Syntheses, Structures, Properties, and Applications of Some Novel Elastomers

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The basic goal of this program is to obtain structure-property relationships that can be used to optimize the properties of elastomeric materials. For example, stress-strain results on a variety of elastomeric materials in elongation, biaxial extension, shear, and torsion will be interpreted using both analytical theories based on entanglement-constrained network junctions, and computer simulations. Elastomers will include both commercially important polymers cross linked by some of the relatively uncontrolled techniques used in the industry, but also some elastomers prepared using more selective reactions designed to give networks of better known structure. Such tailor-made networks will be prepared by end linking functionally-terminated polymer chains, an approach that can also be used to synthesize unusual networks with multimodal network chain-length distributions. These results should give a much better molecular understanding of rubberlike elasticity, and provide guidance in the design of materials of unusually attractive mechanical properties. Experiments on these materials that are of particular interest will be stress-strain measurements for identifying maximum extensibilities and toughness. Novel reinforcing fillers such as silica will be generated in-situ by hydrolyses of precursors such as organosilicates, and simple metal salts such as ferric chloride. Of particular importance will be identifying the particle size that maximized reinforcement, and characterizing the effects of particle size that maximizes reinforcement, and characterizing the effects of particle shape and the orientations of non-spherical particles. Novel materials will be prepared by coating particles of one type with a ceramic of another type. It will also be possible to the thread elastomeric chains through reinforcing zeolites, and to prepare fillers that can be manipulated by a magnetic field. The resulting filler-reinforced elastomers will be characterized primarily by mechanical property measurements, electron microscopy, and by X-ray and neutron scattering. Two newer approaches which already show considerable promise are pulse-propagation measurements and Brillouin spectroscopy.This project is focused on learning how the structures of elastomeric materials can be controlled in order to maximize their mechanical properties. The most important structural features are the chemical natures of the elastomers and how they are linked into networks, and the most important properties are their strengths, extensibilities, and toughness. The approaches taken are primarily experimental, but will be guided by parallel computer simulations and analytical theory.