bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the mechanism of the polymerization of ε‐caprolactam. IV. Polymerization in the presence of water and either an amine or a carboxylic acid
Authors: Heikens D. , Hermans P. H. , Van Der Want G. M. 
Published: April 2003

AbstractIn continuation of previous kinetic work on the hydrolytic polymerization of εcaprolactam (CL) (Part I–III) in which evidence was obtained that all the predominant reactions are catalyzed by endgroups, special experiments were undertaken in order to study the specific role played by the NH2 and COOH endgroups. To that end kinetic runs at 221°C. were performed with Cl‐water systems (containing 5–7 mole‐% of water) in which the symmetry of the concentrations of NH2 and COOH groups was disturbed by the addition of about 1 mole‐% of either an amine or a carboxylic acid [hexamethylenediamine (HMD), adipic acid (ADA), and sebacic acid (SBA) were used]. The concentrations of unconverted lactam and of amino and carboxyl groups were determined as previously described; special techniques were worked out for the determination of the small concentrations of unconverted HMD, ADA, and SBA. The main observations are: (1) added HMD disappears much more rapidly from the reaction mixture than added ADA or SBA; (2) the dicarboxylic acids have considerable accelerating effect on the formation of endgroups. Only a general qualitative discussion of these results is given. The principal deductions may be summarized as follows. (a) The initial reaction of the polymerization process, the hydrolysis of CL, is found to be catalyzed by COOH groups. (b) The main contribution to the increase in chain length is furnished by the addition of CL to NH2 endgroups exclusively (aminolysis of the lactam molecule). (c) This addition reaction is catalyzed by COOH groups. (d) Probably, the polycondensation reaction of NH2 and COOH groups is also catalyzed by COOH groups.
Secondary crystallization of polymers
Authors: Rybnikář F. 
Published: April 2003

AbstractThe course of secondary crystallization in several polymers was investigated by the density balance method. At the end of primary crystallization it was possible to notice a stepwise increase of density with time, which cannot be fitted to the Avrami equation. The stepwise increase of density follow a further slow increase in density, which may be characterized by a linear dependence upon the logarithm of time. The onset of the secondary crystallization was in agreement with the value of two half‐times of primary crystallization, i.e., with the end of primary crystallization. It has been shown that the extent of secondary crystallization is related to the perfection of the structure formed in primary crystallization.
Investigation of the protective ultraviolet absorbers in a space environment. I. Rate of evaporation and vapor pressure studies
Authors: Schmitt Richard G. , Hirt Robert C. 
Published: April 2003

AbstractCompounds which are effective in protecting materials from terrestial ultraviolet radiation may, in a high vacuum environment, suffer loss both by evaporation and by photochemical degradation from the shorter wavelength ultraviolet radiation. The rates of evaporation from a free surface in a high vacuum of the commercially available protective ultraviolet absorbers have been measured as a function of temperature. Vapor pressures of the solid absorbers were calculated from the rate of evaporation data. The equilibrium vapor pressures of the liquid absorbers were determined by a direct vapor spectrophotometric method. Absorbers containing more than one hydroxy group were found to be considerably less volatile than the monohydroxy compounds, probably because of intermolecular hydrogen bonding of the former.
The sorption, diffusion, and permeation of organic vapors in polyethylene
Authors: Rogers C. E. , Stannett V. , Szwarc M. 
Published: April 2003

