bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cleavage of disulfide polymers. II. By thiols
Authors: Fettes E. M. , Mark H. 
Published: April 2003

AbstractThe study of the interchange reaction of thiols with disulfides is extended to include additional thiols and conditions for redistribution. In aqueous suspension, polymeric disulfides are reduced in molecular weight to widely different extents by thiols of varying structures. Water‐soluble thiols as mercaptoethanol, and tertiary thiols as t‐butyl mercaptan, are relatively ineffective in cleaving. The presence of sodium disulfide with some of the thiols, particularly the thiophenols and 2‐mercaptobenzothiazole, retarded cleavage by the thiols. A study of the molecular weight of the polymer as the cleavage by thiols proceeded indicated that short chain lengths were gradually removed from the surface of the polymeric particles. The partial cleavage of a disulfide polymer by a mixture of sodium sulfite and sodium hydrosulfite produces a disulfide polymer of lower molecular weight and terminal thiol groups. This product should be capable of self‐redistribution to a random distribution. The liquid polymer resulting from the cleavage had a high heterogeneity index (M̄w/M̄n). Efforts to randomize in bulk to the theoretical index of 2.0 by heat, ultraviolet light, water, and amines were not successful. It was found possible to effect the reaction of the disulfide polymer with butyl mercaptan in solution in dioxane with sodium phenolate as catalyst. The conclusion is drawn that the reaction of a thiol with a disulfide, both in aqueous suspension and in dioxane, is ionic rather than radical.
X‐ray determination of crystallinity in poly(ethylene terephthalate)
Authors: Bosley D. E. 
Published: April 2003

AbstractThree recently published x‐ray methods for determining the crystallinity of poly(ethylene terephthalate) are discussed and compared with density and infrared methods. The effect of crystallite size is shown to account for most of the disagreement among the several methods. A short method of estimating crystallinity from x‐ray diffraction, suitable for counting techniques and requiring only two measurements, is presented and compared with the density method.
Master curves for some amorphous polymers
Authors: Takahashi M. , Shen M. C. , Taylor R. B. , Tobolsky A. V. 
Published: April 2003

AbstractMaster curves for polystyrene, poly(methyl acrylate), and poly(methyl methacrylate) in stress relaxation are reported. The method used to obtain a wide range in modulus is to combine torsional creep data for high modulus regions with direct stress relaxation data for low moduli. The composite curves obtained are compared with existing literature data. The master curve for polystyrene obtained by a ball indentation method is also reported. Characteristic viscoelastic parameters derived from the data are tabulated.
Rate of crosslinking of gelatin in aqueous solution
Authors: Robinson Ian D. 
Published: April 2003

AbstractThe rate of crosslinking of concentrated gelatin solutions in water has been measured by means of a gelation timer. Some effects of temperature, pH, crosslinking agent, and gelatin concentration have been measured. The crosslinking agents have varied from fast‐acting chrome alum, glutaraldehyde, and a carbodiimide to slow‐acting mucobromic acid and dialdehyde starches. Detailed crosslinking mechanisms are discussed for dimethylol urea, mucobromic acid, and several dialdehyde crosslinking agents. Some effects of urea and other additives on the dimethylol urea crosslinking rate are described.
Measurement and interpretation of nonlinear mechanical energy losses in high polymer fibers
Authors: Moseley Walter W. 
Published: April 2003

