Polymers borazine-derived

Hydrogels and amphiphilic membranes Poly(carbophosphazenes) and poly(thiophosphazenes) New condensation syntheses NLO and high refractive index polymers Microencapsulation of mammalian cells (PCPP) Polyphosphazene polymer blends and IPN s Borazine derivatives Poly(phosphazophosphazenes)... 

Alternative synthetic approaches to Si-B-C-N-H polymers starting from functionalized borazine derivatives were published by Srivastava et al. " and Haber-echt et al." Srivastava et al. published a method for synthesizing a soluble borazine-based Si-B-C-N-H polymer by reacting B-chloroborazines with LiSi(Si(CH3)3)3 followed by subsequent polymerization with hexamethyldisilazane. 

Initially, BN was synthesized by the pyrolysis of boric acid and urea in the presence of ammonia [27]. In this reaction, boric acid presumably reacts with urea to form a urea-boric acid complex gel, which on pyrolysis in an ammonia atmosphere results in the formation of BN [28]. Precursors for BN recently received the greatest attention, with emphasis on borazine-derived polymers. It has been recognized that borazine (1) can form polymeric chains of B and N, which can form BN ceramics on thermal pyrolysis [29]. The polymerization gives a graphitelike hexagonal layered structure (2) ... 

Polymers included in this category are generally called polyborazylenes. Synthetic route to these polymers have been reviewed [8] thus, we provide an overview of typical synthesis procedures starting from borazine derivatives and leading to BN preceramic polymers. 

Abstract - Studies of the syntheses, properties and ceramic conversion reactions of the new processable borazine-derived polymer systems, poly(vinylborazine), poly(vinylborazine/styrene) and poly(borazylene), along with selected applications of these polymer precursors for the formation of boron nitride ceramics are described. 

The area of organoboron polymers containing borazine and its derivatives is covered in Chapter 5 of this book by Miele and co-workers. Miele and Bernard also describe the utilization of these polymers in ceramics, fibers, and so on, in Chapter 3 of this book. In this section, the utilization of polymers containing borazine or in some cases the bicyclic boron ligand, 9-BBN, for the production of SiC or Si/C/B fibers is briefly described. Recent advances in polypyrazolylborate or pyrazabole-containing polymers and other boron ring system-derived polymers also have been briefly described. 

The photochemistry of borazine delineated in detail in these pages stands in sharp contrast to that of benzene. The present data on borazine photochemistry shows that similarities between the two compounds are minimal. This is due in large part to the polar nature of the BN bond in borazine relative to the non-polar CC bond in benzene. Irradiation of benzene in the gas phase produces valence isomerization to fulvene and l,3-hexadien-5-ynes Fluorescence and phosphorescence have been observed from benzene In contrast, fluorescence or phosphorescence has not been found from borazine, despite numerous attempts to observe it. Product formation results from a borazine intermediate (produced photochemically) which reacts with another borazine molecule to form borazanaphthalene and a polymer. While benzene shows polymer formation, the benzyne intermediate is not known to be formed from photolysis of benzene, but rather from photolysis of substituted derivatives such as l,2-diiodobenzene ... 

Alternative routes to boron nitride have been examined that do not require those challenging reaction conditions. These fall into three categories, which are (1) the pyrolysis of borazines (2) pyrolysis of organic or inorganic polymers that bear borazine groups as side units and (3) pyrolysis of polyhedral borane derivatives. 

Borazine is isoelectronic and isostructural with benzene. Poly(borazylene), a polymer of borazine and its derivatives, is reported extensively as a precursor of BN-coated ceramic libers.86 Polymeric borazine oxide derivative is claimed to be flame resistant (Figure 9.10).87... 

Bradford, J.L. and Wagner, R.I. 1967. Borazine oxide derivative polymers and preparation thereof. U.S. Patent 3,341,474. 

Syntheses of Si-B-C-N polymers in which borazine units are directly attached to polysilazanes were investigated in detail by Sneddon et al." " The principle was to join borazine or its derivatives to oligomeric or polymeric silazanes by dehydrocoupling or dehydrosilylative (elimination of HSiRj) coupling reactions. For example, hydridopolysilazane was treated with borazine at temperatures... 

Borazine and its derivatives are also possible educts to synthesize precursors for Si-B-N-C ceramics. Sneddon and co-workers prepared Si-B-N-C preceramic precursors via the thermal dehydrocoupling of polysilazanes and borazines [7]. A further synthesis route is the hydroboration of borazines. The work group of Sneddon found that definite transition metal reagents catalyze hydroboration reactions with olefins and alkynes to give 5-substituted borazines [8]. Recently, Jeon et al. reported the synthesis of polymer-derived Si-B-N-C ceramics even by uncatalyzed hydroboration reactions from borazines and dimethyldivinylsilane [9]. 

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