Polymerization of silanes

Investigations of silicon-metal systems are of fundamental interest, since stable coordination compounds with low valent silicon are still rare [64], and furthermore, silicon transition-metal complexes have a high potential for technical applications. For instance, coordination compounds of Ti, Zr, and Hf are effective catalysts for the polymerization of silanes to oligomeric chain-silanes. The mechanism of this polymerization reaction has not yet been fully elucidated, but silylene complexes as intermediates have been the subject of discussion. Polysilanes find wide use in important applications, e.g., as preceramics [65-67] or as photoresists [68-83],... 

Dehydrogenative Coupling. Transition-metal catalyzed polymerization of silanes appears to hold promise as a viable route to polysilanes. A number of transition-metal complexes have been investigated, with titanium and zirconium complexes being the most promising (105—108). Only primary silanes are active toward polymerization, and molecular weights are rather low. The dehydrogenative polymerization is depicted in reaction 11, where Cp = cyclopentadienyl ... 

Figure 8.1 Horizontal (a) and vertical (b) polymerization of silanes on a silica surface.

Tilley, T. D. Woo, H.-G. Catalytic Dehydrogenative Polymerization of Silanes to Polysilanes by Zirconocene and Hafnocene Catalysts. A New polymerization Mechanism, (H. F. Harrod, R. M. Laine, Eds.) Inorganic and Organometallic Oligomers and Polymers, Kluwer Academic Publishers, Netherlands, 1991, p. 3. 

Some mechanistic material is included in an annual review of silicon chemistry. A novel mechanism for the dehydrogenative polymerization of silanes... 

Polymerization of Silanes with Platinum Metal Catalysts... 

Polymerization of Silanes with Platinium Metal Catalysts 555... 

Tilley TD (1993) The coordination polymerization of silanes to poiysiianes by a o-bond metathesis mechanism. Implications for linear chain growth. Acc Chem Res 26(l) 22-29... 

T. D. Tilley, Acc. Chem. Res., 26, 22 (1993). The Coordination Polymerization of Silanes to Polysilanes by a cr-Bond Metathesis Mechanism. Implications for Linear Chain Growth. 

Indenylnickel complex catalyzes the polymerization of silanes, olefins, and alkynes. An... 

CATALYTIC DEHYDROGENATIVE POLYMERIZATION OF SILANES TO POLYSILANES BY ZIRCONOCENE AND HAFNOCENE CATALYSTS. A NEW POLYMERIZATION MECHANISM. 

In general, d silyl complexes are reactive toward primary and secondary silanes. We have found that a number of metallocene derivatives of the type Cp2M(SiR3)R (Cp = Cp, Cp s TlS-CsMes M = Zr, Hf R = Me, Ph, SiMes R = Cl, alkyl, silyl) are catalyst precursors for the dehydrogenative polymerization of silanes. An example of such a polymerization is shown in equation 3. The polymer s molecular weight... 

Catalytic Dehydrogenative Polymerization of Silanes to Polysilanes by Zirconocene and Hafnocene Catalysts. A New Polymerization Mechanism. 

Choice of Silanes for SiOx Film Deposition. Plasma polymerization of silanes results in plasma polymer films which contain carbonaceous components such as Si-C and CH2-CH2 groups within SiOx networks. In order to form SiOx networks without the carbonaceous components, carbonaceous components should be excluded from the deposited SiOx films. Many researchers have followed a heating procedure for the elimination of the carbonaceous components from the deposited SiOx films but this procedure is not applicable to SiOx-deposited PET films because of poor thermal-resistance of the film. In this study, a silane that was suitable for the SiOx deposition with less carbonaceous component was investigated. Five silanes, TEOS, TrEOS, TMOS, DMDMOS, and TMS, which contained different C/Si atomic ratio of 8 to 4 and different bond structure (Si-O-C and Si-C bonds) between Si and C atoms, were used for the plasma polymerization. Table I compares file C/Si atomic ratio in the deposited SiOx films from the five silanes. The C/Si atom ratio in the deposited SiOx films, as shown in Table I, depends on the C/Si atomic ratio and the bond structure in the starting silanes Silanes with a small C/Si atom ratio deposit SiOx films with a low carbon content, and silanes with Si-O-C bonds also deposit SiOx films with a low carbon content. From this viewpoint, TMOS is preferable to TEOS, TrEOS, DMDMOS, and TMS as a silane for SiOx deposition with a less carbonaceous component, although TMOS is not yet a satisfactory material for the SiOx deposition. The SiOx film deposited from TMOS reveals a C/Si atom ratio of 1.5. 

Three factors for the SiOx deposition by plasma polymerization of silanes were investigated. The three processes are (1) choice of silane compounds used as a starting material for the SiOx film deposition by the plasma CVD, (2) oxidation processes by the oxygen plasma, and (3) etching processes occurring near an electrode surface. The chemical composition of the deposited SiOx films and the oxygen gas barrier capability of the SiOx-deposited PET films were investigated. Results are summarized as follows. 

Frequently plasma polymers are not classified in respect of the type of monomer but from a point of view of their chemical composition and morphology. For example, amorphous (a-) covalent material obtained by plasma polymerization of silane (SiFLj), which is composed of silicon and hydrogen, can be termed as a-Si H. In turn, amorphous plasma polymer deposited from acrylonitrile (C3H3N) can be called as plasma-polymerized (pp-) acrylonitrile or a-CxNy H. It is usually met, but it is not a rule, that if the plasma polymer structure is close to a covalent glass structure, the latter notation is used. If plasma polymer reveals nano- or microcrystalline structures, prefixes nc- or pc- are put in the place of a-. 

Polysilanes have also been synthesized by dehydrogenative polymerization of silanes (i.e. S1H2R2 -[-Si(R2H-) using zirconocene and h ocene catalysts. So far, these... 

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