bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and stress‐strain properties of aba block copolymers of α‐methylstyrene and butadiene
Authors: Cunningham Robert E. 
Published: April 2003

AbstractABA‐type “tapered” block copolymers of α‐methylstyrene (monomer A) and butadiene were prepared using four commercially available dilithio initiators. Polymerizations were run at 25°C in benzene solvent, or at 40°C with butadiene dissolved in neat α‐methylstyrene. Although α‐methylstyrene has a rather low ceiling temperature, triblock copolymers could be made at these temperatures by using α‐methylstyrene concentrations well in excess of the [M]evalues at the respective temperatures. Its concentration was such that molecular weights of at least 15,000–20,000 for the A blocks could be attained. The course of the copolymerization at 40°C was followed, showing that copolymers containing about 40% α‐methylstyrene could be formed in 4–8 hr, depending on the initiator used. They showed the usual behavior of triblock thermoplastic elastomers, with tensile strengths > 3000 lb/in.2at 24°C. However, because of the highTgof poly(α‐methylstyrene) (172°C), they also had tensiles of several hundred lb/in.2at 100°C, unlike comparable polymers with polystyrene end blocks, which have practically no strength at this temperature. Microstructures of polybutadienes made with these initiators are also given.
Expansion of aromatic heterocyclic polymers in salt solution
Authors: Hanley Thomas R. , Helminiak Thaddeus E. , Benner Charles L. 
Published: April 2003

AbstractThe addition of lithium chloride to solutions of poly(5,5′‐bibenzimidazole‐2,2′‐diyl‐1,3‐phenylene) (PBI) and N,N‐dimethylacetamide (DMAC) resulted in the elongation of the PBI molecule in solution. This elongation is due to the association of lithium and/or chloride ions in the region of the nitrogen atoms on the polymer chain. The presence of these ions expands the polymer chain by means of electrostatic repulsion. This effect was reflected in the results of the conductivity and viscosity studies. In general, LiCl can be used for both increased solubility and increased viscosity for this system. A ratio of 0.125 g LiCl/gram PBI was determined to be the optimum amount of LiCl to be added. This amount corresponds to mole of LiCl for every mole of PBI repeat unit. The PBI molecule was determined to have entanglements in concentrated solution at every 27 or 28 molecules along the polymer chain. This length between the entanglements is very low in comparison to other polymers indicating a strongly matrixed system. The chain length between entanglements was approximately the same for both PBI‐DMAC and PBI‐LiCl solutions.
Graft copolymerization onto starch. IV. Grafting of methyl methacrylate to granular native potato starch by manganic pyrophosphate initiation
Authors: Mehrotra Rakesh , Rånby Bengt 
Published: April 2003

AbstractA study has been made of graft copolymerization of methyl methacrylate onto native potato starch in aqueous slurry at 30°C. As Mn3+ concentration was increased from 0.15 X 10‐3M to 1.0 X 10‐3M, conversion of monomer to polymer and add‐on of polymer to starch increased and frequency of grafts (anhydroglucose units per grafted chain) decreased sharply. The average molecular weights of the PMMA grafts also decreased in this range. At Mn3+ concentrations from 1.0 X 10‐3M to 3.0 X 10‐3M, only minor changes in grafting parameters were observed. When the amount of starch charged per batch was increased threefold, the add‐on decreased sharply, the molecular weight increased slightly, and the conversion of MMA monomer to polymer remained almost constant. The increase in frequency of grafts (AGU/chain) was almost directly proportional to the increase in the amount of starch charged. In all cases the average molecular weights of grafts were of the order of 106 and the grafting efficiencies high, normally greater than 85%. These results were compared with those previously obtained for grafting of acrylonitrile onto starch. They were interpreted in terms of initial (Mn3+)/(AGU) ratio, total number of radicals initiating grafting, and compatibility of methyl methacrylate monomer with poly(methyl methacrylate) chains.
Relaxation properties of styrene–butadiene block copolymers. A comparative study of thermally stimulated currents and thermoluminescence
Authors: Linkens A. , Vanderschueren J. 
Published: April 2003

