bluuebunny/crossref_metadata_2025_split huggingface dataset:
A critical investigation of polyethylene gas permeability
Authors: Alter Harvey 
Published: April 2003

AbstractThe effect of polymer density on the gas permeability of polyethylene film has been studied. The experimental data for permeability P are described by the equation P = K(1 — d)n, where K is a constant characteristic of each gas and d is the sample density. This equation is similar to previous analytical descriptions of the permeability—density relation. Values of K and n (n ≈ 2) and confidence limits for P are given for N2, O2, and CO2. Permeability—density values are reported for approximately 100 film samples for each of the three gases over a density range from 0.899 to 0.975 g./cc. The density was measured for each sample inserted in the permeability apparatus. The above mathematical model chosen to describe the experimental data is interpreted to mean that the effect of the crystalline phase is to decrease both the gas solubility and diffusion. Gas solubility and diffusion are linear functions of the volume fraction of amorphous material. Permeability, the product of diffusion and solubility, is consequently proportional to the square of the volume fraction of amorphous material. Permeability is related to density rather than volume fraction of amorphous material to avoid choosing a single value for the density of the amorphous fraction. The experimental results suggest additional lowering of the permeability due to restraints on the segmental motion of the amorphous chains.
Permanganate–oxalic acid as a redox initiator in aqueous media. Part II. Kinetics and degree of polymerization
Authors: Palit Santi R. , Konar Ranjit S. 
Published: April 2003

AbstractThe rate of polymerization of aqueous methyl methacrylate under nitrogen at 32°C. is proportional to the first power of catalyst (MnO4−) concentration (0.633 to 15.83 × 10−5 mole/l.) at fixed concentrations of the activator (0.8 × 10−2 mole/l.) and monomer (6.204 × 10−2 mole/l.), independent of activator concentration over a wide range (0.50 to 0.0625 × 10−2 mole/l.), and proportional to the first power of monomer concentration within the range (0.94 to 7.52 × 10−2 mole/l.) at fixed concentrations of the catalyst (3.16 × 10−6 mole/l.) and the activator (0.8 × 10−2 mole/l.). The initial rate of polymerization attains a maximum value at 45°C., but falls with further rise in temperature. The rate of polymerisation is depressed by agitation after initiation, salts and organic solvents, and is accelerated by MnSO4 and complexing agent like NaF (only at low monomer concentration), and in presence of peptizers like sodium cetyl sulfate or cetyltrimethylammonium bromide. The separating phase in the absence of peptizers is a course coagulum, and possibly a steady state with respect to radicals is not attained at high catalyst concentration. Injection of catalyst late in a run increases both the rate of polymerization and yield in unpeptized systems and does the reverse in peptized systems. The molecular weight of the polymers increases in the course of a run and is also affected by change of catalyst concentration but not by activator concentration in the range where the rate of polymerization is independent of activator concentration.
Orientation studies on drawn polyolefins
Authors: Hoshino S. , Powers J. , Legrand D. G. , Kawai H. , Stein R. S. 
Published: April 2003

AbstractThe effect of different thermal treatments on the degree and type of orientation produced by cold drawing three polyolefin films: polyethylene, polypropylene, and polybutene‐1, was studied by two complementary techniques: x‐ray diffraction for the measurement of crystal orientation and birefringence for the measurement of the total film orientation. Variations in the texture of these polymer films were characterized by these techniques as well as by density, tensile stress measurements and photomicrographs. The birefringence–strain data showed a decrease in birefringence values at a given strain as the polymer side group size increased. This decrease appears to be associated with a more symmetrical polarizability ellipsoid and hence a decrease in crystal birefringence. The birefringence–strain curves for the same polymer system showed a decrease in birefringence value at a constant strain with increased annealing. X‐ray diffraction data indicate that the a and b axes in both polyethylene and polybutene‐1 film orient by different amounts at a given strain. Polypropylene, on the other hand, shows equal amounts orientation of the a and b axes. The different orientation behavior for these polymer systems is discussed in terms of variation in the ease with which polymer crystals may be deformed.
Low temperature polymerization of methyl methacrylate initiated by ethylsilver
Authors: Bawn C. E. H. , Janes W. H. , North A. M. 
Published: April 2003

