bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photopolymerization of acrylamide. I. Formation of the initiating redox system
Authors: Delzenne G. , Toppet S. , Smets G. 
Published: April 2003

AbstractThe photopolymerization of acrylamide in aqueous solution can be sensitized by various dye–reducing agent systems. The reaction is initiated by free radicals produced during the decomposition, in the presence of reducing agents, of hydrogen peroxide. This substance is formed during the reoxidation reaction by the oxygen present in the solution of the leuco derivative or the semiquinone which are produced in the photoreduction of the dyes. The formation of hydrogen peroxide during the photoreduction of dyes in the presence of oxygen has been demonstrated polarographically for the following systems: tetrabromofluorescein (eosin), 3,6‐diaminoacridine (acriflavin), 3,6‐bis(dimethylamino)acridine (acridine orange) as dyes and l(+)‐ascorbic acid or thiourea as reducing agents.
The structures and reversible polymerization of cyclic oligomers from poly(ethylene terephthalate)
Authors: Goodman I. , Nesbitt B. F. 
Published: April 2003

AbstractPoly(ethylene terephthalate) prepared or fabricated by melt processes is shown to contain about 1.5% of extractable, oligomeric material composed mainly of cyclic ethylene terephthalates which exist, at high temperatures, in equilibrium with the molten polymer. An ester interchange‐elimination reaction is proposed as the main route of formation of these compounds. An additional minor component of the polymer, produced by side reactions, is the mixed cyclic bisterephthalate of ethylene and 3‐oxapentamethylene glycols. This compound, together with cyclic bis(3‐oxapentamethylene terephthalate) is also formed in the forced thermal depolymerisation of ethylene/3‐oxapentamethylene terephthalate copolymers.
Greffage sur polychlorure de vinyle par préozonisation
Authors: Landler Y. , Lebel P. 
Published: April 2003

AbstractUne bréve discussion est faite au sujet du greffage de monomères polymérisant par un mécanisme radicalaire au départ d'un tronc polymérique préalablement ozonisé, sujet déjà décrit précédemment par de nombreux auteurs. Dans le présent travail, une étude détaillée a été faite dans le cas particulier du greffage sur le chlorure de polyvinyle. On considère séparément le comportement du chlorure de polyvinyle obtenu par polymérisation en suspension et soumis à l'action de l'ozone à l'état sec. Tout d'abord on a étudié la vitesse d'ozonisation en fonction de la durée du processus, ce qui a permis de préciser ce que l'on peut attendre de conditions variées d'ozonisation. Ensuite on a étudié la cinétique de décomposition thermique du chlorure de polyvinyle ozonisé à
diverses températures. Les variations de poids moléculaire du PVC ont été suivies en fonction des conditions d'ozonisation et des conditions de dégradations du polymère ozonisé, à savoir, sous vide en présence d'oxygètne, ou en présence d'un inhibiteur de radicaux libres. Le comportement du PVC à l'égard de l'ozone et le comportement thermique du polymère ozonisé ont montré que le polymère subit aisément l'ozonisation et que les groupes formés sont thermolabiles. L'ozonisation et la décomposition ultérieure des groupes peroxydiques ne sont pas accompagnées d'une dégradation considérable de la chaîne macromoléculaire. Le PVC est un substrat excellent pour le greffage par ozonisation préliminaire. Les vitesses de polymérisation de divers monomères éthylèniqiies en présence du PVC ozonisé comme initiateur ont été étudiées. Les résultats obtenus ont été examinés du point de vue de la réactivité relative des divers monomères. L'effet du milieu a également été étudié. De cette manière divers polymères greffés de composition très variable ont été obtenus. Ainsi certains copolymères qui ne peuvent être obtenus par simple copolymérisation radicalaire ont été préparés, par exemple, des copolymères de styrène et de chlorure de vinyle. En variant les conditions d'ozonisation et de décomposition des groupes peroxydiques fixés sur le polymère, une grande variété de produits de composition et structures diverses a pu être obtenue. Ce travail est limité à la synthèse de copolymères greffés à base de PVC. Une étude détaillée des diverses propriétés en fonction de ces facteurs, fera l'objet de publications ultérieures. Les auteurs remarquent qu'une modification des propriétés du PVC est causée par l'incorporation de groupes étrangers au moyen du greffage.
A kinetic study of the mild oxidation of wheat starch by sodium hypochlorite in the alkaline pH range
Authors: Schmorak J. , Mejzler D. , Lewin M. 
Published: April 2003

