Dialkylamino-substituted polysilanes

Polymerization ofiVIasked Disilenes. A novel approach, namely, the anionic polymerization of masked disilenes, has been used to synthesize a number of poly(dialkylsilanes) as well as the first dialkylamino substituted polysilanes (eq. 13) (111,112). The route is capable of providing monodisperse polymers with relatively high molecular weight M = lO" — 10 ), and holds promise of being a good method for the synthesis of alternating and block copolymers. 

The masked disilene strategy was also successfully applied to the synthesis of dialkylamino-substituted polysilanes,60 61 63 by the -butyllithium-initiated polymerization of dialkylamino-substituted phenyldisilabicycloocta-dienes, as shown in Scheme 23. 

Polyphenylsilane, (PhSiH) , can be derivatized by free-radical hydrosilylation in the presence of a radical initiator. Alkenes, ketones and aldehydes react readily, to replace up to 93% of the Si-H bonds. This route can be employed to make polysilanes with hydrophilic groups, such as hydroxy, amino and carboxylic acid functions.43 Dialkylamino substituted polysilanes, made by the anionic polymerization of masked disilenes (see equation (17)), when treated with acetyl chloride give chloro-substituted poly silanes. The chlorine can then be displaced by other nucleophiles.27... 

Scheme 23 Preparation of dialkylamino-substituted heteroatom polysilanes by masked disilene method.

The chemical and physical properties of polysilanes are strongly influenced by substituents attached to the polymer backbone. In this respect, heteroatom-substituted polysilanes should be very much intriguing on their properties. However, heteroatom-functional substituents such as amino and alkoxy groups on silicon cannot survive under the vigorous synthetic conditions of polysilanes by the conventional Wurtz-type condensation of dichlorosilanes. Therefore, it is difficult to prepare heteroatom-functional polysilanes. We have recently found that amino-substituted masked disilenes can be prepared and polymerized successfully to unprecedented amino-substituted polysilane of the completely alternative structure, poly[l,l,2-trimethyl-2-(dialkylamino)disilene]. 

---