AbstractThe thermoluminescence (TL) and thermally stimulated current (TSC) curves observed in styrene—butadiene block copolymers, undoped and doped with different dyes, have been compared in order to test to what extent the thermoluminescence phenomenon can be correlated with intrinsic relaxation properties of the macromolecular chains. Generally, good agreement has been found between the two types of curves. However, the observance of a significant shifting of TL peaks as a function of the nature of the added dye shows that strict correspondence between the kinetics of the two phenomena is unlikely. Consequently, it seems actually dangerous to deduce the characteristic relaxation parameters of the polymer from TL curves.
On semicontinuous polymerization of vinyl acetate
Authors: Bataille P. , Van B. T. , Pham Q. B. 
Published: April 2003

AbstractA semicontinuous emulsion process was used to polymerize vinyl acetate. The parameters studied were the rate of addition of the various ingredients. The polymerization evolution was followed as samples were taken at regular intervals. These emulsion samples were analyzed for monomer conversion, rate of polymerization as well as for the size and the size distribution of the particles. The molecular weight and molecular weight distribution were obtained by gel permeation chromatography (GPC). Our study showed that the total surface of the particles is an important factor, that the reaction mechanism follows Krackeler's and Wessling's theory, and that the Smith‐Ewart ideal case does not apply here.
Swelling and diffusion properties from elongation of two‐phase polymer membranes
Authors: Penati Amabile , Pegoraro Mario 
Published: April 2003

AbstractExperimental results were presented dealing with the water permeance and diffusion rate in two‐phase membranes consisting of hydrophilic domains of polyacrylic acid chemically bound by grafting to hydrophobic matrices: these are either rigid crystalline (polypropylene) or elastomeric amorphous (EPDM). Permeance is higher in rigid matrices: this is attributed to the wide net of microfractures originated from swelling of the hydrophilic domains whose formation is only possible in the case of a rigid matrix. A calculation method was proposed, which allows the evaluation of the apparent diffusion coefficient of both water and salt, starting from dilatometric measurements of membranes contacted with water and salt water. The apparent diffusion coefficient of water in rigid membranes is of the order of 10‐8 cm2 sec‐1, whereas in elastomeric membranes it appeared about 100 times lower. The apparent diffusion coefficient of salt is of the order of 10‐12 cm2 sec‐1 for both rigid‐matrix and elastomeric membranes when previously swollen.
Studies in chemically modified celluloses. XI. Hypochlorite oxidation of cellulose in the presence of chromium oxide
Authors: Shenai V. A. , Patil A. S. 
Published: April 2003

AbstractIn the dyeing of mineral Khaki on cotton fabrics, which are mainly used for military uniforms in India, a mixture of Fe2O3 and Cr2O3 is deposited in the fabric. When these garments are laundered using bleaching powder solution, the chromium oxide is likely to accelerate the oxidation of cotton cellulose. This aspect has been studied by oxidizing cotton yarn with sodium hypochlorite solution in the presence of chromium oxide, varying the chromium content, the pH of the oxidizing medium, and the concentration of the oxidizing agent. The properties of these chemically modified celluloses indicate that chromium oxide does accelerate the hypochlorite oxidation of cellulose and that the maximum extent of acceleration takes place when the oxidation is carried out at pH 7. The oxidized products were further modified separately by treatment with chlorous acid and sodium borohydride, and the effects of these agents on the properties of the oxidized products were studied.
Diffusion of gases through polyurethane block polymers
Authors: McBride John S. , Massaro Thomas A. , Cooper Stuart L. 
Published: April 2003

AbstractThe diffusivities of simple gases through a series of polyurethane block copolymers of differing aromatic urethane content and type of soft segment were measured using a quadrapole mass spectrometer as a detecting device. Although an Arrhenius expression generally described the temperature dependence of diffusion in this system, a discontinuity was observed in the Arrhenius plots for some materials, and the discontinuity was found to be related to the onset of the glass transition in the hard domains. Increasing the hard segment content of the materials decreased the diffusivity due to the increase in the activation energy of diffusion. Increasing the soft segment length brought about a decrease in the activation energy with an increase in diffusivity. Polyster urethanes had lower activation energies for diffusion than polyether urethanes of similar hard segment composition. Finally, as the penetrant diameter was increased, a decrease in the diffusivity and an increase in the activation energy was noted.
Structure of cellulose II
Authors: Hunter Regulus E. , Dweltz Neville E. 
Published: April 2003