AbstractAn investigation has been made of the sorption, diffusion, and permeation of several organic vapors in polyethylenes of different density over wide ranges of vapor activity and concentration. It was found that the equilibrium sorption isotherms, in terms of the solubility coefficient S, could be represented as exponential functions of the sorbed vapor concentration. The limits and physical significance of the relationship are briefly discussed in terms of the two parameters which characterize the sorption for a given solvent, polymer and temperature. The integral diffusion coefficients were estimated by three independent methods encompassing both the transient and the steady‐state of flow. The diffusion coefficients determined by the different methods generally agreed within experimental error, even though the rate of sorption—desorption indicated that some time‐dependent effects were present. These integral diffusion coefficients were found to be exponential functions of vapor activity. By combining the relation describing the dependence of the diffusion coefficient on vapor activity with the expression for the dependence of the solubility on concentration, it is shown that for an ideal vapor or, at least, low concentrations of sorbed vapor, the combined equation reduces to those equations previously reported in the literature describing the concentration dependence of the integral and differential diffusion constants. The observed trends of the permeability constant with vapor activity and concentration are then related to the activity and concentration dependence of the diffusion and solubility coefficients.
An investigation of lead tetraacetate, N‐bromosuccinimide, p‐toluenesulfonyl azide, benzenediazonium fluoborate, and saccharine–dimethylaniline as chain initiators
Authors: Dannley Ralph L. , Esayian Manuel 
Published: April 2003

AbstractThe thermal decomposition of several common materials in equimolar mixtures of styrene and methyl methacrylate has determined the initiator efficiency of the materials and permitted classification of the mechanisms as ionic or free radical. Both lead tetraacetate and p‐toluenesulfonyl azide are such weak catalysts for homolytic polymerization that careful work is required to differentiate catalyzed and blank runs. The proposed catalyst system, saccharine–dimethylaniline, is also homolytic in nature but is even less efficient (1% conversion in 1 hr. at 60°). Benzenediazonium fluoborate is a good initiator but is carbonium ion in nature. The active species is not proved but may be the phenyl carbonium ion. N‐Bromosuccinimide is an inhibitor not only for the monomer mixture but also for the homopolymerization of styrene. It is a catalyst however for the homopolymerization of methyl methacrylate. Apparently styryl free radicals are efficiently scavenged by N‐bromosuccinimide or its fragments to terminate the radical chain. The principal products are probably the brominated materials.
Thermal degradation of plastics. I. The kinetics of polymer chain degradation
Authors: Friedman Henry L. 
Published: April 2003

AbstractKinetic equations were derived for polymer chain degradation. The usual type of initiation‐depropagation‐termination mechanism was postulated. Chain transfer was ignored. Random and terminal initiation were considered as well as unimolecular, bimolecular, and no‐termination (complete unzipping). It was assumed that a steady state of radicals was achieved, and that monomer product rapidly diffused out of the polymer bulk as soon as it formed. Only average molecular weights were considered. Polymer and radical molecule concentrations were employed in the kinetic equations, while in all the previous work, polymer and radical molecule numbers were used. The same kinetic equations resulted for unimolecular termination and complete unzipping for both treatments, but for bimolecular termination, the results were different. Where the use of number units predicted that the rate of loss of polymer weight should be half‐order in polymer weight, concentration units gave a first‐order relationship. The equations that were derived in this work were found to be similar to those that were previously derived in treatments where number units were employed together with the assumption of exponential molecular weight distribution. A comparison of the various treatments showed that the similarities were not necessarily due to the use of the distribution assumption, but may have been a consequence of the forms of the basic kinetic equations that were utilized in the earlier work.
Dielectric properties of polypeptide solutions. V. Molecular association of the α‐helix in solution
Authors: Wada Akiyoshi 
Published: April 2003

AbstractA device to study the molecular association of the α‐helix from the two sets of information in the dielectric dispersion curve; that is, specific polarization P2° and critical frequency v0, is proposed. The P2° is plotted against log v0 for each solution of associated helix. Comparing these plots with that of the perfect helix, the process of association is considered. The model in which side‐by‐side random orientation and head‐to‐tail types are superposed is suggested as the most probable association of the PBLG α‐helix in the dioxane—dimethylformamide mixed solvent.
Evaluation of surface treatment of glass fiber in fabric‐reinforced plastics
Authors: Ito Katsuhiko 
Published: April 2003

