bluuebunny/crossref_metadata_2025 huggingface dataset:
Local regularity of chain substances. I
Authors: Miyake Akira , Chûjô Riichirô
Published: April 2003

The local regularity of chain substances composed of N linked elements, of which each can be in either of two states, the L‐configuration and the H‐configuration, is examined by means of statistical‐mechanical calculations. Introducing a virtual boundary energy at every boundary between the L‐regions, consisting of elements of the L‐configuration only, and H‐regions of H‐configuration elements only, we can deduce any average property of the chain from the logarithmic differentiation of the largest eigen‐value of the transition matrix. The average numbers of L‐ and H‐elements are NL = NB/(B + 1) and NH = N/(B + 1), respectively; that of L‐ or H‐parts is n = NLNH/N, and those of elements per L‐part and per H‐part are 〈l〉 = N/NH and 〈h〉 = N/NL, respectively, where B = exp {J/kT}, k is the Boltzmann constant and T the temperature. We can show the usual combinatory method gives the same results. Application of these relationships to a discussion of the stereospecificity of vinyl polymerization is referred to.
Active centers in the polymerization of ethylene using titanium tetrachloride–alkylaluminum catalysts
Authors: Feldman C. F. , Perry Eli
Published: April 2003

A method was developed to measure the active centers in a titanium tetrachloridealkylaluminum catalyst system for the polymerization of ethylene. The method depends on the assertion that the active carbon atom of the growing chain is relatively basic and will react with alcohol‐O‐t. The tritium becomes incorporated in the polymer. The relationship used is N = AG/a, where N is the corrected active center concentration, A is the radioactivity of the polyethylene in counts/min./g., G is the polymer concentration at the time of sampling and a is the specific activity of the quench methanol‐O‐t in counts/min./mole. The data were corrected for the kH/kT isotope effect of 3.7 which was measured for the alcohol‐O‐t reaction. This isotope effect was unchanged over a wide range of molecular weights and reaction conditions. The basicity of the carbon on the growing polymer chain was proved by quenching the reaction with C14‐labelled alcohol. The resulting polymer was not radioactive. The values of N could be correlated with polymerization rates. Values of the active center concentration and polymer chain lifetime were calculated as a function of molecular weight using fractionated polymer. The centers are very heterogeneous and the lifetimes of polymer chains range from 1 to 30 min. (with an average of 4 min. for the particular conditions used). Calculated values of viscosity‐ (M̄v) and number‐average molecular weights as a function of time of reaction agreed well with the experimental data. Because of the long lifetime of some chains, a steady state in M̄v is not reached, and M̄v increases throughout the course of the reaction. Catalyst efficiency was calculated from a knowledge of N. The efficiency, which can vary from 0.3 to 15% based on the titanium, is a function of how the catalyst components are brought together. The value of N in these systems is about 10−3 to 10−4 moles/liter compared to 10−7 to 10−9 for the concentration of active species in free radical systems. The value of the propagation constant, kp, is comparable in both systems. It is concluded that the very rapid polymerization rate in these heterogeneous systems is due solely to high values of N. These high values of N argue against bimolecular termination of centers. The stability of the centers when refluxed under argon support this idea and cast doubt on chain termination via hydride ion transfer or transfer to solvent. The value for the activation energy of kp is 11.8 over the range of 40 to 68°C. The value of the activation energy for initiation of centers is deduced to be 11.8 kcal./mole, also.
Crystalline acrylic polymers. I. Stereospecific anionic polymerization of methyl methacrylate
Authors: Goode W. E. , Owens F. H. , Fellmann R. P. , Snyder W. H. , Moore J. E.
Published: April 2003

Isotactic (type II)polymers of methyl methacrylate are obtained from anionic polymerizations initiated by organolithium compounds at low temperature ( −70°)in toluene solution. The presence of small amounts of various ethers leads to polymers of reduced isotacticity; the effectiveness of these ethers in disrupting stereospecificity can be related semiquantitatively to their Lewis base strength. Certain Grignard reagents also produce highly isotactic polymer of methyl methacrylate, while others lead to less stereospecific results. The nature of the inorganic component of such initiators appears to determine the steric course of the addition reaction. The formation of a magnesium halide–monomer complex may be involved.
A kinetic mechanism for the heterogeneous stereospecific polymerization of propylene
Authors: Saltman William M.
Published: April 2003

A 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

High 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

The 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

Stress 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

The 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

Large 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

The 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

Polymethyl 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

The 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

On 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

The 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

It 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

Promoted 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

Notre 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

On 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

It 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

Owing 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

This 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

A number of polymethylene sulfide and polymethylene oxide polymers have been synthesized in order to study the influence of sulfur and oxygen atoms on melting temperature and rate of crystallization. Substituting oxygen for sulfur lowers the melting temperature but does not markedly change the rate of crystallization. In the copolymers of structure [(CH2)4S(CH2)mS]x the melting temperature and the rate of crystallization do not depend on the distribution of sulfur in the chain but only upon the carbon/sulfur ratio.