bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphological changes in segmented polyurethane elastomers by varying the NCO/OH ratio
Authors: Spathis G. , Niaounakis M. , Kontou E. , Apekis L. , Pissis P. , Christodoulides C. 
Published: April 2003

AbstractThe morphological changes induced to segmented polyurethane elastomers by varying the NCO/OH ratio during the second step of polymerization, while keeping constant the total hard‐segment content (∼ 30%), were studied by means of fourier transform infared spectroscopy (FTIR), differential scanning calorimetry (DSC), and the thermally stimulated depolarization current method (TSDC). The DSC results gave evidence for the existence of phase separation in thermoplastic polyurethanes, whereas the elastomerc ones appeared to form a more homogeneous network. The FTIR results gave additional evidence regarding phase separation be detecting the sterength of the hydrogen bonds. Moreover, an attempt was made to assess the relative contribution made to the hydrogen bonding in such systems by the two potential acceptors: ester and urethane carbonyls. The TSDC results gave a relaxation mechnism that is due to interfacial (Maxwell–Wagner–Sillars) polarization, providing evidence of the existence of an interfacial phase. The introduced secondary chemical cross‐links was found to affect mainly the irregularly packed hard domains and to form a more homegeneous network at higher values of the NCO/OH ratio. © 1994 John Wiley & Sons, Inc.
Chelating resins supporting dithiocarbamate and methylthiourea groups in adsorption of heavy metal ions
Authors: Lezzi A. , Cobianco S. 
Published: April 2003

AbstractTwo different sulfur atom containing functional groups were introduced into poly(styrene‐g‐ethylene glycols), PSR‐ET (13) OH, consisting of a cross‐linked polystyrene backbone grafted with linear poly(ethylene glycol) chains. Reaction of an amino derivative of the polymeric substrate with carbon disulfide and methylisothiocyanate produced new chelating resins of dithiocarbamate type, PSR‐ET (13) CS2Na, and methylthiourea type, PSR‐ET (13) TU, respectively. The adsorption behavior of these resins was studied toward Hg(II), Cd(II), Cu(II), and Pb(II) ions in different experimental conditions. The order of metal adsorption for dithiocarbamate‐supported resins was Hg(II) > Pb(II) ≫ Cd(II) > Cu(II) and for methylthiourea‐supported resins was Hg(II) ≫ Cu(II) > Cd(II) ≫ Pb(II). Different regeneration methods were performed with the dithiocarbamate and methylthiourea resins; the former was regenerated by complete mineralization of the metal complexes, the latter by treatment with a solution of 6 N HCl and 10% of thiourea. © 1994 John Wiley & Sons, Inc.
Polymer morphology of CO2‐blown rigid polyurethane foams: Its fractal nature
Authors: Grünbauer H. J. M. , Folmer J. C. W. 
Published: April 2003

AbstractSmall‐angle x‐ray scatting (SAXES) and transmission electron microscopy (TEM) have been applied to study polymer morphologies of CO2,‐blown rigid polyurethane foam samples of varying isocyanate index. The results are consistent with an irregular (meso) phase segregated structure with phase boundaries showing fractal symmetry. Phase segregation persists, througtout the index range, althougt the interfacial surfaces tends to smooothen with increasing isocyanate index to evetually results in a significant degree of energetic ‘sharing’ across the4 phase boundary. The latter can satisfactorily be explained by a free volume double layer (PVDL) model. Mechanistically. Fractal symmetry was attributed to the competition between crossliking and phase segregation tendencies in rigid PU foam polymers. The resulting frozen‐in morphology represents an early stage of the development towards a more regular spinodal phase segregation, as occurring in polyuethane foam systems of lower crosslink density (e.g. flexible foams). © 1994 John Wiley & Sons, Inc.
Step‐growth polymerization of unsaturated aldehydes with aliphatic amines
Authors: Šebenik Anton 
Published: April 2003

AbstractThe step‐growth polymerization of unsaturated aldehydes (acrolein, crotonaldehyde, cinnamaldehyde) and aliphatic amines (butylamine, ethylenediamine, triethylenetetramine, diethylenetriamine, hexamethylenediamine) took place intensively in the temperature range between 50 and 90°C. The rates of individual reactions depended on the type of individual aldehydes and amines. The quantity of individual unreacted monomers was mostly under 1%. The average molecular weights of oligomers were between 290 and 710. The individual resins consisted of oligomers with free OH, NH, CHN, and CHCH groups, which are further able to cross‐link the resins with three blocked isocyanate to insoluble, elastic film with high adhesion to glass and metal substratum. © 1994 John Wiley & Sons, Inc.
Polymerization initiation by N‐p‐tolylglycine: Free‐radical reactions studied by pulse and steady‐state radiolysis
Authors: Al‐Sheikhly Mohamad , Farahani Mahnaz , Bowen R. L. 
Published: April 2003