AbstractDynamic mechanical loss measurements were made on fibers at large tensile strains which caused nonlinear viscoelastic behavior. Measurements on fibers from polyethylene, polypropylene, nylon 66, nylon 4 and an experimental polymer led to seven energy loss peaks for each sample in the temperature range of 120–350°K. The peaks were evenly spaced in temperature at intervals of 30–35°K. rather than at unequal temperature intervals of approximately 100–150°K. normally observed under conditions of linear viscoelastic behavior. In every case, the array of evenly spaced peaks occurred only at temperatures below the glass transition temperature. The temperatures at the energy loss peaks were virtually independent of crystallinity and molecular orientation and were interpreted in terms of polymer molecular structure. The data could be explained only by a single mechanism, common to all polymers, which could operate in a quantized manner, e. g., diffusional motion of molecular chain segments. To account for the constant temperature spacing between peaks of a given sample, it was necessary to assume that the rate controlling step in the energy loss process is the return of a displaced segment to equilibrium. Calculations from the experimental data indicated that peaks at higher temperatures stem from displaced molecular segments which experience high potential energy barriers and which have to be excited to higher skeletal vibrational energies to overcome the barrier. Precedence for this interpretation is provided by Tanaka and Ishida, who have associated molecular vibrations with the well‐known β loss peaks in polymers.
Influence of melt spinning variables on the tensile properties of high density polyethylene fibers
Authors: Higgins T. D. , Bryant G. M. 
Published: April 2003

AbstractThe tenacity and stiffness modulus of yarns melt‐spun from high density polyethylene are functions of the sum of the logarithm of the take‐up velocity in melt drawing and the true (logarithmic) deformation imparted in the cold‐drawing process (i.e., stretching at a temperature below the polymer melting temperature). Thus, for the conditions investigated the effective melt drawing deformation is independent of the calculated velocity of the melt in the spinneret orifices. The maximum cold draw ratio is shown to be a function of the production rate, increasing to a maximum value and then decreasing as the production rate is increased. The maximum cold draw ratio at a given production rate is found to be a function of the yarn temperature and the deformation introduced in melt drawing. The tenacity and stiffness modulus of yarns melt‐spun from polypropylene may also be expressed as functions of the summation of the logarithm of the take‐up velocity of melt drawing and the true deformation imparted in cold drawing. The orientation, as measured by birefringence, of yarns spun from an experimental polyester are a function of the ratio of the take‐up velocity and the orifice velocity, wheras the same measurement of the orientation of polyethylene is a function of the extrusion velocity alone. Equations of state for the tenacity and stiffness modulus of melt‐spun polyethylene yarns were found to be of the same form as for a wet‐spun madacrylic fiber.
Analysis of the finite cone‐plate viscometer and of the finite parallel‐plate viscometer
Authors: Slattery John C. 
Published: April 2003

AbstractThe analyses for flow of a simple fluid of Noll both in the infinite cone‐plate viscometer and in the infinite parallel‐plate viscometer are shown to be consistent with the existence of a free surface in the finite instruments. Neglected in the description of the free surface are: the effect of any gradients in surface tension, the effect of the rate‐of‐deformation of the free surface upon the surface stress tensor, the effect of mass transfer at the free surface, inertial and gravitational effects in the free surface, and distortion of the free surface at solid boundaries.
Strainwork dependence of filler‐loaded vulcanizates
Authors: Payne A. R. 
Published: April 2003

AbstractThe modulus and loss angle of carbon black filler‐loaded rubbers varies with the dynamic amplitude of oscillation. The dynamic modulus change with amplitude is of a sigmoid nature. This allows the data to be reduced by a normalization technique. It is the purpose of the paper to show how the normalized data are substantially independent of the carbon black loading and of the polymer type when the normalized modulus is plotted against the energy of deformation (or strainwork).
Radiochemical yields of graft polymerization reactions of cellulose
Authors: Arthur Jett C. , Blouin Florine A. 
Published: April 2003

AbstractThe preparation of radiation‐induced graft polymers of cotton cellulose, while retaining the fibrous nature and high molecular weight of the cellulose, depended primarily on the radiochemical yields of cellulose reactions and of graft polymerization reactions. Yields of the initial major molecular changes in cellulosic polymer indicated that, in the case of scission of the molecule and carboxyl group formation, chain reactions were not initiated by radiation; however, in the case of carbonyl group formation chain reactions were initiated but quickly terminated. Generally, experimental procedures, used in graft polymerization reactions, were: (1) simultaneous irradiation reactions, that is, application of monomers or solutions of monomers to cellulose or chemically modified celluloses, then irradiation; and (2) post‐irradiation reactions, that is, irradiation of cellulose or chemically modified celluloses, then after removal from the field of radiation, contacting the irradiated cellulose with monomer. Some of the most important factors influencing the radiochemical yields of graft polymerization reactions of styrene and acrylonitrile onto cellulose were: concentration of monomer in treating solution; solvent; ratio of monomer solution to cellulose; prior chemical modification of cellulose; and absence of oxygen, particularly in post‐irradiation reactions. Experimental data were presented, and the direct and indirect effects of Co60 γ‐radiation on these reactions were discussed.
Oxygen‐transfer resins, a new type of oxidation–reduction polymers
Authors: Helfferich F. , Luten D. B. 
Published: April 2003