Abstract(1) Some kinetic aspects of mild oxidation of wheat starch by sodium hypochlorite in the pH range 7.5–11.0 were studied. (2) No significant chlorate formation was observed at any time. From this and from other experimental evidence it is concluded that the reaction is most likely to be purely chemical in type and to proceed according to the overall scheme:

(3) The reaction appears to be of the first order with respect to starch. (4) The reaction appears to be of the first order with respect to hypochlorite at pH = 8.0. At pH = 9.0 and 10.0, the reaction velocity is still approximately proportional to the concentration of the oxidant present, but the course of the reaction appears to be more complicated. (5) The reaction rate decreases with increasing pH of the oxidizing medium. An approximate empirical equation is proposed adequately representing the interdependence of the first‐order constant and pH in the pH range 7.5–10.0. (6) The activation energy of the reaction is within the range of 21–23 kcal./mole, i.e., that obtained for many homogeneous, truly chemical reactions. (7) The fact that the reaction rate of a starch solution is about 50% higher than the corresponding rate for a starch suspension would seem to indicate that the number of sites available for oxidation in a granule is about two‐thirds of that available when that granule is dissolved. (8) The addition of neutral salts had an accelerating effect on the reaction rate. Under the experimental conditions of the present paper, this effect was negligible, but at much higher salt concentrations it would have to be taken into account.
The effect of C‐substitution of caprolactam on the ring‐opening polymerization reaction
Authors: Wolinski L. E. , Mighton H. R. 
Published: April 2003

AbstractCaprolactam was modified with alkyl groups of various sizes and in different positions on the ring. The resulting substituted caprolactams were polymerized and the comparative degree of polymerization was used as a measure of the inhibiting effect of the substituting group. There was less inhibition on substitutions in 5‐ and 7‐positions than in the 4‐ and 6‐positions. The order of increasing inhibition of alkyl groups was methyl, ethyl, n‐propyl, isopropyl, cyclohexyl, tert‐butyl and gem‐dimethyl.
Isomorphous replacement in a copolyamide system
Authors: Levine M. , Temin S. C. 
Published: April 2003

AbstractIn a study of isomorphic behavior, it was found that the melting point—composition curve of the copolyamides prepared from caprolactam and p‐aminomethylcyclohexylcarboxylic acid was sigmoidal, indicating that the methylcyclohexyl group was interchangeable in the crystal lattice with aliphatic carbon atoms of ω‐aminocaproic acid. On the other hand, the benzyl group in the copolymers of caprolactam and p‐aminomethylbenzoic acid did not interchange as well, and only partial isomorphism occurred. The analogous meta derivatives, m‐aminomethylcyclohexylcarboxylic acid and m‐aminomethylbenzoic acid, did not fulfill the spatial requirements of caprolactam. Although V‐shaped melting point—composition curves resulted, the disturbance in the crystal network was more severe with the m‐phenyl derivative than with the m‐cyclohexyl derivative.
Radiation grafting of allylic monomers to solid polymeric substrates
Authors: Zimmerman J. 
Published: April 2003

