bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical considerations on the mechanism of stereospecific cationic polymerization in homogeneous systems
Authors: Higashimura T. , Yonezawa T. , Okamura S. , Fukui K. 
Published: April 2003

AbstractA theoretical interpretation of the mechanism of stereospecific cationic polymerization in a homogeneous system at low temperature is given. The existance of a counterion in the vicinity of a charged carbon atom of a growing polymer ion is assumed and a repulsive interaction is considered to be between the substituent of the attacking monomer and that of the polymer. The most probable geometrical conformation of a monomer and a polymer ion in the transition state is determined by the magnitude of stabilization due to the overlap between atomic orbitals of ion and monomer. Our experimental results can be explained satisfactorily by this mechanism.
The oxidation of polyvinyl alcohol by ceric ion
Authors: Mino G. , Kaizerman S. , Rasmussen E. 
Published: April 2003

AbstractThe rate of reaction of ceric nitrate with the 1,2‐glycol units and the alcohol units of polyvinyl alcohol was determined at 20°C. It was found that the glycol units are oxidized much faster than the alcohol units even though they are outnumbered about one hundred to one in the polymer chain. Under the conditions studied, at least 83 glycol units reacted per 100 hours oxidized. Since the oxidation of the glycol units is accompanied by chain splitting, the free radicals are produced predominantly at the fragments end.
Transient catalysts for the polymerization of organosiloxanes
Authors: Gilbert Alfred R. , Kantor Simon W. 
Published: April 2003

AbstractA study was made of the polymerization of siloxances with transient basic catalysts. These catalysts are active as polymerization catalysts for siloxanes and will decompose rapidly to inactive products at elevated temperatures with the formation of stable polymers. Several quaternary ammonium bases were studied as polymerization catalysts. It was found that bases such as tetramethylammonium hydroxide and benzyltrimethylammonium hydroxide were efficient catalysts. Similar bases having β‐hydrogen atoms decomposed too rapidly via an elimination reaction and were not good catalysts. The polymerizations of organosiloxanes with quanternary phosphonium hydroxides were also studied. The phosphonium bases decomposed thermally in a different manner than the ammonium bases to give phosphine oxides and hydrocarbones. The most efficient transient catalysts were found to be phosphonium silanolates. Tetrabutylphosphonium silanolate was conveniently prepared in an anhydrous form and it proved to be extremely efficient for the preparation of homopolymers and copolymers of organosiloxanes.
Isoprene polymerization by organometallic compounds. II
Authors: Tobolsky Arthur V. , Rogers Charles E. 
Published: April 2003

AbstractDispersions of metallic lithium, sodium, and potassium and some of their organoderivatives were used to initiate the polymerization of isoprene in several solvents. The propagating species in all cases were ion pairs of the type . The structure of the resultant polyisoprene depends on the character of the propagating pair. This in turn depends mainly on the counterion M+ and the solvent type. One quality of this ion pair which is of utmost importance is its ionic character (or degree of charge separation). In solvents such as diethyl ether and tetrahydrofuran, where we might expect large charge separation in the ion pair, all initiatiors produce similar, though not necessarily identical, polymer structures comprising 1,2 ‐3,4‐, and trans‐1,4‐adducts. With potassium‐dependent initiators, very nearly the same polymer structure is obtained in hydrocarbons as in the more basic ethers, attesting to the highly ionic character of the potassium‐carbon bond; this might perhaps be considered as the “limiting anionic behavior”. Sodium has smaller inherent ionic‐character and is more sensitive to changes in solvent basicity, but still it parallels the behavior of potassium. With lithium, the most covalent of the alkali metals, a dramatic change in behavior occurs when polymerization is conducted in hydrocarbon media; a 93% cis‐1,4‐,7% 3, 4‐polyisoprene structure is obtained. This may be merely a limiting structural from at the low end of the scale of ionic character of the propagating ion‐pair. The steric factors arising from complexes formed between the propagating ion‐pair. The steric factors arising from complexes may also have an important influence on the polymer structures product in the various solvents. A continuous seriese of polyisoprene structures intermediate between those formed in hydrocarbons with Li and the limiting “anionic structure” can be obtained by use of such solvents as phenyl ether or anisole, or by judicious choice of appropriate hydrocarbon–solvent ratios with a number of suitable cosolvents.
Relationship between the flow of polymeric substances in a parallel plate compression rheometer and in an extrusion rheometer
Authors: Ito Katsuhiko 
Published: April 2003

