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  • Polymer and Materials Science  (112,478)
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  • 1
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We are studying the use of PS-PMMA block copolymer systems to improve the mechanical properties of immiscible PS-PVC blends. For a particular PS-PMMA block copolymer system, we found that effective compatibilization occurs at compatibilizer levels of 1-5 wt % in a 50/50 PS-PVC blend. In the samples, storage and stress relaxation moduli were at least midway between those of pure PS and PVC. On the other hand, the equivalent uncompatibilized blend exhibited storage and stress relaxation moduli that are much lower than those of the soft PVC component. Stress relaxation moduli of pure PS remained fairly constant with time, while a 25% drop was observed for pure PVC after 120 sec. Also after 120 s, stress relaxation moduli for the uncompatibilized blend exhibited a 20% drop, while a less than 10% drop was observed for the compatibilized PS-PVC blends.
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  • 2
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The key to preparation of commercially useful blends based on immiscible polymer pairs is compatibilization. Advances over the past ten years have considerably enhanced the understanding of this phenomenon. The selection of an appropriate compatibilizer and the processing technique to enhance the compatibilization is quite complex. The selection of the compatibilizer is aided by the application of the principles of miscibility and of organic interactions. It may be advantageous to prepare the compatibilizer in situ. Chemical modification of the base components to enhance interactions between the components is an important option. Processing and rheological effects must also be taken into account. The combination of the compatibilizer and the processing conditions must yield a morphology that will preserve the desired properties of each component while minimizing the undesirable properties. This morphology must be reproducible and stable in the ultimate product and through subsequent recycling processes.
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  • 3
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Extrudate swell studies of a high-density polyethylene (HDPE) melt have been undertaken in flows through slit and capillary dies with the purpose of finding out the effect of die-length/diameter (gap) (L/D or L/2H) ratio on the viscoelastic behavior. Numerical solutions have been obtained by using the finite element method (FEM) and an integral constitutive equation of the K-BKZ type with a spectrum of relaxation times. The material parameters have been obtained by fitting experimental viscosity and normal stress data for the melt as measured in shear, and elongational viscosity data available in the literature. Different L/D (L/2H) ratios have been considered ranging from very short to infinitely long dies. The numerical simulations reveal that as the flow rate increases, viscoelastic effects exhibited by the HDPE melt become important and manifest themselves in an enhanced swelling behavior after the die exit, while small, Newtonian-like vortices exist in the contraction before entry to the die. Elastic recovery is also captured in an enhanced extrudate swell, which is always higher at the same apparent shear rate for the capillary than the slit dies and decreases drastically as the L/D (L/2H) ratio increases, reaching asymptotic values for very long dies. Such behavior is in agreement with experimental findings from flows through slit and capillary dies and in sharp contrast with purely viscous simulations which cannot predict such strong viscoelastic phenomena associated with the memory of the polymer melt. © 1993 John Wiley & Sons, Inc.
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  • 4
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 12 (1993), S. 313-324 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 12 (1993), S. 325-325 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 12 (1993), S. 327-327 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: As large components of fiber reinforced composite materials are being more frequently produced by Resin Transfer Molding (RTM), a computer simulation of the injection process can help the mold designer to accomplish three important tasks: (1) to ensure a complete filling of the mold through adequate positioning of the injection ports and of the air vents; (2) to verify the integrity of the mold during the filling process through knowledge of the pressure distribution; and (3) to optimize the production cycle using information about the filling time. The resin impregnation is usually modeled as a flow through a porous medium. It is governed by Darcy's law, which states that the flow rate is proportional to the pressure gradient. In our model, Darcy equation is solved at each time step inside the saturated part of the mold using nonconforming finite elements. This method was chosen because the approximated flow rates, contrary to conforming finite elements, satisfy locally the important physical condition of resin conservation across inter-element boundaries. This permits simplification of the numerical procedure. It is no longer necessary to resort to a control volume approach to move the flow front forward. The resin pressure distribution and the resin front positions are obtained by the computer simulation and calculated results for selected mold geometries are compared with experimental observations. Molds with inserts, multiple injection ports, and the case of anisotropic preforms can be analyzed by the computer program. © 1993 by John Wiley & Sons, Inc.
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  • 8
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Research in understanding the mechanisms behind driving forces in the fully filled nonintermeshing twin screw extruder concentrated on experimental analysis of the relation between stagger, screw speed, and cross-channel flow due to measured pressure differential in the nip region. A new measure of the pressure driving force was also sought out, to correlate new data to previous findings from visual studies. The first part of the study was to obtain the values for the dynamic pressure on both sides of the nip region. Further refinements to the equipment used in previous studies allowed closer placement of the transducers in the nip region. After the data were stored, analysis started by determining the δp values from the trace of the pressure differential. By plotting these values, we obtain a highly repeatable curve confirming that the greatest pressure flow occurs at small staggers. A simple 2-D model for pressure flow in the nip region was used to estimate the effect of the cross-channel pressure differential. Values for the cross-channel pressure flow were calculated and compared with the drag flow and found to be significant. © 1993 by John Wiley & Sons, Inc.
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  • 9
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The Intelligent Processing of Materials (IMP) concept has been applied to the calendering process with the goal of improving shape quality and process efficiency. All four basic features of the IPM, including modeling, data processing, sensing, and controlling, are considered. In the process modeling, bending and thermal models are developed. With these models, the relationship between the process parameters and quality of the calendered sheets has been established. A material data bank has been established to couple with the process modeling and real-time sensing data. In sensing, ultrasonic and temperature sensors have been implemented to measure critical quality and process parameters in situ. The sensing data have been used not only to verify the modeling prediction but also to establish information needed to diagnose the causes of the layflat problem. Based on the model prediction as well as sensing information, a better control system to alleviate layflatness problems has been developed. Finally, a control strategy for future improvement of the calendering system is proposed. © 1993 by John Wiley & Sons, Inc.
