Soluble polysilane synthesis

This adventitious finding led to synthesis of the "polysilastyrene" family of Me2Si-PhMeSi copolymers.(11) At almost the same time, soluble polysilanes were reported by Trujillo(12) at Sandia Laboratories and by Wesson and Williams(12) at Union Carbide Co. 

Shortly after Burkhard s publication, a patent by Clark claimed the synthesis of soluble polysilanes, but since this work was never published it was somewhat overlooked. See H. A. Clark,... 

This synthetic strategy has allowed us to synthesize a real head-to-tail polysilastyiene. In 1981 West et al. reported the first synthesis of a soluble polysilane copolymer from methylphenyldichlorosilane and dimethyldichlorosilane [10]. The copolymer was called polysilastyrene, based on its structural similarity to carbon-based polymer, i.e., polystyrene. 

Synthesis. The first report of a soluble polysilane appeared in 1978 and the material was prepared by the treatment of a mixture of organodichlorosilanes with sodium metal (33). Instead of only the expected cyclic oligomers, a polymeric product, termed polysilastyrene (10), was formed. Poly(dimethylsilane) had been previously prepared as a highly crystalline insoluble material (1,27,28). The introduction of phenyl groups in the random copolymer reduces the crystallinity and allows the material to be soluble and processible. 

Since their discovery in the early 80 s soluble polysilanes became the subject of numerous papers in differents fields synthesis, physical properties, optical properties and applications. Among them very few are devoted to the actual molecular wei t determination by... 

Figure 4. shows the route from the high boiling residue of the direct synthesis to silicon carbo-nitride fibers. Methylchlorodisilanes and trichlorosilanes as additives are mixed in a specific ratio and react with methylamine and a small amount of ammonia to form an aminodisilane/oligosilazane. The subsequent polycondensation reaction of this mixture by heating to 250 °C yields a soluble and melt spinnable polysilazane. In comparision with the polysilane the properties of the polysilazane depend on the ratios of the disilanes/silanes and methylamine/ammonia and also on the reaction conditions. 

With the success of CgK in the syntheses of 41 and related co-polymers, the same methodology was applied to the synthesis of polysilanes bearing pendant crown ether substituents, viz. 42-44,150,151 which were synthesized in yields from 6% to 28%, with molecular weights of the order of 104. The polymers were found to be water soluble and thermochromic in accordance with the Schweizer thermochromism theory (see Section 3.11.5.2.4).152... 

Soluble and well-characterized polygermane homopolymers. (R Ciel,. and their copolymers with polysilanes have been prepared by the alkali metal coupling of diorgano-stbstiluled dihalogermancs, via clectrochemicul methods, and by tnmsition-metal catalyzed routes, as with the synthesis of polysilanes. 

Interest in polysilanes was reawakened in 1975, when Yajima and Hayashi found that permethylpolysilane could be transformed into silicon carbide by heating at high temperatures. Soon afterward, papers on soluble, meltable polysilanes began to appear. The literature on polysilanes has grown rapidly since that time. The early focus on the synthesis and simple characterization of polysilanes has given way to detailed physical studies of the structure of these polymers, and of their electronic and photophysical properties. 

The modern era in polysilane chemistry began about 10 years ago with the synthesis of a number of soluble homo- and copolymers (3-5). The current interest in substituted polysilanes has resulted in a rapidly expanding list of new potential applications, which include the use of polysilanes as ... 

Because of the low solubility of most poly silanes in combination with expandable processing, that is, purification including the above mentioned hydrolysis steps, product yields and purity are often unsatisfactory if obtained by reductive coupling of chlorosilanes. A further negative aspect of this approach is the limited functional group tolerance. Accordingly, only the synthesis of polysilanes with inert pendant groups such as alkyl or aryl can be adequately achieved. 

West et al. described the synthesis of polysilastyrene , a copolymer of dimethyldichlorosilane and phenylmethyldichlorosilane [46], the first polysilane which is soluble in organic solvents ... 

However, the structure of the copolymer was blocky with runs of the respective monomer units, and hence the polymer was not the real polysilastyrene [11]. Phenylation of the chloro-substituted polysilane 3 with phenyllittuum gave poly(l,l,2-trimethyl-2-phenyldisilene) in good yield. The structure of the polymer was confirmed with the SEC and NMR spectra. We have now succeeded in the preparation of the real head-to-tail polysilastyrene (4, R = Ph) about 20 years after the first reported synthesis of soluble polysilastyrene. This procedure is a simple method for preparing polysilanes of special structure with functional groups which are otherwise very difficult to prepare. 

At the present time, most of the work is centered on the development of silicon carbide and silicon-nitride powders. Polysilanes are the basic precursor for the synthesis of silicon carbide from sol-gel. This was first achieved by the conversion of polydimethyl silane through a carbosilane intermediate. However this silane has poor solubility and low char yield and considerable shrinkage occurs during conversion to the final product. Precursors are being developed with a much larger SiC yield notably those based on trifiinctional alkoxides and chlorosilanes. These materials are being evaluated for the production of powders.P JP l... 

Additionally, it is known that cyclic SiaClg can be polymerized in an ROP via radical species to yield an insoluble but moisture sensitive polymer with an estimated degree of polymerization of about 35 and a molecular weight of about 3,500gmor [45]. Due to the insolubility and the high sensitivity to moisture, there have been no further reports on a ring opening type synthesis of perchlorinated polysilanes [42,45]. Nevertheless, a functionalization by reaction with isopropanol has been accomplished which led to an increased solubility and enabled a SEC-analysis [45]. 

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