Polymers and the periodic table: Recent developments in inorganic polymer science

Polysiloxanes [-R2Si-O-]n, polyphos-phazenes [-R2P=N-]n, and polysilanes [-R2Si-], illustrate that the incorporation of inorganic elements into a polymer main chain can lead to useful properties. These include low temperature flexibility, high thermal and oxidative stability, flame retardancy, novel forms of chemical reactivity, and intriguing electrical and optical characteristics arising from unusual electronic effects such as the delocalization oftr electrons. However, until recently, the development of inorganic polymer science has been held back by the synthetic problem of finding ways to join atoms of inorganic elements together into long chains. This review surveys many of the exciting advances in the field ofinorgan-ic polymers over the past decade and focuses mainly on the new inorganic polymer systems that have been prepared during this period. These include ran-dom-network polysilynes, poly(carbo-phosphazene)s, sulfur-nitrogen-phos-phorus polymers, poly(organooxothi-azene)s, and, very recently, the first examples of polystannanes that possess a main chain of tin atoms. Transition metal based polymer science has also experienced a number of synthetic breakthroughs and new materials include high molecular weight metallocene-based polymers, polymetallaynes incorporating elements such as iron, nickel, and rhodium, liquid crystalline organocobalt and organochromium polymers, and lanthanide-based polymers.