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  • 10
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The present article summarizes the author's recent work on the computer-based molecular modeling of polysilanes [-SiR2-]. First, conformational energies were calculated by molecular mechanics on model compounds for poly(dimethylsilane) (PDMS), poly(diethylsilane) (PDES), and poly(di-n-hexylsilane) (PDHS). Discrepancies in conformational preferences between calculated and experimental results are attributed to factors not accounted for in these calculations, such as electronic stabilization and packing forces. Second, molecular dynamics simulations carried out on a model compound for PDHS suggest the presence of an abrupt “gas phase” thermochromic transition, analogous to the abrupt thermochromic transitions observed for PDHS both in solution and in the solid state. Third, we develop a methodology for testing Schweizer's theory of polysilane thermochromism based on the existence of a unique polymer-solvent conformation-dependent stabilization energy present in conjugated chains. In his treatment of the polysilanes, Schweizer adopted reasonable estimated values for this stabilization energy term VD. Presented here is a derivation of an analytical expression for VD based on a first-principles approach. © 1993 by John Wiley & Sons, Inc.
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  • 11
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The polydispersity index (PI) of polypropylene (PP) obtained from plotting the crossover point of shear storage modulus (G′) and loss modulus (G″) was comparable to that using gel permeation chromatography (GPC). The precise PI determination was dependent upon the material properties of PP and rheological measurement technique. The effect of testing percent strain on PI was determined over a wide range of melt flow rate (MFR). The employed percent strain could affect PI of this percent strain was not independent of the frequency at the crossover frequency of the resin. To measure PI precisely, a 5% strain was recommended for MFR ≥ 30, while a 15% strain was suitable for MFR < 30. © 1993 by John Wiley & Sons, Inc.
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  • 12
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: To provide a computer assisted system in finding optimum conditions for injection molding operations, an Expert System based on Artificial Intelligence (AI) technique and knowledge or “know-how” from many skilled injection molding operators has been developed. For the construction of this Expert System, we have originally applied a new method of “Multi-dimensional Matrix” that represents the relationship between the parameters of each molding condition and expert's knowledge. In this article we describe an outline of the system and the process of converting expert knowledge into AI rules, and demonstrate some molded samples obtained using this Expert System. © 1993 by John Wiley & Sons, Inc.
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  • 13
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 12 (1993), S. 419-428 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: PLASSEX is a forward-chaining rule-based expert system for plastic selection written in CParaOPS5. This system prompts the user for desired properties, and lists all plastics suitable for a particular application. At present, PLASSEX has 393 plastics in the data base and considers up to 39 polymer properties in order to select the right plastic. More properties can be added to the system with some understanding of the code. This system also provides the user with a help facility. PLASSEX has a number of other features; for instance it gives the user an opportunity to modify any property in case the system fails to come up with a suitable plastic the first time. © 1993 by John Wiley & Sons, Inc.
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  • 14
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 14 (1995), S. 253-259 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 15
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Process developments in reactive extrusion or reactive compounding are largely carried out in closely intermeshing corotating twin-screw extruders. The aim of this article is to present an analytical process model for this reactor type in order to facilitate the design of screw geometry and the settings of process parameters. Taking simultaneously into account aspects of flow behavior, heat transfer, thermodynamics, physics, and chemistry, a powerful mathematical model has been developed which was compared with practical results (e.g., residence time, pressure buildup, drive energy, bulk temperature, and conversion) on lab and production scale machines. The experiments were mostly carried out for the anionic bulk polymerizations of nylon 6 and polystyrene. Furthermore the reactive blending of nylon 6 and polyethyleneterephthalate was examined. Based on these chemical systems the practical use of computer-aided process design will be discussed. © 1995 John Wiley & Sons, Inc.
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  • 16
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: For design, optimization, and process-engineering applications of mold-cooling computer-aided engineering (CAE) technology, it is important that the software is sensitive to changes in cooling channel design for different materials and process conditions. In the present work, an attempt has been made to perform a detailed and rigorous verification to check for these design sensitivities from the CAE analysis. For four design and polymer material combinations, both molding and simulation trials were performed. C-COOL™ v. 3.0 mold cooling simulation software was used for the simulation trials. For each of these trials, measurements were taken for part planar-surface temperature distributions using infrared thermography, and for mold-wall temperatures at specific locations in the cavity using thermocouples. These experimental data have been compared with the predicted values and a favorable agreement has been observed for sensitivities most critical for design purposes. © 1996 John Wiley & Sons, Inc.
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  • 17
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In the accompanying article, Part I, we have described the basic mechanism of chaotic mixings due to a new “Chaos Screw” in single-screw extrusion processes, and presented experimental evidence of the chaotic mixing in a single-screw extruder with a typical Chaos Screw installed. The present article, Part II, will be focused on the numerical investigations of the chaotic flows via the Chaos Screw in a single-screw extruder. The three-dimensional velocity fields in both the no-barrier and barrier regions were separately calculated via a finite element analysis of the quasi-three-dimensional flow in each region, and were subsequently used in the numerical simulations of chaotic flow behaviors. Extensive numerical simulation results will be presented in terms of particle trajectories, Poincaré sections, and mixing patterns for several dimensionless parameters. It was found that invariant manifolds obtained by numerical simulations were in good agreement with those from experiments. © 1996 John Wiley & Sons, Inc.
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  • 18
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 15 (1996), S. 111-111 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 19
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Moisture transmission can be a factor in the selection of materials for load-bearing structural composites. This article considers the methods currently available for measuring the permeability to moisture of membranes, and their applicability to thick laminates. It summarizes the experimental results available in the literature, and discusses the available means of reducing moisture permeability without resorting to metallic barrier films. New experimental results are presented, comparing the three main categories of thermosetting laminating resins (epoxy, polyester, and vinyl ester) and two moisture barrier coatings. The vinyl ester resin showed the lowest permeability. Both barrier coatings reduced the water transmission rates, although their robustness and long-term adhesion to the substrates have yet to be evaluated. © 1996 John Wiley & Sons, Inc.
