bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical thermodynamics of swollen polymer networks
Authors: Hermans J. J. 
Published: April 2003

AbstractTo obtain an expression for the entropy S of a polymer network at volume V, the assumption is made that a volume V0 can be defined a which the distribution of end‐to‐end distances is the same as in a solution of freely dispersed chains and is Gaussian, and that the distribution of end‐to‐end distances at the volume V is likewise Gaussian. Although these assumptions are the same as those made by Flory, the formula obtained differs from Flory's. The results is

where n is the number of solvent molecules, ϕ the volume fraction of polymer, G the number of chains (i. e., chain portions between crosslinks), and Ω the factor by which the structural pattern of the network reduces the number of accessible configurations. The customary assumption is made that Ω is volume independent. The consequences of the result obtained for S are discussed. Flory's method was to calculated the “entropy of crosslinking” by considering the probability that in a polymer solution certain segments are found in each other's vicinity. The error in the calculation lies in the assumption that the probability for two arbitrary segments to be in each other's vicinity is independent of whether other pairs of segments are or not. If this error is avoided, Flory's result becomes identical with the one derived in the present article. Arguments are given to show that the distribution of end‐to‐end distances assumed by Guth and James is erroneous. A consideration of the equilibrium between the network and a polymer solution proves that their formula must be rejected also on experimental grounds.
The chemistry of xylylenes. XIII. The problem of crystallinity and crosslinking in poly(p‐xylylene)
Authors: Errede L. A. , Gregorian R. S. 
Published: April 2003

AbstractThe problem of crystallinity and crosslinking in poly(p‐xylylene) was re‐investigated with the use of polymer that was prepared by polymerization of p‐xylylene in solution. It was found that amorphous polymer is converted irreversibly to α‐crystalline polymer at 50–140°C. The α‐form in turn is converted irreversibly to the β‐form at 220–260°C. The rate of change and the ultimate proportion of change is dependent upon the temperature. The polymer appears to soften and reharden at 220–250°C. and subsequently to melt at 410–420°C. This is followed by rapid thermal degradation. It was shown that the properties associated with a three‐dimensional network are imparted to poly(p‐xylylene) by reactions that occur when the mixture of insoluble polymer and residual monomer (<0.01M) is warmed from −78°C. to room temperature. This result appears to be independent of reactions that commonly afford covalent crosslinks. On the other hand, there is a close correlation with the experimental conditions that afford low molecular weight cyclic poly(p‐xylylene). It is spectulated that some cycllization might occur in such a way that two or more chains of poly(p‐xylylene) from an interlaced structure which might be responsible for the properties of poly(p‐xylyene) heretofore attributed to covalent crosslinks.
Elasticity of crosslinked amorphous polymers in swelling equilibrium with diluents
Authors: Hoeve C. A. J. , Flory P. J. 
Published: April 2003

AbstractThermoelastic measurements conducted at constant pressure on systems of fixed composition must be corrected to constant volume in order to achieve the desired resolution of the stress into its energy and entropy components. In the case of simple elongation deduction of the energy component f9 =(∂E/∂L)T,V = [∂(f/T)/∂(1/T)]L,Vof the tension f from measurements at constant pressure requires the equation of state p(T, V, L), or equivalent information. If the system is a polymer network swollen with a diluent or a diluent mixture, and equilibrium is maintained with a surrounding diluent phase, additional complications may arise from changes in composition with deformation and/or temperature. If, however, the diluent mixture is so chosen as to render the equilibrium volume of swelling independent of temperature, then, as we have pointed out previously, fe may be equated to the coefficient = [∂(f/T)/∂(1/T)]L,p,eq, which may be determined directly from measurements on the system maintained in equilibrium with excess diluent. The basis for this simplification is set forth in detail. The conversion of measurements conducted at constant pressure to constant volume is obviated by this procedure, and a simple means is provided for evaluating the internal energy changes accompanying distortion of a polymer network and the concurrent orientation of the chains of which it is composed. Allegations that the indicated procedure is invalidated by disregard of changes of composition of the network phase with temperature and deformation are unfounded. Inconsistencies in recent publications on the analysis of thermoelastic data for networks in swelling equilibrium are pointed out.
Kinetics of anionic copolymerization of monomers of similar polarities
Authors: O'Driscoll K. F. , Kuntz Irving 
Published: April 2003

