bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymer/solvent interactions in dilute solution
Authors: Rosen Bernard 
Published: April 2003

AbstractApparent specific volumes of two, previously well‐characterized, polystyrene fractions were determined at 25° in solvents offering an interesting display of polymer/solvent interactions. Adaptations of differential pycnometry techniques permitted a sensitive detection of the small density differences between solvents and solutions, allowing four significant figures in the apparent specific volumes at concentrations as low as 0.20%. The measurements unambiguously confirm the solvent and concentration dependencies. The solvent dependency at high dilutions also confirms the anomaly that the extremes in polymer/solvent interactions causing very good and very poor polymer solubility yield higher values for the partial specific volumes of polystyrene than obtained for the intermediate range of interactions. The concentration dependency permits indirect approximations of the functions, ΔH̄1 and ΔH̄2 vs. poIymer concentration. The deviations from athermal mixing are greater and more irregular than anticipated, and are shown frequently to complicate both experimental and theoretical studies of the properties of dilute solutions. The thermodynamic behavior of dilute solutions of polystyrene in butanone appears to be particularly complex.
Streaming birefringence behavior of dextrans produced by leuconostoc mesenteroides
Authors: Yang Jen Tsi , Foster Joseph F. 
Published: April 2003

AbstractThe results of a large number of streaming birefringence studies on dextran fractions, both native and degraded, produced by Leuconostoc mesenteroides are reported. The following solvents have been examined, all in admixture with varying proportions of glycerol (to enhance the solvent viscosity): water (with and without prior autoclaving), aqueous sodium hydroxide, formamide, and ethylenediamine. The results are surprisingly independent of the solvent used. Ethylenediamine–glycerol (equal parts by weight) was adopted for further investigation because of the high solvent viscosity. This solvent was found to yield a small birefringence with extinction angle near zero degrees, which, however, contributed no appreciable error except at polymer concentrations below 0.3%. Results were found to be substantially independent of polymer concentration and of temperature. Characteristically, the dependence of extinction angle on gradient was found to be much less than is to be expected for solutions of homogeneous, rigid molecules. It is concluded that this cannot be due to heterogeneity, at least in the case of certain well‐fractionated preparation, and must be attributed to flexibility of the polymer molecule. It is shown that extrapolation of the apparent rotary diffusion constants to zero gradient can be carried out in most cases with some confidence. The resulting values, which should characterize the rotary diffusion properties of the undistorted polymers, are shown to be quite reasonable in terms of the known intrinsic viscosity and molecular weight of the fractions. The reduced birefringence of the various fractions is shown to be rather rigorously proportional to their intrinsic viscosity. Further, the extinction angles are found to approach a lower limit, at high gradient, which is related also to the intrinsic viscosity through the empirical equation Xlim = 24/[η]1/4.
Ultrasonic studies of high polymers
Authors: Maeda Y. 
Published: April 2003

AbstractThe variations of elastic modulus and mechanical tan δ with temperature and frequency have been studied for polyvinyl chloride, natural rubber, Hycar OR‐15, GR‐S 65, and GR‐I using pulsed ultrasonic waves of 2.67 and 8.01 Mc. Tricresyl phosphate and dioctyl phthalate were used as plasticiziers for polyvinyl chloride. PVC‐plasticizer system, when the amount of plasticizer is large, shows the steep decrease in effective modulus and the peak of the value of tan δ within the range of measuring temperature from 10 to 90°C. The peak of tan δ shifts to lower temperature with an increase of the amount of plasticizer, and its value becomes smaller. Heat and enttropy of activation derived from the difference between the temperatures of peaks in two frequencies decrease with the amount of plasticizer. Within the range of measuring temperature from −60 to + 80°C., all rubbers used in this measurement show a sudden decrease of the modulus of elasticity and the peak of tan δ. The peaks become higher in the order of GR‐S, Hycar OR, natural rubber, and GR‐I, and heat and entropy of activation become smaller in this order. As a mechanism of viscoelasticity to explain the results of this measurement, we think of the break and remake of secondary bonds by thermal motion of segments and assume that shear modulus is proportional to the number of segments per cc. The changing of modulus of elasticity with temperature, the effect of plasticizer, and the relation between tan δ and heat, and entropy of activation can be understood on this assumption. The dielectric constants of the samples of PVC‐plasticizer systems used in this experiment are measured at the same frequency. As a result of comparison with those dielectric constants, it can be said that electrical tan δ shows the peak at 40–50°C. higher temperature than mechanical tan δ, and that heat and entropy of activation show considerable differences.
Effect of substituents upon melting points of linear polyesters
Authors: Doak Kenneth W. , Campbell Herbert N. 
Published: April 2003