AbstractThe use of electron diffraction and adhesive strength tests as a method of direct evaluation of the effects of surface treatment of glass fiber on mechanical properties of fabric‐reinforced plastics is proposed. Glass plates, similar in quality to the glass fiber used in fabric‐reinforced plastics and surface‐treated with Volan and silane finishing compounds, are used as test specimens in these tests in order to eliminate complicated factors due to glass cloth reinforcement. The results obtained from tests of adhesive strength of lap joints are closely correlated with the improvement of mechanical properties fabric‐reinforced plastics by surface treatments of glass fiber; however, the molecular orientation of surface‐finishing compounds on glass plates, as determined from the electron diffraction pattern, has no such close relationship. In 18‐8 stainless steel plate surface‐treated by the procedures (chosen as the test specimen for comparing the effect of surface treatments on other materials) no such improvement due to surface treatment was noted.
Triethylaluminum—titanium tetrachloride catalysts for preparation of crystalline polystyrene
Authors: Kern R. J. , Hurst H. G. , Richard W. R. 
Published: April 2003

AbstractThe reaction between Et3Al and TiCl4 is discussed, with emphasis on the effect of temperature, concentration, stoichiometry, and order of component addition on the ability of products to catalyze the isotactic polymerization of styrene. A well‐defined peak in relative catalyst activity becomes apparent when the interaction of these variables is followed by measuring the average oxidation state of titanium. Experimentally, the polymerization is first‐order with respect to styrene and titanium, although efficiency of Ti use is small. The mode of polymerization is characterized by a lower activation energy for active site generation and a higher activation energy for termination than is typical of free‐radical polymerization. A convenient procedure for laboratory preparation of isotactic polystyrene employing the Et3Al/TiCl4 catalyst is given.
The flow of gases through high polymer films in equilibrium with sorbed vapors
Authors: Pilar Frank L. 
Published: April 2003

AbstractA new apparatus is described for the measurement of the permeability constants of polymer—vapor film systems to atmospheric gases. The permeability constants of regenerated cellulose to oxygen, nitrogen, and carbon dioxide were found to increase rapidly and nonlinearly with increasing relative humidity. The permeability constants of polyethylene to oxygen and nitrogen were found to increase in a like manner with increasing relative pressures of n‐hexane and carbon tetrachloride. In the case of the polyethylene—organic vapor and gas systems the activation energy for the permeation process appears to be independent of sorbed vapor concentration. Furthermore, it was found that the permeability constants of the polymer—vapor films increased linearly with sorbed vapor concentration. A theory based on an analogy with electrical conductivity is proposed to explain the form of this relationship. The theory appears to give good quantitative agreement for the polyethylene—hexane—oxygen system, but further experimental data are needed to establish the generality of the theory.
A new method for measuring the degree of crosslinking in elastomers
Authors: Cluff E. F. , Gladding E. K. , Pariser R. 
Published: April 2003

AbstractA rapid method for determining the degree of crosslinking in elastomers is described which involves measuring equilibrium compression modulus at very small deformations on solvent‐swollen samples. The elastomer used was a polyether urethane vulcanized by an accelerated sulfur recipe. The degree of crosslinking as measured by the compression method agreed with that measured by the extension method within 1–3%. Both methods agreed reasonably well with the theoretical values calculated from the sulfur level, polymer molecular weight, and crosslink structure.
Equilibrium polymerization of α‐methylstyrene. Part I. Initiation by means of sodium naphthalene and sodium diphenylacetylene at 0°C.
Authors: Tobolsky A. V. , Rembaum A. , Eisenberg A. 
Published: April 2003

AbstractThe equilibrium polymerization of α‐methylstyrene at 0°C. has been investigated, sodium naphthalene and sodium diphenylacetylene being used as initiators. With both initiators, the extrapolated equilibrium monomer concentration has been found to be equal to 0.89 mole/kg. This value remained unchanged when the sodium counterion accompanying the initiator was replaced by cesium. When sodium naphthalene is used for the polymerization, the initiator step consists of an equilibrium electron transfer reaction, where the equilibrium constant has a high value. In the sodium diphenylacetylene system, the initiation consists of an equilibrium step involving bond formation between the monomer and initiator, and the equilibrium constant has a sufficiently low value to be determined practically. Spectroscopic evidence for the presence of an initiator fragment in the polymer chain has been presented. The general equilibrium theory of polymerization has been applied to the present system and equations have been derived correlating degree of polymerization with the initial monomer and initiator concentration as well as with the equilibrium constants. Good agreement has been obtained between the theoretical calculations and experimental results.
Polymerization of allyl acetate
Authors: Litt Morton , Eirich F. R. 
Published: April 2003