AbstractThe extensive use of N‐p‐tolylglycine (NTG) and analogous compounds in adhesive bonding technologies requires a better understanding of their role in initiating free‐radical polymerization. The fast oxidation and reduction reactions of NTG proceed via the formation of various free radicals and radical cation and anion intermediates. These intermediates were identified and their reactivity with oxygen, to produce the corresponding peroxyl radicals, was measured. Hydroxyl radicals (ȮH) were used to initiate oxidation reactions of NTG, while the reduction reactions were initiated with hydrated electrons (e). OH radicals react with NTG predominately by addition to the aromatic ring followed by OHÞ elimination to produce NTG+· radical cations. In the presence of oxygen, the OH–NTG• adduct also reacts with oxygen to produce peroxyl radicals. The reaction of NTG with e forms the radical anion, which subsequently protonates on the aromatic ring to produce cyclohexadienyl radicals, or undergoes an amine elimination to yield an acetic acid free radical and 4‐methylaniline. Hydroperoxyl radicals (HO) abstract hydrogen from the α position of NTG to form the corresponding alkyl free radical. © 1994 John Wiley & Sons, Inc.This article is a US Government work and, as such, is in the public domain in the United States of America.
Rheology of polycarbonate/poly(butylene terephthalate) blends containing a core‐shell modifier and high‐molecular‐weight acrylic polymers: Extrusion blow‐moldable resins
Authors: Memon Nazir A. 
Published: April 2003

AbstractSeveral different polymer modifications are currently used to produce commercial plastic materials, especially engineering resins, that have significantly improved melt strength. However, these modifications rarely produce materials that can be formed into very large parts. This study shows that the melt strength of engineering resins can be enhanced by rubber particles having grafted shells that are compatible with the resin. The melt strength of the engineering resin can be further improved by the incorporation of compatible highmolecular‐weight polymers. The melt strength improvements thus obtained facilitate the formation of very large parts requiring 8–10 ft long parisons. The effects of shear rate on complex viscosity indicate that the extent of interaction between the polycarbonate matrix and the core‐shell impact modifier decreases with increasing shear rate. Therefore, the impact strength of the part molded from a matrix modified with a core‐shell rubber may depend on the process history. Dynamic mechanical measurements may provide a means to evaluate the interaction between the matrix and a core‐shell modifier in an actual blend. © 1994 John Wiley & Sons, Inc.
Bromination and gas permeability of poly(1‐trimethylsilyl‐1‐propyne) membrane
Authors: Nagai K. , Higuchi A. , Nakagawa T. 
Published: April 2003

AbstractThe bromination of poly(1‐trimethylsilyl‐1‐propyne) (PMSP) was carried out by immersing a PMSP membrane in bromine water at 25°C. The bromine mainly reacted at the carbon–carbon double bonds in the backbone chain, and carbon–carbon single bonds were produced, which was determined from the infrared (IR) and ultravilet (UV)–visible analyses. The glass transition temperature of the PMSP is above 350°C, but a new endothermic peak appeared between 50 and 80°C in the differential scanning calorimetry (DSC) curves of all brominated PMSPs. The permeability for 12 gases in the PMSP membrane and its brominated membranes was investigated between 30 and 90°C below 1 atm. With increasing bromine content in the membrane, the permeability coefficient for all gases decreased together with the diffusion coefficient, and the ideal separation factor for the industrially important gas pairs increased at 30°C. A distinct change in slopes at near the endothermic temperature determined by the DSC analysis was observed in Arrhenius plots of the permeability coefficients in all brominated PMSP membranes. © 1994 John Wiley & Sons, Inc.
Synthesis of poly(2,6‐dimethyl‐1,4‐phenylene ether) catalyzed by copper–diamine system
Authors: Li Kuo‐Tseng 
Published: April 2003

