239 research outputs found
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Properties of Parially Cured Networks. 1. Curing Kinetics of a Model Network
Model networks based on a,w-dihydroxypoly(propylene oxides) and tris(4-isocyanatophenyl) thiophosphate were prepared. The curing kinetics were followed up to 97% conversion by measuring the change in the infrared absorption intensity of the isocyanate stretching band at 2200-23?0 cm·1. The ovall reaction kinetics were found to be second order and are described well by a scheme cons1stmg _ of competitive consecutive order reactions up to an extent of reaction of about 85% (the gel point). The observed incease in reaction rate at conversions greater than 85% is attributed to an increase in intramolecular reactions
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Critical Evaluation of Electron Microscopy of Ionomers
Electron microscopy has been used to examine the morphology of four ionomers. The transfertheory of imaging, which has been overlooked in previous ionomer studies, has been used to interpret theimages of both solvent-cast and microtomed thin films. Solvent casting was found to produce a number ofinteresting artifacts but no useful information about ionic domains. Microtomed sections of a copolymer ofethylene and methacrylic acid, sulfonated polypentenamer, and sulfonated polystyrene contained no preparativeartifacts but showed no distinct domain structure even in the ionomers neutralized with cesium, probablybecause of film thickness problems. Microtomed sections of sulfonated EPDM, however, contain 300-nmphase-separated regions. Osmium tetraoxide staining of these EPDM sections showed domains averagingless than 3 nm in size primarily inside these regions. Unfortunately, the section thickness prohibits an accuratedetermination of the size distribution or the detailed shape of these domains and hence the selection of themost appropriate model of domain structure
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Ionomeric Blends of Poly(ethyl acrylate-co-4-vinylpyridine) with Metal-Neutralized Sulfonated Poly(ethylene terephthalate). 4. Effects of Counterions
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Stochiometric Complexes of Synthetic Polypeptides and Oppositely Charged Surfactants in Organic Solvents and in the Solid State
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Methyl Ester Carboxylates: A Nuclear Magnetic Resonance Study
Nuclear magnetic resonance has been used to investigate relaxation in the methyl ester precursor of a perfluorocarboxylate ionomer. Whereas the findings are broadly consistent with earlier interpretations of dynamic mechanical relaxation, minor interpretative changes are indicated, principally a revision of the assignment of the \u27Y relaxation peak in the DMA data. Further insight is also obtained into the way in which even quite small amounts of water can influence in an important way the overall relaxation response of the system
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Vinyl-Substituted Silphenylene Siloxane Copolymers: Novel High-Temperature Elastomers
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