AbstractThe kinetics of grafting of allylic monomers to a solid polymeric substrate are compared with those for normal vinyl monomers which have been treated in a previous paper. The particular case treated theoretically for both types of monomers (using well established basic principles) is the sequence where the polymer is soaked in a solution of the monomer, the excess monomer is removed from the surface, the polymer is then irradiated at −78°C. at a high dose rate, and the system subsequently allowed to condition at 25°C. under an oxygen free atmosphere. It was previously shown theoretically that with a normal vinyl monomer in a very viscous matrix, the conversion of monomer to polymer increases indefinitely with post‐irradiation time and that radiation dose and post‐irradiation time are interchangeable in the absence of inhibitors. It is shown here that under similar conditions with allylic monomers, the existence of degradative chain transfer to the monomer places a definite limit on the maximum conversion and makes this conversion quite dependent on dose. The theory for the case involving degradative chain transfer is applied to data on the grafting of itaconic acid to 66 nylon and values are deduced for the ratio of transfer to propagation constants and transfer to termination constants. Lower limits for the absolute values of these constants are also deduced. The ratio of propagation kp and termination kt rate constant in this very viscous medium is kp/2kt = 0.58.
The ionic polymerization of cyclic olefins using optically active gegen ions
Authors: Schmitt G. J. , Schuerch C. 
Published: April 2003

AbstractThe cyclic olefins 4, 5‐dihydro‐2‐methylfuran, indene, 1‐methylcylcopentene, and αhyphen;angelica lactone were polymerized using catalyst‐cocatalyst complexes of boron triflu‐oride with asymmetric Lewis bases. Various conditions of temperature and dielectric constant of the media were employed but in no case was optical activity observed in the polymers produced. The stereochemistry of the addition polymerization of cyclic olefins is discussed and it is proposed that a thermodynamically preferred trans‐trans addition may predominate over any asymmetric inductive effect to yield an internally compensated polymer. The anionic polymerization of 1‐cyanocyclopentene is also described.
Twisting of bundles of bacterial cellulose microfibrils
Authors: Colvin J. Ross 
Published: April 2003

AbstractThe majority of, but not all, bundles of bacterial cellulose microfibrils show a characteristic left‐handed twist which has a pitch of about 1 μ. The remainder show no apparent coiling. The twist must reflect an internal strain in the component microfibrils which may be due to a slight progressive molecular asymmetry in the way in which glucose residues are incorporated into the microfibril.
The scission step in hevea oxidation
Authors: Bevilacqua E. M. , English E. S. 
Published: April 2003

AbstractThree recent attempts to formulate a reaction mechanism for scission during the oxidation of rubber have been evaluated with respect to their predictions concerning the formation of formic acid and the step at which scission occurs. Two do not account directly for formic acid as a principal product or for the failure of antioxidants to influence scission yield. The third, while consistent with available evidence, does not predict the observed product distribution as a necessary consequence of decomposition of the postulated intermediate.
Thermodynamics of crystalline linear high polymers. I. Comparison of the melting transitions of solution and melt‐crystallized polyethylene
Authors: Wunderlich Bernhard , Kashdan W. H. 
Published: April 2003

AbstractDifferential thermal analysis (DTA) of the melting range of annealed and solution‐crystallized low‐pressure polyethylene (Marlex 50) has been carried out and found to be comparable in precision with earlier calorimetric determinations. The melting range of the single‐crystalline material is shifted by 3.7°C. to lower temperature with respect to the melt‐annealed polyethylene. Heat of fusion estimates from the peak height and area of the DTA curves as well as density determinations gave a ratio of about 1.08 for the crystallinities of annealed and single‐crystalline polyethylene. The per cent crystallinity calculated from density for annealed polyethylene was found to be 90 ± 3, which is in good accord with calorimetric and x‐ray determinations.
Oxyluminescence from polypropylene
Authors: Ashby G. E. 
Published: April 2003

