Academic literature on the topic 'Unique Continuation Property'

In polysilane polymers, the polymer backbone is made up entirely of silicon atoms. Therefore these materials differ from other important inorganic polymers, the siloxanes and phosphazenes, in which the polymer chain is heteroatomic. Structurally, they are more closely related to homoatomic organic polymers such as the polyolefins. However, because the units in the main chain are all silicon atoms, the polysilanes exhibit quite unusual properties. The cumulated silicon-silicon bonds in the polymer chain allow extensive electron delocalization to take place, and this delocalization of the sigma electrons in the Si-Si bonds gives the polysilanes unique optical and electronic properties. Many of the potential technical uses, as well as the remarkable properties, of polysilanes result from this unusual mobility of the sigma electrons. The polysilanes can be regarded as one-dimensional analogs to elemental silicon, on which, of course, nearly all of modern electronics is based. The photophysical behavior of polysilanes is not approached by any other materials, save for the less stable and more costly polygermanes and polystannanes. The remarkable properties of polysilanes have led to intense interest, and to numerous proposed high-tech applications. But the great promise of polysilanes as materials has yet to be realized. Their only commercial use at present is as precursors to silicon carbide ceramics, an application which takes no advantage of their optical or electronic properties. Linear polysilane polymers, properly called poly(silylene)s, can be obtained as homopolymers or copolymers. Continuation of the polysilane chain consumes two of the four valences of each silicon atom; the other two are taken up by pendent groups, which may be the same or different. Copolymers, which contain two or more kinds of silicon atoms, can be made up from units. A typical example is the copolymer of Me2Si and PhMeSi units, poly(dimethylsilylene-co-phenylmethylsilylene), which bears the popular name “polysilastyrene.” The pendent groups are typically organic units and can include alkyl, aryl, substituted aryl, hydrogen, Me3Si, ferrocenyl, and so on. An unlimited number of different polymers are possible, and several hundred compositions have been described in the literature.