Polysilanes, linear

Physical properties of the polysilanes depend greatly upon the nature of the organic groups bound to silicon. A few of the many polysilanes are listed in Table I. Typically the linear polysilanes are thermoplastics, soluble in organic solvents like toluene, ethers,... 

The second approach to linear polysilanes is based on the modification of polysilanes prepared by the reductive coupling method. The severe conditions of this reaction allow only alkyl or aryl substituents at the silicon atom in the starting dichlorosilane. Therefore only alkyl or aryl substituted polysilanes are known. We have successfully prepared new polysilanes with pendant alkoxy and amino side groups. This approach allows fine tuning of the properties of... 

By way of contrast, methyl-containing silanes form linear polysilanes in yields up to 60 %, depending on the starting material ... 

Fig. 10. Lowest transition energies for ladder and linear polysilanes. Values for linear poly silanes are cited from reference 44.

The experimental observations of red shifts of the UV absorptions tails with increase in silicon dimensionality were corroborated by ZINDO-calculated spectra comparing linear polysilane, network polysilyne, crystalline cluster, and amorphous cluster structures, which showed respectively lowest absorption transition energies of 5.38 eV (230.4 nm), 4.60eV (269.5nm), 4.57eV (271.2nm), and 2.46eV (503.9nm), as shown in Figure 57.362... 

Catalytic dehydrogenative coupling of organohydrosilanes, a common method for the formation of linear polysilanes, can also be applied to cyclopolysilane synthesis. Thus, benzylsilane reacts to give all-fraws-hexabenzylcyclohexasilane in the presence of dimethyltitanocene (equation 3). However, extremely long reaction times are required and only moderate yields are obtained15. 

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 (5.1) or different (5.2). Copolymers (5.3), which contain two or more kinds of silicon atoms, can be made up from units like those in 5.1 or 5.2. A typical example is the copolymer of Me2Si and PhMeSi units,... 

Other linear polysilanes can also be used as ceramic precursors. Solid objects of silicon carbide are manufactured by Nippon Soda Co. from polysilastyrene and finely divided silicon carbide powder.133 These materials are blended, injection molded to the... 

The three types of compounds to be considered here are a homologous series of linear polysilanes with the general formula CH3[Si(CH3)2]BCH3, where n equals 2 through 12 a few branched-chain compounds and three cyclic polysilanes of the formula [(CH3)2Si] , n being 5, 6, and 7. 

The homologous series of linear polysilanes with the formula (XIII) are prepared by treating appropriate methylchlorosilanes with sodium-... 

Fig. 1. Variation of melting point with the number of silicon atoms in the case of permethylated linear polysilanes.

The cleavage of decamethyltetrasilane by sodium-potassium alloy followed by coupling with trimethylchlorosilane gives several lower homologs of methylpolysilanes of both linear and cyclic type (179). Although the formation of linear polysilanes up to the tetrasilane is understood in terms... 

Completely networked polysilanes show a variation of n and k with the degree of cross-linking compared to parent linear polysilanes. 

Most linear polysilanes show bright resonant luminescence in the UV region but network and branched polysilanes show luminescence in the visible... 

The branched polysilanes show a broad emission peak around 450 nm, where the large red shift in the fluorescence spectra is due to the influence of aryl substituents and the introduction of branched points. For (opto)electronic applications, the UV irradiation and thermal stability are crucial to device stability. Branched polysilanes have better thermostability and are more resistant to UV irradiation than are linear polysilanes. 

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