bluuebunny/crossref_metadata_2025_split huggingface dataset:
A kinetic mechanism for the heterogeneous stereospecific polymerization of propylene
Authors: Saltman William M. 
Published: April 2003

AbstractA theoretical examination of the kinetics of the polymerization of propylene with Al(C2H5)3–TiCl3 has been made. A reaction scheme is proposed which, with the use of adsorption equations, allows the calculation of propagation and termination rates. The calculated degree of polymerization is in semiquantitative agreement with the experimental results reported by Natta and indicates that a single termination reaction can account for the major part of the experimental results. The role of the solid is still somewhat obscure but it probably takes part in a second termination reaction. Propagation is due to the growth of the adsorbed aluminum alkyl, and the experimental propagation rate indicates that polymerization proceeds when the alkyl, on the almost completely covered surface, reacts with monomer which may be adsorbed or not. Before termination occurs, the now long‐chain aluminum alkyl is desorbed and may exist free in solution. Termination occurs when this alkyl is readsorbed on or reacts with a second type of surface site which is active only for termination. The overall process is akin to those proposed for enzyme reactions.
Polyethers. X. Endgroups in polyethylene oxide
Authors: Ebert Philip E. , Price Charles C. 
Published: April 2003

AbstractHigh concentrations (10% or greater)of zinc chloride or mixtures of aluminum isopropoxide–zinc chloride catalyzed the polymerization of ethylene oxide to low molecular weight polymer. Endgroup analysis of the polymer gave a 1:1 ratio of hydroxyl to chloride when zinc chloride was the catalyst. Using the aluminum–zinc system as the catalyst, the polymer had a 2:1 ratio of hydroxyl to chloride endgroups in addition to isopropoxyl endgroups. These polymer structures are in accord with the coordinate propagation mechanism proposed earlier, followed by termination by hydrolysis of the catalyst–polymer linkage. Zinc chloride reacted at room temperature with both ethylene oxide and propylene oxide to form insoluble “complexes.” The complexes could be recovered and were found to be catalysts for the polymerization of ethylene oxide. However, they were not as active as zinc chloride itself, and they were poor catalysts for the polymerization of propylene oxide. Analysis of the complexes indicated they were mixtures containing a large percentage of zinc hydroxide. Zinc hydroxide, but not zinc oxide, was found to be an effective catalyst for the polymerization of ethylene oxide.
Time‐dependent tensile properties. Part II. Porosity of deformed glasses
Authors: Rosen Bernard 
Published: April 2003

AbstractThe slow growth and recovery of tensile microfractures in films of organic glasses create an apparent tensile creep‐enhancement of the coefficient of penetrant diffusion. These effects, although of a greater magnitude, are strikingly similar to those found by McAfee with Pyrex glass. This situation encourages the notion of progressive submicrofracture in inorganic glasses. The advent of increased porosity under tension suggests a role of localized vapor absorption in the environmental‐stress crazing and in the “anomalous” vapor diffusion in organic glasses. It becomes increasingly apparent that progressive breakdown is a critical consideration in the mechanical behavior of viscoelastic solids.
Effect of polydispersity in polystyrene on stress relaxation
Authors: Tobolsky A. V. , Murakami K. 
Published: April 2003

AbstractStress relaxation master curves are presented for twenty‐three polystyrene samples whose weight‐average molecular weights Mw varied from 20,800 to 310,000 and whose heterogeneity indices varied from 1.0 to 15.92. The maximum relaxation times τm, the associated partial modulus Em, and the flow viscosity η were determined for these samples at 115°C. It is shown that at 115°C. the relation log τm (minutes) = −15.10 + 3.4 Mw is obeyed. It is also shown that the quantity αB = τmEm/η correlates with the heterogeneity index of the sample. It is concluded that stress relaxation studies can be used to obtain weight‐average molecular weights and also to provide a qualitative measure of the heterogeneity index.
Crystalline acrylic polymers. II. Mechanism studies
Authors: Goode W. E. , Owens F. H. , Myers W. L. 
Published: April 2003

