Inorganic polymer
Inorganic polymers are polymers with a skeletal structure that does not include carbon atoms in the backbone. Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are hybrid polymers. One of the best known examples is polydimethylsiloxane, otherwise known commonly as silicone rubber. Inorganic polymers offer some properties not found in organic materials including low temperature flexibility, electrical conductivity, and nonflammability. Inorganic polymers focus on 1-dimensional polymers, not heavily crosslinked materials such as silicate minerals. Inorganic polymers with tunable or responsive properties are sometimes called smart inorganic polymers. A special class of inorganic polymers are geopolymers, which may be anthropogenic or naturally occurring.
Traditionally, the area of inorganic polymers focuses on materials in which the backbone is composed exclusively of main group elements.
Homochain polymers have only one kind of atom in the main chain. One member is polymeric sulfur, which forms reversibly upon melting any of the cyclic allotropes, such as S8. Organic polysulfides and polysulfanes feature short chains of sulfur atoms, capped respectively with alkyl and H. Elemental tellurium and the gray allotrope of elemental selenium also are polymers, although they are not processable.
Polymeric forms of the group IV elements are well known. The premier materials are polysilanes, which are analogous to polyethylene and related organic polymers. They are more fragile than the organic analogues and, because of the longer Si-Si bonds, carry larger substituents. Poly(dimethylsilane) is prepared by reduction of dimethyldichlorosilane. Pyrolysis of poly(dimethylsilane) gives SiC fibers.
Heavier analogues of polysilanes are also known to some extent. These include polygermanes, (R2Ge)n, and polystannanes, (R2Sn)n.
Heterochain polymers have more than one type of atom in the main chain. Typically two types of atoms alternate along the main chain. Of great commercial interest are the polysiloxanes where the main chain features Si and O centers, -Si-O-Si-O-. Each Si center has two substituents, usually methyl or phenyl. Examples include polydimethylsiloxane (PDMS, (Me2SiO)n), polymethylhydrosiloxane (PMHS (MeSi(H)O)n) and polydiphenylsiloxane (Ph2SiO)n). Related to the siloxanes are the polysilazanes. These materials have the backbone formula Si-N-Si-N-. One example is perhydridopolysilazane PHPS. Such materials are of academic interest.
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