AbstractOxidative polymerization of 2,6‐dimethylphenol to poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE) was studied in a high‐pressure batch reactor using a copper‐diamine catalyst. In the presence of air, the effect of monomer sources, catalyst formulation (copper salts, ligands, surfactant), and reaction conditions (air flow rate and pressure, temperature, agitation, monomer and catalyst concentrations) on the catalyst performance was investigated. The sensitivity of PPE molecular weight and the sensitivity of polymerization rates to these factors were found to be quite different, indicating that little correlation existed between the PPE molecular weight and the 2,6‐DMP polymerization rates. Mechanical test showed that the PPE produced with the copper–diamine catalyst had modulus significantly higher than that produced with the copper–dibutylamine catalyst system. © 1994 John Wiley & Sons, Inc.
Studies on the preparation and properties of conductive polymers. VII. Use of two‐stage method to prepare Ag–Hg alloy on polymer films
Authors: Chang Liang‐Tau , Yen Chih‐Chao 
Published: April 2003

AbstractPolymer metal chelate films were prepared by silver nitrate mixed with polymers containing functional groups such as poly(vinyl alcohol) (PVA) by using two‐stage method to prepare Ag–Hg alloy on polymer films. In the first stage, polymer silver chelate was treated with doping agents. In the second stage, these treated films were further treated with Hg metal. After the two stage treatment, films with good electrical conductivity can be obtained. © 1994 John Wiley & Sons, Inc.
Size‐exclusion calibration curves from light‐scattering detection: Application to poly(ethylene terephthalate)
Authors: Mourey T. H. , Balke S. T. 
Published: April 2003

AbstractA simple method is proposed for using a size‐exclusion chromatograph equipped with both concentration and light‐scattering detectors to calibrate other chromatographs having only concentration detectors. The method is developed and demonstrated for poly(ethylene terephthalate) in methylene chloride/dichloroacetic acid. It is shown that, in addition to circumventing the need for a light‐scattering instrument on other chromatographs to be used for the analysis of PET, precision and accuracy of results are improved over those obtainable with light‐scattering detection. The method uses averaging of the light‐scattering detector data to establish a correlation between the molecular weight of the polymer of interest and the molecular weight of polystyrene at each retention volume. This correlation can then be used for other instruments employing the same mobile phase and only a concentration detector. Although the method assumes the validity of the universal calibration curve, the actual curve is not required, nor are Mark–Houwink constants or intrinsic viscosities. © 1994 John Wiley & Sons, Inc.
Chemical modification of polypyrrole. II. Thermal stability, dielectric, and conductivity characteristics of polypyrrole substituted with phthalic and pyromellitic dianhydride
Authors: Biswas Mukul , Roy Anindita 
Published: April 2003

AbstractPolypyrrole (PPY) was electrophilically polycondensed with phthalic anhydride (PA) and pyromellitic dianhydride (PMDA). PPY–PA and PPY–PMDA polycondensates were evaluated in regard to their thermal stability and dielectric and conductivity behavior. The overall thermal stability is in the order PPY < PPY–PA < PPY–PMDA, which may be rationalized in terms of intra‐ and intermolecularly cross‐linked structures of the polycondensates. IR spectral analyses of PPY–PA and PPY–PMDA subjected to heating at 300, 400, 500, and 550°C, respectively, were conducted to understand some of the structural changes in the polymer matrices. Both PPY–PA and PPY–PMDA exhibit high dielectric constants (200 and 125) at low frequency (103 Hz), which fall monotonically with increasing frequency, suggesting the possibility of interfacial polarization. The conductivity values of PPY–PA and PPY–PMDA are in the range 10−3–10−4 ohm−1 cm−1, which are conspicuously lower than that for unmodified PPY (2.5). This is due to the adverse effect of incresing temperature on the PPY chain stability, whereby structural conjugation and eventually conductivity will be affected. © 1994 John Wiley & Sons, Inc.
Study of some polyurethane elastomers using electrical methods
Authors: Murthy S. S. N. , Sobhanadri J. 
Published: April 2003

AbstractA study of some poly ether/ester urethanes has been carried out using electrical methods, viz. dielectric spectroscopy (400–105 Hz), dc conductivity, and dc step‐response techniques. X‐ray diffraction and thermal analysis also are used for characterization of the samples. The studies indicate a hard‐segment glass transition Tgh around 318–322 K in addition to a soft‐segment glass transition around 233–270 K. The breakage of hydrogen bonding mainly starts above Tgh. The studies also show a hard‐segment melting around 1.5–1.8 Tgh, but do not reveal any soft‐segment melting except in the case of the polyetherurethane sample. © 1994 John Wiley & Sons, Inc.
Poly(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)/Poly‐L‐lactide blends: Thermal and mechanical properties
Authors: Iannace S. , Ambrosio L. , Huang S. J. , Nicolais L. 
Published: April 2003