AbstractThe parallel plate compression rheometer is a typical measuring apparatus for the plastic flow of high polymers. In this rheometer, compressive creep curves of test specimens were studied at low rates of shear at constant temperature. Assuming Newtonian flow in the test specimen between the parallel plates, the coefficient of apparent viscosity was calculated from the lapsed viscous‐flow portion of these creep curves. The test specimen was a disk type with an initial‐diameter‐to‐initial‐height ratio of more than 30. Under low rates of shear, structural viscosity has little effect on the experimental results with cellulose acetate derivative plastics. At high rates of shear in the extrusion rheometer, however, the coefficient of apparent viscosity increases with a decrease of extrusion pressure. The experimental results in the parallel plate compression rheometer corresponds to those of zero extrusion pressure in the extrusion rheometer by the extrapolation method. The intrinsic flow energy, Uint., as a comparative value of the flow behavior of various kinds of linear polymers, is measured directly by the parallel plate compression rheometer.
Studies on the low pressure polymerization of propylene using catalysts containing alkali metal alkyls
Authors: Zilkha Albert , Calderon Nissim , Ottolenghi Ariel , Frankel Max 
Published: April 2003

AbstractThe low pressure polymerization of propylene was investigated using catalysts prepared from alkali metal alkyls and titanium tetrachloride. In all cases the efficiency of the catalysts depended on the molecular ratio of the metal alkyl to the titanium tetrachloride. In general the polymerization conditions were similar to those for ethylene although the propylene polymerized much more slowly. With n‐butyllithium–titanium tetrachloride, optimum molecular ratios were found between 1.8–2.5, with sharp drops on both sides. With amylsodium–titanium tetrachloride the optimum extended over a wide range (5.7–15), the activity decreasing sharply with lower molecular ratios. The catalysts prepared from sodium alkyls were more active than those prepared from lithium alkyls. Increasing yield was obtained on lowering the concentration of the catalyst. Up to a pressure of about 3 atmospheres, increase in the rate of polymerization was observed with increase in pressure; above this no influence of the pressure was observed. Isotactic polymers were isolated from the polymerization products by successive fractionation of the crude polymers in acetone, ether, and isooctane which dissolved the atactic polymers. With butyllithium–titanium tetrachloride catalysts, at and above optimum ratios, the isotactic fractions were about 60%. At lower ratios there was a great increase in atactic polymers. With amylsodium–titanium tetrachloride catalysts the isotactic fractions were about 70%. Phenylsodium–titanium tetrachloride catalysts were found to be very weak in the polymerization of propylene.
Polymers and group interaction. VIII. Synthesis of a styrene–amino acid copolymer
Authors: Goethals E. , Smets G. 
Published: April 2003

AbstractA copolymer of styrene–maleimide has been obtained by reaction of a styrene–maleic anhydride copolymer with ammonia under pressure in acetone solution at 70–90°C. The co(styrene–maleimide) polymer was submitted to Hofmann degradation reaction in aqueous medium and in water–tert‐butyl alcohol solution. In aqueous solution the amine formation is accompanied by partial lactam formation resulting from interaction between acid and amine groups. In water–tert‐butanol this cyclization reaction did not take place, since there was formation of tert‐butyl carbamates. These carbamate groups may be hydrolyzed in acetic acid solution in the presence of hydrochloric acid, and afford free amino groups. In both media, appreciable hydrolysis proceeds simultaneously with the Hofmann reaction, so that the number of carboxyl groups exceeds by far the number of amino groups (75 vs. 20–25%).
The viscosities of concentrated polymer solutions. II. Extremely concentrated solutions
Authors: Hirai Nishio 
Published: April 2003

