bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative activity of hexafluorobutadiene‐1,3 in polymerization and copolymerization reactions with other dienes
Authors: Klebanskiĭ A. L. , Timofeev O. A. 
Published: April 2003

AbstractThe effect of conjugation on the reactivity of perfluorinated diolefins has been little investigated. A characteristic representative of this class of compounds is hexafluorobutadiene, the activity of which in polymerization reactions is much less than that of tetrafluoroethylene. There is an inadequacy of published data on the polymerization of hexafluorobutadiene. We have investigated the conditions for the polymerization of this compound and have found that it takes place only in emulsions in the presence of a cationactive emulsifier in acid medium (pH 1–3) in the presence of a radical type of initiator. The effect of the basic parameters on the emulsion polymerization was investigated. The hexafluorobutadiene polymer obtained in emulsion, in contrast to the polytetrafluoroethylene, is characterized by a low melting point and little stability. It is insoluble in most organic solvents. To ascertain the relative activity of hexafluorobutadiene as compared with other dienic compounds a study was made of copolymerization with chloroprene, fluoroprene, and isoprene, both in emulsion and in solution, and the reactivity constants were determined. The monomer reactivity ratios of the systems are as follows. Chloroprene‐hexaflurobutadiene: r1 = r2 = 0.1; fluoroprene‐hexafluorobutadiene: r1 = 2.93, r2 = 0.24; isoprene‐hexafluorobutadiene: r1 = 1.19, r2 = 0.78. On the basis of the monomer reactivity ratios in the monomer‐hexafluorobutadiene systems and of reported data on the ratios for chloroprene‐fluoroprene and isoprene‐fluoroprene copolymerization, the relative reactivity of the monomers was calculated with respect to a common radical, the relative reactivity constant of the radical and its monomer being taken as unity. Chloroprene is 10 times more active than hexafluorobutadiene with respect to the radical of the latter; it is 8 times as reactive as isoprene and 2.4 times as reactive as fluoroprene. The results are in conformity with data on the separate polymerization of the monomers in emulsion. The considerable fall in activity of hexafluorobutadiene in polymerization and copolymerization reactions can probably be interpreted by localization of π‐electrons at the double‐bonded carbon atoms and weakening of the conjugation effect owing to a shift in electron density to the highly polar fluorine atom. Similar effects were observed for hexafluorobutadiene in diene synthesis.
Microtacticity of polymers and methods of its investigation
Authors: Birshteĭn T. M. , Gotlib Yu. Ya. , Ptitsyn O. B. 
Published: April 2003

AbstractThe microtacticity (degree of stereoregularity) of vinylic polymers with asymmetric side groups is determined by the competition between the stereospecific influence of the catalyst (if the polymerization is of a catalytic nature) and of the end of the growing chain. The stereospecific influence of the latter is due to the differences in the transition state energies corresponding to isotactic and syndiotactic addition. These differences are associated with van der Waals repulsion of the bulky side chains, determining also chain flexibility. The concept developed by the authors of the effect of chain flexibility on the physical properties of a polymer shows that an important part is played by the interaction not only between neighboring side groups but also between the nearest nonneighboring groups. This leads to dependence of the probability of isotactic or syndiotactic addition of the monomer on the manner of addition of the previous monomer, explaining the formation of stereoblock polymers the chains of which consist of alternate iso‐ and syndiotactic arrangements. A quantitative method of studying the effect of polymerization conditions on the microtactic state of the polymers should be based on physical properties depending directly on the probability of iso‐ and syndiotactic addition rather than on the stereoregularity of large regions (such as degree of crystallinity). A theory of the geometrical, electrical, and optical properties of macromolecules has been developed, predicting the relation between these properties and the microtactic state of the chain. The theory recently received experimental verification as to the sizes (Krigbaum, Carpenter, and Newman), dipole moments (Krigbaum and Roig) and optical anisotropy (Tsvetkov and Magarik) of isotactic and atactic polystyrene molecules. A method of investigating the microtacticity on the basis of determination of infrared dichroism in stereoisomeric polymers has also been proposed.
Une methode d'etude de la vitesse de la polymérisation à haute conversion
Authors: Kryszewski M. , Grosmanowa B. 
Published: April 2003

