New polymerization and substitution reactions of monomeric and polymeric boron-nitrogen species [electronic resource].

Fazen, Paul J.
170 p.
Chemistry, Inorganic.
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Penn dissertations -- Chemistry. (search)
Chemistry -- Penn dissertations. (search)
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Mode of access: World Wide Web.
Boron nitride ceramics posses unique thermal, electronic, and optical properties. New technologies require boron nitride in forms not accessible by conventional powder techniques. In order to exploit these properties there is a need to develop new high yield, processable precursors to boron nitride. The overall goal of this research was to develop new high yield synthetic routes to boron-nitrogen molecular and polymeric species. An emphasis was placed on those species which could be used in the development of polymeric precursors to boron nitride ceramics. The major accomplishments of this work are summarized below.
The synthesis and ceramic conversion reactions of polyborazylene, (B${\rm \sb3N\sb3H\sb{\sim4})\sb{x}},$ were investigated. The polymer was produced in high yields by simply heating borazine at relatively low temperatures (70-110$\sp\circ{\rm C})$ for 48h. The polymer was found to be soluble in polar ethers such as glyme and THF. Spectroscopic and molecular weight data indicate that the polymer appears to have a complex structure, having linear, branched-chain, and fused-cyclic segments, related to those of the organic polyphenylenes. The isolation and structural characterization of small amounts of the polycyclic boron-nitrogen compounds diborazine, 1:2$\sp\prime$-($B\sb3N\sb3H\sb5)\sb2,$ and borazanaphthalene, ${\rm B\sb5N\sb5H\sb8},$ supports this conclusion. Pyrolysis studies show that the polymer converts to boron nitride in excellent chemical, 89 to 99%, and ceramic yields, 84 to 93%. The quality of the resulting boron nitride was determined by elemental analysis, DRIFT spectra, powder XRD, density measurements, and TGA oxidation studies. Studies of the polymer/ceramic conversion process, as followed by TGA, TGA/MS, DRIFT, XRD, and micro analysis of materials produced at intermediate temperatures, suggest that the polymer has a layered structure in the solid state and that the conversion to boron nitride occurs by means of a two-dimensional cross-linking reaction. The polymer was also useful for producing boron nitride coatings on ceramic and carbon fiber yarn bundles.
A new method was also developed that allows the systematic controlled alkylation of borazine, as well as polyborazylene. Borazine was found to react with a wide variety of olefins, including ethylene, propene, 1-butene, cis- and trans-2-butene, 3,3,3-trifluoropropene, styrene, $\alpha$-methylstyrene, and 4-allylanisole, in the presence of catalytic amounts of RhH(CO)(PPh$\sb3)\sb3$ to selectively produce the mono-, di- and tri-B-alkylborazines in excellent yields. The degree of substitution was controlled by altering the reactant ratios. Unsymmetrically substituted tri-B-alkylborazines are produced by the catalyzed reaction of mono- or di-B-substituted borazines with a different olefin. RhH(CO)(PPh$\sb3)\sb3$ is also used to catalyze direct alkylation of borazine-based polymers. Thus, the catalyzed addition of either ethylene or propene with polyborazylene, (${\rm B\sb3N\sb3H\sb{\sim4})\sb{x}},$ yielded the B-alkylated polymers (${\rm C\sb2H\sb5)\sb{y}(B\sb3N\sb3H\sb{\sim4-y}})$ and (${\rm C\sb3H\sb7)\sb{y}(B\sb3N\sb3H\sb{\sim4-y}}),$ respectively.
Thesis (Ph.D in Chemistry) -- University of Pennsylvania, 1995.
Source: Dissertation Abstracts International, Volume: 56-06, Section: B, page: 3187.
Supervisor: Larry G. Sneddon.
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School code: 0175.
Sneddon, Larry G., advisor
University of Pennsylvania.
Contained In:
Dissertation Abstracts International 56-06B.
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