bluuebunny/crossref_metadata_2025_split huggingface dataset:
The polymerization of propylene oxide by trimethyl aluminum
Authors: Colclough R. O. , Gee Geoffrey , Jagger A. H. 
Published: April 2003

AbstractThe polymerization of propylene oxide at 80°C. catalyzed by aluminium trimethyl has been studied kinetically, using a dilatometric method combined with a high‐vacuum technique to exclude adventitious water and oxygen. Both in bulk and in methylene chloride solution, the reaction is not stereospecific in the absence of oxygen or moisture. When catalytic quantities of water are present, approximately 5% of the product is crystallizable. The reaction shows first‐order dependence on monomer concentration and a complex variation with water and catalyst concentrations, the critical factor being their molar ratio. In bulk, the reaction goes to completion smoothyl, giving maximum molecular weights of approximately 300,000 for the crystalline polymer and 20,000 for the amorphous product. In solution, the reaction involves two distinct stages: in the first, a rapid reaction up to a conversion determined by the water/catalyst ratio is followed by a much slower rate; only the second slow stage appears to produce crystallizable polymer. At critical ratios of the water/catalyst concentrations, the system becomes heterogeneous and the initial rate falls sharply. In the bulk reaction, these two effects occur simultaneously at a ratio [H2O]/[Al2Me6] = 3:1. In solution, the rate falls at a ratio 0.4:1, and the reaction mixture becomes heterogeneous at a 1:1 ratio. Mechanisms are proposed for the various stages of the reaction, and a bridge‐bonded hydrolytic complex is suggested as the active catalyst for the stereospecific stage.
Ion binding and the formation of insoluble polymethacrylic salts
Authors: Michaeli Isaac 
Published: April 2003

AbstractAqueous solutions of polymethacrylic acid partially neutralized with NaOH to a given degree α were precipitated by CaCl2, BaCl2, or MgCl2 in the presence of NaCl. The critical concentrations of the divalent cation at the precipitation point, determined nephelometrically, were found to be linear in the concentration of the total carboxylate neutralized by NaOH, at constant concentrations of total chloride ions and constant α. The linear relation can be interpreted in terms of “ion binding”: The slopes (divalent cation per carboxylate) represent the degree of cation binding, while the intercepts represent the “free cation.” At any given concentration of total chloride the precipitation occurs at a constant degree of binding, independently of the degree of neutralization with NaOH, α. This critical degree of binding, though, is a function of chloride concentration: as the concentration of total chloride is increased, precipitation occurs at lower cation binding, while the corresponding concentrations of the free cation increase. A “solubility product” relation was found to exist between the degree of neutralization α and the critical concentration γ02 of the “free ions” extrapolated to zero concentration of chloride: γ0xα = const., independently of polymer concentration. The precipitation is therefore assumed to be due to intramolecular phase transition (precipitation) in a coiled‐up macromolecule. This is corroborated by observations on the electrophoresis and viscosity in these systems, as well as by previous data on gel systems.
Phase changes in proteins and polypeptides
Authors: Flory P. J. 
Published: April 2003