AbstractBlends of poly(3‐hydroxybutyrate)–poly(3‐hydroxyvalerate) (PHBV) and poly(L‐lactides) (PLLA) have been prepared by solvent casting. Compatibility, thermal behavior, morphology, and mechanical properties of systems with various compositions were studied using differential scanning calorimetry (DSC), dynamic mechanical measurement, tensile tests, scanning electron microscopy (SEM), and wide‐angle X ray (WAXS). Glass transition temperature of solvent cast materials, detected by dynamic mechanical analysis (DMA), showed partial molecular interactions between PHBV and PLLA. Crystallinity of the PLLA phase slightly decreased with increasing amount of PHBV, confirming the partial dispersion of PLLA in the PHBV phase. Mechanical properties were analyzed with theoretical models able to predict the behavior of heterogeneous systems. Phase separation was confirmed by SEM observations. © 1994 John Wiley & Sons, Inc.
Polyolefin–wood filler composite. I. Performance of m‐phenylene bismaleimide‐modified wood fiber in polypropylene composite
Authors: Sain M. M. , Kokta B. V. 
Published: April 2003

AbstractThe properties of the composite of polypropylene (PP) and chemithermomechanical pulp reactively treated with bismaleimide‐modified PP or premodified pulp have been investigated. The results were compared with the properties of unmodified composites of PP and pulp. The effect of some flame retardants on the properties of composites was also studied. Premodifications of PP as well as pulp with m‐phenylene bismaleimide provided a positive response with regard to the mechanical properties of the composites. The tensile strength of a 35 wt % pulp‐filled PP composite was found to be much higher than that of the strength of pure PP. On the other hand, tensile strength decreased considerably with increase in the chemithermomechanical pulp content if unmodified PP was used. The occurrence of chemical grafting reactions between PP and bismaleimide as well as between pulp and bismaleimide have been suggested, which can explain the aforementioned difference in mechanical properties among different composites. In situ addition of sodium borate, boric acid, or phenolic resin during processing of the composite decreased the rate of burning of PP. © 1994 John Wiley & Sons, Inc.
Polyurethane–urea anionomer dispersions. I
Authors: Xiao Hong , Xiao Han X. , Frisch Kurt C. , Malwitz Nelson 
Published: April 2003

AbstractPolyurethane–urea anionomer dispersions with different stoichiometric DMPA/polyol and NCO/OH ratios were preapred from poly(oxypropylene)glycol, toluene diisocyanate (TDI), dimethylolpropionic acid (DMPA), and ethylenediamine (EDA). The dispersion‐cast films were prepared and characterized by mechanical properties, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). Increasing the hard‐segment content by either increasing the DMPA/polyol or the NCO/OH ratios affects the glass transition temperature (Tg) of the soft segments. © 1994 John Wiley & Sons, Inc.
Use of empirical polarity parameters to describe polymer/liquid interactions: Correlation of polymer swelling with solvent polarity in binary and ternary systems
Authors: Jonquières Anne , Roizard Denis , Lochon Pierre 
Published: April 2003

AbstractDimroth and Reichardt polarity parameters ET(30) have been used, in a new approach, to quantitatively describe the swelling features due to polymer liquid interactions in binary and ternary systems. With the help of a polyurethaneimide (PUI) synthesized from polytetramethyleneglycol 650, sorption of pure liquids was first examined, and it was shown that a linear relationship between the molar swelling Gm and the ET(30) values well fits the experimental data of each of the two series studied, i. e., aliphatic alcohols and linear ethers: Gm = a+b ET(30). The slope value b, regarded as the sensitivity of the polymer to the liquid polarity, is 3 times higher for the aprotic series. The proposed correlation was further proved valid from the study of published results concerning nine binary systems polymer–liquid, whatever the polarity of the liquids in a given family (alcohols, esters, ketones, hydrocarbons) and the nature of the polymer. Finally, that method was tested on two types of PUI‐alcohol‐ether ternary systems, and it was found for each case that the partial molar swelling due to an homologous set of solvents can also be described by a similar law. © 1994 John Wiley & Sons, Inc.
Influence of ABS type on morphology and mechanical properties of PC/ABS blends
Authors: Lombardo B. S. , Keskkula H. , Paul D. R. 
Published: April 2003