AbstractThe enormous increases in the viscosity, η, and the associated activation heat, Qη, in concentrated polymer solutions are attributed to two different factors. One is the formation of intermolecular linkages between high polymer molecules, and the other is the increase of glass transition temperature, Tg, with increasing concentration of the solution. In this paper, the effect of the increase of Tg in solutions of extremely high concentration is discussed. The apparent activation heat of viscosity, Qη, in this concentration range is represented by the equation, Qη = 2ΔE + Qη0. The first term is the increase of Qη due to the intermolecular linkages, and ΔE is the energy to form a linkage. The second term is the activation energy for the vitrified solution where intermolecular linkages do not exist, and it is represented by the equations, (Qηs/Qη2)1/2 = 1 − Aw2 and A = 1 − (Qηs/Qη0)1/2, where A is a constant for the solution and Qη2 and Qηs are the activation heats of viscosity for the polymer and the solution, respectively. The value of A remains constant up to 100% for polystyrene in dibenzyl ether, polymethyl methacrylate in diethyl phthalate, and polyvinyl chloride in tricresyl phosphate. The constant A is always very close to unity for polymeric solutions. The general tendency of concentration dependence of Qη in the whole range of concentration is discussed.
Interfacial polycondensation. I.
Authors: Wittbecker Emerson L. , Morgan Paul W. 
Published: April 2003

AbstractInterfacial polycondensation is a rapid, irreversible polymerization at the interface between water containing one difunctional intermediate and an inert immiscible organic solvent containing a complementary difunctional reactant. It is based on the Schotten‐Baumann reaction in which acid chlorides are reacted with compounds containing active hydrogen atoms (OH, NH and SH). A large number of polymers (heat‐sensitive and infusible as well as stable and meltable) can be prepared. The method has been applied to the preparation of polyurethanes, polyamides, polyureas, polysulfonamides, and polyphenyl esters. Interfacial polycondensations are run in simple, open laboratory equipment with or without stirring. With suitable agitation granular or powdered polymers with high molecular weight are prepared at room temperature and isolated within a few minutes. The intermediates need not be absolutely pure or in balance nor is a quantitative yield needed in order to obtain high polymer. The major variables in the interfacial polycondensation process are discussed and the laboratory techniques and principles are contrasted with melt polycondensation.
Interfacial polycondensation. VII. Polyurethanes
Authors: Wittbecker Emerson L. , Katz Manfred 
Published: April 2003

AbstractInterfacial polycondensation of diamines and bischloroformates has been used to prepare a wide variety of high molecular weight polyurethanes, many of which cannot be synthesized by means of the diisocyanate‐glycol addition process. Almost every type of diamine normally used in condensation polymerization, i.e., aliphatic, alicyclic, cyclic secondary, and aromatic diamines, has been found suitable. Aliphatic, alicyclic, and aromatic bischloroformates have been prepared and utilized as coreactants. Of particular interest are the polymers melting above 200°C. which have been obtained from such intermediates as piperazine, ethylenediamine, and the bischloroformates of ethylene glycol, 2,2‐dimethyl‐1,3‐propanediol, hydroquinone, and the cis and trans isomers of 1,4‐cyclohexanediol. The purity of the reactants and the type of organic solvent, acid acceptor, and dispersing agent were found to be important variables which influenced the molecular weight of the polyurethanes.
Interfacial polycondensation. VIII. Application to AB‐type monomers
Authors: Schaefgen J. R. , Koontz F. H. , Tietz R. F. 
Published: April 2003

AbstractThe application of interfacial polycondensation to the preparation of several polyurethanes and polyamides from AB type monomers is described. The monomers are salts of aminoalkyl chloroformates and aminoacid chlorides, respectively. Differences in method and mechanism from the AA plus BB type interfacial polycondensation are discussed. Several new ring‐containing polymers were synthesized.
Interfacial polycondensation. XI. Ordered copolymers
Authors: Lyman Donald J. , Lup Jung S. 
Published: April 2003

AbstractAn alternating copolyurea was prepared by the interfacial polycondensation of 1,4‐piperazinedicarbonyl chloride with hexamethylenediamine. Comparison of this alternating copolyurea with the corresponding copolyurea having a random distribution showed that the alternating copolymer had a higher melting point, greater crystallinity, and was somewhat less soluble than the random copolymer. A series of copolyamideurethanes was prepared by the interfacial polycondensation of 2,5‐dimethylpiperazine with terephthaloyl chloride and ethylene bis(chloroformate), various modes of addition of the two diacid chlorides being used. The degree of order developed in these copolyamide–urethanes was postulated from the probable mechanism of the reaction. The directional “crystallinity” or lattice order of the copolymers, as determined from x‐ray diffraction patterns, was cited to support these postulated structures.
Electron exchange polymers. XII. Potentiometric titration of dicyclopentadienyliron (“ferrocene”) and some derivatives
Authors: Chen Yueh‐Hua , Fernandez‐Refojo Miguel , Cassidy Harold G. 
Published: April 2003