AbstractLa recherche des processus de polymérisation à des hauts degres de conversion n'est pas seulement importante pour la technologie mais est aussi intéressante au point de vue de l'élucidation des processus avec des radicaux libres en milieu non liquide. Une méthode a été développée pour des études de polymérisation à des hauts degrés de conversion. Cette méthode est basée sur la mesure du changement dans la vitesse de polarisation d'une solution de monomère contenant une petite quantité d'une substance fluorescente (si le monomère n'est pas fluorescent). Comme substance fluorescente il faudrait employer un produit qui n'influence pas la cinétique de la polymérisation. La concentration de la substance fluorescente est de l'ordre de 10−6 gr./cm.3. La fluorescence devrait être excitée avec de la lumière d'une telle longueur d'onde, qu'elle n'initie pas la polymérisation. L'appareil consiste en un récipient de polymérisation thermostaté et un montage permetant de mesurer la vitesse de polarisation de la lumière. Par la même technique (avec une petite modification) il est possible de mesurer l'intensité de fluorescence. En utilisant cette méthode, le cours entier de la polymérisation du méthacrylate de méthyle et de méthacrylate de butyle a été examiné. On a trouvé que la vitesse de réaction était constante pour un certain temps et qu'elle croissait alors très rapidement. L'accélération et le changement des constantes de vitesse ont été confirmés par les résultats d'autres auteurs.
Kinetics of formaldehyde polymerization
Authors: Macháček Z. , Mejzlĭk J. , Pác J. 
Published: April 2003

AbstractPolymerization of formaldehyde was studied in diethyl ether solution at −58°C. Monomeric formaldehyde has been prepared through pyrolysis of carefully dried paraformaldehyde and purified by passage through liquid formaldehyde at its boiling point and subsequent condensation in a reservoir. A catalytic system consisting of n‐dibutylamine has been used. The course of polymerization was studied in a dilatometer provided with a stainless steel stirrer, since the polymer formed is insoluble in the reaction mixture. The components (i.e., liquid monomer, solvent, and catalyst solution) were measured into the dilatometer under dry nitrogen so as to form separate layers, one on top of the other. The polymerization reaction was started by mixing the contents. The rates of reaction were chosen so that the initial overall rate of reaction did not exceed 5% conversion per min. It was observed that at constant n‐dibutylamine concentration the overall rate of reaction increases with increasing water concentration, while the molecular weight as checked by viscometry practically did not change. The n‐dibutylamine‐water ratio lay in the range from 1:10 to 1:1000 at a formaldehyde concentration of 5 mole/l. With increasing n‐dibutylamine concentration (in the range from 2.5 to 14 μmole/l.) and at a constant concentration of water (3.5 mole/l.) the overall rate of reaction increases while the molecular weight does not change. The results obtained permit a study of dissociation equilibria of amines with water in nonaqueous media. The role played by water in the formation of the anion ‐OH (which initiates the polymerization) and the influence of the structure of the cation RxNHy+ on molecular termination or possibly transfer are discussed.
Study of some details of the mechanism of polymerization under the action of complex catalysts
Authors: Bresler S. E. , Mosevitskiĭ M. I. , Poddubnyi I. Ya. , Guan‐I Schi 
Published: April 2003

AbstractTo elucidate some details of the mechanism of isoprene polymerization by means of the complex catalyst TiCl4 + Al(i‐C4H9)3 an analysis has been made of the data on the molecular weight distribution of the polymers. A relation has been established between the heterogeneous character of the polymerization process and the degree of dispersity of the polymer. In particular, it has been shown that for very small catalyst particles polymerization proceeds slowly and is a nonstationary process. The molecular weight distribution of the polymers changes with time. On increasing the catalyst particle size above certain, critical dimensions required for carrying out heterogeneous catalysis, a stationary molecular weight distribution of the polymers sets in, remaining unchanged up to the end of the process. An investigation of the molecular weight distribution of the polymers obtained at various catalyst component ratios and various methods of addition to the monomer permitted a number of details of the chain termination mechanism in catalytic polymerization to be elucidated. Chain breaking has been shown to be not the result of reversible interaction of growing chains with the active centers on the surface.
Thermal stability of polydimethylsiloxane. I. Deactivation of basic active centers
Authors: Kučera M. , Láníková J. 
Published: April 2003

