bluuebunny/crossref_metadata_2025_split huggingface dataset:
Density of polyethylene
Authors: Mortimer George A. , Hamner William F. 
Published: April 2003

AbstractThe density of polyethylene produced by free‐radical‐initiated batch polymerization at elevated pressures and temperatures was found to be determined by the amount of short‐chain branching and the molecular weight. The short‐chain branching was shown to depend solely upon the pressure and temperature of polymerization. This branching increased as the pressure was reduced or as the temperature was increased. The molecular weight was shown to have an important influence on the density at much higher molecular weight levels than previously reported (up to 50,000 Mn). The density increased as molecular weight decreased. At a constant polymerization pressure and temperature, the type and amount of initiator and chain‐transfer agent had no effect on short‐chain branching. Inasmuch as the type and amount of these substances do have an effect on molecular weight, they did affect density indirectly through the molecular weight. An equation relating the density, molecular weight, and polymerization pressure and temperature is given.
Random degradation of chain polymers accompanied by partial dissolution of the degraded material
Authors: Mejzler D. 
Published: April 2003

AbstractSome processes of random degradation of chain polymers in suspension are accompanied by the dissolution of the part of the degraded material having the shortest chain lengths. The molecular weight determinations are then usually made not on the total degraded material, but only on its undissolved part. It is shown that if any two of the following three experimentally determinable values are known: (1) weight fraction of undissolved degraded material, (2) number‐average DP of undissolved degraded material, (3) weight‐average DP of undissolved degraded material, the following parameters may be calculated: (1) the third experimental value; (2) the extent of degradation of the total degraded material and, therefore, the true values of the number‐average and weight‐average DP of the total material; (3) the maximum chain length of the degraded material in solution; (4) the number‐average and the weight‐average DP of the dissolved part of the degraded material; (5) the respective number fractions of the dissolved and undissolved chains in the degraded material. The calculations are carried out for the two conventional models of random degradation, that of Kuhn and that of Montroll‐Simha. For the former model, simple approximate formulas are also given, which yield solutions with a satisfactory accuracy.
Critical analysis of molecular weight distributions derived from fractionation data. I. Column elution
Authors: Kotliar A. M. 
Published: April 2003

AbstractThe evaluation of broad molecular weight distributions, based on the fractionation data obtained by column elution techniques and the Schulz‐Dinglinger approximation, is critically analyzed employing an electronic computer and a solubility function based on the Flory‐Huggins theory. The results, based on Schulz and Wesslau type distributions, show that although some characteristic features may be established, the determined values of the distribution parameters may be greatly in error.
Diffusion and viscosity of polyvinyl acetate‐diluent systems
Authors: Kishimoto Akira 
Published: April 2003

AbstractThe diffusion coefficient of methanol in polyvinyl acetate (PVAc) and the steady flow viscosity of the PVAc‐diethyl phthalate (DEP) system have been studied. In diffusion studies the sorption and permeation of methanol vapor in the polymer were measured over a temperature range above and below Tg of the pure polymer. The mutual diffusion coefficient, D, was estimated from the rates of absorption and desorption from and back to nonzero initial and final concentration, and also from the steady state permeability. The D derived by different methods agreed within experimental error. By using the equation of Frisch, the time lag for permeation was calculated as a function of penetrant concentration from the D data. The calculated values were larger than the observed ones at temperatures slightly above and below Tg, but when the temperature was well above Tg both values agreed with each other. At temperatures below Tg anomalous permeation curves which could not be fully explained at the present stage appeared. In viscosity studies measurements were made over the complete range of DEP composition at temperatures from 10 to 100°C. by using four different experimental techniques. The plot for the logarithm of the viscosity against weight fraction of polymer at a fixed temperature was convex upward at low concentration and then became concave upward at high concentration. In the intermediate region an inflection point appeared. Experimental data for the thermodynamic diffusion coefficient of methanol in PVAc and the isothermal viscosity data for the system PVAc‐DEP have been analyzed in terms of the free volume theory presented previously. It was found that experimental data were well represented by the theory.
Temperature dependence of birefringence in irradiated polyethylene
Authors: Keneally E. , Gard J. , Adler G. 
Published: April 2003

