The development of an oriented noncrystalline phase in a semicrystalline polymer filament has been studied via X-ray scattering. These unique PET fibers contain a relatively high noncrystalline content and also have h...
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Blends of polystyrene (PS) and poly(styrene- b -ethylene oxide) (PS- b -PEO) were cast from a ternary solvent mixture containing 85% toluene, 10% tetrahydrofuran, and 5% methanol under conditions that favor crystalliz...
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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 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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