AbstractPolymers bearing the dicyclopentadienyliron (“ferrocene”) functional group fall into the class of electron exchange polymers. Polyvinyl dicyclopentadienyliron is insoluble in common polar solvents suitable for use in electrometric titration. When sulfonated in the ferrocene rings, the material becomes more unstable toward oxidation than alkylsubstituted dicyclopentadienyliron, and upon oxidation readily loses iron. The midpoint potential for dicyclopentadienyliron (in acid alcohol) is −0.5369 ± 0.0005 v.; for cyclopentadienyl(ethylcyclopentadienyl)iron (in acid alcohol) it is −0.5081 ± 0.0005 v.; for the ammonium salt of monosulfonated dicyclopentadienyliron (in 0.5N aqueous sulfuric acid) it is −0.6143 ± 0.0007 v. on oxidation, and −0.6141 ± 0.0008 v. on reduction. The diammonium salts of disulfonated dicyclopentadienyliron and of cyclopentadienyl(ethylcyclopentadienyl)iron could not be titrated successfully. Sulfonated polyvinyldicyclopentadienyliron could not be titrated because of its easy decomposition at potentials in the neighborhood of −0.6 to −0.7 v.
Molecular weight distributions of polystyrene samples by turbidimetric titration
Authors: Gooberman G. 
Published: April 2003

AbstractAn analysis of the light scattered from suspended polymer aggregates formed during turbidimetric titration of the system polystyrene–benzene–methanol has been made. It has been shown that a knowledge of the precipitate composition and total number of aggregates is required before the precipitate mass can be calculated from turbidity measurements. Satisfactory results are obtained if the total number of aggregates is assumed to be proportional to the precipitate mass, provided the initial polymer concentration does not exceed 0.002% (w/v). On the basis of an empirical saturation law, two methods have been used to derive satisfactory molecular weight distributions for two polystyrene samples of known distribution. The better method is based on a Claesson grid. The other method is based on that given originally by Morey and Tamblyn. Turbidimetric titration tends to discriminate against the low‐molecular‐weight end of a distribution.
Molecular orbital considerations on the reactivities of vinyl compounds. I. Radical reactivity
Authors: Fueno Takayuki , Tsuruta Teiji , Furukawa Junji 
Published: April 2003

AbstractAccording to the simple LCAO MO method, the π‐electron localization energies on the β‐carbon of several vinyl monomers (Lβ) and on the α‐carbon of monomer radicals (Lα′) were calculated. Comparison of the calculated values of Lβ and Lα′ with the experimental results so far reported for radical reactivity of vinyl compounds showed (1) that a linear relationship holds between Lβ and the logarithm of methyl affinity, (2) that the smaller the value of Lα′ the larger is the chain termination constant, and (3) that Lβ and Lα′ are parallel, respectively, to the values of Q and P in Price‐Alfrey's notation. These points imply that Lβ and Lα′ would be satisfactory indices for the radical reactivities of vinyl monomers and monomer radicals, respectively. It was also suggested that, in radical copolymerization, the localization energy difference between two monomers, as well as the difference in the π‐conjugation energies with attacking radicals in the transition state of the propagation step, would contribute to the determination of the monomer reactivity ratios.
A description of the rate of contraction‐relaxation of rat tail tendons
Authors: Elden Harry R. , Boucek Robert J. 
Published: April 2003