AbstractThe birefringence of irradiated polyethylene was observed as a function of temperature. The data are consistent with a mechanism in which crosslinking limits the growth and annealing of crystallites. Crosslinks formed in material which was oriented at the time the crosslinks were formed, results in an oriented gel. This effect explains the birefringence and the persistence of nucleation sites at high temperatures.
Role of organic diluents in a sol‐phase polymerization
Authors: Guha T. , Biswas M. , Konar R. S. , Palit S. R. 
Published: April 2003

AbstractThe effect of organic solvents on the rate of heterogeneous aqueous polymerization initiated by the K2S2O8Na2S2O4 redox pair has been studied. The separating polymer phase remains in colloidal dispersion, the stability of which is partly due to charge and partly due to hydration. Both the water‐miscible and water‐immiscible organic liquids decrease the rate of polymerization, the limiting conversion, and the molecular weight of the polymers. It has been suggested that the water‐miscible organic liquids preferentially solvate the latex particles and thereby decrease the hydration stability and monomer concentration in the latex particles, whereas the water‐immiscible organic liquids decrease the monomer concentration in the latex particles due to the partition of the monomer between the aqueous and the nonaqueous phases. Thus the fall in the rate and molecular weight of the polymers may be ascribed to the increase in the termination rate by the faster coagulation of the latex particles and dilution of monomer concentration at the reaction site.
Role of organic diluents in a precipitative aqueous polymerization
Authors: Konar R. S. , Guha T. , Palit S. R. 
Published: April 2003

AbstractThe effect of organic liquids on the rate of heterogeneous aqueous polymerization initiated by the KMnO4H2C2O4 redox pair has been studied. The separating polymer phase is a precipitate under experimental conditions. The rate of polymerization, the limiting yield, and the molecular weight of the polymers were found to decrease in presence of organic liquids. This behavior has been ascribed to (1) the increase in the termination rate due to the swelling of the precipitated polymer particles containing trapped radicals and (2) the fall in the monomer concentration at the reaction site.
Molecular weight distribution and viscosity of multichain polymers in ε‐caprolactam polymerization
Authors: Manabe Tomonobu 
Published: April 2003

AbstractThe molecular weight distribution is calculated on the basis that x − 1 indistinguishable monomer units are distributed in f unnumbered branches with no restrictions on the number per branch. The weight fraction of single‐ and multi‐chain polymer mixture of polymerization degree x is for f = 2,

and for f = 3,

where, p is the extent of reaction, Q the number of equivalents that reacts with one mole of monomer, and L the number of equivalents of unreacted groups per mole of monomer. When the limiting viscosity number [η] and the melt viscosity μ are expressed as the function of the (fractionated) degree of polymerization x: [η] = Kv xα and μ = Kμ xβ, the solution and the melt viscosities are expressed as follows:

The relation among the number‐average, viscosity‐average, weight‐average and melt viscosity‐average degree of polymerization is discussed. The relation between the solution and the melt viscosities is also discussed.
Photosensitized polymerization of acrylic monomers. III. Kinetics of polymerization of acrylamide in the absence of oxygen
Authors: Toppet S. , Delzenne G. , Smets G. 
Published: April 2003

AbstractAcrylamide polymerizes at 25°C. in aqueous solution by photosensitization with eosin, in absence of any reducing agent and of oxygen; a strong photoreduction of the dyestuff proceeds simultaneously. The photopolymerization has been followed gravimetrically, while the rate of photoreduction was followed colorimetrically. The rate of photoreduction is proportional to the absorbed light intensity. The rate constants are proportional to the monomer concentration when this concentration is lower than 0.42 mole/l.; above this value they are independent from it. The rate of photopolymerization is proportional to the square root of the eosin concentration when this concentration is ≤ 10−6 mole/l.; above this value, the rate becomes independent of the eosin concentration. With respect to the monomer the order of reaction varies from 1.5 to 1.85 when the eosin concentration is 0.4 × 10−6 and 6 × 10−6 moles/l., respectively. With respect to the light intensity, the order of reaction is 0.35 when the monomer and eosin concentrations are respectively, 2.8 moles/l. and 0.4 × 10−6 moles/l. The kinetics of photoreduction are interpreted on the basis of a reaction between the excited triplet state of the dye and the monomer, and a kinetic scheme is presented. The kinetics of photopolymerization are explained by a termination process between a growing chain and a primary radical, besides the usual termination process between two growing chains.
Les polymeres à l'interface eau–air
Authors: Jaffe J. , Loutz J.‐M. 
Published: April 2003