AbstractRestrictions on freedom of rotation about the bonds of a polymer chain usually impose drastic limitations on the conformational states of polymer chains, and hence are of foremost importance in affecting the tendency of the polymer to crystallize. The severity of these restrictions notwithstanding, the random coil form almost always prevails when the molecules are dispersed in dilute solution. The conformation of minimum energy, represented by one of several helical forms, or by the planar trans conformation, ordinarily is manifested only in the crystalline state. Important exceptions are provided by polypeptides and related polymers of biological interest; owing to strong co‐operative interactions between neighboring units, the characteristic helical form retains stability in dilute solutions under suitable conditions. Various first‐order transitions which are observed to occur in polymers are discussed. These include (1) the widely observed crystallization and melting of polymers, the crystalline phase comprising close packed molecular chains in their preferred rodlike (helical) conformations; (2) dissolution (and re‐aggregation) of the crystalline polymer to yield a dispersion of individual molecules without alteration of conformation, as exemplified by preparation of solutions of native collagen, and reversal of the process with reconstitution of fibrils; and (3) the now familiar helix–coil transition featured by proteins and synthetic polypeptides dispersed in dilute solution. The helix‐coil transition may be regarded as the most primitive manifestation of polymer melting and crystallization. In order to separate influences of molecular geometry, intermolecular interactions, and solution concentration on the one hand from intrinsic intramolecular factors on the other, it is advantageous to regard (1) as the sum of (2) and (3). A further phase transition, previously predicted by theory and recently observed by Robinson, Ward, and Beevers in solutions of poly‐γ‐benzyl‐L‐glutamate in various organic solvents, is manifested by separation of an anisotropic phase from moderately dilute solutions, of highly anisometric, rodlike particles. This tactoidal phase is only slightly more concentrated than the parent isotropic phase. The rates of the helix ⇄ coil transformations are advantageously treated as stepwise processes through use of the mathematical theory of gambler's ruin.
Time‐dependent tensile properties. Part III. Microfracture and non‐Fickian vapor diffusion in organic glasses
Authors: Rosen Bernard 
Published: April 2003

AbstractAn attempt is made to outline the mechanisms of “anomalous” vapor diffusions in films of organic glasses. The predominant factor appears to be the diffusion medium's need to relax stresses generated by the osmotic swelling. Diffusion‐induced localization of swelling and drying can create severe compressive and tensile film stresses which promote irreversible changes in film properties. Retardations and accelerations of vapor transport can result from these stresses and strains. The very irregular film swelling and vapor absorption kinetics of the system, phenol Novolac resin‐water, are reported. These reflect both the rapid and slow mechanical response of the relatively brittle, low polymeric films. Isotropic surface microfracture obtained under selective conditions of initial drying are described. The circumstances of this fracture characterize an interesting example of a vapor diffusion‐controlled “crazing.” Although a full understanding of the total behavior is not yet available, the general findings offer a fusion in perspectives of vapor diffusion and tensile fracture in organic glasses.
A study by E.P.R. of the reaction between polymer radicals and α,α′‐diphenyl‐β‐picryl hydrazine
Authors: Ovenall Derick W. 
Published: April 2003

AbstractPolymethyl methacrylates and polystyrenes have been prepared by the free radical polymerization of the monomers in the presence of α,α′‐diphenyl‐β‐picryl hydrazine. The polymethyl methacrylates were yellow and on treatment with lead dioxide became violet and showed electron paramagnetic resonance (e.p.r.) absorption. It is concluded from the e.p.r. spectra that the polymethyl methacrylates contain diphenylpicryl hydrazine end groups, which, on oxidation, form diphenylpicryl hydrazyl groups. The e.p.r. spectrum of a 5% benzene solution of a polymethyl methacrylate indicates that, in this solution, the correlation time for reorientation of the free‐radical end groups is less than 10−8 sec. Polystyrenes prepared in this manner were also yellow, but were unaffected by lead dioxide.
Anionic homogeneous polymerization of acrylonitrile and methacrylonitrile by quaternary ammonium hydroxides
Authors: Zilkha Albert , Feit Ben‐Ami , Frankel Max 
Published: April 2003

AbstractAqueous solutions of quaternary ammonium hydroxides were used, for the first time, as initiators for the anionic homogenous polymerization of acrylonitrile and methacrylonitrile in dimethylformamide. The molecular weight of polyacrylonitrile was independent of catalyst and monomer concentrations, while that of polymethacrylonitrile increased linearly with monomer concentration. Infrared spectra showed the presence of primary alcohol groups in both polyacrylonitrile and polymethacrylonitrile. Polyacrylonitrile contained terminal double bonds which were absent in the methacrylonitrile polymers. On the basis of these and additional evidence, initiation by hydroxyl anion and termination by chain transfer to monomer is suggested for acrylonitrile polymerization; while termination of methacrylonitrile polymerization is by water. Molecular weight decreased with increase in size and electropositivity of the quaternary ammonium positive counterion in the following order: (CH3)4NOH > (C2H5)4NOH > (CH3)3C6H5CH2NOH.
An organo‐sulfur urethane elastomer system
Authors: Schonfeld Edward 
Published: April 2003