AbstractThe polymerization of methyl methacrylate and isopropyl acrylate in toluene with phenyl‐H3‐magnesium bromide has been studied at 0 and −70°C., respectively. Comparison of number‐average molecular weights calculated from measurement of radioactivity and from measurements of appropriate colligative properties has shown that there is one and only one phenyl group per chain. Thus, initiation in this system is by 1,4‐addition of the organomagnesium compound to the monomer. Methyl methacrylate, isopropyl acrylate, ethyl acrylate, and methyl acrylate were polymerized in toluene with phenylmagnesium bromide as the initiator. Isolation and identification of all the products have shown that, in addition to polymer, there are formed small amounts of two ketones and a hydrocarbon. Data are presented indicating that the principal mode of termination is via an intramolecular cyclization to give chains having a β‐ketoester group on the end (arising from intramolecular reaction). A rationale for the stereospecificity, the termination reaction, and the large ratios of weight‐average to number‐average molecular weight in these polymerizations is proposed.
The aggregation of random and block copolymers containing acrylonitrile in mixed solvents
Authors: Climie I. E. , White E. F. T. 
Published: April 2003

AbstractLarge time‐dependent changes in solution viscosity and turbidity have been found on adding nonsolvents to solutions of block, random, and homopolymers containing polyacrylonitrile in N,N‐dimethylformamide. These changes have been related to the reversible aggregation of polyacrylonitrile molecules in solution. The effects of polymer concentration, molecular weight, structure and composition have been investigated and a possible mechanism of aggregation suggested.
Irradiation effects in lexan
Authors: Barker R. E. , Moulton W. G. 
Published: April 2003

AbstractThe destruction of free radicals by oxygen diffusion into x‐irradiated Lexan, [OC6H4(CH3CCH3)C6H4O(CO)]n, has been studied by means of optical and electron paramagnetic resonance measurements. Lexan, which is normally amber, appears uniformly green immediately after x‐irradiation, but in a few hours, begins to bleach from the edges toward the interior, and a visible amber border forms about a green core. By direct measurements of the rate of recession of the boundary, it was found that the phenomenon is due to O2 diffusion and that the process obeys an Arrhenius expression (between 0 and 130°C.) with an activation energy of 0.31 e.v. (±3%). It has been shown that Zener's equation for the diffusion “frequency factor,” D0 = γS2v exp {ΛBE/kTm}, is useful in the study of diffusion in polymers even though it was derived for the case of atomic diffusion in metallic crystals. In the spectral region studied (0.3–0.7 μ) there are two bands (near 0.40 and 0.34 μ) present in the irradiated polymer which are not present in the unirradiated material. The center producing the absorption at 0.34 μ is stable over a long period. The absorption at 0.40 μ decays in a few days at room temperature when oxygen is present. At 250 Mcycles/sec. and 9000 Mcycles/sec. there was a single EPR absorption with a width of 13 ± 3 gauss, and at 250 Mcycles/sec., a g value of 2.012 ± 0.007. Measurements of changes in the spin concentrations with irradiation dose and sample age (measured from the instant of removal from the x‐rays) showed that the color center which absorbs near 0.40 μ is paramagnetic. The radiation G value (at 40 k.v. and 18 kr/min.) for the paramagnetic centers was estimated to be about 5 spins/100 e.v. by comparison of the Lexan EPR spectrum with that of a DPPH spin standard. A simplified rate equation which was consistent with the decay data may be written: n = K'n/tα, where n is the average spin concentration as a function of time t and ≃ 1/2. The t−α factor can be interpreted in terms of a diffusion‐limited supply of oxygen in the interior of irradiated Lexan.
Radiolysis of polymethyl isopropenyl ketone
Authors: Shultz Allan R. 
Published: April 2003

AbstractPolymethyl isopropenyl ketone (PMIPK) undergoes random chain scission when irradiated at 23°C. with gamma rays or with ultraviolet light. Total energy absorption per chain scission, Ed, is 94 e.v./scission for PMIPK powders irradiated in vacuo with spent reactor fuel element gamma rays (0.42 Mrad/hr.). Ed is 84 e.v./scission for a PMIPK powder irradiated in vacuo with Co60 gamma rays (0.109 Mrad/hr.). The presence of air lowers the value of Ed to 41 e.v./scission under the former conditions. A film of PMIPK irradiated in air with 2537‐A. wavelength light exhibits Ed = 22 e.v./scission or a quantum yield ϕd = 0.22 chain scissions/absorbed photon. The viscosity‐average molecular weights of this film vary with light exposure in accordance with theoretical predictions.
Microwave absorption and molecular structure in liquids. XL. The dielectric relaxation of a polyester of 1,2‐propylene glycol and adipic acid in solution
Authors: Purcell William P. , Smyth Charles P. 
Published: April 2003