AbstractBifunctional cation exchangers with carboxylic and sulfonic acid groups can be oxidized with aqueous hydrogen peroxide which converts the carboxylic to percarboxylic acid groups. The oxidized resins can be used to hydroxylate compounds with olefinic double bonds to form α‐glycols. The resins thus transfer active oxygen from a peroxide to an unsaturated substrate. Oxidation and reduction of the resins is reversible.
Thermal degradation of fluorine‐containing polymers. Part I. Degradation in vacuum
Authors: Cox J. M. , Wright B. A. , Wright W. W. 
Published: April 2003

AbstractThe thermal degradation in vacuum of a number of fluorine‐containing polymers has been studied by using a weight loss technique. The relative thermal stabilities of the different polymers have been determined and where possible the overall activation energy and frequency factors for their breakdown. The methods of assessment of the weight loss results are discussed. The most stable of the polymers are those which are fully fluorinated.
Methyl α‐cyanoacrylate. II. Copolymerization studies
Authors: Kinsinger J. B. , Panchak J. R. , Kelso R. L. , Bartlett J. S. , Graham R. K. 
Published: April 2003

AbstractCopolymerization of methyl alpha;‐‐cyanoacrylate with five reference monomers gave values e = +2.1 and of log Q = 0.65, with much scatter in the latter value. Alternating copolymers are formed by copolymerization with monomers of e = −0.8 or less. Bulk copolymerization with such monomers could not be accomplished, as a rapid noncatalyzed polymerization occurred upon mixing even at 0°C. Random copolymers with methyl methacrylate could be prepared in bulk; those with ca. 10% methyl methacrylate had physical properties similar to the homopolymer of methyl α‐‐cyanoacrylate, except that the heat distortion temperature was lowered 10–15°C. The alternating copolymers were more thermally stable than the random copolymers. Glass temperature values for alternating copolymers do not appear to agree with values predicted from equations for random copolymers.
Viscosity—molecular weight relationship for masticated natural rubber
Authors: Bristow G. M. , Westall B. 
Published: April 2003

AbstractIntrinsic viscosity and osmotic molecular weight data are presented for toluene solutions of several types of natural rubber after mastication in air. For [η] < ca. 4 all these data fit the relationship, [η] = 7.11 × 10−7 M̄n1.25. At higher molecular weights deviations from this relation are found, the extent of which depend on the type of natural rubber used. These deviations are attributed to differences in initial molecular weight distribution.
Products of flash pyrolysis of phenol–formaldehyde by time‐of‐flight mass spectroscopy
Authors: Friedman Henry L. 
Published: April 2003

AbstractA sample of phenol‐formaldehyde was flash‐pyrolyzed 11 times in the reaction chamber of a time‐of‐flight mass spectrometer. Quantitative analyses were determined for pyrolysis products which were present within 10 sec. after each flash. A high degree of consistency between compositions of products from consecutive flashes resulted. The significance of the results is discussed.
Birefringence, density, and tensile characteristics of oxycelluloses
Authors: Betrabet S. M. , Munshi V. G. , Daruwalla E. H. , Jacob C. J. 
Published: April 2003