AbstractA reduced unit cell derived from the presently accepted unit cell and a new parallel chain arrangement is proposed for cellulose II (regenerated cellulose). In the present structure, all the cellulose chains are identical and there is only one chain passing through each unit cell. The intensity data for all reflections with d spacings greater than 1.747 Å have been calculated and were found to be in good agreement with the corresponding observed x‐ray intensities. The calculated agreement factor is R = 0.50. Two intrachain hydrogen bonds parallel to the fiber axis and one interchain hydrogen bond perpendicular to the fiber axis stabilize the structure. The hydrogen bonding network is in fair agreement with infrared dichroic data, and the chain arrangement conforms to stereo‐chemical criteria. No short contacts are observed. The parallel chain is also compatible with the structure of cellotetraose and the accepted hypothesis of cellulose biosynthesis, as well as the latest parallel structure for Valonia.
Effects of density and structure on load bearing and permeability characteristics of a family of shock mitigating phenolic foams
Authors: Mendelsohn M. A. , Meier J. F. , Rudd G. E. , Rosenblatt G. B. 
Published: April 2003

AbstractThe effects of reaction rate and density on the properties of the phenolic foam described in the first paper were studied. Process and formulation variables were examined through altering the basic chemical composition described below, in which all parts are by weight; phenolic resin two component intermediate, 200 parts; hydrophilic surfactant, 0.25 parts; lipophilic surfactant, 0.50 parts; fluorocarbon blowing agent, 12 parts; 47.5 wt % sulfuric acid, 25 parts; and 80 wt % phosphoric acid, 15 parts. Compressive stress values at 20% deflection were utilized for comparing the effects of the studied parameters on the load bearing cabability of the foam. Pressure drop of air flowing through the foam was employed as a measure of the permeability or breathability. Permeability load bearing functions were identified as a potential means for optimizing the relationship between breathability and compression‐deflection characteristics. The overall effects of cell structure on the relationship between load bearing and density have been related in a qualitative manner.
The effects of weathering and atmospheric pollutants on cotton fabric and cotton fabric treated with selected flame retardants. II. Spectroscopic studies
Authors: Slaten B. L. , Smith B. F. 
Published: April 2003

AbstractSpectroscopic studies of weathered flame retardant cotton fabrics were conducted. The weathering conditions included combined and independent exposure to xenon arc light and low concentrations of SO2, NO2, and O3 gases. Multiple internal reflectance infrared analysis of weathered Pyrovatex 3805‐treated fabric showed that the finish removed after 150 hr of weathering exposure had the same structure as the original finish. Interferometer spectra of Pyrovatex 3805 and THPOH‐NH3 finishes on the fabric indicated no significant changes in the structure for both finishes after exposure to the various weathering conditions.
Reaction variables and a proposed mechanism of open‐pore urea/formaldehyde structure formation
Authors: Salyer Ival O. , Usmani Arthur M. 
Published: April 2003

AbstractFormation of open‐pore urea/formaldehyde structures from nonetherified urea/formaldehyde resins involves reaction of one or more methylol groups with other methylol or amino groups. The structure formation proceeds through particle formation and growth until all the resin is consumed. A strong acid is preferred for achieving a porous structure in urea/formaldehyde resins; weakly ionized acids produce structures with low yield. Colloidal instability is an asset in porous structure formation. An 80:20 polyethylene oxide/polypropylene oxide block copolymer of approximate molecular weight 8500 has been found to be an entropic‐type destabilizer in the formation of porous structures.
Aqueous gel permeation chromatography: The effect of solvent ionic strength
Authors: Cooper Anthony R. , Matzinger David P. 
Published: April 2003

