Poly ceramic precursors

The first type of polycarbosilane synthesized by using ADMET methodology was a poly[carbo(dimethyl)silane].14c Linear poly(carbosilanes) are an important class of silicon-containing polymers due to their thermal, electronic, and optical properties.41 They are also ceramic precursors to silicon carbide after pyrolysis. ADMET opens up a new route to synthesize poly(carbosilanes), one that avoids many of the limitations found in earlier synthetic methods.41... 

Figure 2.13. Photograph of the shaped magnetic ceramics obtained from crosslinked poly(ferrocenylsilane) precursor materials. Reproduced with permission from [96],...

Si-based polymers composed of [ SiRiR2 C=C ](Ri, R2=alkyl, phenyl, or H) units have been prepared because of their potential applications in areas such as ceramic precursors and conducting materials.Poly(phenylsilyle-neethynylene-1,3-phenyleneethynylene), [-Si(Ph)H-C=C-Ph-C=C-] (MSP)... 

Nafion [253], poly(vinyl alcohol) [254], and polyamide-6,6 [255]. A procedure often followed for polymers soluble in tetrahydrofuran (THF) is to add TEOS to a THE solution of the polymer, followed by addition of water (4 moles based on Si) in the form of 0.15 M HCl or 0.1 M NH4OH and allowing the reaction to take place. Films are made by casting on an inert substrate such as Teflon and drying under proper conditions. Nafion composite films are made by impregnating swoDen Nafion films in alcohol solution of TEOS. The micro- or nanocomposite films made by the sol-gel process are expected to have technological opportunities in important arena of gas-liquid separations, heterogeneous catalysis, electronic materials, and ceramic precursors. 

The dimers of type 47 and the B-N-bonded polymers 46 and 48 have been prepared from the corresponding B-chloroborazines and HN[Si(CH3)3]2 or H3CN[Si(CH3)3]2. They are useful as poly(borazinylamine) precursors for boron nitride ceramics [60, 61]. 

Narula, C. K., Schaeffer, R., and Paine, R. T. (1987) Synthesis of Boron Nitride Ceramics from Poly(borazinylamine) Precursors, J. Amer. Chem. Soc. 109,5556-5557. 

A) The coupling of 7t-conjugation in polyacetylene (and related poly-phenylenevinylenes) and cr-conjugation in polysilanes to produce hybrid materials with potentially new or superior optical or optoelectronic properties, and/or to generate efficient ceramic precursors, has been an important... 

Poly(titanocarbosilane) has been employed as a precursor to a ceramic fibre with better resistance to crystallization and grain growth than silicon carbide fibre from a poly(carbosilane) precursor. This precursor is synthesized by heating poly(dimethylsilane) with minor proportions of poly(boro-diphenylsiloxane) and titanium alkoxide. " Little detailed characterization of the polymer has been reported, but it is believed that the titanium alkoxide functions as a crosslinking agent and the poly(borodiphenylsiloxane) as a catalyst. The reaction is carried out at 340 °C under an inert atmosphere. 

A further extension of the concept of thermosetting polysilazanes with peroxide initiators has been the preparation of new polysilazanes with peroxide groups bound directly to the polymer 20). Potential advantages of a peroxide-substituted polysilazane over systems in which the peroxide is simply admixed with the polymer include 1) segregation of the peroxide upon storage cannot occur, 2) dissolution or dispersion of a peroxide in the polysilazane is not necessary, and 3) homogeneous distribution of e peroxide in solid, as well as liquid, polysilazanes is possible. We have prepared a new class of peroxide-substituted polysilazanes by the reaction of a hydroperoxide with a poly(methylvinyl)silazane. The liquid polymers may be thermoset, even with extremely low levels of peroxide substitution. This chemistry provides access to a class of polysilazanes previously unknown as ceramic precursors. 

Turning now to other types of ceramic fibre, the most important material made by pyrolysis of organic polymer precursors is silicon carbide fibre. This is commonly made from a poly(diorgano)silane precursor, as described in detail by Riedel (1996) and more concisely by Chawla (1998). Silicon nitride fibres are also made by this sort of approach. Much of this work originates in Japan, where Yajima (1976) was a notable pioneer. 

Other monomeric precursors similar to 6-hexynyl-decaborane such as 6-norbornenyl-decaborane (129) and 6-cyclooctenyl-decaborane (131) (Fig. 75) underwent ROMP in the presence of either first- or second-generation Grubbs catalysts to produce the corresponding poly(norbornenyl-decaborane) (130) (Fig. 75) and poly(cyclooctenyl-decaborane) (132) (Fig. 75) with Mn > 30 kDa and polydis-persities between 1.1 and 1.8.152 Electrostatic spinning and pyrolysis of poly (norbomenyl-decaborane) was discovered to produce nanoscale, free-standing porous boron-carbide/carbon, ceramic fiber matrices.153... 

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