AbstractThe kinetics of polymerization of allyl acetate with benzoyl peroxide at 65, 80, and 90°C. has been investigated, and was found to parallel normal vinyl kinetics. The reaction which alters the normal picture is the early production, by chain transfer, of a stable allylic radical which generally terminates rather than initiates new chains (degradative chain transfer). A kinetic scheme has been developed including: (1) normal initiation, (2) normal propagation, (3) allylic chain transfer, (4) induced decomposition of the peroxide by allylic and growing radicals, (5) initiation of new chains by the allyl radical, and (6) homo‐ and cross‐termination of the allylic and growing radicals. The equations developed were shown to fit the data quite well at all temperatures.
γ‐Radiation‐induced homopolymerization of diethyl fumarate
Authors: Wiley Richard H. , Parish D. J. 
Published: April 2003

AbstractHomopolymerization of diethyl fumarate at 1.57 × 105−3.75 × 105 rep/hr. from a 1000‐c. cobalt‐60 source at temperatures from −56 to 22°C. has given brittle, solid polymers which are soluble in most organic solvents but insoluble in petroleum ether. These polymers have intrinsic viscosities of 0.123–0.178 in benzene and ebullioscopic molecular weights in toluene of 7500–9300. The viscosity constant K is 2.97 × 10−4−3.21 × 10−4 for an assumed value of a equals; 0.7. Inhibition by diphenylamine and decreased rate of reaction at low temperature indicate a radical initiation process.
The study of the polydispersity of polymers by viscometry
Authors: Lundberg J. L. , Hellman M. Y. , Frisch H. L. 
Published: April 2003

AbstractA viscometric polydispersity index may be calculated by forming the ratio of the viscosity‐average molecular weights of a polymer in a relatively good solvent and in a relatively poor solvent and subtracting 1. This index has been examined by measuring dilute solution viscosities of a polydisperse polystyrene and a polydisperse methyl methacrylate in a variety of solvents, calculating viscosity‐average molecular weights using Mark‐Staudinger‐Houwink equations, and forming the viscometric polydispersity indices. These are compared to Schulz parameters, weight‐average–number‐average molecular weight ratios minus 1, determined from osmotic pressure and light scattering. Viscometric polydispersity indices are more sensitive to polydispersities than expected when compared to Schulz parameters if account is taken of the differences in the powers of molecular weight in the various molecular weight sums. Viscometric polydispersity indices are examined for other polymers, including an almost monodisperse polystyrene. From these measurements it is concluded that the viscometric polydispersity index is valuable for characterizing the polydispersity of polydisperse linear polymers and rough fractions. The weight‐average–viscosity‐average polydispersity index is more sensitive than the viscometric polydispersity index and may be used to characterize relatively monodisperse linear polymers.
Equilibrium polymerization of selenium
Authors: Eisenberg Adi , Tobolsky Arthur V. 
Published: April 2003

AbstractA theory of the ring‐chain equilibrium in liquid selenium is presented which is mathe‐matically identical to our theory for polymer equilibrium in liquid sulfur. The numerical treatment is based on: (a) the entropy and enthalpy of the propagation reaction (Sen* + Se8 ⇌ Sen+8*, the asterisk denoting a diradical) which were calculated from values of the Se8 concentrations in the liquid as given in the literature, and (b) the entropy and enthalpy of the initiation reaction (Se8 ⇌ Se8*) which were estimated by comparison to the sulfur values. The “transition” temperature for the appearance of polymer in the liquid state is calculated as 83°C. (134° below the melting point of selenium), and the chain length at the melting point is estimated as ca. 1300 Se8 units.
Local regularity of chain substances. II
Authors: Miyake Akira 
Published: April 2003