AbstractA method is described for the preparation of hydroxyl‐terminated polymers by the reaction of an aldehyde with a glycol. Thiodiethylene glycol was reacted with benzaldehyde and paraformaldehyde to obtain linear polyacetals containing sulfide linkages. The latter is structurally similar to a typical polysulfide polymer. These polyacetals were reacted with tolylene diisocyanate and crosslinked with polyols to form organo‐sulfur urethane elastomers.
The mechanism of the anionic polymerization of methyl methacrylate. I. Quantitative determination of active chains using radioactive terminators
Authors: Glusker Donald L. , Stiles Elise , Yoncoskie Barbara 
Published: April 2003

AbstractThe polymerization of methyl methacrylate in toluene solution at temperatures in the range of −50 to −78°C. has been studied using 9‐fluorenyllithium as an anionic initiator. The strong ultraviolet absorption of the fluorenyl group has been utilized to calculate number‐average molecular weights after comparison with osmotic pressure measurements had shown that one fluorenyl group becomes chemically attached to each chain. Under the conditions of these polymerizations, the chains are not rapidly self‐terminating. Termination of the reaction with C14‐labelled carbon dioxide or tritium‐labelled acetic acid produces radioactive polymers. Comparison of the activity of a polymer with its fluorenyl content determined from ultraviolet measurements gives the percentage of chains which were active when the terminator was added. For example, polymerizations reaching 70% conversion after one hour still had from 80 to 100% of the chains active. The magnitude of a possible tritium‐hydrogen kinetic isotope effect in the acetic acid termination has been estimated by comparing the specific activity of fluorene prepared under the polymerization conditions by reacting 9‐fluorenyllithium with tritium‐labelled acetic acid at −78°C. in toluene with that of the acetic acid. Appropriate correction factors were therefore applied in calculating the specific activities of the polymers. Isotope dilution studies which detect unreacted fluorenyllithium indicate that the initiation reaction is very rapid.
The preparation and polymerization of some long‐chain mono‐, di‐ and triolefins with metal coordination catalysts
Authors: Marvel C. S. , Rogers John R. 
Published: April 2003

AbstractMethods of synthesis for 1,cis‐9‐octadecadiene, 1,trans‐9‐octadecadiene, 1,cis‐9‐cis‐12‐octadecatriene, 1,9,12‐octadecatriene with 56% trans unsaturation, and several necessary intermediates have been described. The polymerization and copolymerization of these dienes and trienes as well as several long‐chain monoolefins and some branched chain olefins have been described. The octadecadienes yield soluble homopolymers. The octadecatrienes give only crosslinked polymers and there is evidence of bond migration. The catalyst system triisobutylaluminum‐titanium tetrachloride causes bond migration in 1‐octadecene.
Light scattering and viscosity of proteins in anhydrous formic acid
Authors: Harrap B. S. , Woods E. F. 
Published: April 2003

AbstractThe use of anhydrous formic acid as a solvent for proteins has been investigated with a view to its application to proteins which are aggregated or insoluble in aqueous media. Five proteins of known molecular weight–bovine serum albumin, ovalbumin, lysozyme, β‐lactoglobulin, and insulin–have been studied in this solvent by light scattering and viscosity techniques. Bovine serum albumin and ovalbumin showed time‐dependent changes in viscosity which complicated the interpretation of viscosity measurements. These changes in viscosity with time were not due to hydrolysis or aggregation of the protein. It was necessary to correct the light scattering data for fluorescence of the protein in formic acid. The molecular weights determined in formic acid and in the presence of neutral salt indicate that β‐lactoglobulin and insulin are largely dissociated to the monomeric form; the other proteins gave slightly higher molecular weights in formic acid than in aqueous solution. In the absence of salt the concentration dependence of both properties measured is typical of highly charged polyelectrolytes. The KC/R90 vs. C plots show a very steep rise from zero concentration and level off at higher concentrations. The ηsp/C vs. C plots for bovine serum albumin, ovalbumin, and β‐lactoglobulin exhibit maxima at protein concentrations between 0.1 and 0.2%. On addition of neutral salt or water to the formic acid, the light scattering and viscosity show a normal dependence on concentration. The difference in polyelectrolyte behavior between the proteins is attributed to differences in molecular weight, varying degrees of intramolecular crosslinking by disulfide bonds, and different distributions of positively charged side‐chains along the polypeptide backbone. The viscosity measurements show that in formic acid the proteins are in a highly swollen state. Optical rotation measurements indicate that the proteins are denatured in formic acid.
Rheological and spray properties of dilute polymer solutions
Authors: Cohen Leonard , Rodon Gerald W. 
Published: April 2003