AbstractThe reasons underlying the experimental fact that r1r2 = 1 for some ionic copolymerizations are reexamined. It is shown that it is not necessary to consider all propagating ions of equal reactivity in order to explain this fact. It is then shown that anomalous results from anionic copolymerizations may be readily interpreted in terms of classical copolymerization kinetics.
Polymerization of vinyl acetate in aqueous media. Part I. The kinetic behavior in the absence of added stabilizing agents
Authors: Napper D. H. , Parts A. G. 
Published: April 2003

AbstractVinyl acetate has been polymerized in buffered aqueous solution at 40°C., with potassium peroxydisulfate as initiator, a dilatometric method being used to follow the reaction. Without the addition of emulsifying agents, a stable suspension of polymer particles is formed resembling a latex obtained in emulsion polymerization. It has been found that the number of latex particles after increasing in the initial stages remains constant for the major part of the reaction. The kinetics of the polymerization conform to the third case of the Smith and Ewart scheme, if it is assumed that the concentration of the monomer in the latex particles remains constant. The calculated propagation constant compares favorably with that for bulk polymerization, while the termination constant compares with that found for highly viscous systems.
Polymerization of vinyl acetate in aqueous media. Part II. The kinetic behavior in the presence of low concentrations of added soaps
Authors: Napper D. H. , Alexander A. E. 
Published: April 2003

AbstractThe effect of adding low concentrations of the three different types of soaps on the heterogeneous polymerization of vinyl acetate in aqueous solution, with K2S2O8 as initiator, has been studied. Neutral soaps produced no appreciable effect on the polymerization rate, whereas anionic soap increased the rate, the magnitude of the increase being affected by the length of the paraffin chain in the anion. Cationic soaps decreased the rate of polymerization in the early stages of the reaction, but in this case the length of the paraffin chain in the cation had no influence. The results have been interpreted in terms of the adsorption of the soap onto the surface of the small polymer particles, and the resultant reduction or promotion of the coalescence of these small particles.
Studies on the enzymatic synthesis of dextran. Part II
Authors: Braswell Emory , Goodman Albert , Stern Kurt G. 
Published: April 2003

AbstractIncreasing the reaction time or the temperature, or decreasing the enzyme or sucrose concentration, produced dextrans with higher molecular weights (light scattering) and lower intrinsic viscosities. This was consistent with the results of periodate titrations, which indicated that under these conditions the degree of branching of the samples was increased. The increase in branching which occurs when the reaction time is increased or the sucrose concentration is decreased may be due to the resulting increase in the ratio of acceptor sites for branching (chain glucose units) to the number of sucrose molecules. In addition, as the molecule grows larger with increasing reaction time, an increase in steric factors would reduce the availability of the reducing end of the chain. After allowance has been made for the change in the steric factor, it seems that the effect of enzyme concentration on branching is negligible, but that a decrease in the temperature decreases the degree of branching. The effect of temperature on the velocity of synthesis corresponds to an Arrhenius activation energy of 10.6 kcal./mole.
Some results of cesium‐initiated diene polymerization and copolymerization
Authors: Rembaum A. , Ells F. R. , Morrow R. C. , Tobolsky A. V. 
Published: April 2003