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  • 20
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 15 (1996), S. 255-264 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 21
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The phase morphology of injection molded blends of polypropylene and ethylene vinyl alcohol copolymer (EVOH) changes dramatically throughout the sample and especially across the sample thickness. The development of laminar structure was evaluated by image analysis of scanning electron micrographs. The results indicate that laminar morphology is most likely to develop in the shear zone, as maxima in particle size and aspect ratio are observed in directions parallel and transverse to flow in this region of the sample. The laminar structure is more pronounced at high concentrations of the EVOH minor phase, and at low maleation levels of the matrix resin, as well as for low molding thickness. The influence of processing conditions such as injection speed and mold and melt temperatures appears to be small. Intensive preblending of the components in a twin screw extruder hinders the development of the laminar structure. Toluene permeability measurements show that the presence of laminar phase morphology in injection molded samples produces substantial improvements of the barrier characteristics in the materials. However, impact tests indicate that there is need to optimize the conditions employed in producing the laminar morphology, in order to avoid deterioration of mechanical properties. © 1996 John Wiley & Sons, Inc.
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  • 22
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two cases of initiation of vinyl polymerization by radical-ions are considered. In the one case the transfer from radical-ion to monomer is instantaneous and virtually complete. Here the relative amount of free radical propagation as compared to anionic propagation is negligibly small. In the second case a continuous feed of radical-ion initiator is considered. Here the relative amount of free radical propagation as compared to anionic propagation may be considereable. Exact expressions are developed for this relative radical versus ionic propagation as a function of conversion. It is suggested that the results of lithium-initiated copolymerization of methyl methacrylate and styrene may be understood in terms of a model similar to the second case of radical-ion initiation considered in this paper.
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  • 23
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Crosslinked phenol sulfonic acid resins in the form of rods have been prepared. Anion uptake by these resins in equilibrium with aqueous solutions of NaCl, NaBr, Na2CO3, and Na3C6H5O7 at 30°C. in the concentration range 0.001-3.0N, their density, water content, and exchange capacity have been determined. From these data, activity coefficients of small ions in the resin phase have been calculated and compared with the values derived by the existing theories of Mackie and Meares, and Lazare et al. The agreement between the observed and calculated values is not satisfactory.
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  • 24
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: From a measurement of the dielectric increment of methylcellulose in water, including the frequency dependence of this increment, the dielectric relaxation time spectrum has been determined and represented quantitatively by a formula containing three parameters τor, νAh, and θq, each of which can be obtained from earlier published viscosity and birefringence of flow data. On the basis of this relaxation time spectrum, the Cole-Cole diagram of the aqueous solution of methylcellulose can be drawn. It is found that this diagram is dissymmetrical, i.e., different in shape from a circle or part of a circle; the circular form of the Cole-Cole diagram is thus not a general phenomenon, even if it is realized in many cases.
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  • 25
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Oriented polyamides were irradiated with 1.5-M.e.v. electrons and the paramagnetic resonance was examined to determine the radical species. The spectrum is composed of two radical species which decay at different rates. The predominant radical has a spectrum with three main lines (intensity ratio; 1:2:1), each split into two. The doublet splitting changes with the rotation of the magnetic field, while the triplet splittings undergo slight change. The spectrum indicates that the radical is of an unpaired electron interacting with one σ-proton and two equal π-protons. In addition, the width of the individual lines is broad (half width = ca. 18 gauss) and it is presumably due to the ill-resolved hyperfine structure of NH group. These confirm that the radical is —CONHCHCH2— as indicated by the findings of Burrell on irradiated amides. The other radical has a five-line spectrum, which indicates that the radical may be of the type resulting from a —C—C— bond scission, although not fully investigated.
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  • 26
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Macromolecules with very long backbone and a multiplicity of side chains have been prepared. Polystyrene with stearylamido and polystyrene with laurylamido side chains were obtained by the copolymerization of p-vinylstearanilide and of p-vinyllauranilide with styrene. Polymers were made suitable for configurational studies by repetitive precipitation fractionation. Light-scattering and viscosity studies on dilute solutions indicated however that the effect of side chains on molecular volume was secondary in importance to the effect of variations in fractionation efficiency. Hydrogen succinate side groups on secondary cellulose acetate were obtained by a reaction on the polymer which was demonstrated to be nondegradative. A series of polymers was obtained with the same backbone molecular weight and varying substitution. A steric parameter was derived from viscosity measurements in acetic acid and its dependence on increasing extent of succinylation showed a progressive stiffening of the cellulose chain.
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  • 27
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A Couette flow generated by a cylinder rotating perpendicular to the free surface of a fluid is considered and the equations of motion are solved to yield an expression for the surface shape in the vicinity of the rod. The fluid model chosen is one for which the shear stress τrθ and the normal stresses Trr and Tee obey the relations \documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{l} \tau _{r\theta } = {\rm }M\left[ {r\frac{d}{{dr}}\left( {\frac{v}{r}} \right)} \right]^n \\ T_{rr} = a\left( {\tau _{r\theta } } \right)^b \\ T_{\theta \theta } = \kappa T_{rr} \\ \end{array} $\end{document} where M, n, a, b, and κ are constants characteristic of the fluid and v is the flow velocity component in the angular direction. The results are found to be in reasonable agreement with previous experimental observations of the Weissenberg effect.
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  • 28
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymeric materials have been prepared by the reaction of the divalent Cu, Ni, Co, Zn, Cd, and Mg cations with the dipotassium salt of tetraacetylethane in methanol-water solutions. The polymers appear to be of low molecular weight and generally contain potassium in the endgroups. The insoluble, infusible, materials decompose on heating in the absence of air to give, among other products, H2, 3,4-diacetyl-2,5-dimethylfuran, and the free metal or metal oxide. The order of decreasing heat stability is Mg > Ni > Co > tetraacetylethane > Cu > Zn > Cd. The Cd chelate polymer decomposes appreciably at 225°C., while the Mg polymer, heated under the same conditions, begins to decompose at about 350°C.
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  • 29
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The infrared spectra of several alcohols and aminoalcohols were measured in bulk and in dilute solution in the 2800-4000 cm.-1 region to determine the nature of hydrogen bonding in these compounds. An epoxy resin was cured with both an aliphatic monoamine and a diamine, and the OH-stretching bands of the polymers were studied in the temperature range 30-200°C. It is concluded that the hydroxyl groups in the polymers are extensively involved in long-range hydrogen bonding, particularly of the O—H—N type, at room temperature. The shift in the bonded OH band to lower frequency with increasing temperature is attributed to a shift from long range to short range bonds. Even at 200°C. there are relatively few free hydroxyl groups in these polymers.