AbstractThe dielectric constants and losses have been measured at 20°C. and wavelengths of 1.25, 3.22, 10.0, 25, and 50 cm., and 575 m. for a series of dilute benzene solutions of a polyester of 1,2‐propylene glycol and adipic acid with molecular weight between 5,000 and 7,000. The dielectric constant and loss values are plotted against the weight concentrations of the solute and the slopes of the straight lines thus obtained are examined by four different methods of analysis. The data may be represented in terms of two parameters, a most probable relaxation time and a distribution factor, two relaxation times, or a distribution of relaxation times between two limiting values. The values obtained for the relaxation times are close to those previously found for long‐chain fatty acid esters and correspond to relaxation by twisting of short segments containing carboxy groups around bonds in the chain. A value 1.57 × 10—18 obtained for the effective dipole moment of the COOC group as compared to 1.9 × 10—18 in a small monoester indicates some restriction of rotation around the bonds because of mutual repulsion between the polar groups.
The thermal degradation of a polythiolcarbamate
Authors: Dyer Elizabeth , Osborne D. Wendell 
Published: April 2003

AbstractOn pyrolysis at 300° under nitrogen the polythiolcarbamate from methylenebis(4‐phenyl isocyanate) and 1,6‐hexanedithiol decomposed into carbon dioxide, carbonyl sulfide, 6‐mercapto‐1‐hexene, tetrahydro‐2‐methyl‐1‐thiapyran, thiepane, 1,6‐hexanedithiol, and an intractable residue. Carbodiimide and amine groups were shown to be intermediates in the formation of the residue. A quantitative study of the degradation indicated that about 80% of the thiolcarbamate groups decomposed by splitting into isocyanate and mercaptan moieties. Further reaction of the isocyanate moiety produced the carbon dioxide and carbodiimide groups. The remaining thiolcarbamate groups formed carbonyl sulfide, and amine and olefin groups, probably by a direct ester type of degradation. The resulting 6‐mercapto‐1‐hexene was the source of the cyclic sulfides.
The influence of ionic strength on the viscosity of ribonucleic acid and other polyelectrolytes
Authors: Cox R. A. 
Published: April 2003

AbstractThe viscosity of a number of diverse polyelectrolytes varies with the concentration of added electrolyte according to the relation

except in very dilute salt solutions; [η] and [η0] are the limiting viscosity numbers in solutions of electrolyte concentration Csalt and C°salt, respectively (the latter concentration being that of any reference solution), and m is a constant whose value depends on the permeability of the polyion. This relation can be accounted for by the theory of Flory. The viscosities of several polyvinyl derivatives are found to be very similar, indicating that the ionizing group has no specific influence upon coil dimensions. In contrast, polynucleotides do not conform to this pattern; in particular, sodium ribonucleate undergoes an unusually large contraction to a highly compact flexible configuration between sodium chloride concentrations of 1 and 10 mM.
On the growth habits of twinned crystals of polyethylene
Authors: Khoury F. , Padden F. J. , 
Published: April 2003

AbstractIt has been confirmed by means of electron diffraction that lath‐shaped crystals of polyethylene are {110} reflection twins in which the chain molecules adopt a regularly folded conformation. The orientation and habit of the spiral terraces (or steps) which grow on the {001} faces of these crystals through the agency of screw dislocations is governed by the disposition and hand of the dislocations which, in some cases, can lead to the formation of lath‐shaped, twinned‐crystal terraces as well as “epitaxial {110} reflection twins.” The formation of the latter is taken as evidence that it is lateral accretion on a growing polyethylene crystal step which determines its habit and orientation rather than the epitaxial orientational influence of an underlying crystal terrace.It is shown that twinning forms an essential feature of growth of some of the more complex solution‐grown crystals of polyethylene which possess a radially symmetrical structure, in which the chain molecules are normal to the “radial” direction. In contrast with melt‐grown polyethylene spherulites, however, the b crystallographic axis in such crystals has a preferred tangential orientation. A brief indication is given of the influence of crystallization conditions on the preferred growth direction in the twinned terraces of such radiating crystals.
Copolymers from promoted preformed solid catalysts
Authors: Friedlander H. N. , Smith W. E. , Ross R. J. 
Published: April 2003