AbstractA study of the homogeneous polymerization of isoprene and butadiene by means of alkali aromatic complexes confirmed the influence of polarity of the medium on the microstructure of the homopolymer. Cesium napthalene in tetrahydrofuran yielded a high concentration of the 1,2‐adduct (29%) and 3,4‐adduct (43%) in polyisoprene, but a comparatively low concentration of 1,2‐structures (74.5%) in polybutadiene. Practically pure 1,2‐polybutadiene was synthesized by means of Li naphthalene. A gradual decrease in the concentration of 1,2‐polybutadiene structures was noted as the electropositivity of the alkali counterion increased. The influence of solvent, temperature, and molecular weight on the structure of polybutadiene was examined. Copolymerization of the isoprene–styrene monomer pair yielded block polymers. The determination of the torsional modulus–temperature spectrum afforded a simple method for distinguishing block from rando compolymers.
Stress relaxation in nylon and terylene: Influence of strain, temperature, and humidity
Authors: Meredith R. , Hsu Bay‐Sung 
Published: April 2003

AbstractStress relaxation data are presented for nylon 66 and Terylene yarns held at constant extensions from ½% to 15% for dry, 65% R.H. and wet conditions all at 25°C. and in the dry condition at 25, 50, and 75°C. A single composite relaxation curve fitted the data for Terylene at all strains at 25°C. A theory of stress relaxation gives a good fit for the experimental results of dry nylon at all temperatures between 25°C. and 75°C. In moist nylon, there are two relaxation processes superimposed on each other, one due to thermal agitation and the other due to absorption of extra moisture as the fiber is stretched. It is shown that the relaxation caused by the extra moisture absorbed is consistent with the change in moisture regain with strain at constant humidity calculated thermodynamically.
Dynamic bending properties of fibers: Effect of temperature on nylon 66, terylene, orlon, and viscose rayon
Authors: Meredith R. , Hsu Bay‐Sung 
Published: April 2003

AbstractThe dynamic bending modulus and loss modulus have been measured over a range of temperature from −70 to 170°C. for single textile filaments of nylon 66, Terylene, Orlon, and viscose rayon in the dry state, using a vacuum electrostatic method which is described. Maximum loss modulus occurred at −40°C. and 115°C. for nylon, at −60°C. and 140°C. for Terylene, at 70°C. and 110°C. for Orlon, and at −20°C. and 90°C. for viscose rayon. Application of rate process theory to these transition regions gave activation energies in support of the interpretation that the low‐temperature transition is associated with segmental motion and the high‐temperature transition involves breaking of secondary bonds, e.g., hydrogen bonds in nylon 66. In an appendix, the theory of lateral vibration of viscoelastic bars is treated in some detail, in particular as it applies to calculate successfully the large correction for air damping of fine filaments.
Polyallöcimene. II
Authors: Marvel C. S. , Kiener P. E. 
Published: April 2003

AbstractAlloöcimene has been polymerized by a variety of catalysts, including triisobutylaluminium/titanium tetrachloride, triisobutylaluminum/vanadium trichloride, boron fluoride etherate, and titanium tetrachloride. These initiators give polymers at different temperatures and of differing molecular weights but all seem to produce the same recurring structural units in the polymers in approximately the same proportions. It seems that only a slight amount if any cyclopolymerization occurs and it is probable that all of the catalysts are acting as cationic‐type initiators.
Monomers and polymers containing the trifluoromethyl group
Authors: Overberger C. G. , Davidson E. B. 
Published: April 2003

Abstract3,3,3‐Trifluoropropene, 4,4,4‐trifluorobutene‐1, 5,5,5‐trifluoropentene‐1, 3‐trifluoromethylbutene‐1, and 4‐trifluoromethylpentene‐1 were prepared and subjected to polymerization conditions with a variety of heterogeneous catalysts. The latter four monomers were polymerized to crystalline, high melting solids by means of vanadium trichloride–triisobuty aluminum catalyst. Infrared analysis indicates that there was no isomerization of the polymer chain.
Crystal structure and morphology of polyacrylonitrile in dilute solution
Authors: Holland V. F. , Mitchell S. B. , Hunter W. L. , Lindenmeyer P. H. 
Published: April 2003