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  • 30
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Light-scattering studies of well fractionated samples of poly(vinyl acetate) were carried out in four solvents, viz., acetonitrile, ethyl formate, methyl isobutyl ketone, and dioxane, in order to investigate the effect of the polar and nonpolar nature of the solvents on the molecular weight and the viscosity of the samples studied. The molecular weights thus obtained are found to be in good agreement in all the solvents except dioxane, in which the values are twice as high. This twofold increase in dioxane has been explained in terms of secondary bonding. The relation between [η] and Mw are established for the systems poly(vinyl acetate)-ethyl formate, poly(vinyl acetate)-acetonitrile, and poly(vinyl acetate)-methyl isobutyl ketone. The root-mean-square radii and the second virial coefficients are also determined.
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  • 31
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The range of molecular forces and the critical temperature of polystyrene in ethylcyclohexane are calculated from measurements of the angular dependence of critical opalescence. The polystyrene samples have molecular weights ranging from 69,000 to 552,000. The range of molecular forces remains strikingly small and is comparable with values obtained earlier on the system polystyrene-cyclohexane.
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  • 32
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of branching on the depolarization of light scattered from polymer solutions has been investigated employing various branched and unbranched polysaccharides. Two dextran fractions of M̄w 71,000 and 131 × 106 were studied in a strong solvent (aqueous KOH) and an indifferent solvent (water). The other polymers, studied in aqueous KOH only, included unfractionated corn amylopectin, the β-amylase limit dextrin of corn amylopectin, unfractionated corn amylose, and three subfractions of potato amylose (M̄w = 2.4 × 106, 1.14 × 106, and 0.27 × 106). Each polymer system was studied at several concentrations and all components of the scattered light, namely Hu, Vu, Hv, Vv, Hk, and Vh, were measured in each case. In general the results are in agreement with predictions of Krishnan and of Doty. However, certain important deviations from predicted behavior are noted and discussed.
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  • 33
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In a previous paper the end-to-end dimensions of semicrystalline macromolecules were computed by the Markoff chain method, by use of a normalized probability matrix with two probability parameters α and p. The values of these parameters that actually obtain may result from kinetic conditions (as in rapidly quenched specimens) or the values may in some cases be equilibrium values that can be determined by statistical mechanical considerations. In this paper we calculate the overall partition function Q of a semicrystalline macromolecule by a method similar to that employed by Zimm and Bragg for polypeptide chains. Q is computed in terms of segment partition functions fr, fh, and fk. By working out the consequences of this Ising-type model, we are able to relate α and p to fr, fh, and fk. In an appendix we show that the phenomenon of ceiling and floor temperatures in equilibrium polymerization can be regarded from the same mathematical point of view as the helix-coil transition. Moreover, the mathematical results from this approach can be correlated with the results previously obtained by Tobolsky and Eisenberg by direct application of the law of mass action.
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  • 34
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of two molecules of AlRCl2 with an electron donor molecule D, gives rise to the practically quantitative formation of AlR2Cl and AlCl3.D. This can explain the catalytic activity in the stereospecific polymerization of propylene to isotactic polymer of the systems prepared from violet TiCl3, AlRCl2, and an electron-donor substance. These systems have the same degree of stereospecificity as the systems consisting of AlR2Cl—TiCl3 (violet).
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  • 35
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Proton magnetic resonance studies of polyethylene have been extended. The relationship of the rigid fraction (NMR) to the crystalline fraction is discussed, and a case is presented for the relative importance of the rigid fraction (or its complement, the mobile fraction). When the polymer has been swollen by low molecular weight solvents, the NMR spectra yield rather direct evidence that the rigid, and presumably crystalline, regions are unaffected. The nature of the molecular motion is discussed in terms of a model, and it is shown that NMR data imply a rather general type motion.
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  • 36
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A study has been carried out on the molecular weight distributions of polystyrene initiated by sodium naphthalene in tetrahydrofuran solution. Stringent high-vacuum techniques were used in order to minimize initiator destruction or chain termination. Molecular weights were measured by osmotic pressure, dilute solution viscosity, light scattering and sedimentation equilibrium. In general, the molecular weight distributions found were quite narrow, as predicted, and corresponded to a stoichiometry of one polymer chain for two initiator molecules. However, the breadth of the distribution was very sensitive to experimental conditions, the M̄w/M̄n values found ranging from 1.1 to 1.5. At the higher molecular weights, there was some indication of a chain transfer reaction, leading to a lower molecular weight than expected, as well as a broadening of the distribution. This transfer reaction did not appear to be due to any transfer step between the short-lived radical-anions and the solvent.
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  • 37
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A study has been carried out on the molecular weights and their distribution for polystyrene prepared by means of ethyl and butyl lithium initiators, using benzene and tetrahydrofuran as solvents. Stringent high vacuum techniques were employed in order to minimize any destruction of initiator or termination of growing chains in these anionic polymerizations. Under these conditions, it was found that the stoichiometry corresponded to the formation of one chain from each initiator molecule. Furthermore, the molecular weight distribution could be made very narrow (M̄w/M̄n = 1.05 - 1.1) in these cases, where the initiation reaction was very rapid compared to the propagation step. In the case of the benzene systems, the initiation reaction was too slow, leading to a broadening of the molecular weight distribution, and this could be circumvented by a “seeding” technique whereby all the chain anions were pre-initiated before the main polymerization took place. The alkyl lithium initiators were found to react rapidly with THF at room temperature, but the styryl lithium apparently did not.
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  • 38
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A study has been carried out on the molecular weights and their distribution for polyisoprene prepared with butyl lithium as initiator in n-hexane and tetrahydrofuran solvents. A stoichiometry of one chain per initiator molecule was found to apply. As in the case of styrene, the initiation reaction in the hydrocarbon solvent was relatively slow compared to propagation, thus leading to a broadening of the molecular weight distribution. However, narrow distributions were obtained by using a preinitiation technique, whereby all chains had an opportunity of growing simultaneously. In the THF solvent, the molecular weight distribution waa somewhat broader (M̄v/M̄n, ∽ 1.3) presumably due to a slow competitive chain termination reaction between the growing anionic chains and the solvent, a t room temperature.