AbstractThe free‐radical polymerization of methyl methacrylate at low temperatures has been studied in a series of solvents of differing solvent power and ability to form weak complexes with monomer. In every case the polymer was predominantly syndiotactic, which suggests that monomer association or complex formation are not important stereoregulating factors, and that the treatment of the propagation reaction as two concurrent addition reactions between monomer and a free propagating species is justified. The polymerization has been studied over the temperature range −20 to −60°C. with ethylsilver as initiator. Over these temperatures the overall rate law is Rp = K[M]3/2 [Ag]1/2 where K, a composite constant, can be expressed as 1.7 exp{ −5100/RT} 1. mole−1 sec.−1. The polymerization proceeds by a free radical mechanism, the initiation step appearing to be the decomposition of a ethylsilver–monomer complex to form metallic silver, and a free radical capable of initiating polymerization. The first‐order rate constant for this decomposition in ethyl acetate as solvent has the value 1.5 × 102 exp{−6600/RT} sec.−1. The molecular weights of the polymers formed are higher than would be predicted by extrapolation of data from higher temperatures, and also indicate that transfer reactions to catalyst components are negligible in the range of initiator concentrations studied.
Polymerization induced by ionizing radiation at low temperatures. I. Evidence for the simultaneous existence of ionic and free‐radical mechanisms in the polymerization of styrene and 2,4‐dimethylstyrene
Authors: Chen Catherine S. Hsia , Stamm Robert F. 
Published: April 2003

AbstractBy means of initiation with ionizing radiation, styrene and 2,4‐dimethylstyrene have been polymerized in the crystalline solid state, in the pure liquid state, and in solution at different temperatures (−80°C. to 25°C.). In solution polymerization, it has been found that for the same type of initiation, other conditions being constant, the mechanism by which these monomers polymerize is temperature‐dependent. At lower temperatures a cationic mechanism predominates; at higher temperatures a free‐radical mechanism is in the ascendency. At intermediate temperatures, both cationic and freeradical polymerizations take place. Furthermore, these intermediate temperatures are different for different monomers, being higher in a monomer whose electronic structure is more favorable for cationic polymerization. The difference in mechanism at different temperatures has been proved by: (1) the dose rate dependencies, both of the polymerization rates and of the molecular weights of the resulting polymers; (2) the activation energies for the polymerization; and (3) the relative reactivities in the polymerizations of styrene and substituted styrenes.
Kinetics of ethylene polymerization initiated by free radicals
Authors: Friedlander H. N. 
Published: April 2003

AbstractEthylene polymerization can be carried out under milder conditions than heretofore because of the development of peroxydicarbonate catalysts. This simplifies study of polymerization kinetics. Diethyl peroxydicarbonate undergoes first‐order decomposition in tert‐butyl alcohol with an energy of activation of 33 kcal./mole, and a half‐life of 1.5 hr. at 60°C. The rate of decomposition, 1.3 × 10−4 sec.−1, does not change in the presence of polymerizing ethylene. The rate of polymerization can be followed by pressure change. But, because the concentration of ethylene in tert‐butyl alcohol as a function of pressure is not known accurately, it is better to measure polymerization rate by isolating the polymer. A mathematical relationship was developed between initiator decomposition and polymer formation. It is based on a conventional free‐radical polymerization mechanism and is supported by the experimental data. Polymer molecular weight is independent of initiator concentration and increases only slightly with duration of polymerization. The effects of reaction variables of molecular weight are explained by normal free‐radical transfer reactions. The polymer contains ethyl carbonate groups from homolytic scission of diethyl peroxydicarbonate, and it exhibits the same absorption bands in the infrared as does ethyl n‐octyl carbonate. These bands disappear on saponification and are not present in polyethylene made with other peroxide catalysts.
γ‐radiation of p‐substituted polystyrenes
Authors: Burlant W. , Neerman J. , Serment V. 
Published: April 2003

