A simple arithmetic procedure was developed in order to be able to band-ratio dichroic measurements from simple attenuated total reflection (ATR)-IR spectroscopy to measure the surface molecular orientation of any pol...
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A simple arithmetic procedure was developed in order to be able to band-ratio dichroic measurements from simple attenuated total reflection (ATR)-IR spectroscopy to measure the surface molecular orientation of any polymer showing dichroism. This development eliminates the need to get a reproducible contact area or a reference band which does not show dichroism upon drawing. This method is universally applicable to any material showing dichroic IR bands. No assumptions are made regarding the structure of the sample in order to calculate the dichroic ratio. Furthermore, no special attachments are required for the dichroic measurements.
Bis-electrophilic monomers containing 1-chloro-2,2-dicyanovinyl moieties were reacted with dihydrazines, employing a vinylic nucleophilic substitution reaction, to prepare high molecular weight and processable polypyr...
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Bis-electrophilic monomers containing 1-chloro-2,2-dicyanovinyl moieties were reacted with dihydrazines, employing a vinylic nucleophilic substitution reaction, to prepare high molecular weight and processable polypyrazoles. All live polymers synthesized by this route exhibited excellent thermal stability. The polymers were fully characterized by spectroscopic methods, by solution viscosity measurements, and by thermal analysis techniques. These polypyrazoles exhibited excellent thermal stability in both nitrogen and air. Condensation of isophthalic dihydrazide with one of the bis-electrophilic monomers led to a polypyrazole in which N-1 of the pyrazole moiety was benzoylated. This polymer showed poorer thermal stability than that of the pyrazoles derived from the dihydrazines.
Four new polyenaminonitriles, soluble in common organic solvents, are synthesized by condensation of bis(chlorovinyledene cyanide) monomers with two different aromatic diamines. Thermal stability of these heat-resista...
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Four new polyenaminonitriles, soluble in common organic solvents, are synthesized by condensation of bis(chlorovinyledene cyanide) monomers with two different aromatic diamines. Thermal stability of these heat-resistant polymers is discussed in terms of their structure-property relationships. Curing of polyenaminonitriles, which cure without evolution of small molecules, was studied by differential scanning calorimetry (DSC) and infrared spectroscopy.
Pitch-based carbon fiber surfaces were modified using a nickel-catalyzed, dry oxygen etch (NCDO) and a dry oxygen etch (DO), both of which were applied using a continuous process. The treatments differed in that DCDO ...
Pitch-based carbon fiber surfaces were modified using a nickel-catalyzed, dry oxygen etch (NCDO) and a dry oxygen etch (DO), both of which were applied using a continuous process. The treatments differed in that DCDO produced preferential pitting on fiber surfaces at nickel particle sites. Tensile strengths of all etched fibers were slightly lower than values for untreated, or ''as received'' (AR), fibers. Reductions in tensile strength were independent of the type of treatment administered, indicating that most degradation resulted from damage produced by the mechanics of the continuous process, not the etching treatments. Fiber-matrix interfacial shea. strengths (IFSS) of AR and etched fibers were evaluated using the Microbond test At first glance, Microbond test data indicated that NCDO produced large increases in IFSS. However, inconsistencies in the data raised questions regarding the validity and usefulness of the Microbond test when applied to this system. Only after detailed analysis of the data for this series of fibers was it concluded that NCDO did indeed produce an increase in IFSS over AR fibers and DO fibers.
The relative magnitude of the equilibrium constants describing self-association versus inter-association is an important factor in determining the phase behavior of polymers that hydrogen bond. In studies of stericall...
The relative magnitude of the equilibrium constants describing self-association versus inter-association is an important factor in determining the phase behavior of polymers that hydrogen bond. In studies of sterically hindered phenolics we have found that poly(2,6-diisopropyl-4 vinylphenol) (PDIPP) only moderately self-associates, but strongly inter-associates with polymers containing groups such as ester carbonyls, ether oxygens, and the like. PDIPP is miscible with polytetrahydrofuran (PTHF) and simultaneously acts as an efficient polymeric antioxidant. This result points the way to the design of specific miscible polymeric antioxidants for polar polymers.