AbstractInvestigations have been carried out on the changes in the characteristics such as refractive index, density, single fiber breaking strength, and moisture regain of cotton fibers brought about as a result of oxidation with sodium metaperiodate and potassium dichromate‐oxalic acid. The study has also been extended to sodium chlorite‐treated and sodium borohydride‐reduced oxycelluloses obtained from these oxycellulose products. Results indicate that in case of sodium metaperiodate oxidation, birefringence and density first increase, reach a maximum and then decrease sharply as oxidation is continued, while breaking strength decreases in the initial stages, reaches a minimum, and then increases in the later stages. With dichromate‐oxalic acid oxidation, birefringence increases sharply during the initial stages of oxidation and after reaching a maxima, decreases as oxidation progresses, while there is a rapid increase in the values of density during the initial stages followed by a slow rise as oxidation is continued. In case of dichromate‐oxalic acid oxycelluloses, breaking strength decreases continuously with the progress of oxidation. Results are interpreted in terms of changes in gross morphology and fine structure of cotton as a result of oxidation and subsequent chlorite and borohydride treatments.
Rapid method for the determination of molecular weight distribution in high polymers: A thermal gradient‐turbidity technique
Authors: Gamble Leon W. , Wipke W. Todd , Lane Trent 
Published: April 2003

AbstractA rapid method for determining the molecular weight distribution of polymers has been the aim of polymer chemists for a long time. The method presented here requires less than two hours, including dissolution of the polymer. It is an extension of a photoelectric turbidimetric technique presented by Taylor and Tung in 1961. The equipment has been completely redesigned and presently consists of a copper block containing a turbidity cell, optical system and attendant electronic circuitry for measuring relative changes in turbidity of polymer solutions as a function of temperature. An X–Y recorder is used to plot turbidity versus temperature. A parameter determined from the plot is correlated with a measure of molecular weight distribution determined on known samples for each type polymer by another means. Based on this correlation unknown samples may be analyzed. The instrument is easy to operate and has shown excellent stability over a two year period. Polymers studied by this technique include ethylene‐propylene copolymer (EPR), polypropylene, polyethylene, and butyl, however, the only results to be reported here are those on ethylene‐propylene copolymer.
Single‐point determination of intrinsic viscosity
Authors: Shroff Ramesh N. 
Published: April 2003

AbstractLimitations on the use of the equations [η] = {2(ηsp − ln ηre1)}1/2/c and [η] = (ηsp + 3ln ηre1)/4c in determining intrinsic viscosity, [η], by a single point method have been pointed out. Inclusion of higher order terms in the series expansion for ln ηre1 introduces an additional term in the above equations which is negligible when the value of Huggins' constant, k′, is in the vicinity of 0.3–0.4. More accurate values for intrinsic viscosity calculated by a single point method can be obtained using these modified equations provided k′ can be estimated.
Thermogravimetric study of some new transition metal–schiff base coordination polymers
Authors: Horowitz Emanuel , Tryon Max , Christensen Richard G. , Perros Theodore P. 
Published: April 2003

AbstractA condensation reaction between 5‐amino‐8‐hydroxyquinoline and terephthalaldehyde yielded a bis‐bifunctional Schiff base ligand, 5,′5‐[p‐phenylene‐bis(methylidynenitrilo)] di‐8‐quinolinol, which was used to produce coordination polymers containing Mn(II), Co(II), Ni(II), Cu(II), or Zn(II) in the form of insoluble powders. The thermal stabilities of these polymers were evaluated in vacuum over the temperature range of 25–700°C. by using a newly constructed thermobalance having improved sensitivity. The results relate the decomposition of the polymers to the metal in the backbone as well as to the organic ligand to which the metal is coordinated. Some discussion is devoted to the possible modes of decomposition of these polymers.
Semipermeable membranes of cellulose acetate for desalination in the process of reverse osmosis. III. Bound water relationships
Authors: Vincent Arthur L. , Barsh Max K. , Kesting Robert E. 
Published: April 2003