AbstractEven at high superficial dilution (π < 40 mdyne/cm.−1) it is impossible to determine the molecular weight of a flexible polymer. Using statistical equations containing an adjustable parameter it can be accounted for the compression isotherms. This parameter corresponds not to an experimental relation, and is without any physical significance. The polymeric layers can be described by Singer's equation, if one attributes to the term x the significance of an experimental parameter.
Radiolysis of polyisobutene. Part I. Yields of fractures, double bonds, and gas
Authors: Turner D. T. 
Published: April 2003

AbstractPurified polyisobutene with approximately a random molecular weight distribution and a number‐average molecular weight of 3.5 × 105 was irradiated in vacuo at about 25°C. with 4 M.e.v. electrons. The degradation of the polymer was studied by osmometry and viscometry and the G (fracture) value determined as 4.1. The G value for total unsaturation was determined as 5.3 by a chemical method suitable for olefins branched in the vicinity of the double bond. Little or no internal unsaturation was detected by ozonolysis of the irradiated polymer. Hydrogen and methane were formed with G values of 1.3–1.6 and 0.8–0.5, respectively. At doses greater than about 10 Mrad all the above G values decreased. The G value for isobutene formation (≤ 0.1) remained approximately constant up to a dose of at least 150 Mrad. On lowering the temperature of irradiation to −196°C. the yield of fractures was markedly decreased while the yield of hydrogen plus methane was scarcely affected. This is interpreted as evidence that the degradation reaction is due predominantly to the direct fracture of carbon–carbon bonds rather than to any reaction associated with gas formation. The observed ratio of double bonds to fractures is shown to be consistent with this interpretation.
The chemistry of poly(vinyl chloride) stabilization. V. Organotin stabilizers having radioactively tagged Y groups
Authors: Frye Alfred H. , Horst Raymond W. , Paliobagis Marko A. 
Published: April 2003

AbstractExperiments with a select group of radioactively tagged organotin stabilizers of the general formula Bu2Sn Y2, in which the radioactive atoms (14C) are located in the Y groups, have shown, that, under the conditions normally employed to evaluate and screen poly(vinyl chloride) heat stabilizers, a portion of that radioactivity becomes firmly associated with the resin. Under standard conditions, the extent of this association has been found to be dependent upon the nature of the Y group and the duration of the heat treatment. It is suggested that the stabilizing action of these organotin compounds arises in part from reactions between the polymer and the stabilizer wherein certain of the polymer's chlorine atoms are exchanged for the stabilizer's Y groups (or a portion thereof), the resulting structure being more stable toward degradative elimination. Other possibilities for reaction between the polymer and the stabilizer are also considered and it is shown how these can further supplement the organotin compound's stabilizing action and yet be rationalized within the experimental evidence.
Fine texture in necking portions of cold‐drawn polyethylene
Authors: Kasai Nobutami , Kakudo Masao 
Published: April 2003