AbstractIt has been possible to crystallize polyacrylonitrile from dilute solutions of propylene carbonate in the form of thin platelets. These platelets are ellipsoidal in shape and approximately 100 A. thick. Electron diffraction shows that the platelets are essential single crystals and the polymer axis is nearly perpendicular to the plane of the platelet. Five separate reflections were measured and indexed. The spacings calculated for these reflections agree with previously reported x‐ray values obtained from drawn fiber. However, the present electron diffraction data require a different indexing of the reflections resulting in revised unit cell dimensions.
Network polymers. I. Theoretical remarks
Authors: Alfrey T. , Lloyd W. G. 
Published: April 2003

AbstractThis paper consists of some general theoretical comments on the structure and swelling behavior of network polymers. The importance of network topology is emphasized. A hypothetical network consisting of “ghost” chains, which could pass freely through one another, would tend to shrink to submicroscopic size. This supercontraction would be prevented by either a volume exclusion effect or a restriction against cutting through (i.e., against alteration of network topology). In real networks, both of these restrictions are present. The swelling behavior of network polymers which were swollen at the time of network formation is discussed in terms of a crude molecular model.
Dielectric properties of water of adsorption on protein crystals
Authors: Takashima Shiro 
Published: April 2003

AbstractThe dielectric properties of dry and wet protein crystals were studied in a wide frequency range. The dry protein crystals did not have appreciable dielectric constant until the water content was about 15–20%. However, further increase of water of hydration (and/or adsorption) suddenly increased the dielectric constant of the crystals, and it reached a very large value which cannot be explained merely by the orientation of water of hydration (and/or adsorption). However the increase of dielectric constant leveled off rapidly, and further addition of water did not have significant effect. Thus the dielectric constant–water content plot followed a curve which was similar to the Langmuir adsorption isotherm. This fact strongly indicates that the dielectric constant of hydrated crystals arises, for the most part, from the polarizability of the first hydration layer of the protein molecules, which supposedly have an icelike structure.
Analysis of copolymers by pyrolysis and mass spectrometry
Authors: Wanless G. G. 
Published: April 2003

AbstractThe depolymerization behavior of the copolymers of 1‐pentene and 4‐methyl‐1‐pentene has been studied. Regularities found in the spectra are employed to develop an analytical method for assaying such copolymers. The results obtained are confirmed by NMR assays. Variations in cracking severity did not influence the analytical results much. It is concluded that the results are dominated by the bond strengths of the polymer chains, since rapid escape of the fragments from the reaction zone is possible. A direct and simplified analytical method resulted, employing direct depolymerization within the sample system of the mass spectrometer.
Halogenation of polyethylene single crystals
Authors: Keller A. , Matreyek W. , Winslow F. H. 
Published: April 2003

AbstractThe halogenation of melt‐crystallized and solution‐crystallized linear polyethylene indicated that halogen atoms have no effect on the fold length on recrystallization. At temperatures of 60°C. or higher, reaction of the crystal lattice with chlorine proceeded to completion. Extremely thin layers of both solution and melt crystallized polyethylene exhibited no difference in reactivity with chlorine, but the reactivity of molded polyethylene films to chlorine was apparently limited by chemically combined chlorine occupying the free volume in the surface layer of the polymer. There was a coexistence of highly halogenated and essentially unreacted phases during chlorination of individual crystal layers. Finally, this phase separation involved dimensions of about 100 A. and may well be related to some inherent structural feature of single crystals.
Electroinitiated polymerization of methyl methacrylate in a homogeneous medium
Authors: Funt B. L. , Yu K. C. 
Published: April 2003