AbstractPromoted preformed solids catalyze polymerization of ethylene and propylene and formation of copolymers of ethylene with such olefins as propylene and butene‐1. The structure of the copolymers helps explain how they are formed and their properties. Kinetic studies alone do not distinguish between polymerization mechanisms involving either anionic centers or ion‐radicals. Structural studies of ethylene–propylene copolymers of low propylene content show that they contain isolated propylene units in accord with the ion‐radical theory of polymerization in a chemisorbed layer. Isolated short sidechains, so introduced, reduce density and increase flexibility. They give copolymers with flow properties more like those of linear polyethylenes than those of branched polyethylenes with long sidechains. Furthermore, they interfere with recrystallization and crystal growth; the resulting polymers have better stress‐crack resistance and form clearer films.
Irradiation de l'acrylonitrile à l'etat solide
Authors: Bensasson René , Marx Rose 
Published: April 2003

AbstractNotre étude porte sur l'irradiation par rayons X de l'acryldhitrile solide maintenu sous vide. Entre −100°C et −196°C, l'énergie d'activatioq, de la polymérisation observée est de 0,4 kcal/mole. De part et d'autre de la température de fusion, le rendement de la réaction ´ l'état solid est très supéri eurau renaement de la réaction l'état liquide. Les vitesses initiales de la polymérisation sont proportionnelles au débit de dose. Le rendement de la réaction est d'autant plus grand que la vitesse de cristallisation est lente. Si le monomère est maintenu à l'état solide après arrêt de l'irradiation, la polymérisation se poursuit. Le spectre de resonance paragagnétique électronique obtenu à −196°C après une irradiation à la même température aontient 5 raies. Lorsque la température croit, deux des raies disparaissent progressivement. Nos résultats permettent de conclure que la réaction a lieu à l'état solide et que leg conditions de cristallisation du monomère jouent un rôle important.
Influence of unsaturated groups on crosslinking and inhibition of crystallization in the gamma ray irradiation of linear polyethylenes
Authors: Dole Malcolm , Stolki T. J. , Williams T. F. 
Published: April 2003

AbstractOn irradiation of polyethylene at 142° with Co60 γ‐rays the ability of the linear chains to crystallize from the melt is significantly reduced. This effect is about two and one half times as pronounced in a linear polyethylene with terminal (vinyl) unsaturation as it is in a linear polyethylene with internal (vinylene) unsaturation. The decay, during the irradiation, of initially present vinylene groups apparently leads to endlink rather than to crosslink formation. This fact suggests the conclusion that the vinylene groups initially present in the linear polyethylene must be located near the ends of the polymeric chains. The greater effect of vinyl unsaturation in causing inhibition of crystallization compared with that of vinylene unsaturation is due to the greater decay constant of the vinyl group—about threefold that of the vinylene group.
Degradation and crosslinking of polyisoprene in Hevea Brasiliensis latex during processing and storage
Authors: Sekhar B. C. 
Published: April 2003

AbstractIt has been found that storage hardening in rubber is inhibited by certain amines and reagents for carbonyl compounds. The technological importance and theoretical significance of these observations are discussed. It is postulated that carbonyl groups present in the rubber molecule are responsible for crosslinking on storage of dry rubber, while it is known that peroxidation is responsible for degradative changes and a major part of the crosslinking of rubber in preserved latex.
Arylsulfonic polymers. II. Synthesis and polymerization of fluorosulfonylaryl monomers
Authors: Hart R. , Timmerman D. 
Published: April 2003