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  • 39
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rheology of polytetrafluoroethylene above its melting point was studied by the technique of stress relaxation. The temperature shift for the maximum relaxation time at various temperatures fits the WLF equation, if the value of Tg is taken to be 110°C. Degradation of the polymer becomes appreciable above 380°C. Master stress relaxation curves were constructed from the data between 336 and 380°C. The continuous distribution of relaxation times was obtained, and also the discrete distribution of relaxation times by procedure X. The contribution of the maximum relaxation time to the total flow viscosity indicates that the molecular weight distribution of the sample used was narrow.
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  • 40
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spatial orientation of rigid ellipsoidal particles was analyzed as proceeding in a dilute solution flowing in a velocity field with parallel gradient, i.e., in a field characterized by the deformation rate tensor: \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm V}_{ij} = \left( {\begin{array}{*{20}c} q & 0 & 0 \\ 0 & { - 1/2q} & 0 \\ 0 & 0 & { - 1/2q} \\ \end{array}} \right) $\end{document} On the basis of general relations given by Jeffery, the hydrodynamic equations of motion of a single ellipsoid were obtained as Ψ = 0, ϕ = 0, θ = -¾qR sin 2θ, where q = ∂Vκ/∂κ is the parallel velocity gradient and R = (a2 - b2)/(a2 + b2) is the shape coefficient of ellipsoids. Considering the action of velocity field and that of Brownian motion (rotational diffusion), a distribution density function ρ(t, θ) was derived, which describes the spatial orientation of the axes of symmetry of the ellipsoids: \documentclass{article}\pagestyle{empty}\begin{document}$ \rho (t,\theta ){\rm = }F_0 {\rm } - {\rm }[F_0 {\rm } - {\rm (1}/4\pi )]{\rm exp }\left\{ { - {\rm }\lambda _{1{\rm }} tD} \right\} $\end{document} where \documentclass{article}\pagestyle{empty}\begin{document}$ F_0 \left( \theta \right) = \left( {{1 \mathord{\left/ {\vphantom {1 {4\pi }}} \right. \kern-\nulldelimiterspace} {4\pi }}} \right)\left\{ {1{\rm } + {\rm }\left( {{{\alpha R} \mathord{\left/ {\vphantom {{\alpha R} 4}} \right. \kern-\nulldelimiterspace} 4}} \right)\left( {3\cos ^2 \theta {\rm } - {\rm }1} \right) + \left( {{9 \mathord{\left/ {\vphantom {9 4}} \right. \kern-\nulldelimiterspace} 4}} \right)\left( {\alpha R} \right)^2 \left[ {.{\rm }.{\rm }.} \right]{\rm } + {\rm }{\rm . }{\rm . }{\rm . }} \right\} $\end{document} is the steady-state distribution. In a similar way, the axial orientation factor f0 = 1 - 3/2 sin2θ was obtained: \documentclass{article}\pagestyle{empty}\begin{document}$ f_0 = \left( {{7 \mathord{\left/ {\vphantom {7 5}} \right. \kern-\nulldelimiterspace} 5}} \right)\left[ {\left( {{{\alpha R} \mathord{\left/ {\vphantom {{\alpha R} {14}}} \right. \kern-\nulldelimiterspace} {14}}} \right) + \left( {{{\alpha R} \mathord{\left/ {\vphantom {{\alpha R} {14}}} \right. \kern-\nulldelimiterspace} {14}}} \right)^2 - \left( {{7 \mathord{\left/ {\vphantom {7 5}} \right. \kern-\nulldelimiterspace} 5}} \right)\left( {{{\alpha R} \mathord{\left/ {\vphantom {{\alpha R} {14}}} \right. \kern-\nulldelimiterspace} {14}}} \right)^3 + \left( {{{\alpha R} \mathord{\left/ {\vphantom {{\alpha R} {14}}} \right. \kern-\nulldelimiterspace} {14}}} \right)^4 \left( {.{\rm }.{\rm }.} \right) + {\rm }{\rm . }{\rm . }{\rm .}} \right] $\end{document}
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  • 41
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: On the basis of Jeffery's general relations, formulas for the rate of dissipation of energy due to the motion of a rigid rotational ellipsoid in a liquid, uniaxially drawn, were derived. By use of the previously found distribution function, intrinsic viscosity v, was calculated and effects of ellipsoid shape, velocity gradient, diffusion rate constant and time were discussed. The intrinsic viscosity monotonically increases with velocity gradient and with time t. This behavior is quite different from that observed in shear flow. It was stated that phenomena connected with a velocity field with parallel gradient (i.e., flow with uniaxial deformation): \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm V}_{ij} = \left( {\begin{array}{*{20}c} q & 0 & 0 \\ 0 & {{\rm - }\sigma q} & 0 \\ 0 & 0 & {{\rm - }\sigma q} \\ \end{array}} \right) $\end{document} such as liquid jets, fiber spinning etc., cannot be explained in terms of experiments or theories concerning the shear flow (velocity field with perpendicular gradient): \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm V}_{ij} = \left( {\begin{array}{*{20}c} 0 & q & 0 \\ q & 0 & 0 \\ 0 & 0 & 0 \\ \end{array}} \right) $\end{document} as obtained in viscosity measurements in common types of viscometers (capillary, rotational, falling body), or investigations of flow birefringence in coaxial apparatus.
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  • 42
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The depolarization ratios of unpolarized light, vertically polarized light, and horizontally polarized light at 90° have been measured for polyvinyl acetate solutions at high dilutions with the help of a specially designed differential amplifier. Over the concentration range (0.01-0.25%) studied, the values of ρu and ρv decrease sharply with increasing concentrations up to a concentration of about 0.1% and then the curves flatten out. Depending upon the nature of the solvent, there exists for each polymer - solvent system a critical concentration range above which the anisotropy of the molecules does not later further. This behavior is the same both in the good solvent (methyl ethyl ketone) and the relatively poor solvent (ethyl acetate). The experimentally determined ρh values generally are in agreement with the values calculated from the reciprocity theorem, except where ρh values are greater than one. In the case of ρh values which are greater than unity the difference between the experimentally determined and the calculated values is as high as 70%.