AbstractMethyl methacrylate was polymerized in a homogeneous organic medium composed of a solvent of high dielectric constant an ionizable salt and the monomer. Application of a direct current provided a controlled initiation of the polymerization process by the discharged ionic species. The influence of the type of solvent electrode material and salt on the yield and molecular weight of polymer was assessed in preliminary experiments. Polymers of high molecular weight were obtained in contrast to low degrees of polymerization reported in earlier work. The yield of polymer was linearly dependent on the time, and kinetic analysis showed that the rate of reaction was proportional to the current density. The molecular weight showed an inverse dependence on current density. A rate scheme is proposed which provides a kinetic interpretation of the experimental results on the basis of a free radical mechanism initiated by the electrolytic discharge of acetate ions. The electrical control of the physical properties of the resultant polymer by programming of the current‐time dependence is discussed.
Relationship of catalyst composition to catalytic activity for the polymerization of α‐olefins
Authors: Coover H. W. , McConnell Richard L. , Joyner F. B. 
Published: April 2003

AbstractHeterogeneous olefin polymerization catalysts generally consist of a transition metal compound from groups IVB or VB in combination with an organometallic compound from groups I, II, and III of the periodic table of the elements, but in some instances may contain a third component possessing at least one strongly complexing ligand atom. The composition of a coordination catalyst of this type determines both the rate of polymerization of the α‐olefin and the stereoregularity of the polymer produced. In order to predict activity and stereospecificity of catalysts for the polymerization of α‐olefins, data from the polymerization of propylene using catalysts of the following types were correlated: (1) titanium(III) chloride catalysts in which the organometallic component was varied, (2) coordination catalysts containinig a ligand third component in which the ligand was varied, and (3) coordination catalysts in which the transition metal component was varied.The electronegativity of an orgariometallic compound is known to be important in determining its reactivity with ethers, hydrogen, and other reagents. Both the ionic size and the electronegativity of the central atom appear to be important in determining the utility of both the organometallic and the transition metal compounds as components for coordination catalysts. In general, organometallic and transition metal compounds having small central atoms with similar electronegativities favor the formation of stereospecific catalysts.The present correlation has made it possible to predict the activity and stereospecificity of coordination catalysts for olefin polymerization.
Flow reversal effects in a simple laminated membrance diffusion system
Authors: Petropoulos J. H. 
Published: April 2003

AbstractThe dependence of the magnitude of the permeation flux on the sense of flow is studied in the case of a simple membrane laminate AB. The permeability of phase A is assumed to change from a low value at low permeant activity to a higher one at high permeant activity, whereas the permeability of phase B is constant. The results of the analysis of this simple system provide considerable insight into the factors influencing flow reversal effects in binary laminated membranes in general. The conditions under which marked effects of this kind are possible have been established.
Solvent crazing of “dry” polystyrene and “dry” crazing of plasticized polystyrene
Authors: Kambour R. P. , Gruner C. L. , Romagosa E. E. 
Published: April 2003

AbstractThe critical strain εc for crazing of polystyrene in each of a variety of organic liquids has been measured along with the degree of swelling of the polymer by the liquid and the attendant reduction in the glass transition temperature Tg of the polymer. The critical strain for the crazing in air and the Tg of each of a set of specimens molded from mixtures of o‐dichlorobenzene and polystyrene have also been determined. Correlations of εc with Tg in the two cases are identical within experimental error for the first 40°C of Tg reduction; these results imply (1) that organic liquids do not exercise a significant surface energy role in solvent crazing and (2) that their only roles are associated with flow processes. Correlation of solvent crazing εc with solubility parameter of the crazing fluid is very poor for several reasons that are discussed.
Hydrodynamic interaction for time‐dependent motions: Steady rotation of a rigid dumbbell
Authors: Szu Shousun C. , Hermans J. J. 
Published: April 2003

AbstractAn expression for the flow field resulting from a time‐dependent force with time‐dependent point of action is derived from the linearized Navier‐Stokes equations. The result is written as a sum of terms, the first of which is the “slow‐change limit” corresponding to a stationary force acting at a stationary position. The application to the steady rotation of a dumbbell shows that this sum corresponds to a series expansion in powers of (L2|Ω|/v)1/2 where 2L is the length of the dumbbell, Ω is its angular velocity, and v is the kinematic viscosity of the liquid. It is pointed out that the results obtained are relevant to the problem of rotatory Brownian motion and to that of non‐Newtonian viscosity.