AbstractThe eigenvalue method of introducing a virtual boundary energy, examined in the previous article, is extended to take account of next nearest neighbor interactions. To discuss the stereospecific polymerization of the vinyl polymer, an energy −K is assumed for every two consecutive L‐configurations, besides the energy difference J between the H‐ and L‐configurations. To discuss the helix–random coil transformation in synthetic polypeptide chains, a hydrogen‐bonding energy −K is assumed between the first and the fourth monomers to every three successive L‐configurations, and three or more than three successive L‐configurations are regarded as making a helix part, a random coil region being formed otherwise. We can see that the more the value of J/K, the more rapid is the transformation.
A contribution to the study of random degradation of chain polymers
Authors: Mejzler D. , Schmorak J. , Lewis M. 
Published: April 2003

AbstractA uniform rigorous mathematical treatment is presented for the random degradation of chain polymers, including the three fundamental initial states, viz., (a)a finite single chain (b)a number of chains of equal length, and (c)a number of chains of varying lengths. Limiting expressions are derived for the number fraction and weight fraction of chains of a given degree of polymerization, theoretically obtainable for a given degree of degradation in all three cases. The stochastic approach is employed for the derivation of the mathematical expression for the degree of degradation as function of time. It is assumed in the derivation that the probability P that a given bond still unbroken at the time t will break in the time interval between t and t + Δt is of the form P = φ(t)Δt, where φ(t)is not necessarily a constant. Instead of the well known formula α(t)= 1 − exp { − kt} an empirical formula α(t)= 1 − exp { − ktm} is proposed; this formula includes the former as' a special case (when φ(t)= const.), and is shown to better fit the experimental results obtained in studies on the degradation of cellulose and of polystyrene solutions.
On the characterization of stereoregular polymers. I. Theory
Authors: Miller Robert L. , Nielsen Lawrence E. 
Published: April 2003

AbstractThrough an extension of a generalized copolymer theory, a mathematical description of the chain structure of homopolymers (whether stereospecific or not)has been obtained, relating distributions of sequences, sequence lengths, and bonds formed to the kinetics of the propagation step in the polymerization reaction. Existence of stereoblock structures is accounted for by the model and chain structural details sensitive to directing influences (such as the so‐called “penultimate” monomer effect or the catalyst surface)are predicted. It has been shown that in the general case, knowledge of at least two independent parameters is required to characterize the chain structure. The tacticity definitions currently used have been shown to have simple mathematical expressions and to be equivalent and interchangeable.
A theory of the thermodynamic behavior of nonelectrolyte solutions. IV. Application to low molecular weight systems
Authors: Maron Samuel H. , Wang Mei‐Mei , Nakajima Nobuyuki 
Published: April 2003

AbstractA study has been made to show that Maron's theory of the thermodynamic behavior of nonelectrolyte solutions is applicable to systems with low molecular weight solutes as well as polymers. In this connection were investigated three systems of varying degrees of complexity, namely: (1)carbon tetrachloride–cyclohexane, (2)acetone–chloroform, and (3)water–ethyl alcohol. The first of these systems yields a small positive interaction parameter μ which is essentially independent of volume fraction v2 but which decreases with temperature T. On the other hand, the system acetone–chloroform gives μ's which are large, negative, and strongly dependent on both T and v2. Similarly the system water–ethyl alcohol yields μ's which vary with both v2 and T, but in this case they are large and positive. The relations deduced for the μ's as a function of T and v2 reproduce very satisfactorily the available thermodynamic data for these systems. A discussion is also given of the significance of the observed interaction parameters.
Thermoelasticity of open systems
Authors: Oplatka A. , Michaeli I. , Katchalsky A. 
Published: April 2003

AbstractThe thermoelastic properties of contractile open systems, in equilibrium with an external bath containing permeating components, are related to those of the corresponding closed systems, in terms of two isothermal parameters, the change of the degree of swelling with elongation and the isometric enthalpy of dilution of the swollen contractile phase. The thermodynamic analysis is applied to evaluate the thermoelastic properties of the Flory‐Rehner model for swollen rubber, and experimental results from the literature are discussed.