AbstractA method is demonstrated whereby the rheological and spray properties of dilute polymer solutions can be studied by means of a jet extrusion instrument and a capillary flow consistometer. The rheological properties that can be determined at any shear rate of extrusion are the normal (tensile) stress, the elastic shear modulus, the elastic recoverable shear strain, and viscosity. The spray properties of dilute polymer solutions can be qualitatively described in various terms such as knotted rod, knotted ligaments, long ligaments, threaded drops, grouped drops, or combinations thereof. The method has been successfully employed with dibutyl phthalate solutions of high molecular weight polyisobutyl methacrylates ranging in concentration from 0.5 to 2.0% by weight, and also with several linear polystyrenes of different molecular weights at various concentrations.
Molecular association complexes of polymers. Urea and thiourea complexes of high molecular weight poly(ethylene oxide)
Authors: Bailey F. E. , France H. G. 
Published: April 2003

AbstractComplexes have been formed by mixing urea or thiourea with high molecular weight yoly(ethylene oxide) on a hot roll mill and by precipitation of the complex from benzene solution. The most dramatic method of complex formation, however, is observed when finely divided urea or thiourea is suspended in a benzene solution of poly(ethylene oxide). The complex forms quantitatively, abstracting all the polymer from solution. The rate of complex formation from solid urea or thiourea and poly(ethylene oxide) in solution has been observed, the thiourea complex forming more rapidly than that of urea. This process of formation can be followed by microscopic examination of the suspended urea particles. The crystalline complex appears to form in a ratio of 2 moles of urea or thiourea to 1 mole of oxyethylene monomer unit. The urea complex melts at 143°C. in comparison with the melting point of urea, 132°C., and of poly(ethylene oxide), 65°C. The complex with either urea or thiourea shows distinct x‐ray diffraction patterns, and the presence of complex in a poly(ethylene oxide) matrix can be detected both by x‐ray diffraction and by stiffness–temperature measurements. Both complexes are water‐soluble.
Electron microscopy of solvent‐etched polyethylene surfaces
Authors: Mackie J. S. , Rudin A. 
Published: April 2003

AbstractA solvent‐etching technique, reported by Reding and Walter, is used to reveal the spherulitic structure of molded polyethylene surfaces. This technique was found to be limited in application to some polyethylenes because the etched surfaces were obscured by reprecipitated polymer. When precautions were taken to prevent reprecipitation the characteristic spherulitic structure of molded polyethylene was exposed. The polymer dissolved by the etchant often reprecipitated on polyethylene surfaces in the form of long, fibrous, crystalline ribbons about 200 A. thick. On carbon surfaces, the same polymers precipitated as diamond‐shaped crystals, sometimes with dendritic outgrowths. Thus the nature of the substrate influences the crystal form of the precipitate. The polymer which was studied in the original work of Reding and Walter precipitates on itself in a formless mass with few fibers. This explains the fiber‐free appearance of the surfaces etched by the former method.
Polydialkyl‐ and polydiphenyltin oxides: Physical properties and chemical reactions
Authors: Reichle W. T. 
Published: April 2003