AbstractThe electronic environment about the main chain atoms in polystyrenes has been varied systematically by introducing electronegative or electropositive substituents (H3C, CH3O, Br, Cl, NC, and O2N groups) in the p‐position of the ring. Energy yields for γ‐initiated H2 formation and crosslinking, both a measure of the radiation sensitivity of the backbone, were determined above and below Tg from (1) mass spectrometric examination of the decomposition gases and (2) molecular weight changes. For most of the polymers, it is concluded that the backbones of p‐substituted polystyrenes are more radiation stable than that of polystyrene, and that main chain macroradicals formed early in the reaction are responsible for the major changes observed, i.e., hydrogen evolution and crosslinking. The role of the p‐substituent on the latter effects is interpreted qualitatively in terms of the contribution by the substituent to the resonance stability of these intermediate polymer radicals. In the case of poly‐p‐bromo‐ and poly‐p‐chlorostyrene, the inordinately high sensitivity to crosslinking and the absence of halogen atoms in the decomposition gases suggest the importance of a chain reaction in the radiation chemistry of these molecules.
Polyperfluoroalkyl oxetanes: A new class of thermally stable polymers
Authors: Case L. C. , Todd C. C. 
Published: April 2003

AbstractTwo perfluoroalkyl oxetanes, 2‐heptafluoropropyloxetane and 3‐ethyl‐3‐nonafluorobutyloxetane, were synthesized and polymerized. The 2‐heptafluoropropyloxetane was prepared by the ring closure of heptafluoro‐1,3‐hexanediol with sulfuric acid and sodium hydroxide. The 3‐ethyl‐3‐nonafluorobutyloxetane was prepared from diethyl ethylmalonate and perfluorobutyryl chloride. The sodium salt of the ester was acylated with the acid chloride. The resulting ketodiester was reacted with sulfur tetrafluoride to give diethyl α‐ethyl‐α‐perfluorobutylmalonate. This ester was then reduced with lithium aluminum hydride to give 2‐ethyl‐2‐perfluorobutyl‐1,3‐propanediol. This diol was then converted to the oxetane with sulfuric acid and sodium hydroxide. These oxetanes were polymerized in methylene chloride solution with boron trifluoride as the catalyst. Both polymers were viscous oils. The oxetane polymers were exposed as thin molten films to air at 300°F. Also tested under these conditions were polyethylene oxide, polypropylene oxide, polytrimethylene oxide, poly(3,3‐dimethyl)oxetane, and Teracol 30. The polymer from 2‐perfluoropropyloxetane was more stable than all the nonfluorinated polyethers tested. After an initial high weight loss, attributed to impurities, the polymer from 3‐ethyl‐3‐perfluorobutyloxetane was the most stable polyether tested.
Thermal decomposition of natural cellulose in vacuo
Authors: Murphy E. J. 
Published: April 2003

AbstractAn investigation of the thermal decomposition of natural cellulose is described, in which the rate of the reaction was determined by the rate of evolution of gas in vacuo in the temperature range 100–250°C. Two states of the material could be distinguished with respect to thermal decomposition behavior, the “initial” state and a state produced by protracted heating which is described as the “stable” state. In the initial state the rate of evolution of CO is given by k = 2.8 × 109 exp {−34.0 × 103 RT}, in the stable state by k = 1.0 × 1011 exp {−39.4 × 103/RT}, where k is expressed in moles of CO per mole of cellobiose per second, R is the gas constant, and T the absolute temperature in degrees Kelvin. The composition of the gas evolved in the initial state is given by xH2O:yCO2:1CO, where x is observed as a range of values fairly close to 3, and y to 1, depending upon the stage of the reaction. In the stable state the composition of the gas evolved is about 10H2O:2.5CO2:1CO; these ratios remain within rather close limits (about 10%) in observations made over a considerable range of conditions. The ratio 2.8 × 109/1.0 × 1011 may be interpreted, on the basis of simplifying assumptions, to represent the fraction of the structure which decomposes with the lower activation energy (i.e., 34.0 kcal./mole). This fraction may be regarded as a measure of the concentration of some secondary aspect of the structure of the material which may be described as internal surfaces, a micellar structure, or the endgroups of long‐chain molecules. Because of the stability of the value 39.4 kcal./mole with respect to protracted heating and to variations in secondary composition, this value is regarded as the activation energy for the thermal decomposition of the α‐cellulose present in natural cellulose. At all temperatures natural cellulose decomposes at rates given by the first of the above equations for the initial stage and by the second equation for later stages of the reaction. (There are, of course, intermediate states between the extremes represented by these equations.) The effect of partial thermal decomposition of natural cellulose on its physical properties, such as water adsorption, can be studied as a function of the degree of thermal decomposition as measured by the rates given by these equations. The “endpoint” in the drying of cellulosic materials can also be determined from the thermal decomposition data. Water removed after this point has been reached does not result in increased dryness of the material, but is a measure of the progress of the thermal decomposition reaction.
Macromolecular stable free nitrogen radicals
Authors: Braun D. , Löflund I. , Fischer H. 
Published: April 2003