AbstractThe thermal stability of polydimethylsiloxane is determined by both the resistance of the siloxane chain to depolymerization and the resistance of the hydrocarbon side groups to various forms of degradation. Basic and acidic impurities present in the polymer promote depolymerization as well as degradation. Especially efficient in decreasing the thermal stability are the centers remaining “alive” in the polymer after completed polymerization.The rates of depolymerization and degradation of unstabilized polydimethylsiloxane were measured and compared with those of polymers with active centers deactivated through the formation of complexes with CO2 and iodine. Also measured was the stability of a polymer prepared by using Bu4P(OH) as catalyst and containing only decomposition products of active centers. Inasmuch as high molecular weight polydimethylsiloxanes are seldom used alone, the authors have studied the ability of some oxides (commonly used as fillers) to form complexes with basic active centers and so to influence the thermal stability of polydimethylsiloxane.
Infrared spectra of crystalline and stereoregular polymers. III. Spectra of polypropylene and some deuterated polypropylenes in the region 650 to 1550 cm.−1
Authors: Liang C. Y. , Lytton M. R. , Boone C. J. 
Published: April 2003

AbstractFrom an infrared study of partially deuterated polypropylenes, the spectrum of polypropylene was interpreted in the region 650 to 1550 cm.−1. It was found that the internal carbon‐hydrogen vibrational modes are associated with “group frequencies”. The A and E components of each of these modes have been observed at the same frequency. The external carbon‐hydrogen vibrational modes as well as the skeletal modes are complicated mixed modes which do not give rise to “group frequencies”. The A and E components of some of these mixed modes were found to split into different frequencies.
The copolymerization of 1,3‐butadiene with styrene by butyllithium initiation
Authors: Kuntz Irving 
Published: April 2003

AbstractThe homopolymerization of styrene (1M) by n‐butyllithium (0.006M) in n‐heptane at 30°C. is approximately six times faster than the homopolymerization of butadiene under the same conditions. In copolymerizations 1M in each monomer, butadiene is the more reactive comonomer. When 90% of the butadiene monomer has been converted to polymer, more than 80% of the styrene monomer present at the beginning of the reaction still remains. The initial copolymerization rate is the same as that observed in the polymerization of butadiene alone, and about 10 mole‐% styrene is incorporated into the copolymer initially produced. When the butadiene has all reacted a marked increase in polymerization rate is observed. The copolymer reactivity ratios for initial reaction appear to be 7 for butadiene and nearly 0 for styrene. When the copolymerization is carried out in the presence of concentrations of tetrahydrofuran similar to the concentration of butyllithium, increased polymerization rate is observed. Kinetic experiments indicate that the reaction is first‐order with respect to tetrahydrofuran. The amount of 1,2‐addition in the polybutadiene segments of the copolymer increased from the 7% observed in the absence of ether to 15 and 43% as the ratio of (THF)/(BuLi) was varied from 0.4–20. The copolymer initially produced contained 30 mole‐% styrene over this entire range of ether concentrations. The implications of these observations on the polymerization mechanism are discussed.
Dielectric dispersion of polar polymers
Authors: Bueche F. 
Published: April 2003

AbstractA simple molecular theory is presented for the dielectric dispersion behavior of polar polymers. It is shown that the α dispersion involves movement of the chain backbone. The relaxation time for this dispersion is given by a relation of form τα = a2f0/4kt, where a, and f0 are, respectively, the jump distance and friction factor for a chain segment. Although the numberical factor in this relation will depend somewhat on the exact model used for the computation, the general form of the relation is independent of the model as long as the chain can be considered a statistical coil. If the dipole is not rigidly attached to the chain backbone, a second, β dispersion region will result. The causes of the broadening of the dispersions are discussed.
Polymerization of alkynes by ziegler‐type catalyst
Authors: Watson William H. , McMordie Warren C. , Lands Larry G. 
Published: April 2003