AbstractPolydimethyltin oxide, polydi‐n‐butyltin oxide, polydi‐n‐octyltin oxide and polydiphenyltin oxide have been shown to have the structure:
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Only the polydi‐n‐octyltin oxide was soluble in xylene and in this case a number‐average molecular weight measurement showed that n was 25. The other polymers were found to be uniformly insoluble without reaction, even in polar solvents like dimethylsulfoxide or N‐methyl‐2‐pyrrolidone. These polymers are high melting substances (300–400°) which decompose at or slightly above their melting points; they are hard, brittle, crystalline (x‐ray) solids. On pyrolysis at 400° the polydiphenyltin oxide yields tetraphenyltin; the polydi‐n‐octyltin oxide mostly 1‐octene. These polymers react with aqueous sodium sulfide to yield, after acidification, the dialkyl‐ or diaryl‐tin sulfides which are trimeric. These unusual properties have been contrasted to the low melting, amorphous, soluble polydialkylsiloxanes. The differences in these physical properties have been explained on the basis of a highly ionic tin‐oxygen bond leading to a R2Sn+2O−2 crystal lattice which would be expected to exhibit the properties found experimentally.
A comparison of melting temperatures and rates of crystallization of polymethylene sulfide and polymethylene oxide polymers
Authors: Lal Joginder , Trick G. S. 
Published: April 2003

AbstractA number of polymethylene sulfide and polymethylene oxide polymers have been synthesized in order to study the influence of sulfur and oxygen atoms on melting temperature and rate of crystallization. Substituting oxygen for sulfur lowers the melting temperature but does not markedly change the rate of crystallization. In the copolymers of structure [(CH2)4S(CH2)mS]x the melting temperature and the rate of crystallization do not depend on the distribution of sulfur in the chain but only upon the carbon/sulfur ratio.
Effects of irradiation and rolling on the tensile behavior of polyethylene
Authors: Tsunekawa Yoshinori , Oyane Moriya , Kojima Kohei 
Published: April 2003

AbstractTensile properties of low‐pressure polyethylene subjected to both irradiation and rolling have been studied. Co60 was used as the γ‐ray source. The anisotropic properties induced by rolling and irradiation were measured by testing the tensile behavior of specimens cut at 0°, 45°, and 90° to the direction of rolling. The yield strengths of specimens cut parallel to the direction of rolling increased with increasing reduction in thickness, but the yield strengths of those cut at 45° and 90° were scarcely affected. The yield strengths of specimens that were irradiated, or irradiated and rolled, increased doses, and then decreased with increasing irradiation, regardless of whether the specimens were irradiated after rolling or rolled after irradiation. The final elongations of the specimens that were irradiated after rolling and cut parallel to the direction of rolling decreased slowly with increasing irradiation, but those of the specimens cut at right angles to the direction of rolling decreased very rapidly. In contrast, the final elongations of all specimens that were rolled after irradiation decreased very slowly regardless of the cutting direction. It may be concluded from the experimental results that the tensile properties of polyethylene irradiated after rolling are more anisotropic than those of the polyethylene rolled after irradiation.
Formation of carboxyl endgroups in polymers and their detection by the dye partition test
Authors: Palit Santi R. , Mukherjee Barunanda N. , Konar Ranjit Singh 
Published: April 2003

AbstractCarboxyl groups or endgroups have been introduced into polymers by use of the following four general methods: (1) use of a carboxyl‐bearing initiator, (2) copolymerization with a carboxyl‐bearing monomer, (3) chain transfer with a molecule containing an actual or potential COOH group, and (4) transformation of a reactive group already present in the polymer. The presence of the carboxyl endgroup in the polymer has been tested for a new technique called the “dye partition test,” developed in this laboratory. It has been demonstrated that all these methods can be used successfully to incorporate COOH groups in the polymer. Of particular interest is the fact that the incorporation of solvent fragments in polymers by chain transfer can be demonstrated very simply and conveniently by this method.
Differential thermal analysis of high polymers. II. Effects of diluents on melting behavior of polyethylenes
Authors: Ke Bacon 
Published: April 2003

AbstractStudies of the nature and magnitude of the interaction between a polymer and a diluent are of both theoretical and practical importance. The effects of several liquid and solid diluents on the melting behavior of both high‐ and low‐density polyethylene have been studied by differential thermal analysis. The depression of melting point was related by a thermodynamic equation to the type and amount of the diluent. The thermodynamically derived true heat of fusion of polyethylene agrees well with the currently accepted value.