From Poly silanes

Further evidence of the importance of Si-H bonding in the precursor comes from comparison of a poly(carbosilane) produced from poly(dimethylsilane) in the conventional manner with a similar polymer produced by pyrolysis of tetramethylsilane and containing a lesser degree of Si-H bonding. These studies demonstrated the superiority of the material derived from poly silane in terms of both processing and ultimate properties of the ceramic fibre. 

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

The fluorescence of polysilanes has received much attention in recent years, in part because of the discovery that some poly silanes are electroluminescent, and so may have applications in display technology. Fluorescence spectra, quantum yields, lifetimes and other properties for dialkylpolysilanes have been thoroughly investigated by Sun and coworkers.98 Dialkylpolysilanes exhibit fluorescence of a rather normal type, in which the emission is a mirror image of the absorption, with a rather small Stokes shift. This suggests that the emission takes place from a highly delocalized state, probably an... 

An array of 10- i,m microlenses was fabricated from the adhesion of an aminated silicasol on a poly[methyl(phenyl)silane-co-methyl(3,3,3-tri-fluoropropyl)silane] (CF3PMPS) film patterned by UV light irradiation.132 By soaking the UV-patterned polysilane film into the sol-gel solution, a convex xerogel layer adhered only to the UV-exposed poly silane, which was cured to form a glass that functioned as a condensing lens. 

Fig. 20 Micellar fibers of PMPSnPEOtn in mixtures of THF and water (25/75 by volume). TEM images (a) visualizing the poly silane core of miceUar fibers (unstained, bar represents 250 nm) (b) revealing the PEO shell using nranyl acetate staining, (c) showing an example of the bulges found for many of these fibers, (d) Schematic representation of the structure of the micellar fibers showing the PMPS core and the PEO shell. Reproduced with permission from [79], Sommerdijk et al. (2000) Macromolecules 33 8289. American Chemical Society...

The rapid and quantitative displacement of phenyl groups from model silanes suggests that similar reactions with aryl-substituted polysilanes should lead to the triflated polymer. We have carried out this displacement under different conditions. Approximately the first 80% of the phenyl groups were removed rapidly from poly(phenylmethylsilylene). No free acid was observed... 

Effect of Polyhalogenated Additives. We (36) have also observed that the rate of bleaching of solid polysilane films upon irradiation is considerably slower than that observed for solutions at comparable optical densities. Although this result is consistent with the observed decrease in the quantum yields for scission, 4>(s), in going from solution to the solid state (24) (vide infra), this decreased sensitivity is inconvenient for imaging processes. For this reason, a search was made for compatible additives that might influence the bleaching rate of poly silane derivatives in the solid state. 

These results support current interpretations of the bathochromic shifts observed in dialkyl-substituted poly silane. Experimental results for poly(di-n-hexylsilane) indicate that as the temperature is cooled below a transition temperature of roughly -35 °C, the major absorption peak shifts from a broad peak at about 310-320 nm (3.9-4.0 eV) to a narrower peak at about 350-370 nm (3.3-3.5 eV), with the red shift being attributed to a transition from a disordered system with a large population of gauche bond twists in the silicon backbone and in the alkyl substituent to a planar dll-trans backbone conformation (5-8, 15). Results from polarized absorption spectra of stretch-oriented samples for the cooled samples exhibit absorbance only for polarizations parallel to the stretch (and presumably the chain axis) direction (22). 

Figure 3.56. UV spectra of an aliphatic poly silane demonstrating bleaching and blue shifting. Reproduced with permission from reference 192. Copyright 1984 Society of Photo-Optical Instrumentation Engineers.)...

Figure 3,57. SEMs of high aspect ratio images transferred into a hard-baked photoresist by oxygen RIE after mid-UV projection printing of a 0.25-ixm-thick poly silane resist. (Reproduced from r erence 193. Copyright 1984 American Chemical Society.)...

The standard method for synthesis of poly silanes follows the original preparation of (Me2Si) by Burkhard. Diorganodichlorosilanes are treated with finely dispersed sodium metal in an inert diluent, usually above the melting point of sodium. Homopolymers are obtained from single dichlorosUanes, whUe cocondensation of mixtures of dichlorosilanes yields copolymers (equation 33). Toluene is the most commonly used solvent, but other aliphatic or aromatic solvents are also effective. After completion of the reaction, the mixture is quenched with alcohol and/or water to destroy any excess sodium and silyl anion, then filtered and... 

We have shown that similar networks formed from bis(chloromethyl)biphenyl (BCMBP) exhibit surface areas as high as 1,904 m g [31]. Webster and coworkers have prepared HCPs by treating 4,4 -dilithiobiphenyl (as well as other multi-lithiated aromatic compounds) with dimethylcarbonate to generate polymeric carbinol networks with surface areas of 400-1,000 m g [24]. More recently, poly silane element-organic frameworks was synthesized via a lithiation route to yield microporous networks with BET surface areas in the range 780-1,046 m g" [40]. 

It has been established from conductivity measurements that thermally activated and field-assisted hole hopping is responsible for the charge transport in solid poly silanes [48,49], The mobility of the hole is as high as 10 m /V sec, while the mobility of the electron is a few orders of magnitude lower. In this section, we will show the reason why only the hole is mobile in polysilanes and how we can construct electron-conductive polysilanes. 

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