AbstractPorous glass packing materials have been used for gel permeation chromatography using an aqueous phosphate buffer. Elution volumes were determined for polystyrene sulfonates, dextrans, and small neutral and charged molecules at three different ionic strengths, viz., 0.01M, 0.1M, and 1.0M phosphate, pH 7.0. The pore diameters of the glasses studied were 75, 240, 700, and 2000 Å. Elution volumes of nonionic species were unaffected by changing the solvent ionic strength. Elution volumes of charged species were markedly affected by the ionic strength of the solvent. This was attributed to a combination of decreased polymer dimensions and decreased ionic exclusion with increasing buffer concentration. The use of low ionic strength solvents may be exploited to tailor the separating range for polyelectrolytes with porous glass packings. This is particularly useful in the low molecular weight range where the lowest pore size available is 75 Å.
The effect of low molecular weight additives on the properties of aromatic polyamide membranes
Authors: Kraus M. A. , Nemas M. , Frommer M. A. 
Published: April 2003

AbstractSalts contained in aromatic polyamide solutions were found to have a considerable effect on the performance and structure of reverse osmosis membrannes cast from these solutions. As in cellulose acetate membranes, certain salts greatly increase membrane fluxes without a detrimental effect on rejection. Highly dissociated salts such as LiClO4 or Mg(ClO4)2 exert a stronger influence than the commonly used LiCl. With mixtures of different salts, stronger effects may be obtained than with a single additive. Many experimental facts indicate that the “salt effect” in aromatic polyamide membranes is due to a general effect on solvent activity and thus on the kinetics and equilibria associated with evaporation and coagulation process.
Process and fiber spinning studies for the cellulose/paraformaldehyde/dimethyl sulfoxide system
Authors: Hammer R. B. , O'Shaughnessy M. E. , Strauch E. R. , Turbak A. F. 
Published: April 2003

AbstractA cellulose pulp of about 550 D.P. was readily dissolved in a combination of (CH2O)x/DMSO to afford an initial 6/6/88 cellulose/(CH2O)x/DMSO composition solution. The concentration of formaldehyde was found to be a function of solution heating time and temperature. The solutions were microscopically free of gels and undissolved cellulose fibers. Cellulosic articles such as fibers and films are easily regenerated from these cellulose solutions in the presence of coagulants such as methanol or water. Fibers with high wet modulus, intermediate tenacity, and low elongations were produced from these regenerations systems. Fibers have been spun with conditioned and wet tenacities as high as 2.9 and 2.1 g/d, respectively, with wet modulus (at 5% elongation) as high as 1.3 g/d and solubility in 6.5% NaOH in the low range of 3.0%–15%. In many respects, these fibers are comparable to those produced in the viscose process. However, the low elongations of these fibers probably would not permit normal textile processing. The cellulose/(CH2O)x/DMSO solutions were modified with compounds containing reactive NH functional groups which are known to react with excess formaldehyde to yield the corresponding N‐methylol derivatives. However, the resulting fiber physical properties were not significantly improved compared to those obtained from unmodified cellulose solutions. Addition of acrylic acid derivatives such as methyl acrylate, butyl methacrylate, or acrylonitrile to the cellulose solutions did not result in the formation of the expected 1,4‐type adducts.
Chemical transformations of polymers. XI. Mercuration of polystyrene
Authors: Štamberg J. , Petrus V. , Gregor H. P. 
Published: April 2003

AbstractThe mercuration of soluble polystyrene was investigated, and it was found that an addition of perchoric acid to the reaction mixture significantly accelerated the polymer transformation. The mercuration proceeds as a polymer analogous reaction, i.e., without any change in the degree of the polymerization. The mercurated product could be converted back to the original polystyrene by hydrolysis or to the corresponding bromopolystyrene by bromination. Ultracentrifuge measurements show that even at low conversion rates all macromolecules were mercurated and unreacted polystyrene could not be identified in the product. Calorimetry indicated the presence of styrene–mercuric acetate blocks in copolymers with high mercury contents.
Cationic latex interaction with pulp fibers. II. Modification of sheet properties by styrene butadiene latex with quaternized amino groups
Authors: Alince B. 
Published: April 2003