AbstractOwing to the stability of the sulfonyl fluoride group and the reactivity of the amino group, aminobenzenesulfonyl fluorides enable the synthesis of a large number of polymers and copolymers bearing sulfonic acid groups. It is indeed possible to react aminobenzenesulfonyl fluorides with acrylic or methacrylic acid chloride or with vinyl isocyanate to obtain substituted acrylamides or vinylureas which can be polymerized or copolymerized with other vinyl monomers. Another method of preparing arylsulfonic polymers with the use of aminobenzenesulfonyl fluorides is the reaction of the latter with polymers containing reactive groups, such as polyacrylic anhydride and copolymers of maleic anhydride. The fluorosulfonyl‐substituted polymers and copolymers can easily be hydrolyzed in slightly alkaline medium.
On the mechanism of emulsion polymerization of styrene. III. Polymerization initiated by oil‐soluble compounds
Authors: Van der Hoff B. M. E. 
Published: April 2003

AbstractThis report is concerned with the kinetics of the emulsion polymerization of styrene initiated by the thermal decomposition of oil‐soluble initiators particularly cumene hydroperoxide (CHP). Only those systems are considered in which the latex particles are so small that two radicals cannot coexit for a significant length of time. Polymerization rate, particle size, and molecular weight of the polymer have been determined at 40, 50, and 70°C. as a function of initiator concentration. At low CHP concentrations the polymerization rate per particle conforms to Smith‐Ewart kinetics, i.e., on the average one polymer radical propagates during half the time in each particle. Therefore it is concluded that, although CHP may decompose into radical pairs, polymer radicals are formed one by one. It is shown that even very low rates of transfer of single radicals from the particles to the aqueous phase, or vice versa, suffice to account for the observed polymerization rates per particle. An alternative mechanism is considered in which CHP decomposes on the surface of the particle, the organic radical enters the particle, and the hydroxyl radical remains in the aqueous phase. The rate of polymerization per particle is observed to decrease with increasing CHP concentration. The fact that the transfer coefficient of this initiator is several orders of magnitude higher than that of cumene sustains the supposition that the polystyryl radical abstracts the periodic hydrogen from the peroxide. The decrease in polymerization‐rate is attributed to the inactivity of the resulting ROO·radical. The Mayo formula for the reciprocal degree of polymerization is reformulated to incorporate this kinetic feature. The dependence of polymerization rate on CHP concentration, derived from the new formula, generally agrees with experimental results. Transfer coefficients of the polystyryl radical to CHP and other organic peroxides are given. From the data it can also be concluded that the decomposition rate of CHP in emulsion polymerization is an order of magnitude larger than in styrene solution.
Grignard reagent‐catalyzed polymerization of methyl methacrylate
Authors: Nishioka Atsuo , Watanabe Haruaki , Abe Ko , Sono Yasunosuke 
Published: April 2003

AbstractThe stereoregular polymerization of methyl methacrylate by Grignard reagents as affected by various alkyl groups, polymerization temperatures, and organic additives has been studied. These three factors were found to be effective in controlling the stereoregularity of PMMA. It has been confirmed that bands sensitive to stereoregularity at 757 and 749 cm.−1 correspond to isotactic and syndiotactic segments, respectively. Isotaxy and syndiotaxy were determined by the infrared method. Proton magnetic resonance spectra were found to be useful in analyzing the stereoregularity of PMMA and in estimating the amounts of stereoregular components in the polymer chains. Three elementary stereoregular units were proposed: isotactic, syndiotactic, and disyndiotactic. The kinetics of the polymerization reactions were studied in the cases of n‐butyl and isobutyl magnesium bromide. The rates of polymerization were found to be proportional to monomer concentration and to the square of the initiator concentration and molecular weight was proportional to monomer concentration and inversely proportional to initiator concentration. The rate of polymerization is maximum at a certain temperature. Branched‐alkyl Grignard reagents were found to produce isotactic polymer. Straight‐chain, alkyl‐type Grignard reagents, with the exceptions of n‐octyl‐ and n‐hexylmagnesium bromide, produce usually stereoblock polymer. Phenylmagnesium bromide (above 0°C.) and cyclohexylmagnesium bromide produce isotactic polymer. Low‐temperature, free‐radical polymerization results in almost wholly syndiotactic polymer. Ordinary free‐radical polymer has a stereoblock strucutre composed of syndiotactic and disynodiotactic units with smaller amounts of isotactic material. The addition of dioxane, pyridine, diphenylamine, or diethylamine promotes polymerization. Use of the latter two amines results in isotactic polymer.