AbstractMelting points were determined for several series of linear polyesters containing substituents either in the acid or glycol unit. The number of substituents was progressively increased by preparing copolyesters containing both unsubstituted and substituted glycol or acid units. The following systems were studied: (1) Those with trimethylene and 2‐methyltrimethylene glycols show decreasing melting points as the number of methyl groups is increased, because they introduce tetrahedral asymmetry. If the structrual unit is relatively short, crystallinity is completely destroyed. (2) Those with trimethylene and 2,2‐dimethyltrimethylene glycols show eutectic type melting point curves, since the substituent groups do not introduce asymmetry. The completely substituted polyesters have new crystal structures which give sharp X‐ray patterns. Those from short acids (C2–4) have higher melting points than the unsubstituted polyesters, while the others have lower melting points. The polyesters with an odd number of chain atoms in the unit have higher melting points than the even ones. The ability to pack closely into the crystal lattice appears to be important, a view supported by melting points of certain polyesters of β,β‐dimethylgultaric acid. (3) Those with trimethylene and 2‐methylenetrimethylene glycols and sebacic acid give a eutectic type curve, because of the appearance of a new crystal structure. (4) Those with succinic and α‐methylsuccinic acids and decamethylene glycol give progressively decreased melting points, decreased breaks in heating curves, and an increasingly distorted lattice as the number of methyl groups is increased, because random “head‐to‐head” and “head‐to‐tail” polymerization makes the completely substituted polyester irregular. (5) The polyester of d‐α,β‐dimethoxysuccinic acid and tetramethylene glycol is highly crystalline because the substituent groups are oriented in a regular manner. The meso‐polyester did not crystallize because of more random orientation of substituents. Decamethylene d‐tartrate similarly melts higher than the meso‐tartrate.
A comparison of the dynamic properties of natural rubber and GR‐S
Authors: Zapas L. J. , Shufler S. L. , DeWitt T. W. 
Published: April 2003

AbstractThe dynamic moduli and loss factors have been determined for high molecular samples of GR‐S and natural rubber. Comparison of the two sets of data shows that the general characteristics of the two materials are quite similar. The main differences are that GR‐S shows a higher temperature for the apparent second order transition, and also a higher value for the modulus in the relatively level portion of the highly elastic region. The usual superposition procedures are used for correlating the data. Several indications that the equivalence of frequency and temperature may not be of universal applicability are noted. It is suggested that the higher elastic plateau modulus of GR‐S my, in conjunction with usual levels of vulcanization, lead to a modulus dispersiion with its attendant loss and thus be a contributing factor to the lower resilience and higher heat development characteristic of GR‐S.
Effects of salts on the viscosity of polyelectrolyte solutions
Authors: Conway B. E. 
Published: April 2003

AbstractThe viscosities of preparations of sodium polymethacrylate and polyvinyl‐n‐butylpyridinium bromide have been measured in water and salt solutions in the Couette viscometer down to very low concentrations and rates of shear. The dependence of reduced specific viscosity upon polymer concentration has been compared with that for DNA in water and salt solutions. It is concluded that there is a finite effect of salts upon the intrinsic viscosity of the synthetic polyelectrolytes in contrast to the result found with DNA. The viscosity behavior of solutions of intermediate concentration is very similar to the of DNA solutions. The shape of the reduced viscosity–concentration plots has been interpreted as arising from the combined effect of interaction and contraction of the molecules with increasing concentration.
Association effects in polymer solutions
Authors: Frisch H. L. 
Published: April 2003

AbstractThe equilibrium theory of polymer solutions capable of association into complexes is presented. The principal thermodynamic functions of such a solution are given; in particular the average molecular weight of such a solution determined by extrapolation of the reduced osmotic pressure is that of the unassociated polymer. It appears unlikely that data on the temperature variation of the second osmotic virial coefficient can give reliable estimates of the degree of association.
Polymer to metal adhesion. The system polyvinyl acetate–steel
Authors: Lasoski S. W. , Kraus Gerard 
Published: April 2003

AbstractIn the limit of small film thickness the effective tensile adhesion of polyvinyl acetate to steel is of the order of the tensile strength of the polymer. Furthermore, the dependence of the limiting tensile adhesion on temperature, rate of loading, molecular weight, molecular weight distribution, and plasticizer content is the same as that of the cohesional tensile strength suggesting that in thin adhesive films the mechanism of failure is in cohesion. At greater thicknesses, shear components derived from strains in the adhesive film initiate failure at progressively lower tensile loads, causing the effective tensile adhesion to be lowered. The above results are realized with clean, though at least partially oxidized metal surfaces and carefully purified polymer. Even minute traces of fatty acids as surface impurities are capable of reducing the adhesion to less than one‐half of the original value. In a particular example, 0.05 of a calculated monolayer of decanoic acid reduced the limiting effective tensile adhesion from 7000 to 3900 p.s.i. Inasmuch as the adsorbed impurity is soluble in the polymer, it can be desorbed on prolonged heating, and, provided the polymer film is thick enough, the original adhesive strength can be restored. In extremely thin films, some permanent loss in adhesion will result from the establishment of an adsorption equilibrium in which appreciable amounts of fatty acid are left on the surface. The effect of perfluorodecanoic acid on the adhesion of polyvinyl acetate to steel is almost exactly the same as that of decanoic acid. The adhesion of polyethylene to steel is likewise critically dependent on surface purity. The results of this research point to the need for extreme cleanliness in studies of adhesion, a fact which, though seemingly obvious, has all too often been overlooked in past investigations.
Styrene popcorn polymers
Authors: Miller Glenn H. , Perizzolo Arl F. 
Published: April 2003