AbstractContinuous structure change in the necking part of the cold‐drawn polyethylene has been examined by the wide‐ small‐angle x‐ray diffractions. A specially designed microbeam x‐ray camera which permits both wide‐ and small‐angle diagrams to be obtained at the same position at the same time was used. With increasing draw ratio, along the center axis of the specimen, first the crystallites are aligned with the a axes perpendicular to the draw direction; this is followed by a gradual orientation of the c axis to the draw direction. On the other hand, an isotropic ring‐shaped small‐angle halo continuously changes to an elliptical halo with its minor axis on the meridian. After this stage, a meridional scattering in layer streaks appears superposed on the flat elliptical halo, then the elliptical halo disappears and the layer streaks on the meridian remain, and finally the quadrant meridional scattering appears as diffuse layer streaks with intensity maxima on both sides of the meridian. On the stream line, nearly the same variations of the wide‐ and small‐angle diagrams as those on the center axis are observed; however, the meridian of each diagram is not parallel to the draw direction but coincides with the tangent of the stream line at each irradiated position. The stream line was conventionally defined so as to divide the y coordinates from the center axis to the surface at every point on the line into the same ratio. One characteristic diagram along the stream line is a small‐angle oblique two‐point pattern, appearing as off‐meridian layer streaks. From each wide‐angle diagram, the average orientation angle between the c axis and the meridian, degree of crystallite parallelity, and the apparent crystallite size were estimated. The Bragg distance, identity period along the meridian, and the azimuthal angle on the film between the meridian and the direction from center to the diffraction peak were determined by the small‐angle scattering. In considering these results, a series of plausible models for continuous structure change in necking is presented.
Analysis of the gases evolved from irradiated polyethylene
Authors: Salovey R. , Pascale J. V. 
Published: April 2003

AbstractSaturated hydrocarbons evolved during electron irradiation of polyethylene are characteristic of short side chains in the polymer. A convenient analysis is effected by programmed temperature gas chromatography. In order to minimize the relative concentrations of extraneous hydrocarbons, i.e., those not arising from selective scission of complete side chains, it is necessary to irradiate at low temperatures and doses. Such analyses of a high pressure polyethylene (DYNK) indicates that the two methyls per 100 carbon atoms detected in infrared absorption are probably equal amounts of ethyl and butyl branches. These arise by intramolecular chain transfer during polymerization. At a dose of 10 Mrad about 1/4% of the alkyl groups are removed. Methane is the only hydrocarbon detected on irradiation of polypropylene, indicating little combination of methyl radicals to form ethane during irradiation.
The reaction between dicumyl peroxide and butyl rubbers
Authors: Loan L. D. 
Published: April 2003

AbstractThe reaction between dicumyl peroxide and butyl rubbers has been followed by means of molecular weight measurements. In all cases except that of the rubber with highest unsaturation the molecular weight falls, and the scission efficiency of the peroxide is found to depend quite markedly upon the unsaturation. For the rubber of highest unsaturation a small overall crosslinking reaction was observed. The results are interpreted as showing that cumyloxy radicals react with isoprene units in the chain about 300 times as fast as with isobutylene units. The molecular weight depen dance upon time during the reaction has been investigated but has not been satisfactorily explained.
Radiation‐initiated copolymerization of styrene with unsaturated esters
Authors: Burlant W. , Hinsch J. 
Published: April 2003

AbstractThe kinetics of the γ‐ray‐initiated, gel‐forming copolymerization of styrene with the unsaturated ester containing 1.5 double bonds per molecule of number‐average molecular weight of 890 (derived from maleic anhydride, phthalic anhydride, and propylene glycol) have been studied with initial ester concentrations ranging from 65% to 2.4%. From experimentally determined gel fractions, rates of disappearance of styrene and ester unsaturation (measured up to complete conversion of ester unsaturation), and the degree of polymerization of the growing chains, a model is suggested based on a free radical copolymerization, assuming a single effective propagation and termination rate constant (kp and kt, respectively), and bimolecular chain termination except between a pair of immobile gel radicals. Three ester concentration ranges were considered. At high ester concentrations (≥ 50%), styrene and ester enter the gel at a constant rate (molar ratio of styrene:ester double bond of 2:1), precluding application of conventional copolymer composition theory. The rate at which overall unsaturation, α, disappears, is given by dα/dt = (kp2/kt)M2° where M2° is the initial molar concentration of ester unsaturation. The rate at which styrene, α1, disappears is given by dα1/dt = 2/3(kp2/kt)M2°(M1° + M2°)/M1°. The rate at which styrene is consumed in the dilute esterstyrene solutions (⩽4.6%), where M2° is negligibly small, is given by dα1/dt = kp(k1/2kt)1/2. Polymerization rates of the intermediate ester concentration ranges (10% to 30%) are higher than predicted from the simple model. An empirical rate expression is presented which describes these systems to 40% conversion of styrene: dα1/dt = (kp2/kt)M2° {[(1 + m)(r1 + M)]/(r1 + 2M)}, where M is the ratio of ester unsaturation to styrene in the starting mixture and r1 is the reactivity ratio for styrene, defined in the usual manner. For initial conversions of ester unsaturation (to 10%) dα/dt = (kp2/kt)M2°.
Poly(1,2‐dimethyl‐5‐vinylpyridinium methyl sulfate). Part I. Polymerization studies
Authors: Shyluk W. P. 
Published: April 2003