AbstractSeveral polymers emit light when heated in the presence of oxygen. Experimental observations are made concerning the light from polypropylene. The portion of light detectable with a RCA‐5819 photomultiplier tube is blue‐violet in color. When polypropylene is at 180°C. the wavelengths of the light are between 3000 and 5150 A. The intensity of the light is determined by the temperature of the polymer, the concentration of oxygen in contact with the polymer surface, and the concentration and type of antioxidants present. For every photon of light emitted by polypropylene about 104 carbonyl groups are formed. The behavior of antioxidants in polypropylene, including concentration and synergistic effects, are illustrated by measurement of this light.
Fracture processes in polymeric materials. I. The surface energy of poly(methyl methacrylate)
Authors: Berry J. P. 
Published: April 2003

AbstractThe general aspects of the problem of fracture and strength are briefly reviewed. The discrepancy between the observed strength of materials and the theoretical value calculated from the molecular structure is usually ascribed to the presence of adventitious flaws present in all samples tested. The Griffith theory of brittle fracture gives the relation between the tensile strength T and the size of the flaw in the sample c as T = A(Eγ/c)1/2. The tensile strengths of samples of poly(methyl methacrylate) containing artificially induced cracks of known size were determined. The results could be represented over a wide range of experimental conditions by the form of the Griffith theory. The value of the specific surface energy obtained from the position of the theoretical curve was ∼3 × 105 ergs/cm.2. The value calculated from the molecular structure of the material is ∼450 ergs/cm.2. The discrepancy is attributed to the energy consumed in a viscous flow process in a thin layer of material at the fracture surface. As a result of this process it is believed that in the surface layer polymer molecules are oriented normally to the fracture plane. This mechanism accounts for the colors observed on the fracture surface and for their lability on exposure to solvents or heating. The Griffith theory postulates a strong dependence of tensile strength on surface energy. In poly(methyl methacrylate) the largest contribution to the surface energy appears to arise from a viscous flow process. Hence for polymers the strength may depend much more on the intermolecular (van der Waals) forces than on then ature of the intramolecular primary valence bonds.
Some physical properties of polyoxymethylene dimethyl ethers
Authors: Boyd Richard H. 
Published: April 2003

AbstractThe vapor pressures, liquid density (25°C.), and melting points of the lower members of a homologous series of compounds of simple linear structure have been measured. These are the polyoxymethylene dimethyl ethers, CH3O(CH2O)nCH3, where n = 2 to 5. The heats of vaporiziation derived from the vapor pressures are used in establishing the heat of vaporization of high molecular weight polyoxymethylene. The densities of these compounds allow the density of the high molecular weight liquid polymer (25°C.) to be determined. The values were used for calculating the cohesive energy density of liquid polymer at 104 cal./cc. at 25°C. The limiting heat of vaporization is used with other thermochemical data in the estimation of the lattice energy (heat of sublimation at 0°K.) of polymer; this estimate is 3.8 ± 0.4 kcal./mole of CH2O.
Transition metal catalysts. V. Methyltitanium trichloride
Authors: Karapinka George L. , Smith Joseph J. , Carrick Wayne L. 
Published: April 2003

AbstractThe reported preparation of methyltitanium trichloride has been refined to give a product free of aluminum compounds. The infrared spectrum of this material in the 2–15 μ region was recorded, and suggested assignments for the various vibrations are given. Aluminum‐free methyltitanium trichloride is not a catalyst for the low‐pressure polymerization of ethylene, but it forms an active catalyst in the presence of its lower valence, thermal decomposition products. Mixtures of methyltitanium trichloride with vanadium tetrachloride or vanadium oxytrichloride lead to reduction of the vanadium valence and are active polymerization catalysts. In these bimetallic cases, polymer growth seems to occur at the vanadium center.
Chemistry of the silylamines. II. The condensation of silylamines with silanediols
Authors: Pike Ronald M. 
Published: April 2003

AbstractThe condensation of mono‐ and difunctional silylamines with (C6H5)2Si(OH)2, (C2H5)2Si(OH)2, HO[Si(C6H5)2O]2H, HO[Si(CH3)2O]3H, and a 1530 mol. wt. hydroxy endblocked dimethylsilicone fluid was investigated. The structure of the reacting species, the addition of acid catalyst, temperature, and solvent were shown to have a marked effect on the reaction rate. The rate of reaction of silylamines toward a given silanediol decreased in the order