AbstractA study of the growth of butadiene popcorn polymer seeds in the presence of styrene monomer vapor at 60° has shown the growth to be logarithmic with time. The growth appears to be independent of the peroxide content of the seeds and can be retarded by the presence of various sulfur containing compound. Oxidation of the butadiene seeds grown in styrene by air exposure destroys their activity for continued growth.
The nature of tensile rupture
Authors: Gruntfest I. J. 
Published: April 2003

AbstractThe problem of tensile failure is discussed in terms of the conditions for mechanical stability. Data are not available for detailed examination of the usefulness of this approach. However, some measurements on plasticized polyvinyl chloride, cellulose acetate, and polymethyl methacrylate suggest that the arguments may have some validity. The toughness and brittleness of materials are also considered briefly in the same terms. Attention is called to the complications that may arises from the adiabatic character of the failure process.
Rates of termination in polymerizations initiated by benzoyl peroxide and by ammonium persulfate
Authors: Jarkovsky I. , Stannett V. , Szwarc M. 
Published: April 2003

AbstractPolymerizations of styrene have been carried out in solution using as initiators benzoyl peroxide or ammonium persulfate. It has been shown that the ammonium persulfate initiated polymerizations proceed at a faster rate and produce polymers of higher molecular weight than those initiated by benzoyl peroxide, although all the conditions for polymerization remained identical in both cases. This behavior is explained in terms of a reduced rate of termination. It is suggested tentatively that the reduction in the rate of termination may be due to the mutual electrostatic repulsion of the chains caused by the presence of electrically charged end groups arising from initiation by the sulfate ion radical. Calculations are presented showing the essential conditions that have to be fulfilled to make the explanation tenable.
Vulcanization studies
Authors: Barton Bernard C. 
Published: April 2003

AbstractUse has been made of the statistical theory of elasticity to calculate the number of crosslinks in vulcanizates that have been formulated and vulcanized in such a manner as to have the greatest number of crosslinks for the amount of sulfur present. These calculations suggest that the formation of up to 80% of the crosslinks are accompanied by the formation of a molecule of sulfide sulfur and that the crosslinks are largely, if not entirely, of the monosulfide type.
Mastication. Part III. Chemical verification of the mechanical degradation mechanism of cold mastication
Authors: Ayrey G. , Moore C. G. , Watson W. F. 
Published: April 2003

AbstractThe mechanism of cold mastication of natural and synthetic rubbers, as proposed by Kauzmann and Eyring, and by Pike and Watson, in volves the mechanical rupture of the polymer chain yielding polymer radicals which are stabilized by interaction with radical‐acceptor molecules to give the degraded polymer. This mechanism has been verified by a spectroscopic study of the cold mastication of natural rubber with 1,1‐diphenyl1‐2‐picryl hydrazyl and a radioisotopic tracer study of the cold mastication of GR‐S using [S35]‐labeled 1,1′‐dinaphthyl disulfide as the radical‐acceptor molecule. Correlation of the decrease in molecular weight of the polymer and the amount of radical acceptor in corporated during the cold mastication process agrees with prediction according to the mechanical degradation mechanism.
Ladder structures for representation of viscoelastic systems
Authors: Gross Bernhard , Fuoss Raymond M. 
Published: April 2003

AbstractThe theory of a finite continuous system representing the limiting case of a springdashpot ladder network is developed. The partial differential equation which describes this system has the form of the diffusion equation. A complete mathematical treatment is given. The result is shown to be practically identical with that of Rouse's theory. Formally it represents an extension of Blizard's treatment.
Inhibition of polymerization. II. Methyl acrylate
Authors: Kice John L. 
Published: April 2003