AbstractLow molecular stable free nitrogen radicals have been investigated frequently. There are, however, only a few records on corresponding high polymers. Preparation of macromolecular radicals of the diphenylpicrylhydrazyl type is described. Poly‐4‐fluorostyrene is nitrated to poly‐3,5‐dinitro‐4‐fluorostyrene, a compound in which the fluorine by analogy with similar low molecular compounds, is very reactive. By reaction with diphenylhydrazine, poly(α‐vinyldinitrophenyl‐β,β‐diphenyl hydrazine) is obtained; this can be oxidized without difficulty to the corresponding hydrazyl. The polymer is a stable free nitrogen radical. Its structure follows from the comparison of the absorption spectra and the electron spin resonance spectrum with suitable compounds. The polymer corresponds in its chemical behavior to the low molecular free nitrogen radicals, e.g., it easily oxidizes hydroquinone, ascorbic acid, or hydrazobenzene. It is a typical high polymer inhibitor for the polymerization of styrene, whereas the polymer hydrazine has no inhibiting effect.
Use of dimaleimides as accelerators for the radiation‐induced vulcanization of hydrocarbon polymers
Authors: Miller S. M. , Roberts R. , Vale R. L. 
Published: April 2003

AbstractThe effect of alkyl and aryl dimaleimides on the rate of crosslinking of natural rubber is described by means of experiments with ionizing radiation. The dose for vulcanization can be reduced from 5 × 107 to 2.0 × 106 rad by use of purified rubber and 5% of additive, and the reaction is dose‐rate dependent with an intensity exponent of 0.57. The reaction is further accelerated by the addition of small quantities of solvents. By use of C14‐labeled dimaleimides it is shown that there is approximately one dimaleimide unit to each crosslink. Possible chain mechanisms for the reaction are discussed.
Formation and characteristics of the crystalline cellulose x modification of cellulose
Authors: Ellefsen Ø. , Norman N. 
Published: April 2003

AbstractPreviously reported experiments dealing with the formation of the new cellulose × modification in precipitates after treatment of cotton and wood pulp with strong hydrochloric acid are summarized and discussed in connection with results from a recent investigation where other swelling systems have been applied. It has been demonstrated that very pure precipitates of cellulose x may be obtained by means of treatment with phosphoric acid (84.5%) at 50°C. The hypothesis for the formation of the new modification has been discussed, and it is suggested that the necessary condition for the formation of cellulose x is swelling to such a degree that the complexes (C6H10O5·4H2O·HCl)n and (C6H10O5·2H2O·H3PO4)n are obtained. The most probable unit cell for cellulose x, as judged from the x‐ray experiments, is one having the same dimensions as cellulose IV, but with different reciprocal positions of the corner and central cellulose chains in the lattice. The infrared spectrum of cellulose x lies between those of cellulose II and IV, and bears a somewhat closer resemblance to that of cellulose II.
Differential thermal studies on plant gums
Authors: Kulshrestha V. K. 
Published: April 2003

AbstractDifferential thermal analysis studies have been done on nine different gums belonging to different families and genera and differing in their chemical constituents and structure, along with their respective gum acid and hydrolysis products. The gums studied include gum sterculia urens, gum azadirechta indica, gum acacia catechu, gum limmonia accidissma, gum lannea grandis, gum anogesius latifolia, gum acacia leucopholea, gum prosopis galandulosa, and gum swietenia mahagony. Certain reactions take place when these substances are heated uniformly to an elevated temperature, which are manifested in the form of endothermic or exothermic peaks depending on the nature of the reaction. These are due to the removal of the adsorbed moisture, the removal of the structural (OH) groups with the elimination of water and CO2, partial decomposition of the gum followed by a rearrangement of the molecule, etc. The thermograms so obtained are quite distinct from each other and afford a “finger print” device in the identification and characterization of these substances. The DTA studies have been further correlated with infrared studies and these support the views already expressed.
Studies on biocolloids and polyelectrolytes: The plant gums. Electrochemistry of azrechtic acid
Authors: Kulshrestha V. K. 
Published: April 2003