AbstractA study has been made of the polymerization of acetylene, propyne, and butyne‐1 using aluminum triisobutyl, n‐butyllithium, or zinc diethyl in combination with titanium tetrachloride as catalyst. Optimum conditions for polymerization were determined by varying the catalyst composition. The major product was a black insoluble polymer whose spectrum indicates a high degree of conjugation. A small quantity of soluble low molecular weight polymer was also obtained. Reactions were run at atmospheric pressure and 21–62°C.
Properties of polyvinylidene fluoride. Part II. Infrared transmission of normal and thermally decomposed polymer
Authors: Wentink Tunis , Willwerth Lawrence J. , Phaneuf Jean P. 
Published: April 2003

AbstractThe infrared transmission of the plastic polyvinylidene fluoride has been measured. Normal and thermally decomposed samples were used. Bands yielding information on phase transitions and behavior during pyrolytic decomposition have been observed. The mechanism of thermal degradation is briefly discussed. Absorption coefficients of important bands have been evaluated.
A new synthetic elastomer based on a chlorophosphonated polyolefin. II. Effect of polyolefin structure on vulcanizate properties
Authors: Leonard E. C. , Loeb W. E. , Mason J. H. , Stenstrom J. A. 
Published: April 2003

AbstractThe paper describes the effect of ethylene‐propylene copolymer structure on the properties of vulcanized, chlorophosphonated ethylene–propylene copolymer. The crystallinity of copolymer has a marked effect on vulcanizate properties. The more crystalline the copolymer, the higher hysteresis values and permanent set are for the vulcanizate. The catalyst used for the copolymerization of ethylene and propylene affects crystallinity markedly, titanium trichloride as a catalyst component giving a more crystalline copolymer than does the use of vanadium salts. Copolymer molecular weight has an effect on vulcanizate tensile strength but no effect on heat stability, elongation, and hysteresis loss.
Crystal structure of polyketone (1:1 ethylene/carbon monoxide copolymer)
Authors: Chatani Yōzō , Takizawa Takeo , Murahashi Shunsuke , Sakata Yoshiaki , Nishimura Yasushi 
Published: April 2003

AbstractThe crystal structure of polyketone (1:1 ethylene/carbon monoxide copolymer) obtained by γ‐irradiation copolymerization of ethylene and carbon monoxide was determined by x‐ray diffraction. An orthorhombic unit cell was found, having space group D (Pnam) of dimensions a = 7.97, b = 4.76, c (fiber axis) = 7.57 A. The unit cell contains four repeating units (CH2CH2CHO). The main chain has a planar zigzag form. The side‐by‐side molecular packing is analogous to that of polyethylene, and CO groups arrange at two equivalent levels, z = 1/4 and 3/4. An apparent anisotropic thermal vibration of the molecule was recognized; i.e., the thermal vibration in the direction perpendicular to the fiber axis is about three times that along the fiber axis. Furthermore, from a preliminary investigation on polyketones having several mole ratios of ethylene and carbon monoxide, an interesting result was found: the larger the fraction of CO, the longer the a axis and the shorter the b axis.
Precipitation of polyelectrolytes by salts
Authors: Ikegami Akira , Imai Nobuhisa 
Published: April 2003

AbstractPrecipitation of poly(acrylic acid) by added salts has been investigated under various conditions. The PAA was neutralized to various degrees of ionization α by tetra‐n‐butyl ammonium hydroxide. The minimum salt concentration C̄s at which precipitation occurs was determined at various polymer concentration Cp, temperature T, and α. The amount of bound cations to polyions, the change in ion hydration, and the polymer expansion near C̄s were estimated by conductance, refractive index, and viscosity measurements, respectively. It is concluded that there are two kinds of precipitation; The L type which satisfies the relation C̄s ≐ αCp and occurs at high α due to cation binding to the polyions, and the H type in which C̄s is independent of Cp and which appears at low α with salts other than those having large ions. This classification of the precipitation is justified also by the C̄s – T relation; in the L type, C̄s is nearly independent of T, and in the H type C̄s increases with T. At intermediate α‐values pronounced specificities of salt ions are found in the precipitation; at α = 0.25, with Mg2+ the H type appears, while with Ba2+ or Ca2+ the L type appears, although all of these divalent cations are bound to polyions to the same degree. This is due to the difference in the hydration of the polyion‐cation complexes. In the L‐type the formation of cation bindings, such as salt bridge, makes the polymer hydrophobic, while in the H type highly concentrated salt ions render the polymer solution unstable by changing the arrangement of the water molecule.
Report on nomenclature dealing with steric regularity in high polymers
Authors: Huggins M. L. , Natta G. , Desreux V. , Mark H. 
Published: April 2003