Small-Angle X-ray Scattering (SAXS) has been used as an analytical tool to study the development of microstructure with increasing Heat Treatment Temperature (HTT) of a carbonized phenolic resin, which is often used a...
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Small-Angle X-ray Scattering (SAXS) has been used as an analytical tool to study the development of microstructure with increasing Heat Treatment Temperature (HTT) of a carbonized phenolic resin, which is often used as matrix in commercial carbon-carbon composites. Processing parameters-heating rate and maximum heat treatment temperature-were the primary variables of interest. Results from SAXS have led to the consideration of a model for microstructure development in carbonized phenolic resins. Local density variations on the 10 angstrom-100 angstrom scale seem to be the predominant feature of these carbonized resins in the temperature range studied (450-900-degrees-C). Heat treatment results in a gradual destruction of crosslinks, which leads to clustering of the aromatic units. These clusters enclose pores, the high concentrations of which give rise to scattering maxima in SAXS data. Concentration and dimensions of pores are sensitive both to the heating rate used and the maximum carbonization temperature.
Thermal stability of [(CH3SiH)30(C6H5SiCH3)70]n a hydropolysilane copolymer, in vacuum and its crosslinking reactions with vinylic silanes as crosslinking agents was evaluated in order to obtain high yields of oxygen-...
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A nanostructured FeCrMoVM50 type steel was prepared via a chemical route. The process involved the thermal decomposition of organometallic precursors Fe(CO) 5 , Cr(CO) 6 , Mo(CO) 6 and V(CO) 6 , at 150°C ...
A nanostructured FeCrMoVM50 type steel was prepared via a chemical route. The process involved the thermal decomposition of organometallic precursors Fe(CO) 5 , Cr(CO) 6 , Mo(CO) 6 and V(CO) 6 , at 150°C for the formation of nanostructured M50 type steel powders. In addition to the thermal decomposition of these carbonyls, the results of the reduction of respective metal halides for the production of the same steel are also presented. The nanostructured steel powders obtained were also consolidated samples, were characterized using x-ray synthesized powders, as well as the consolidated samples, were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution electron microscopy (HRTEM). Possible mechanisms for the formation of nanostructured particles are also discussed.
The objectives of this research were (I) to determine whether the use of partially absorbable vascular grafts would improve their nonthrombogenic performance and whether they are more prone to aneurysmal dilation and ...
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The objectives of this research were (I) to determine whether the use of partially absorbable vascular grafts would improve their nonthrombogenic performance and whether they are more prone to aneurysmal dilation and subsequent failure in vivo. and (2) to find out the relationships, if any. between these in vivo and the previously reported in vitro data with an emphasis on how the in vitro changes in fabric structure and properties related to these in vivo data. Bicomponent vascular fabrics were made from Dacron and polyglycolic acid (PGA) yarns with a range of composition ratios of the PGA to Dacron. Both woven and single Jersey knit fabrics were made, and implanted in dogs for 4 months. The following findings and relationships were obtained. (1) The bicomponent vascular fabrics resulted in a full-wall healing in the thoracic aorta of dogs. All bicomponent vascular grafts in survived dogs exhibited 100% patency, no thrombus or aneurysmal formation, no hematoma or seroma around the grafts, and no fibrin coagula in the inner capsules. The gross morphology of the regenerated tissues was very similar visually to the adjacent original arterial tissue. Histologically, the luminal surface was lined with a layer of endothelial cells with myofibroblasts, fibroblasts. and collagens underneath. (2) The extent of the full-wall healing depended on the type of fabric structure. the concentration of absorbable yarns, the location of absorbable yarns (for the woven group only), and initial water permeability. It is believed that the concentration effect was related to the level of macrophage activation from the degradation products of the absorbable yarns, while the location effect was attributed to the various types of fabric structure change on the degradation of the absorbable yarns. (3) In general, the knitted group (K), was better than the woven group (W). K3 showed the best in vivo performance in the knitted group. (4) In the woven group, W3 was the best. The incorporation o
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