AbstractThe mechanism by which water and dissolved salts permeate selectively through membranes has been investigated. It has been demonstrated that the predominant mechanism of permeation involves the interaction of the various species with specific sites and their associated bound water molecules. The extent of the bound water held by the cellulosic membranes of interest has been determined. Correlation has been found between the permeation characteristics demonstrated by membranes at various steps in their preparation and its bound water content. The mechanism of rejection of salts has been shown to be related to the relative inability of their ions to become solvated by bound water. A model has been hypothesized which correctly describes the behavior of the desalination membrane with reference to water and soluble inorganic salts.
Kinetics of vinyl polymerization initiated by ceric ion in aqueous solution
Authors: Ananthanarayanan V. S. , Santappa M. 
Published: April 2003

AbstractA systematic kinetic study of the thermal polymerization of methyl methacrylate, methyl acrylate, and acrylonitrile initiated by ceric ion in aqueous perchloric, nitric, and sulfuric acid solutions, has been made. The polymerization experiments were conducted in the dark at 35°C. under conditions of negligible oxidation of water by ceric ion. The polymerization was found to proceed without an induction period, and the steady‐state rate was attained in a short time. The rate of monomer disappearance (followed by gravimetry) was found to bear a square dependence on monomer concentration and is independent of both the ceric and hydrogen ion concentrations. The rate of ceric disappearance (followed by titrimetry or spectrophotometry) was found to be directly proportional to the ceric, monomer, and hydrogen ion concentrations. The chain lengths of the polymers (determined viscometrically) were directly proportional to the monomer concentration and inversely to the ceric and hydrogen ion concentrations. Initially added cerous ion had negligible effect on the rates. Increase in ionic strength caused a slight increase in the rates. From experiments conducted at different temperatures, the activation energies for the various processes in the reaction were calculated. Most of the experimental results were suitably explained by a kinetic scheme involving initiation and termination by ceric ion in the unhydrolyzed Ce4+ form.
Characterization studies for polyethylene formed by Co60 γ‐radiation under constant conditions in a nonflow system
Authors: Colombo P. , Fontana J. , Kukacka L. E. , Steinberg M. 
Published: April 2003

AbstractSeveral properties of polyethylene, synthesized by Co60 gamma radiation have been investigated. The polymerization reactions were carried out in static experiments over a wide range of conditions. Measurements include molecular weight, molecular weight distribution, density, methyl group content, crystalline melting point, and melt index. The density of polyethylene formed at 20°C. was found to be 0.94 g./cc. This value appears to be independent of pressure from 170 to 1700 atm. and radiation intensity from 0.58 × 105 to 4.7 × 105 rads./hr. Increasing temperature results in increasing methyl group content and a decrease in density to 0.91 g./cc. at 200°C. The polymers formed, over the entire range of experimental conditions, were completely soluble in o‐dichlorobenzene at 135°C. Intrinsic viscosities were determined and their dependence on temperature, pressure, intensity, and radiation dose are shown. An attempt was made to correlate melt index to molecular weight and molecular weight distribution.
Effect of volatilization of stabilizers and oxidation products on polypropylene lifetimes
Authors: Blumberg M. , Boss C. R. , Chien J. C. W. 
Published: April 2003

AbstractThree methods of measuring thermal oxidative stability of polypropylene have been compared. The oxygen absorption and the sealed tube tests give comparable results. The polymer lifetimes in circulating oven‐aging tests differ significantly from those obtained by the first two methods. The oven‐aging lifetime is aparently influenced to a large extent by the volatilization of the added stabilizer and of the oxidation products, the former decreases whereas the latter increases the polymer lifetime. The optimum composition of a synergistic stabilizer system was found to vary with the test method.
Estimation of molecular weights of epichlorohydrin–bisphenol a polymers by gel permeation chromatography
Authors: Edwards G. D. 
Published: April 2003

AbstractDuring a program to evaluate the gel permeation chromatography (GPC) technique for measuring the molecular size distribution of polymers, three experimental epichlorohydrin–bisphenol A polymers were sent to Waters Associates for analysis with the commercially available instrument. The resulting distribution curves were used to calculate weight‐average and number‐average chain lengths of the samples. These values were found to give good straight‐line correlations with weight‐average and number‐average molecular weights measured by absolute methods. Thus the GPC method gives meaningful information about the molecular size distribution of polymers which can be used to obtain rapid estimates of molecular weight.