AbstractThe conductivity and pH of azrechtic acid (ARA), a polyelectrolyte obtained from the electrodialysis of gum azadirechta indica have been investigated under different experimental conditions. The plot of equivalent conductivity A versus √C (phoreogram) is much steeper than for a comparable simple electrolyte. The phoreogram is strongly concave upward. It is shown that the conductivity is largely due to the hydrogen counterions. The equivalent conductivity has been expressed by the equation Λ = KCb where K and b are constants, K = 18.2 and b = −0.1452. The conductivity further follows the equation Λ −° Λ = −√C/(A + B√C), Λ° is the equivalent conductivity of ARA at infinite dilution and equals 73.5, A = 8.4 × 10−4 and B = 1.831 × 10−2. The degree of dissociation has been determined from measurement of electrical conductivity and pH. A discrepancy in the results has been tentatively explained. The degree of dissociation decreases with the concentration of ARA. It is noted that the conductance of an ARA—electrolyte mixture is 5–12% higher than the calculated value. The pH of ARA with dilution follows the equation pH = D + E log C, where D = 2.96 and E = −0.85. It has been further shown that the pH with dilution also follows the expression pH = A1Ca, where A1 = 2.96 and a = −0.1009.
Some mechanical aspects of the swelling and shrinking of polymeric solids. Part I. External and internal restraints
Authors: Rosen Bernard 
Published: April 2003

AbstractThe osmotic or swelling pressures of polymeric gels are necessarily complicated by structural stresses generated by the swelling or expansion against the longer‐ranged cohesive contributions of the bulk. For externally unrestrained, true swelling equilibria, one need only consider the hydrostatic tensile stresses created by the fixed resistance against the polymer expansions afforded by the primary bonded crosslinks of truly long‐ranged three‐dimensional networks. However, in trivial expansions of extremely slowly relaxing polymeric gels, one need also consider the effective permanency of internal, near‐range structural restraints afforded by these virtually elastic gels. When the structural relaxation times are shorter, this latter hydrostatic stress takes on a time dependency which affects one's experimental perspective of the swelling equilibria to a degree which is a function of the time employed for the measurements. Therefore, one encounters a “drift” in the apparent swelling equilibria. This ambiguous situation, frequently met in the swelling equilibria of slowly relaxing polymeric gels, is also encountered in their thermal expansions and appears to be a general consideration involving relaxations of flux‐generated, structural tensions. Although admittedly very approximate, this is a preliminary attempt to extend the major conceptual perspective of the swelling of rubbers towards the relative volume expansion processes in glassy polymeric solids. It appears that this unorthodox approach is still demanded for any proper explanation of the basis for the abnormal solute absorption and drying kinetics of these glasses. This approach also has some conceptual advantages in the general interpretation of the abnormal heat absorption kinetics in these same, and other types of glassy systems. The major effect tentatively appears to be related to the isotropic, anelastic deformational responses to flux‐induced volume changes in these solids. This possibly is an intrinsic peculiarity of all anelastic solids, but is most strongly felt in considerations of the very highly anelastic, polymeric solids.
Examination of kinetics of thermal decomposition of peroxides of polymethyl methacrylate
Authors: Turska E. , Połowiński S. 
Published: April 2003

AbstractThe kinetics of thermal decomposition of the peroxides obtained by γ‐irradiation of polymethyl methacrylate in air was investigated. The method of examination of the velocity of this reaction based on the reaction of DPPH with free radicals. The measurements resulted in finding the reaction to be of the first order. The rate constants for the thermal decomposition of the peroxides at temperatures of 70, 80, 90, and 100°C. were determined. The constants for the Arrhenius formula were determined and the relationship k = 3.61 × 105e−8e−15,000/RT was found.