Decaborane polymer

The incorporation of decaborane into polycarbosilane-based polymers has been used in the densification of the polymer-derived SiC fibers. Improved densifi-cation resulted in the formation of fibers with density as high as 2840 kg/m3 corresponding to an increase of 89%.154... 

The literature3 contains some limited work on decaborane-based polymer systems. Typically, most utilize the Lewis acid/base reaction between decaborane (Lewis acid, B10H12) and amines and phosphines (Lewis bases, L) resulting in the formation of complexes (see scheme 2) having the general formulas B10H12L2. For example, the... 

Polymers derived from the preceding type of reaction with nitriles,5 amines,6 and phosphines,7 have been reported. Green8 has reported the preparation of a resin-type material composed of at least 10 repeat units from the reaction between decaborane and adiponitrile (NC(CH2)4CN). Also reported,9 is the inclusion of flexible siloxanes and ether linkages into a diamine, and of their subsequent reaction with decaborane to give adduct polymers (see 2, 3). 

In general, the polymers incorporating decaborane that have been reported in the literature tend to be soluble in polar solvents, and generally have poor stability in solution with degradation of the decarborane cage.4... 

This disilaborane was an unexpected co-product in the synthesis of decaborane-alkylamine polymers. The Si2Bio cluster core consists of a distorted icosahedron in which the two silicon atoms occupy adjacent positions. The Si-Si interatomic distance is 2.308(2) A, which is slightly less than the Si-Si distance in organodisilanes (2.35 A) and the Si-B distances [2.017(3) to 2.116(3) A] are very close to the sum of the covalent radii of the two atoms (2.07 A). Further derivatives with disilaborane cluster geometry are known for the phenyl substituted compounds l,2-Ph2-doso-l,2-Si2B1oH1o and l-Me-2-Ph-doso-l,2-Si2BioHi0 [6, 7]. In addition to these disila-doso-dodecaborane clusters one example with two different group 14 elements as a part of the cluster core is known. In Scheme 3.3-2 the synthesis of this sila-stanna-doso-dodecaborate is shown. The structure of this heteroborate was determined in the solid state and the Si-Sn distance is 2.608(4) A (Scheme 3.3-2) [8]. 

A preceramic, carrier polymer route to boron carbide has been reported via the pyrolysis of a polynorbomene that bears decaborane side groups.69 An important feature of this development is the ability to produce nanofibers of boron carbide in the following way. A solution of the poly(norbomenyldecaborane) in THF is subjected to the process of... 

Su and Sneddon [53] reported the formation of Ti and Zr borides by solid-state reactions involving the respective metal oxides intimately dispersed in a decaborane-dinitrile polymer at temperatures greater than 1450°C, presumably according to... 

The polymers 7a-7d were prepared via polymer reactions as shown in eqn (14.10). To the precursor polymer 28 (35.7mg, lOOmmol M = 4900, M j Mn = 2.40) were added decaborane (610 mg, 5 mmol) and A,A -dimethylaniline (1200 mg, 10 mmol) dissolved in toluene (2.5 mL) and THF (2.5 mL). The mixture was heated at 110 °C for 24 h. The reaction was quenched by rapid cooling with liquid nitrogen. The reaction mixture was diluted in chloroform, and the insoluble product was filtered off. The filtrate was evaporated and reprecipitated in methanol. The product was isolated by filtration and dried under vacuum. The resulting polymer 7a was obtained as a brown powder in 90% yield. The and M jM of the polymer 7a were 10 700 and 2.33, respectively. By changing the feed ratio of decaborane to the triple bonds (0.05, 0.10, 0.20 and 0.40) in the polymer 28, the introduction rates were modulated to obtain the polymers 7b-d. 

Toxicity studies on m-carbaboranes used for synthesis of some heat resistant polymers and indices for carbaborane toxicity evaluation have been reported. The potential use of carbaboranes in biological systems continues to be investigated. The (4-carbaboranylalanine-5-leucine)-enkephalin has been studied as a structural probe for the opiate receptor. L-Carbaboranylalanine substituted Tobacco mosaic virus, synthesized from B enriched decaborane has been investigated as a model for slow neutron therapy of tumours. "... 

Figure 5 ROMP polymer containing decaborane side chains. Reproduced with permission from Wei, X. Carroll, P. J. Sneddon, L G. Chem. Mater. 2m, 75,1113. ...

Dinitrile polymers satisfy these criteria and can be prepared in good yield from the condensation polymerization of deca-borane with dinitriles. Su et al. (1991) have obtained the polymer precursor by dispersing ZrO into decaborane dicyano-pentane polymer, (-BjgHj2-NC-(CH2)j-CN-). Subsequent pyrolysis of the precursor at 1450°C yielded crystalline ZrB. ... 

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