Abstract1,2‐Dimethyl‐5‐vinylpyridinium methyl sulfate is readily polymerizable in aqueous solution under mild free radical conditions to a high molecular weight, cationic polyelectrolyte. A three‐halves order dependence of the rate of polymerization on monomer concentration is indicated for about 75% of the polymerization of 1,2‐dimethyl‐5‐vinylpyridinium methyl sulfate in aqueous solution with potassium persulfate as initiator. A normal dependence of the polymerization rate on the square root of the initiator concentration is also indicated by these data. The overall activation energy is estimated to be about 17 kcal./mole. Preliminary experiments related to the effect of changing the ionic strength of the reaction medium by addition of sodium chloride led to a change in the kinetics with a dramatic slowing‐down of the polymerization. Copolymerization studies indicate that the reactivity of this cationic monomer is higher than that of acrylamide, methacrylamide, and methyl methacrylate, but close to that of methacrylic acid.
Theoretical consideration of linear condensation polymerization in a dispersed medium
Authors: Nanda V. S. 
Published: April 2003

AbstractThe combinatorial approach to the problem of linear polymers, developed earlier, is applied in the present paper in order to study the statistical nature of condensation polymers obtained from a large number of very small systems. The results of the customary theory become inapplicable in such cases for sufficiently high degrees of polymerization which should be attainable experimentally. The possibility of realizing homogeneous samples by direct polymerization is discussed from a theoretical standpoint.
The polymerizing system: Vinyl acetate–diphenyl
Authors: Haas Howard C. , Husek Helen 
Published: April 2003

AbstractThe polymerization of vinyl acetate in the presence of diphenyl has been studied. A chain transfer constant for diphenyl of 6.4 × 10−4 was obtained from conventional kinetic analysis and Pn data. This value is in reasonable agreement with values obtained from an estimation of the combined diphenyl residues in the corresponding polyvinyl alcohols by ultraviolet spectroscopy. The conclusion, that diphenyl behaves in this system predominantly as a transfer agent and not as a comonomer, is supported by an evaluation of the data in terms of a kinetic scheme for retarded polymerization. Retardation of the rate of polymerization of vinyl acetate is observed in the presence of diphenyl and it is on this basis that abstraction of hydrogen from diphenyl as being the transfer step is discarded in favor of addition of the vinyl acetate radical chain to diphenyl. The ultraviolet dichroism of an oriented polyvinyl alcohol film containing combined diphenyl residues is presented.
Temperature‐independent viscosity characteristics of polymer systems
Authors: Vinogradov G. V. , Malkin A. Ya. 
Published: April 2003

AbstractThe possibility of construction of temperature‐independent viscosity characteristics of polymer systems by means of a “reduced variables” method similar to that of Ferry is discussed. It is stated that the viscosity as a function of temperature and shear rate can generally be regarded as the product of two functions, one of which depends only on the temperature and the other only on the shear rate. It is shown by dimension analysis and by assuming the flow of polymer systems to be viscoelastic in nature, that the ratio of apparent viscosity to initial Newtonian viscosity is a temperature‐independent function of the product of the shear rate by the initial Newtonian viscosity. Hence, the latter (observed at shear rates tending to zero) appears to be a most important physical parameter governing the flow properties of polymer systems. At sufficiently low shear rates the apparent viscosity was found to be an exponential function of shear stress, so that the initial Newtonian viscosity can be determined by extrapolation. The above theoretical considerations were checked for the most reliable published data on the flow properties of condensed polymer systems over a wide range of shear rates and temperatures. Experimental results obtained for polymer systems of different nature can be represented satisfactorily by corresponding temperature‐independent viscosity curves.