published: April 2003

AbstractThe change in x‐ray diffraction intensity with time following rapid stretching by various amounts is measured for a low‐density polyethylene sample at several temperatures. An appreciable decrease in intensity with time at the meridian of the diffraction from the 110 and 200 planes is observed to occur within the first 5 sec following stretching. The change takes considerably longer times at lower temperatures. By use of a calibration curve, the change in crystal orientation functions for the a, b, and c crystal axes were calculated, and an increase in c‐axis orientation was shown. From the results of birerringence measurements on the same sample, the crystalline and amorphous contributions to birefringence were calculated. It was shown that stretching is initially accompanied by a greater amount of amorphous than crystalline orientation, and that relaxation involves an increase in crystalline orientation accompanied by a decrease in amorphous orientation.
Conformation of random polypeptide chains
Authors: Srinivasan A. R. , Rao V. S. R. 
Published: April 2003

AbstractThe characteristic ratios Cof and C∞ are calculated for infinitely long poly(L‐amino acid) chains having aCH2R′ substitution at the Cα atom, as functions of the valence angle τ at the Cα atom. The value of Cof is found to increase from 1.6 to 2.3 as τ varies from 105 to 115°. On the other hand, C∞ decreases with increasing τ in the range 105–111°, passes through a minimum at 111°, and then increases slowly. Since, C∞ is much less dependent on τ in the most commonly observed range (110–115°), any variation in τ in this range due to solvent would not appreciably affect C∞. The calculated temperature coefficient of C∞ is negative and increases significantly in absolute magnitude even for small deviations in τ from 110°.
Differential scanning calorimetry of chlorinated polyethylenes
Authors: Erä Väinö A. , Lindberg J. Johan 
Published: April 2003

AbstractThe heats of fusion of low‐density polyethylene and chlorinated polyethylenes of varying chlorine content have been investigated by differential scanning colorimetry (DSC). Linear correlations are found between the chlorine content and the apparent heat of fusion, crystallinity, and the maximum specific heat measured in the temperature range 90–120°C. The effect of heat treatment on crystallinity is shown to be strongly dependent on the chlorine content of the polymers.
Influence of entanglements on viscoelastic properties of polyisoprenes
Authors: Barešová V. , Szilágyi L. , Danusso F. 
Published: April 2003

AbstractThe contribution of entanglements to the relaxation modulus of four samples of cis‐polyisoprene has been studied in detail. The average number of chain atoms between neighboring entanglements has been calculated according to the theory of Chompff et al. Relaxation spectra and modulus produced by the entanglements were also calculated from the theoretical model. Good agreement was achieved between the modulus measured experimentally and the values predicted theoretically.
Adsorption of polymers at the solution‐solid interface. VII. Poly(acrylic acids), model compounds, and vapors on nylon fibers
Authors: Cole D. , Howard G. J. 
Published: April 2003

AbstractNylon fibers of various draw ratios have been used as the adsorbents in the adsorption of low molecular weight acids and of polyacrylic acids from solution. Polymer adsorption is lower than on a precipitated nylon and decreases with fiber orientation; however, propionic acid and glutaric acids do not show this dependence on nylon structure. The structural alterations consequent on fiber drawing also reduce swelling in hydroxylated liquids. The greater accessibility of the precipitated nylon is shown by vapor sorption and extends to nonhydroxylated vapors; however, the differences in behavior between polyamide powder and fiber cannot be fully attributed to the former possessing a porous structure, in the sense normally employed in surface chemistry.
Adsorption of polymers at the solution‐solid interface. VIII. Competitive effects in the adsorption of polystyrenes on silica
Authors: Howard G. J. , Woods S. J. 
Published: April 2003

AbstractThe adsorption behavior on silica of some polystrenes of moderate molecular weight distribution, both singly and in mixtures, has been examined. The adsorption isotherms indicate that, in both a good solvent (trichloroethylene) and under theta conditions, the species of higher molecular weight is preferentially adsorbed at or near full surface coverage, but that the smaller adsorbate has an improved opportunity for adsorption at low surface coverage. The use of tritiated adsorbates substantiate the isotherm data in cyclohexane solution.
Permeation phenomena near the penetrant condensation point
Authors: Leitão Dorodame Moura 
Published: April 2003