The information obtained from the condensation of hexamethyltrisiloxane‐1,5‐diol and N,N‐diethylaminotrimethylsilane demonstrated that self‐condensation of the silanediol did not occur to any extent under the reaction conditions employed. This condensation reaction offers a unique approach to the synthesis of silicone polymers and copolymers allows control of the location of crosslinking sites in the silicone polymer chain, and affords a method for the preparation of silicone block copolymers.
The autoorientation mechanism of crystallization
Authors: Schuur G. 
Published: April 2003

AbstractAttempts have been made to explain a few details of the sometimes misunderstood autoorientation mechanism of crystallization. The autoorientation mechanism is not a model for a particular type of spherulite, but one of the fundamental factors which influence the structure of substances with linear molecules or linear aggregates of molecules or atoms. It is possible to explain on this basis why spherulitic structures are formed or not formed, depending on circumstances. Another argument for autoorientation is that under certain conditions the molecules in adjacent regions are perpendicular to each other. From that point of view the structure of “herringbone” spherulites and ringed spherulities is pertinent to autoorientation. These structures have been investigated and models for these spherulites are proposed. Herringbone spherulites are easily reproducible in gutta‐percha. The ringed spherulites have a rhythmic layer structure. The molecules in adjacent layers are perpendicular to the radius and perpendicular to each other. They grow probably by a process of twinning at regular intervals. The visibility of the rings, especially when the rings are out of focus in unpolarized light, is caused by Becke lines. Clear evidence for the layer structure is the fact that borderlines between adjacent spherulites sometimes follow a zigzag path. The structure of the center of spherulites is also in agreement with autoorientation. Popoff's double leaves in gutta‐percha spherulites are formed if regions at both sides of the sheaflike structure, in the center of spherulites, crystallize in a different manner from that of the sheaf itself. Spherulites formed at low temperatures usually have only an apparent fibrosity, whereas spherulites formed at high temperatures can consist of real needle‐shaped crystals, sometimes separated by less crystalline interstitial material. These and other aspects of the crystallization of polyolefins and other polymers are shown to be in general agreement with the conception of autoorientation.
Fracture processes in polymeric materials. II. The tensile strength of polystyrene
Authors: Berry J. P. 
Published: April 2003

AbstractThe Griffith treatment of brittle fracture predicts that the tensile strength of a material should vary inversely as the square root of the length of a crack or flaw which it contains, the proportionality constant being a function of the surface energy. This relation has been verified experimentally for a series of polystyrene samples which contained deliberately introduced cracks. The value of the surface energy obtained from the results is 1.7 × 106 ergs/cm.2. This is much larger than would be predicted from the molecular constitution, and also higher than the value found from similar experiments on poly(methylmethacrylate). Deviation from the theoretical relationship occurs at small crack sizes, an effect which is attributed to the tendency of the polymer to craze. The effective size of the crazing cracks is estimated to be ∼0.04 in. Because of its higher surface energy, polystyrene is intrinsically stronger than poly(methyl methacrylate). However, the effective flaw size of poly(methyl methacrylate) is only ∼0.002 in., and the tensile strength of conventional samples of this polymer is higher than that of similar samples of polystyrene. These results indicate the importance of two factors which determine the strength of glassy polymers: (1) the surface energy, and (2) the effective flaw size. It is believed that a viscous flow process which occurs during fracture makes a large contribution to the surface energy, but the factors which govern the effective flaw size are, at present, little understood.
The specification of biaxial orientation of polymer films
Authors: Stein Richard S. 
Published: April 2003

AbstractIt is shown that at least four functions are necessary to generally specify the state of orientation of a single phase of a biaxially oriented film. Relationships among these functions under particular constraints are discussed and are described in terms of three dimensional figures in “orientation space.” Only certain combinations of values of these functions are permitted. The physical properties of a film may be specified in terms of these functions.