AbstractThe morphology and the mechanical properties of polycarbonate (PC) blends with different acrylonitrile–butadiene–styrene (ABS) materials were investigated. PC/ABS blends based on a mass‐made ABS with 16% rubber and large (0.5–1μm) rubber particles are compared to blends based on an emulsion‐made ABS with 50% rubber and small, monodisperse (0.12 μm) rubber particles over the full range of blend compositions. The blends with the bulk ABS showed excellent impact strength for most compositions, and those containing 50 and 70% PC exhibited ductile to brittle transition temperatures below that of PC. The blends with the emulsion ABS showed excellent toughness in sharp notch Izod impact tests at room temperature and in standard notch Izod impact tests at low temperatures near the Tg of the rubber. By melt blending the various ABS materials with a styrene–acrylonitrile (SAN 25) copolymer, materials with lower rubber concentrations were obtained. These materials were used in blends with PC to make comparisons at constant rubber concentration of 5, 10, and 15%. The results of this investigation show that brittle ABS materials can produce tough PC–ABS blends. It is apparent that small rubber particles toughen PC–ABS blends at lower rubber concentrations and at lower temperatures than is possible with large rubber particles. However, additional work is needed to understand the nature of toughening in these PC–ABS blends with different rubber phase morphologies. It is of particular interest to understand the exceptional ductility of some of the blends at low temperatures. © 1994 John Wiley & Sons, Inc.
Morphology and mechanical properties of biaxially oriented films of polypropylene and HDPE blends
Authors: Kim Woo Nyon , Hong Suk‐In , Choi Jin‐Sung , Lee Kwang‐Ho 
Published: April 2003

AbstractBiaxially oriented films of blends of high‐density polyethylene (HDPE) with polypropylene (PP) homopolymer and PP copolymers prepared by twin‐screw extrusion and lab‐stretcher have been investigated by scanning electron microscopy (SEM), polarized microscopy, differential‐scanning calorimeter, and universal testing machine. Three different kinds of PP copolymers were used: (i) ethylene–propylene (EP) random copolymer; (ii) ethylene–propylene (EP) block copolymer; (iii) ethylene–propylene–buttylene (EPB) terpolymer. In the SEM study of the morphology of films of HDPE with various PP blends, phase separation is observed between the PP phase and the HDPE phase for all blends and compositions. In all blends, HDPE serves to reduce the average spherulites size, probably acting as a nucleating agent for PP. The reduction of spherulite size appeared most significantly in the blend of EPB terpolymer and HDPE. A large increase of crystallization temperature was found in the blend of EPB terpolymer and HDPE compared with the unblended EPB terpolymer. For the blend of EPB terpolymer and HDPE, the improvement of tensile strength and modulus is observed with an increase of HDPE content, and this can be considered as a result of the role of HDPE in reducing average spherulite size. © 1994 John Wiley & Sons, Inc.
Flow method for study of gas transport in polymers. Application to the study of oxygen, nitrogen, and carbon dioxide permeation through cellulose acetate membranes
Authors: Nguyen X. Q. , Šipek M. , Hynek V. , Nguyen Q. T. 
Published: April 2003

AbstractTransient permeation of oxygen, nitrogen, and carbon dioxide through certain cellulose acetate (CA) dense membrances made from solutions in dioxane and dioxane‐added ethanol were studied by the flow method. In order to explain the overshoots for transient permeation rates in the latter case, a new model is proposed. It postulates a time‐dependence solubility coefficient, in the form of a series of exponential terms, which is combined in Fick's second law and solved. The model fits well the obtained permeation kinetics, leading to values of the diffusion, and permeation coefficients, and the structure change‐related time. The overshoots are explained by the formation of unstable structure from dioxane‐ethanol solvent mixtures, a memory effect of aggregated chains, which undergoes consolidation upon gas penetration. The stable state which results from the consolidation process is the same as that of membrances obtained from pure dioxane solutions. © 1994 John Wiley & Sons, Inc.
Nonlinear viscoelasticity of a vulcanized elastomer
Authors: Kontou E. 
Published: April 2003

AbstractThe material nonlinearities in the viscoelastic behavior of rubbers at modest‐to‐large deformations have been studied. A vulcanized network based on the styrene–butadiene elastomer has been tested in stress‐relaxation experiments at room temperature for a wide range of deformations. After time–strain separabality was confirmed, the damping function could be calculated and introduced into the Boltzmann superposition integral. The equilibrium stress–strain behavior of the system could then be described, while comparison with other theoretical equations has also been made. © 1994 John Wiley & Sons, Inc.