Polycarbosilane synthesis

Corriu et al. achieved polycarbosilane synthesis by catalytic hydrosilylation of vinylsilanes. For example, polydichlorosilaethane (49) was prepared from vinyldichlorosilane (48) using a platinum-on-carbon catalyst (Scheme 14). The product 49 was hydrolytically sensitive. However, owing to the reactivity of the Si l bonds, 49 could be chemically modified to a variety of products containing either Si H (50), SFR [R=Me (51), naphthyl, vinyl], or Si-alkoxy substituents and Si-F (52). 

See also PBT degradation structure and properties of, 44-46 synthesis of, 106, 191 Polycaprolactam (PCA), 530, 541 Poly(e-caprolactone) (CAPA, PCL), 28, 42, 86. See also PCL degradation OH-terminated, 98-99 Polycaprolactones, 213 Poly(carbo[dimethyl]silane)s, 450, 451 Polycarbonate glycols, 207 Polycarbonate-polysulfone block copolymer, 360 Polycarbonates, 213 chemical structure of, 5 Polycarbosilanes, 450-456 Poly(chlorocarbosilanes), 454 Polycondensations, 57, 100 Poly(l,4-cyclohexylenedimethylene terephthalate) (PCT), 25 Polydimethyl siloxanes, 4 Poly(dioxanone) (PDO), 27 Poly (4,4 -dipheny lpheny lpho sphine oxide) (PAPO), 347 Polydispersity, 57 Polydispersity index, 444 Poly(D-lactic acid) (PDLA), 41 Poly(DL-lactic acid) (PDLLA), 42 Polyester amides, 18 Polyester-based networks, 58-60 Polyester carbonates, 18 Polyester-ether block copolymers, 20 Polyester-ethers, 26... 

West (p. 6), Miller (p. 43), Zeigler (10), and Sawan (p. 112) outline the synthesis of a wide variety of soluble, processable polydiorganosilanes, a class of polymers which not long ago was thought to be intractable. Matyjaszewski (p. 78) has found significant improvements in the synthetic method for polydiorganosilane synthesis as well as new synthetic routes to unusual substituted polydiorganosilanes. Seyferth (p. 21, 143) reports synthetic routes to a number of new polycarbosilanes and polysilazanes which may be used as precursors to ceramic materials. 

Yajima, S.. Ha.segawa, Y., Hayashi, J., limura, M. (1978). Synthesis of continuous silicon carbide fiber with high tensile strength and high Young s modulus, part I, synthesis of polycarbosilane as precursor. J. Mater. Sci. 13, 2569-2576. 

The dehydrogenative double silylation method is extended to the synthesis of fused cyclic polycarbosilanes by the condensation of various diynes with l,2,4,5-tetrakis(dimethylsilyl)benzene.62 Polymeric compounds are formed with elimination of H2 [Eq. (20)]. 

Polycarbosilanes have also attracted much interest as starting material for silicon carbide fiber production. Reactive metal such as Mg88, Cu86,89,90 and Al91 electrodes have been shown to be highly effective for electrochemical synthesis of polycarbosilanes, as shown in Table 21. 

Hydrosilylation was also applied to the preparation of thiophene-terminated dimethyl-siloxane macromonomer, which is used for the synthesis of thiophene-dimethylsiloxane graft copolymers by oxidative polymerization281. Polycarbosilanes have been prepared by hydrosilylation-polymerization of l,4-bis(ethenylmethylphenylsilyl)benzene with 1,4-bis(methylphenylsilyl)benzene in various ratios282. 

This synthesis has been used to prepare polycarbosilanes with pendant aniline substituents.202... 

ROP of cyclic carbosilanes is one of the most promising techniques for the synthesis of well-defined polycarbosilanes. ROP of four-membered ring compounds, 1,3-disilacyclobutanes, and monosilacyclobutanes, as well as copolymerizations of mixtures of monomers, have been widely investigated in the last decades <1996JOMl, B-1996MI7621, B-2000MI247>. 

Preparative organosilicon chemistry offers manifold possibilities for the synthesis of precursors for nonoxide ceramics (Scheme 18.1). The focus has been on the synthesis of polymers such as polysilanes A, polysilazanes B, polycarbosilanes... 

In the following, the synthesis of different types of organosilicon polymers as potential precursors for ceramics is highlighted topologically, starting from polysilanes with Si-Si linkages, followed by polycarbosilanes. Subsequently polysilazanes with Si-N building blocks and polymers with multi-element sequences, such as PSCs (Si-N=C=N), will be discussed. 

SCHEME 18.8 Synthesis of a polycarbosilane to nearly stoichiometric SiC ceramics. The initial step is a Grignard coupling of dichloromethane and methyldichlorosUane. ... 

Synthesis by hydrosilylation of (R )(R2)SiH(HC=CH2) (R, R = H, Cl, alkyl, aryl, NR2) and the suitability of polycarbosilanes [(R )(R )Si-C2H4] obtained as precursors for silicon carbide/carbon composites were thoroughly investigated by Corriu et al. ... 

Previously it was shown that ROP of 1,3-disilacyclobutane is an efhcient method for the synthesis of polycarbosilanes (Scheme 18.9). Likewise, ROP of 1,3-disiladiazetanes, cyclo-(SiR2-NR )2, delivers linear high-molecular weight polysilazanes. Synthesis of 1,3-disiladiazetanes from bis(amido)silanes [R2Si(NRLi)2] and dichlorosilanes [R2SiCl2] was reviewed in detail by Fink in 1966.9 ... 

Acyclic diene metathesis (ADMET) polymerization of dialkenyl-substituted oiganosilicon derivatives occurring in the presence of molybdenum, tungsten, and ruthenium alkylidenes has been commonly used for the synthesis of a wide range of linear unsaturated organosilicon polymers, e.g., polycarbosilanes, polycarbosiloxanes, and related polymers [1-8]. 

Summary The stepwise synthesis of the polycarbosilanes (Cl2SiCH2CH2) (5) and (H2SiCH2CH2)n (6) are described. On addition of catalytical amounts of transition metal complexes to polymer 6 dehydrogenation occurs and a further crosslinked carbosilane (8) is obtained by formation of new silicon-silicon bonds. Pyrolysis of carbosilane 8 produces a black ceramic material, containing P-SiC together with carbon. The ceramic yield after pyrolysis of 8 is approximately four times the yield obtained when 6 is employed as the starting material. From polymeric 8 preceramic fibers are accessible subsequent pyrolysis yields ceramic fibers. Moreover, the carbosilane 8 can be utilized as a binder for ceramic powders. 

We here describe the synthesis of the polycarbosilane (H2SiCH2CH2) and its use as a preceramic compound for the preparation of silicon carbide in form of a powder or fibers. 

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