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Polymers are fundamentally covalently bonded molecules of extremely large molecular size. All of them exploit the ability of certain covalent bonds to concatenate in a stable manner. Sufficiently stable single bonds include carbon-carbon, carbon-oxygen, and silicon-oxygen. Bonds such as sulfur-sulfur and selenium-selenium, though stable at ambient temperature, destabilize at elevated temperatures. Depolymerization occurs, and the materials revert to atomic solids. Selected atoms, such as nitrogen, sulfur, and even some transition metals, may be incorporated singly into the covalently bonded polymer chain, provided they are stabilized by a neighboring link, such as a carbon-oxygen bond. In recent years more exotic polymeric systems have been produced. These include chains of alternating phosphorus-nitrogen, sulfur-nitrogen, and boron-nitrogen. All of these newer systems are based on pairs of elements which produce relatively unstable single bonds. The successful polymers contain double bonds of enhanced stability; many are oxidation resistant. Double bonding can produce special electrical properties, and the possibility exists of synthesizing polymeric materials which are intrinsically conductive or semiconductive.
University of Utah, Salt Lake City, Utah