Synthesis and fabrication of polymeric composites, nanofilaments and nanofibers

by Gu, Bin.

Aluminum oxide particles were modified with 2-bromopropionic acid to afford particles with atom transfer radical polymerization (ATRP) initiators on the surface. Poly(methyl methacrylate)-co-poly(butyl acrylate) (PMMA-co-PBA) copolymer was then grafted onto the alumina particles by ATRP using CuBr/PMDETA (N,N,N’,N’,N’’- pentamethyldiethylenetriamine) as the catalyst. Kinetic and mechanistic studies revealed that the copolymerization process is living and follows the same trends as in liquid-phase ATRP, resulting in the formation of controlled gradient copolymer chains. The aluminum oxide/copolymer composites form stable suspensions in organic solvents. Nitroxide initiator: 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane was synthesized and used in controlled radical polymerization of methyl acrylate with 1-alkenes. Kinetic studies reveal the polymerization displays living characteristics. Copolymers of methyl acrylate with simple 1-alkenes with controlled molecular weight, polydispersity and composition can be prepared by nitroxide mediated polymerization (NMP). Methyl acrylate-norbornene derivative copolymers can also be polymerized by NMP. The polymers are free of metal catalysts and opens up new applications of nitroxide mediated polymerization systems. Channels with nanodimensional cross-sections were fabricated by e-beam lithography and top-down silicon processing and used as templates for controlled polymerization. The dimensions of these nanotemplates are 20 nm high, 20 nm to 200 nm wide, and 100 µm long. It was established that these channels are open all the way iii without any collapsed regions. Nanostructured polymer filaments with controlled size, location and orientation were grown inside the channels by either radical, coordination and photopolymerization. The presence of the polymers in the channels was verified by oxygen plasma etching, fluorescence mapping, and solubility test. The polymer filaments produced are continuous and, when released from the template, can twist without breaking. Nanochannels with “built-in” electrode contacts were fabricated and used as growth templates for conductive polymers. Conductive polymers can be either introduced or chemically grown in nanochannels. Conductivity measurements of polypyrrole indicate that channels electrode contacts are ohmic to polymer. A new “jet-blowing” technique was developed to process polymer into micro and nanofibers. A variety of polymers, including “non-melt processible” polytetrafluoroethylene can be processed in this technique. Polytetrafluoroethylene can form micro and nanofibers below its melting temperature from this process. The fibers have porous, expanded structure and can be coated on surfaces of choice. Surfaces coated with these nanofibers are highly hydrophobic. iv