AbstractThis report deals with the classification and naming of high polymers composed of molecules possessing steric regularity, and with related problems of nomenclature. It has been tentatively approved, for one year, by the Commission on Macromolecules of the International Union of Pure and Applied Chemistry.
Effect of gases on the electron spin resonance spectra of irradiated acrylamide and methacrylamide
Authors: Ueda Hisashi , Kuri Zen'Ichiro , Shida Shoji 
Published: April 2003

AbstractThe effects of various gases on irradiated acrylamide and methacrylamide were studied by ESR. The results are not the same with irradiated monomers and irradiated polymers. Nitrogen oxide and hydrogen sulfide are known as radical scavenger, but they act as radical transformers for these samples. In source and postirradiation reaction of polyacrylamide or polymethacrylamide with hydrogen sulfide give rise to broad spectra having a g factor of 2.0267 and the new radicals produced here are concluded to be of the RS. type.
Photolysis of poly‐α‐methylstyrene
Authors: Stokes Suzanne , Fox R. B. 
Published: April 2003

AbstractThe photodegradation of thin films of poly‐α‐methylstyrene by near ultraviolet radiation has been studied in vacuum at 27 and 115°C. Changes taking place during photolysis were followed by a determination of monomer formation by ultraviolet spectroscopy, residue molecular weight through a measurement of intrinsic viscosity, and volatile products by mass spectroscopy. Gross features of the photolysis include random chain scission in the polymer with subsequent depolymerization of the radicals formed to yield small amounts of monomer; the kinetic chain length is on the order of 15 in the temperature range studied. Quantum yields at 27°C. for chain scission and monomer formation are 1 × 10−3 and 7 × 10−3, respectively. At 115°C. the quantum yields are 2 × 10‐2 and 0.5. Small quantities of hydrogen, CO2, CO, and a number of hydrocarbons were liberated during irradiation. An approximate one‐to‐one correlation between the number of main chain scissions and CO2 + CO molecules evolved was found, suggesting the occurrence of chain scission at weak linkages involving oxygen.
Thermal conductivity of high polymers from −180°C. to 90°C.
Authors: Eiermann K. , Hellwege K.‐xH. 
Published: April 2003

AbstractSystematic measurements of the thermal conductivity of plastics have been undertaken by various methods and checked against each other. Between −180 and +100°C. the thermal conductivity depends only slightly on the temperature. For instance, amorphous plastics and natural rubber show a break in the curve at the second‐order transition temperature. This break probably is connected with the break in the volume versus temperature curve. In stretched samples, the thermal conductivity was found to be larger when stretching was in a direction parallel than perpendicular to the chains. Partially crystalline plastics show a more complex behavior.
Equilibrium ultracentrifuge for molecular weight measurement
Authors: Beams J. W. , Boyle R. D. , Hexner P. E. 
Published: April 2003

AbstractThe magnetically supported vacuum‐type equilibrium ultracentrifuge previously described has been improved and used for the measurement of the molecular weights of a number of substances. The modifications include an electric motor drive which accelerates the rotor to operating speed. The rotor coasts freely during the sedimentation, and the operating speed may have any desired value from a few revolutions per second to the maximum safe speed of the rotor. Improvements have been made in the ultracentrifuge cell, and both white light and monocromatic light fringes can be used interchangeably in the interferometer. These modifications make possible the determination of the molecular weight quickly either without waiting for equilibrium to take place or after equilibrium has been established. The overall precision is the order of one part in a thousand for the centrifuge measurements themselves. Molecular weight data are given for a number of substances, including sucrose, ribonuclease, and insulin. The application of the centrifuge to the determination of molecular weight distributions is discussed.