Polymeric precursors boron nitride

Potential Non-Cvcllc Precursors of Preceramic Polymers. Boranes such as bis(trimethylsilyl(aminotrimethylsilylaminochloroboranes can be viewed as monomers for preceramic polymer and, ultimately, boron nitride production. Intermolecular dehydrohalogenation of this borane would be thus expected to yield either the dimer or the polymeric system. 

Renewed interest in borazine derivatives has resulted from their possible application as precursors to boron nitride ceramics. For example, the inorganic analogue of styrene, (H->C=CH)B3NjH5i has been polymerized and decomposed to produce BN.72... 

Hexagonal boron nitride can be conveniently prepared by pyrolysis in an inert atmosphere of polymeric precursors such as polyborazilene, the structure of which has been investigated by B and N NMR (Gervais et al. 1998, 2001). Signals at 31 and 26 ppm in the B MAS NMR spectrum of the polymer are in the region of tricoordinated boron, and are attributed to BN2H and BN3 sites. Since the central transition in these... 

Yajima s trendsetting work has not only renewed interest in polysilanes but also in other polymeric materials that can function as precursors for ceramics such as silicon nitride, Si3N4 and boron nitride, BN [6]. 

P. J. Fazen, J. S. Beck, A. T. Lynch, E. E. Remsen, and L. G. Sneddon (1990), Thermally induced borazine dehydropolymerization reactions. Synthesis and ceramic conversion reactions of a new high-yield polymeric precursor to boron nitride, Chem. Mater. 2, 96. 

One attractive molecular species upon which polymeric boron nitride precursors could be based is the ring-compound borazine, BaNsHe The compound is easily made and has both the correct boron/nitrogen ratio and a hexagonal structure. Indeed, Paine and Paciorek have each demonstrated the use of linked polyborazine gels or polymers as precursors for boron nitride. 

We are presently exploring the use of both poly(vinylborazine) and poly(borazylene) as prcscursors for the formation of boron nitride films, coatings and fibers. Because of its technological importance, one application that we have been pai ticularly interested in is the use of polymeric precursors for the formation of boron nitride coatings on... 

ABSTRACT. The conventional approach to produce polymeric ceramic precursors of non-oxidic materials involves condensation reactions of reactive intermediates. In many cases these reactions lead to intractable products. An alternative approach was examined which could afford better control over the properties of the product. This involved the derivatization of preformed polymers of appropriate molecular weight and functionality. Polyethyleneimine, (CH2-CH2-NH)n was derivatized to introduce the -BH2, -BH2CN, and -BH2-CH2-NBH functionalities. These materials produced boron nitride upon pyrolysis and could be used to spin-coat a variety of substrates. 

New processes for the production of powders have been developed. Molecular precursor methods for preparing nitrides are currently being explored. A precursor processible to metal boride is obtained by dispersing a metal source in a boron carbide polymeric precursor. Electro-chemically prepared polymeric precursors have been used for the formation of pure nitride and carbide powders. Direct formation of carbides and diborides by mechanical alloying of metal powder and carbon or boron powder is also an effective method for synthesizing nanocrystalline powders. 

Borazine-Modified Hydridopolysilazanes. Polysilazanes have been shown to be excellent polymeric precursors to silicon nitride or SiNC ceramic materials. Chemical modification of polysilazanes has also been proposed as a means of modifying and enhancing e properties of the polymer and/or the final ceramic materials. For example, the incorporation of boron in the polysilazane has been claimed to decrease the crystallinity of the silicon nitride deriv from these polymers and thereby extend the effective use-temperature of these ceramics. Given the potential importance of SiNCB ceramics, investigations of the generation of new classes of hybrid polymers that might serve as processable precursors to such composites were initiate. 

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