AbstractAging alters the contraction‐relaxation of rat tail tendons; this has been attributed to an increase in the degree of crosslinking of collagen and its surrounding mucopoly‐saccharides. An analysis was made of tendon mechanics after acetic acid exposure in the untreated and formaldehyde treated state as well as the properties of acetic acid–water solutions. Tendons were treated with formaldehyde solutions (pH 7–8) over a wide range of dilution (100,000: 1 to 1: 1, pF = 5 to 0) of a stock 37% formalin. The contraction‐relaxation and extractability were followed after exposure to 0.5M acetic acid. An empirical analysis of the length vs. time curves yielded the initial rate of contraction, dL/dtC, the rate of relaxation, dL/dtR, and a specifie rate constant for the process, KCR. There was a parallent dependence of formaldehyde concentration on the effect of incurbes as well as the exteractability of tendons. On the length‐vs.‐time curves as well as the extractability of tendons. This was interpreted as evidence of the effect of induced crosslinking on the properties of the macromolecule collagen. Since similar effects are observed as a function of natural aging the role of added crosslinking as the mechanism for this change is suggested again. Contimuous variation analyses of spectroscopic and viscometric data of the acetic spectroscopic and viscometric data of the acetic acid–water system demonstrated extensive molecular interaction. The hydrogen bond‐forming tendencies of the carboxyl CO and HO may be as the basis for the action of the solvent in the contraction‐relaxation process.
The influence of temperature on the viscosity of polystyrene solutions
Authors: Bianchi Umberto , Magnasco Valerio 
Published: April 2003

AbstractThermodynamical parameters for the system polystyrene–toluene at 25°C. have been calculated on the basis of the Flory theory from results of viscosity measurements in toluene and in ideal solvents at 25, 34, and 45°C. for 11 fractions of polystyrene. The results obtained are compared with those given in the literature. The values obtained for thermodynamical parameters permit calculation of intrinsic viscosities at different temperatures; these values are accurate to within ±2%.
A revised Q–e diagram
Authors: Thompson B. R. , Raines R. H. 
Published: April 2003

AbstractNew data are presented to establish the Q and e values of vinylidene chloride, acrylonitrile, and vinyl chloride relative to styrene as the reference monomer. Within the experimental error these values are shown to be entirely consistent with the observed copolymer compositions. Only the values for vinyl chloride are appreciably different from those published in the original paper of Alfrey and Price in 1947. With these better data it is hoped that renewed efforts will be made to place this empirical device on a sound theoretical basis.
Column fractionation of polymers
Authors: Krigbaum W. R. , Kurz J. E. 
Published: April 2003

AbstractMixtures of fractions of atactic polystyrene dissolved in cyclohexane were resolved by elution from a column at different temperatures. A coarse‐grained Ottawa sand was used to minimize the surface area of the support. Comparison with the critical miscibility temperature data of Schultz and Flory shows that the lower molecular weights are eluted from the column at a temperature somewhat below the critical miscibility temperature, as expected, but for molecular weights above 3 × 105 the elution temperature increases abruptly, and even exceeds the critical miscibility temperature. This rapid rise occurred at 1.5 × 105 when the surface area of the support was increased by use of a very fine Celite. We conclude that for the higher molecular weights additional thermal energy is required to desorb the polymer, and hence the partitioning of these species is not determined solely by solubility considerations. Concerning the efficiency of the column extraction, considerable resolution of each component was obtained, and attempts to determine the M̄w/M̄n ratios of the individual components were at least partially successful. As predicted by theory, for a given molecular weight interval the range of elution temperature was increased fivefold by the use of a mixed solvent, benzene–ethanol, in place of the single poor solvent, cyclohexane. Customary fractionation procedures are very inefficient when applied to high‐melting crystalline polymers. For these polymers we investigated selective precipitation upon a column having a temperature gradient, rather than elution from the column. For dilute solutions, amorphous phase separation may precede crystallization, particularly in the case of polymers whose rates of crystallization are low, owing to the presence of bulky side groups. The column precipitation method failed to give improved fractionation of polyacrylonitrile, owing to phase separation of the dimethylformamide–heptane mixture part way down the column. On the other hand, good resolution was obtained for an unfractionated sample of isotactic polystyrene up to 1.5 × 106. Molecular weights above this level were compressed into a narrow band at the top of the column. Thus, if the distribution is extremely broad, a second fractionation with a different solvent:‐ precipitant ratio may be required. Even so, a single pass through the column resulted in a better resolution than that obtained by a large‐scale, two‐stage extraction‐precipitation procedure, indicating that the column precipitation method does posses an advantage for the fractionation of crystalline polymers.