Polysilanes backbone functionalized poly

An LCAO (linear combination of atomic orbitals) local-density functional approach was used to calculate the band structures of a series of polymer chain conformations unsubstituted polysilane in the all-trans conformation and in a 411 helical conformation, and all-trans poly(dimethylsilane). Calculated absorption spectra predict a highly anisotropic absorption for the all-trans conformation of polysilane, with the threshold absorption peak arising strictly from polarizations parallel to the chain axis. The absorption spectrum for the helical conformation is much more isotropic. Results for the dimethyl-substituted polysilane chain suggest that the states immediately surrounding the Fermi level retain their silicon-backbone a character upon alkyl-group substitution, although the band gap decreases by I eV because of contributions from alkyl substituent states both below the valence band and above the conduction band to the frontier states. 

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]. 

Free radical chlorination of poly(phenylsilane) produces poly(chlorophenylsilane) These chlorinated polymers can be substituted with a variety of nucleophiles such as MeOH or MeMgBr with high selectivities. The spectroscopic properties of these materials are extremely sensitive to the nature of the substituent attached to the polymer backbone. The UV properties of a series of polysilanes containing Si-H, Si-Cl, Si-R and Si-OR functionalities are reported. The absorption maximum of poly(phenylsilane) appears at 294 ran (esi-si = 2489 cm-iM 0 whereas that of poly(methylphenylsilane) appears at 328 nm (esi-si = 4539 cm-iM-i). The absorption spectra of poly(metiioxyphenylsilane) are red shifted considerably relative to the other polymers (X = 348 nm, esi-si = 2710 cm- M-O. These substituent effects are likely due both to conformational as well as electronic perturbations on tfie Si-Si backbone chromophore. 

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