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  • 43
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It has been shown that a nonreinforcing solid such as titanium dioxide can radically alter the glass transition temperature of the model polymer, poly(vinyl chloride-vinyl acetate) copolymer after being mechanically incorporated within it. The Tg values were either higher or lower than that of the original unfilled polymer, depending on the volume fraction of the solid. The magnitude of these changes is in some cases as great as 49°C. This phenomenon was explained on the basis of adsorption of the acetate radicals on the surface of the solid and the breaking of interchain hydrogen bonds. The changes in segmental mobility of the polymer as indicated by the variation in Tg were also verified by gaseous diffusion studies.
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  • 44
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Crystalline solids, as exemplified by TiO2 incorporated within a film of a model polymer, poly(vinyl chloride-vinyl acetate) copolymer, have been shown to absorb relatively large amounts of water vapor on the surface. In some cases all of the crystal surface may participate in the sorption process, despite evidence that the polymer has been initially present on the surface of the former. This, coupled with anomalous density changes in the film, suggests the possibility of measuring crystal flocculation within the membranes as well as the displacement of adsorbed polymer segments by means of water vapor. The anomalous density determinations were correlated with water transport measurements, and an equation for calculation of the heat of wetting of a crystal with a solid polymer is presented.
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  • 45
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The heterogeneous polymerization of acrylonitrile in tetrahydrofuran by chain transfer catalysts: monosodium anthracene, disodium anthracene, sodium naphthalene, monolithium anthracene, and lithium naphthalene was investigated. The free radical formed in the initiation was found to participate in the polymerization process only in the case of lithium naphthalene at low catalyst concentrations. Also, block copolymerization with styrene, which is more reactive in free radical polymerization than acrylonitrile and less in anionic, succeeded only with lithium naphthalene. The absence of dimerization of the free radicals is mainly due to their occlusion caused by the high rate of the anionic polymerization of acrylonitrile and the low polymerization temperature, and in the case of the anthracene catalysts also due to inhibition of the free radical dimerization by the liberated anthracene. The mechanism of the termination of the polymerization was found to depend on the catalyst concentration and the ratio [MI]/[C]. At high catalyst concentrations and relatively low [M]/[C] values, termination was by chain transfer to the monomer, as can be seen from the independence of the molecular weights on both monomer and catalyst concentrations. At low catalyst concentrations and relatively high [M]/[C] values, the molecular weights were found to increase with monomer concentration and decrease with catalyst concentration. This was found to be due to the anionic mechanism of the polymerization, and the results are similar to those obtained in a typical anionic polymerization of acrylonitrile with butyllithium.
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  • 46
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 47
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 48
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Log-normal particle size distributions in polymer solutions have been measured with the Coulter counter. Qualitative membrane diffusion measurements were performed to substantiate the presence in these solutions of particles in the micron size range. Particle size was found to be dependent upon the thermal history of a polymer solution and upon the shearing forces to which it had been subjected. Further, particle size decreased upon dilution of a polyelectrolyte solution or upon an increase in the salt content. It is concluded that polymeric aggregates are the species being counted. These aggregates apparently originated during the polymerization of the polystyrene or of the styrene maleic anhydride studied. Bimodal distributions were observed in polystyrene solutions and in polystyrene sulfonate (Na+) solutions. The latter bimodal systems were resolved by graphical means, and it was found that the two populations are present in the ratio 65:35. The two distributions have the same dispersions (0.04) and only slightly different means (3.7 versus 4.5 microns). The mechanism of formation of this bimodal system may be that proposed by van der Hoff; namely, that particles are formed consecutively in the micellar and in the aqueous phase of an emulsion polymerization system when the soap concentration is near the critical micelle concentration.
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  • 49
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The paper deals with theoretical and experimental data on polymeric products with semiconducting properties. The data show the possibility of producing, on the basis of polymers, particularly polyacrylonitrile, substances characterized by high electroconductivity and exponential dependence of the latter on temperature. Possible changes in electrophysical properties of the materials are discussed. A quasimetallic model of a polymeric semiconductor is described.
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  • 50
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 51
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Copolymerizations of styrene with p-tert-butyl-, o-methyl-, 2,6-dimethyl-, and p-fluorostyrene were carried out with an alkyl aluminum - titanium trichloride catalyst. Overall composition of the product indicated that substituted styrenes were less reactive than expected for a conventional free-radical or ionic mechanism in solution. This fact led to a suggestion of a special steric interaction of the penultimate monomeric unit in the propagation step for this heterogeneous system. A styrene-p-tert-butylstyrene copolymer was fractionated, showing that it was composed of two or more copolymers of different compositions. The similar situation holds for the other cases except for 2,6-dimethylstyrene, which did not homopolymerize and did not copolymerize. The result was explained by the assumption of either multiactivity of the catalyst due to differences in site activity or a diffusion-controlled process.
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  • 52
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Graft copolymers of polyacrylic acid with DNA were prepared and isolated. The grafted DNA copolymers had different solubility behaviors and ultraviolet absorption characteristics than those of the DNA.
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  • 53
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A number of commercial and experimental samples of crystalline polypropylene were fractionated by sand column solvent gradient elution techniques. Two different solvent - nonsolvent systems were studied under several sets of experimental conditions. Deposition of polymer upon the sand from a thermodynamically poor solvent was found to be necessary to achieve selective fractionation according to molecular weights. Both selective and nonselective fractionation results are illustrated with the latter occurring whenever the polymer is deposited upon the substrate from a thermodynamically good solvent. Molecular weight distributions for ten samples are given as obtained from elution fractionation using o-dichlorobenzene - diethylene glycol monomethyl ether as solvent - nonsolvent system at 168°C. These molecular weight distributions could be adequately described by the logarithmic-normal probability distribution function found by Wesslau and others to be applicable for linear polyethylene and by Davis and Tobias for polypropylene. Many of the distributions observed in this work were found to be narrower than those previously reported in the literature.
