Polysilanes siloxanes

Polysilanes bearing triflate groups are very reactive and form an insoluble gel with a trace of moisture. The triflate group is hydrolized to silanol which rapidly condenses with the remaining triflate groups to a siloxane unit, linking intra or intermolecularly silicon atoms ... 

Polysilane co-polymers with pendant siloxane groups were also synthesized, aiming at air oxidation-resistant polysilanes, utilizing the partial tendency for phase separation of polar side chain and apolar main chain, resulting in surface accumulation of siloxane groups,154 155 as shown in Scheme 20. 

Scheme 37 m-CPBA oxidation of ladder polysilanes to hybrid silane/siloxane polymers (substituents /-Pr). 

Siloxanes Polyphosphazenes Polyphosphate esters Polysilanes Sol-gel networks... 

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. 

Various methods may be used to examine configurations of polysilanes, but 29Si NMR spectroscopy has been the most useful. Silicon-29, like carbon-13, has spin 1/2 and a relatively low abundance, 4.7%. Nuclear magnetic resonance (NMR) spectroscopy using 29Si has been important for the characterization of siloxane polymers, and is proving to be equally useful for polysilanes. 

Oxidation by Oxygen, Perbenzoic Acid, and Other Substances Acyclic peralkylated polysilanes are sufficiently stable to air oxidation to be handled at moderate to relatively high temperature without specific precautions. On the other hand, five-membered ring compounds are easily attacked by molecular oxygen and converted to siloxanes 21, 115, 122). 

The interaction of polysilanes with X-ray photoelectrons (XPS) has been used for theoretical studies" and for analytical purposes.19 Seven polymers with silane, carbosilane, and siloxane fragments—(-Si(CH3)2-)n (PDMS),... 

The reaction chemistry of the polysilanes (particularly those formed from PhSiH3) have been studied to a limited extent and will only be mentioned briefly here. The polysilanes, H(RSiH)raH, obtained from dehydrocoupling are air-sensitive producing a siloxane-type structure for the polymer... 

It is not clear whether enrichment will find use in organosilicon studies even if isotopic enrichments become feasible for polysilanes or siloxanes. 

The MM2 force field has also been parameterized for silicon-containing molecules by Grigoras and Lane.i- The parameters were based on ab initio calculations and included new bond stretch, angle bend, torsional, and van der Waals parameters, which accurately reproduced the ab initio calculated properties of small silanes, polysilanes, and siloxanes. The same authors used this force field to study the structures of some biologically active compounds containing silicon. The siloxane 2,6-c/s-diphenylhexamethylcyclotetrasiloxane (9) has estrogenlike activity. Grigoras and Lane compared the distance between... 

Of these, the siloxanes or silicone polymers have been studied the most and are also of the greatest commercial importance (3-8). Increasingly important, at least for some specialized applications, are the polysilanes (3, 9),... 

Industrially produced organo-silicon compounds include monomeric low molecular compounds, almost exclusively belonging to the class of silanes, and oligomers and polymeric compounds including oligomeric silanes, polysilanes, oligomeric silazanes, polysilazanes and particularly oligomeric siloxanes and polysiloxanes (silicones). 

---