AbstractThe permeation and solubility of propylene in polyethylene films were measured at temperatures and pressures near the condensation point of the vapor. Diffusion coefficients were calculated from these data. On the basis of the behavior of activation energies with relative vapor pressure, it is shown how diffusion and sorption influence permeation phenomena in this region.
Thermal behavior of annealed organic glasses
Authors: Petrie S. E. B. 
Published: April 2003

AbstractThe influence of annealing processes on the thermal behavior of organic glasses in the glass‐transition interval has been investigated and analyzed quantitatively. In detailed annealing studies of atactic polystyrene and Aroclor 5460, the absorption of thermal energy superposed on the increase in the specific heat at the glass transition, observed with suitably chosen heating rates, was followed by the differential thermal method. It is concluded that the absorption of thermal energy observed under these conditions parallels the extent of molecular relaxation that has taken place during the annealing period. It is not necessary to postulate a first‐order process to account for the energy absorption. Moreover, such a postulate leads to severe conceptual difficulties regarding the development of crystallinity in crystallizable materials. The areas and the shapes of the endotherms are considered in terms of the original physical properties of the quenched glasses and the anticipated equilibrium properties. Relationships between the extent of energy absorption and time‐dependent processes such as volume relaxation are discussed.
Multiple endotherm melting behavior in relation to polymer morphology
Authors: Sweet G. E. , Bell J. P. 
Published: April 2003

AbstractThe two endotherms found during DSC analysis of annealed or drawn poly(ethylene terephthalate), PET, are discussed in greater. detail. Earlier workers proposed that the endotherms were the result of separate morphologies, i.e., extended‐chain and folded‐chain crystals, but more recently Roberts and others have presented data on the effect of DSC heating rate on annealed PET endotherm areas which indicate that the higher temperature endotherm is the result of recrystallization in the DSC. The present work explains the reasons for recrystallization, and presents data showing that samples cooled at various rates from the melt also exhibit recrystallization in the DSC, in much the same manner as samples annealed for different lengths of time. Further, by prolonged annealing before analysis, part of the recrystallization exotherm can be observed in the DSC scan. Drawn nylon 66 also exhibits recrystallization in the DSC, in a manner similar to annealed or slowly crystallized PET. The amount of material that recrystallizes is determined by the time and supercooling available between first melting and the ultimate recrystallization temperature, i.e., a temperature at which there is too little time and temperature driving force for further recrystallization to occur. Infrared absorption data show an increase in “regular” fold content during prolonged annealing of PET, while dynamic mechanical data show a marked decrease in a dispersion that is likely associated with the looser fold crystal morphologies. Annealed PET does superheat in the DSC, leaving unanswered the question as to whether any partially extended material is present along with the regular‐fold material. For cold‐drawn PET, the infrared data indicate disappearance of regular folds and the dynamic mechanical data indicate disappearance of the looser folds. Cold‐drawn PET also superheats. These data indicate a likelihood of at least partially extended morphologies in cold‐drawn PET; these observations do not apply to PET drawn at high temperatures or to polyethylene.
Pulsed photoconductivity and current oscillations in poly(vinyl chloride)
Authors: Ranicar J. H. , Fleming R. J. 
Published: April 2003

AbstractTransient photocurrents in poly(vinyl chloride) films are shown to be due to photo‐injection of electrons from metallic cathodes. Most of the injected electrons are promptly trapped, but some drift across the sample to the anode under the influence of an external electric field. The mobility of these electrons, determined by transient photoconductivity techniques, is 4.7 ± 0.5 × 10−4 cm2/V‐sec at 27°C, and rises to 3.4 ± 0.5 × 10−3 cm2/V‐sec at 43°C, the measuring cell having been evacuated to a pressure of 10−6 torr at both temperatures. Diffusion of helium into the samples appears to decrease the electron, mobility. It is suggested that electron transport is correctly described by using an energy‐band model for intramolecular motion and an activated hopping model for intermolecular transfer. Oscillations observed in the transient photocurrents in the frequency range 103–105 Hz are attributed to electron avalanche formation at the anode, with photosuccessors.