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  • 54
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymerization of α-methylstyrene was carried out in the presence of AlEt3-TiCl4 at -78°C. The activity of the catalyst and the degree of polymerization were affected by the AlR3/TiCl4 molar ratio, the mixing and the aging conditions of catalyst, and the kinds of solvent. The advantageous AlR3/TiCl4 molar ratio was found to be between 1.0 and 1.2; at ratios higher than 2.0 the polymerization did not proceed. For this catalyst to have enough activity, the mixing and the aging of catalyst must be carried out below room temperature, and the valence state of titanium must be kept between IV and III after the reaction between AlEt3 and TiCl4. From comparison of the present results with other catalyst systems it is speculated that the polymerization reaction by this catalyst system is cationic, and that its active species are the intermediate complex [(TiCl3)+-(AlEt3Cl)-] and the reaction product AlEt2Cl. This speculation is confirmed by the molecular weight distribution curves of the poly-α-methylstyrene obtained, measured by a column fractionation method. The distribution curves have two maxima, at molecular weights of about 5 × 104 and 65 × 104. This suggests that two kinds of active species are present, in agreement with the above hypothesis. The resultant poly-α-methylstyrene shows superior stereoregularity, compared with that prepared with other catalyst systems.
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  • 55
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A comparison of dynamic methods for osmotic pressure molecular weight determinations has been made between the authors' method, the recently published method of Elias, and two other commonly used procedures. Samples containing various amounts of membrane-permeating solute were studied while using the same osmometer and gel-cellophane membrane. Good agreement is shown between the authors' method and that of Elias for all of the samples. The Fuoss-Mead technique and Philipp's method do not measure as much of the permeating solute when present in large amounts. The method of Elias is subject to continual calibration because of pore blockage and was found to be considerably more time-consuming than the authors' method.
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  • 56
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An attempt is made in this paper to calculate G values for simultaneous crosslinking and degradation during irradiation of polymers with side chains. Equations are given for the change in the weight-average to number-average molecular weight ratio as a function of dose for the case of degradation only. It is shown that the change in the logarithm of this ratio with the square root of the dose goes through a broad maximum over a certain dose range. This result coupled with estimates of Katsuura of the effect of branching on the intrinsic viscosity is used to explain the relationship discovered by Keyser, Clegg, and Dole between the logarithm of the intrinsic viscosity and the square root of the dose. It is concluded that the G value for degradation must change with dose; in the case of poly-1-hexene, for example, it is believed that G(S) falls from an initial value of about 0.15 to about 0.04 at high doses. Similar conclusions result from an application of the equations to polypropylene, but with higher values of G(S), about 1.1 initially and dropping about tenfold at doses above the gel point.
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  • 57
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Calorimetric measurements of the heat of sorption of water vapor on a dry swollen cellulose sample have been made for various swelling states of the sample. The state of swelling was characterized by the surface area of the sample as determined by nitrogen adsorption (B.E.T.) Six runs were made with the surface area varying from 140 m.2/g. to 2 m.2/g. The initial heats do not vary significantly with change in surface area and were found to be 15 to 16 kcal. per mole of water sorbed. The energetics of water sorption and the water regain, at low water concentrations, are entirely independent of the surface area range (swelling state) of the cellulose. The surface area was found to decrease logarithmically with the quantity of water sorbed on the cellulose. It is concluded that the interaction of water and cellulose is a bulk rather than a surface effect.
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  • 58
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactivity ratios for the copolymerization of lauryl methacrylate (LMA) with diallyl phenylphosphonate (DAPP), diallyl butylphosphonate (DABP), and diethyl allylphosphonate (DEAP), respectively, have been measured at 80°. \documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{l} {\rm LMA - DAPP, }r_1 = 19.5,{\rm }r_2 = 0.072 \\ {\rm LMA - DABP, }r_1 = 18.7,{\rm }r_2 = 0.091 \\ {\rm LMA - DEAP, }r_1 = 52.5,{\rm }r_2 = 0.066 \\ \end{array} $\end{document} None of the phosphonates are active for copolymerization with LMA but the DAPP and DABP have similar activities which are greater than that of DEAP. The variation with conversion in composition of the LMA-DAPP copolymer formed at any instant has been calculated using Skiest's equation and the calculations have been extended to show the variation of the overall composition of the copolymer with conversion. Intrinsic viscosities and molecular weights have been measured for some LMA-DAPP copolymers and these values are found to depend on the phosphorus contents of the copolymers.
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  • 59
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The homogeneous anionic polymerization of acrylonitrile in dimethylformamide with n-butyllithium was studied. Two different termination reactions were found to exist depending on catalyst concentration. At high catalyst concentrations termination was bimolecular by chain transfer to monomer, while at relatively low catalyst concentrations termination was monomolecular, by an inner cyclization reaction of the growing chain end. The existence of chain transfer only at high catalyst concentrations suggests the possibility of free catalyst molecules participating in the transfer reaction. At intermediate catalyst concentrations, both monomolecular and bimolecular terminations were found to occur side by side, and DP = Kp[M]/(Ktr[C][M] + Kt). Study of the dependence of molecular weight on per cent conversion at low catalyst concentrations showed that, up to about 30% conversion, there is a linear relationship between molecular weight and concentration of monomer consumed which is independent of temperature and monomer. After this degree of conversion, molecular weight stopped to increase and remained constant due to monomolecular termination. All over the wide range of catalyst concentrations investigated, the catalyst efficiency in initiating polymerization was found to be low. In the lowest range where there is a linear dependence of molecular weight on per cent conversion it was also found that the molecular weights are proportional to [M]/[C], which is a property of “living” systems.
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  • 60
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The copolymerization of acrylonitrile (AN) with sodium p-styrenesulfonate (SSS) in aqueous solutions (of pH 3 and pH 7) has been investigated. Monomer reactivity ratios at 45°C. for AN and SSS are found to be r1 = 0.10 ± 0.02, r2 = 1.20 ± 0.10 at pH 3 and r1 = 0.05 ± 0.01, r2 = 1.40 ± 0.04 at pH 7, from which Price Q and e values for SSS of 0.76 and -0.26 at pH 3 and of 1.25 and -0.43 at pH 7 are calculated. Initial rates of copolymerization at 45°C. with ammonium persulfate (APS) as initiators were determined over the entire range of composition from pure AN to pure SSS, and it has been found that there is a sharp rise in copolymerization rates within 0.2-5 mole-% monomer feed, sometimes being eight times larger than those in the neighboring range. The copolymerization in SSS monomer feed of 0.2-5 mole-% occurs in the transition phase from homogeneous to heterogeneous, and the system is very viscous and slightly cloudy. From the investigation of the effect of initiator concentration on the copolymerization rate and the direct observation by an electron microscope, the sharp rise in copolymerization rates may reasonably be interpreted in terms of the emulsion copolymerization mechanism.