AbstractUnbeaten kraft fibers covered with experimental cationic latexes were formed into sheets in which direct fiber‐fiber bonds are replaced by polymeric bonds. The effect on sheet properties—breaking length, elongation at break, folding endurance, opacity, and light scattering—was evaluated as a function of latex composition. The composition was altered by either the ratios of styrene to butadiene in the polymer or by mixing soft film‐forming and hard nonfilming latex. It is shown that, regardless of latex composition and mechanical properties of the polymeric film, all the latexes can modify the sheet properties to a similar extent, providing that the sheets are heated above the polymer's glass transition temperature. An improvement of tensile strength is accompanied by increased elongation. As a probable mechanism of reinforcement, it is suggested that the polymer acts as a filler of the fiber's surface irregularities, thus providing a larger contact area between fibers and an improved stress transfer between them.
Photolysis of poly(p‐tert‐‐butylstyrene)
Authors: Weir N. A. , Milkie T. H. , Nicholas D. 
Published: April 2003

AbstractThe photodegradation of thin films of poly(p‐tert‐butylstyrene) with 254‐nm radiation under high vacuum has been studied. The principal gaseous product is hydrogen, but smaller amounts (in decreasing order of yield) of methane, ethane, and isobutane are also formed, indicating that fission of bonds in the tert‐butyl group is also involved. Ultraviolet and visible spectra of degraded films indicate the presence of unsaturated groups, initial rates of formation of these being considerably higher than those for polystyrene films. Solubility data indicate that crosslinking apparently occurs less readily than in the case of polystyrene, and this is interpreted in terms of the enhanced stability (due to the +I effect of the tert‐butyl group) of the radicals formed by chain scission and also of the inhibiting steric effect of the tert‐butyl group, particularly on crosslinking reactions involving the benzene rings. Quantum yields for the gaseous products and for chain scission and crosslinking were determined, and the mechanism of the various reactions are discussed.
Thermal ignition phenomena in chain‐addition copolymerizations
Authors: Sebastian D. H. , Biesenberger J. A. 
Published: April 2003

AbstractThermal ignition theory has been extended to include free‐radical copolymerizations resulting in dimensionless criteria for runaway and ignition. These criteria were verified by computer simulation and preliminary experimentation. Approximate, but greatly simplified, material and energy balances describing nonisothermal copolymerizations were developed which are similar in form to those describing nonisothermal homopolymerizations. Regions of close agreement, as well as disagreement, between conversion and temperature histories from these approximations and those from the exact balances are described.
Environmental influence on the fracture strength of coated glass fibers
Authors: Schonhorn H. 
Published: April 2003

AbstractThe effect of the environment on the fracture strength of coated glass fibers is described. Simple expressions relating the thermodynamic work of adhesion, in the presence and absence of stress to the permanence of the composite, are derived. The need for interactions other than dispersion‐type interactions between silica and coating systems is emphasized. A prognosis is offered for achieving a permanently bonded structure, provided that reasonable wetting can be facilitated at the oxide–coating interface or that there is generated a strongly bound species to the silica, shifting the potential locus of failure.
Wear mechanisms for ultrahigh molecular weight polyethylene in the total hip prosthesis
Authors: Nusbaum Henry J. , Rose Robert M. , Paul Igor L. , Crugnola Aldo M. , Radin Eric L. 
Published: April 2003

AbstractUltrahigh molecular weight polyethylene is now extensively used in total joint replacements, and there is ample clinical evidence that this material wears at a significant rate in such applications. Six commercially available total hip replacements were subjected to an accurate simulation of clinical mechanical and chemical conditions, and the wear behavior of the polyethylene components was analyzed by friction coefficient measurements and scanning electron micrography of the wear surfaces. The results indicate that all of the proposed wear mechanisms excepting adhesive and abrasive wear may be eliminated. It is highly likely that abrasion fatigue and related phenomena are central to the wear process in many prostheses, but the wear process may be ultimately determined in many cases by the type of defects present in the manufactured material.