AbstractThe effect of nine inhibitors on the 2,2′‐azobisisobutyronitrile initiated polymerization of methyl acrylate in methyl propionate solution has been studied kinetically by a dilatometric method. The rate constants obtained are compared with those found for these same compounds in methyl methacrylate polymerization. The ratio of the reactivity of an inhibitor toward methyl acrylate and methyl methacrylate radicals is found to vary considerably from inhibitor to inhibitor; these variations in behavior seem readily interpretable in terms of polar and steric effects. Specifically, it is found that the three quinones—benzoquinone, 2,6‐dichloroquinone, and 2,5‐dichloroquinone—show a smaller increase in reactivity on going from methacrylate to acrylate than any of the other compounds studied. This is consistent with the presumably strongly “electron‐accepting” nature of the quinone ring. On the other hand, the tetrachloroquinone, chloranil, shows a much larger increase in reactivity on going from methacrylate to acrylate. Models indicate that this different behavior is due to the existence of considerable steric hindrance in the reaction of the bulky methacrylate radical with chloranil and not to any difference among these quinones as regards their mechanisms of reaction with methacrylate and acrylate radicals. With the other compounds which showed inhibitory activity—trinitrotoluene, furfurylidene malononitrile, dinitrobenzene, and sulfur—the relative magnitude of the increase in reactivity varies in a manner consistent with the differing polarities of these four compounds.
Improvement of bonding properties of polyethylene
Authors: Rossmann Kurt 
Published: April 2003

AbstractIf the surface of a polyethylene film is subjected to certain treatments, printing on the surface becomes possible, or, in other words, the bonding properties of the polyethylene film are improved. Two forms of treatment, involving the use of a Tesla coil discharge at atmospheric pressure and of a glow discharge at reduced pressure, have been developed. Through the use of a Beckman IR‐3 spectrophotometer, it has been found that the treatments cause formation of unsaturated (CC) bonds and carbonyl (CO) groups in the polyethylene molecule. The improved bonding properties may be due to oxidation of the plastic surface.
Ozone attack on rubber vulcanizates
Authors: Buckley D. J. , Robison S. B. 
Published: April 2003

AbstractCracking on the surface of vulcanizates exposed to ozone under strain has been studied quantitatively. Butyl rubber vulcanizates were used to allow ready variation of polymer unsaturation. A relaxed sample under tension when exposed to ozone undergoes a work change manifested by increased length and decreased stress as cracking occurs. The change in work is considered related to generation of new surface in the form of cracks. Cracking is found to be primarily a surface phenomenon and in this wise permeation of the ozone into the sample assumes an important role in this phenomenon since it defines the “depth of the surface.” Polymer structure as it affects permeation appears as important as chemical inertness in controlling ozone cracking. The amount of cracking judged by change of work measured in these experiments is related linearly to the time squared. The rate of cracking is related linearly to ozone concentration squared over the range 0.03–0.20 volume per cent in air. The rate and type of cracking is dependent on extension. The analysis of this relation is complicated by relaxation effects. The state of relaxation of a sample under tension has a profound effect on the rate of ozone cracking. This effect is discussed in terms of distribution of strain of the network chains. Although cracking requires a stored energy to produce new surface, the chemical action of ozone proceeds in the absence of strain. Whether the effects of polymer degradation under conditions of zero strain become large enough to be measurable depends on the rate of permeation of ozonized air into the specimen.Vulcanization has an important bearing on ozone cracking in Butyl rubber. This is probably due to a significant decreases in the percentage of unreacted double bonds and also to a local densification of the network in the region of the double bond involved in a crosslink. Cracking is particularly sensitive to the onset of reversion. This sensitivity may arise because state of reversion may be a gradient, greatest on the surface and least at the center of the sample.
Determination of degree of crosslinking in natural rubber vulcanizates. Part II
Authors: Moore C. G. , Watson W. F. 
Published: April 2003

AbstractNatural rubber vulcanizates have been prepared by a method permitting determinations by chemical analysis of the number of crosslinking introduced. The crosslinking agent was di‐tert‐butyl peroxide, and the peroxide and its decomposition products–tert‐butanol, acetone, methane, and ethane—were determined by infrared spectroscopic and manometric methods. tert‐Butanol and methane result from the abstraction of α‐methylenic hydrogen atoms from the rubber hydrocarbon by means of tert‐butoxy and methyl radicals, respectively. On the assumption that the resultant rubber hydrocarbon radicals undergo exclusive mutual combination a chemical evaluation of degree of crosslinking, 1/2 Mc, is given by ½(moles of tert‐butanol + moles of methane), where Mc is the average molecular weight between crosslinks. Physical values of 1/2 Mc for rubber of infinite initial molecular weight have been obtained by determining the volume fraction of swollen rubber, vr‐, in n‐decane, and by using the method described in Part I for correcting for the finite initial molecular weight of the rubber. A comparison of the physical and chemical values of 1/2 Mc indicates that the former is greater than the latter for all degrees of crosslinking, the major divergence being accounted for by an additive term which is pictorially visualized as due to entanglements.