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  • 61
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The x-ray diffraction patterns of nylon 66 at small and large angles have been correlated with the densities of samples prepared in various ways. Quenching from the melt to 0°C. produces structures which are less than 40% crystalline, as determined by density and have structures similar to nematic liquid crystals. More dense specimens have a triclinic structure and appear to contain lamellae 50-100 A. thick which consist of outer amorphous layers and a central portion which is about 80% crystalline. Thermodynamic and spectroscopic evidence indicates that the disorder on melting consists of rotations about the bonds connecting CH2 groups.
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  • 62
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Strain birefringence of swollen sodium hyaluronate films was measured. Typical Wiener curves were obtained in solvents with different refractive indices. The orientation birefringence of sodium hyaluronate was evaluated from the minima of the Wiener curves and was found to increase with increasing elongation. Up to 30% elongation, the swollen hyaluronate films show quasi-rubberlike behavior. Above this elongation, the interchain hydrogen bonding further hinders the chain mobility and the orientation increases only slightly.
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  • 63
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The temperature coefficients of the retractive force at successive fixed lengths were measured for a Viton fluoroelastomer sample. At each elongation the sample was held for at least 40 hr. before the tension measurement in order to minimize the relaxation effect. The range of elongations covered was confined to α values smaller than 1.65 because of the limited tensile strength of the sample. The results show departures from the predictions of simple gaussian theory of rubber elasticity in two respects. First, the tension f at 45°C. follows the Mooney equation with nonvanishing C2 values (2C1 = 3.324 kg./cm.2 and 2C2 = 2.865 kg./cm.2). Secondly, the internal energy makes a negative contribution to the elastic force, and moreover the ratio of the internal energy component to the total tension fe/f decreases with increasing α. The thermodynamic behavior of the Viton sample is thus qualitatively similar to that observed previously with a natural rubber network, except that the internal energy makes positive contribution in the latter. The experimental results were also compared with recent theories which purport to improve upon the simple Gaussian theory of rubber elasticity, but it is found that none of them can explain the results in satisfactory detail.
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  • 64
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It is a well-known fact that the relaxation spectra in the rubbery region of linear amorphous polymers show “box-type” functions which are characterized by three elements, τe τm and E0, the minimum relaxation time, maximum relaxation time, and height of the curve, respectively. The equation (τm - τe)/log (τm/τe) = 2.303 αMwβ/Er(τe) can be derived by a simple treatment described in this paper. Then log τe = -log E0/α(1 -1/10K) + β log M̄w can be obtained from the above equation for the polymers synthesized by us. According to Fujita's results, however, τm is independent of molecular weight and τm becomes τ3 when M̄w conforms to Mc. For such a case the above equation is transformed into log (τm/τe - 1) - log log τm/τm = β log M̄w/Mc. On the other hand, log τm experimentally obtained was plotted against log M̄w for the same polymers and it was found that the results were raher on the straight line indicated by the former equation than on the curve shown by the latter. Also log (τm + 0.234) =  - 5.87 + 1.65 log M̄w was found to be suitable for the polymers in the vicinity of Mc.
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  • 65
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Peroxide radicals are formed by oxidation of carbon radicals in irradiated isotactic polypropylene. An interpretation of their ESR-spectra is given. The recombination of the peroxide radicals follows a chain reaction mechanism, which is derived from the reversibility of formation of peroxide radicals, the time dependence of their concentration, and from the oxygen consumption of samples containing peroxide radicals. The reactions are discussed in view of the radiation induced oxidative degradation of polypropylene.
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  • 66
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The simple additivity of osmotic pressure and ionic activity observed in polyelectrolyte - salt solutions is derived from a straightforward thermodynamic consideration. The basic assumption of this work is that the activity coefficient of the coions is practically uneffected by the presence of the largely screened polymeric ions.
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  • 67
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of graft copolymerization of vinyl acetate on polymethyl methacrylate has been investigated. Polymethyl methacrylate was preirradiated in the presence of air by γ-rays, the polymer being used as the initiator of the polymerization in the one-phase system. The rate of reaction for low conversion is proportional to the concentration of monomer raised to the power of 3/2 and to the concentration of initiator to the 1/2 power. The reaction satisfied the kinetic equation for ordinary addition polymerization if the decrease of the amount of the initiator during the process is taken into consideration. The activation energy of this process has been found. The quantity of the homopolymers produced in this reaction is negligible and need not be taken into account in rough calculations as far as kinetics are concerned.
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  • 68
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of copolymers of partially neutralized crotonic acid and vinyl alcohol have been prepared with acid monomer contents ranging from 4 to 43 mole-%. The extent of binding of sodium counterions was studied by a transference method employing radiotracers. Comparison of these data with those obtained previously by Nagasawa and Rice for maleic acid copolymers and Wall and co-workers for poly(acrylic acid) gives further support to the contention that the overall charge density on a polyion governs the total counterion binding. Results of potentiometric titrations and viscosity measurements are also reported.
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  • 69
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Anionic block polymerization of styrene onto polystyrene anions was found to be a useful diagnostic method which can readily reveal when the chosen polymerization conditions are conducive to complete catalyst consumption and quantitative block polymerization. With Na-naphthalene as initiator, it was shown that under the proper polymerization conditions (a) the initiator is essentially completely consumed in the first polymerization step, thus avoiding initiation of new chains in the following polymerization steps, (b) in each block polymerization step, styrene adds quantitatively to the preformed live anions, and (c) essentially no termination is observed throughout the successive block polymerization steps. The ratio of monomer to initiator greatly affects the efficiency of initiator consumption. The rate of agitation is also considered to play a dominant role.
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