Synthesis of flame-retardant polymers and the functionalization and use of carbon nanotubes for materials applications
Stephenson, Jason Jeffery
Tour, James M.
Doctor of Philosophy
New classes of inherently flame retardant polymers have been synthesized using vinyl or acroyl bisphenol C (BPC) monomers. BPC compounds decompose thermally, releasing HCl gas and forming polycyclic aromatic compounds. These two decomposition products provide vapor phase and condensed phase inhibition to a flame, respectively. Vinyl and acrylate polymers made using BPC-based chain growth systems contain the excellent fire resistance qualities inherent in BPC while maintaining the benefits of having a flexible, vinyl backbone. This provides the ability to create high molecular weight, easily processed polymers that maintain a V-0 rating as tested by UL-94 standards. Each of the BPC-based polymers showed significant char formation as well as low heat release values. It is also shown that BPC analogues can be used as reactive additives in the chain growth synthesis of polydibromostyrene. The addition of BPC to polydibromostyrene showed an increase in char formation over the commercially available polymer. Carbon nanotubes (CNTs) have also been functionalized and utilized in new material applications. Three new methods for functionalizing single walled nanotubes (SWNTs) and multi walled nanotubes (MWNTs) have been developed to facilitate the use and handling of these materials. Functionalization of SWNTs in 96% sulfuric acid with ammonium persulfate to aid in dispersion has shown that individualized SWNTs can be produced from bulk material. This method causes SWNTs to disperse in solution, allowing for functionalization to take place on individual tubes. Functionalization of MWNTs has also been shown to work well using reductive alkylation and arylation. Adapting the Billups method for functionalizing SWNTs, it is shown that MWNTs, which are unreactive towards diazonium based functionalization, functionalize well under these conditions, providing chloroform and water-soluble tubes. A new method for creating individual multi-functionalized SWNTs from bulk material is also shown. Using water-soluble functionalized SWNTs, it is possible to functionalize again using diazonium salts to synthesize multi-functionalized SWNTs that resemble a nanovector, a multifunctional delivery agent to cells. This process provides the ability to attach several different functional groups to a SWNT in one pot with high fidelity. Blends of CNTs in materials have been used to enable rapid thermal curing of elastomers and to provide low-loss materials for use in radome systems. MWNTs that absorb microwave radiation have been used to provide rapid curing to thermoset composites. The addition of MWNTs to RTV silicone composites has reduced curing times from 18 h to 8 h using low wattage microwave irradiation. The addition of SWNTs to NuSil silicone elastomers has shown low-loss dielectric materials properties for enhanced RF transparency. Permittivity values of SWNT/NuSil composites range from ∼60 - 4 based on functionalization and blending methods.
Organic chemistry; Pure sciences; Carbon nanotubes; Flame retardants; Polymers