Masters Theses

Date of Award

12-2006

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

Mark Dadmun

Committee Members

Jimmy Mays, Kevin Kit

Abstract

The dispersion of nanoparticles in a polymer matrix is a critical parameter to design and realize targeted morphologies and properties of a final polymer-based nanocomposite. This thesis presents experimental studies to investigate the dispersion of nanoparticles is polymer matrices using specific intermolecular hydrogen bonding between the nanoparticles and polymer matrices under two main topics.

The first topic is the impact of sample preparation processes on the properties of polymer carbon nanotube nanocomposites. Polymer nanocomposites composed of poly(styrene-co-vinyl phenol) (PSVPh) copolymers and 5 wt % multi-walled carbon nanotubes (MWNTs) were prepared from three different methods, including melt-mixing and solution casting. The MWNTs were either oxidized to incorporate oxygenated defects or utilized as received. The mechanical properties of the nanocomposites were measured by DMA, and the extent of intermolecular hydrogen bonding between MWNTs and PSVPh was quantified by IR. Our DMA results suggest that melt-mixing leads to more stable morphologies of the final nanocomposites than solution casting does. Additionally, the IR analysis of the nanocomposites indicates melt-mixing can result in the formation of more intermolecular hydrogen bonding between the MWNTs and PSVPh than solution casting, and thus suggests that melt-mixing leads to more reproducible mechanical properties than solution casting. Our DMA and IR results may provide guidelines to realize the desired morphologies and to improve the properties of polymer carbon nanotube nanocomposites by optimizing intermolecular interactions between MWNTs and polymers.

The other topic examined seeks to synthesize the starting materials to sequester surface-modified gold nanoparticles in a diblock copolymer matrix. The long term goal of this project is to investigate the impact of enthalpic attractions between the gold nanoparticles and one phase of the diblock copolymer on the nanocomposite morphologies. That is, this system is designed such that the hydroxyl groups on the gold nanoparticles can hydrogen bond with poly(2-vinyl pyridine) blocks of poly(styrene-b-2vinyl pyridine) diblock copolymers. Polystyrene-coated gold nanoparticles were synthesized using thiol-terminated polystyrene (PS-SH) as a stabilizing ligand. The low molecular weight PS-Sh was obtained by the thiolation of bromine-terminated polystyrene (PS-Br), which was synthesized by ATRP. TEM images of the gold nanoparticles shows that the size of the gold nanoparticles can be controlled using this PS-SH as a stabilizing ligand. Additionally, the synthesis of thiol-terminated poly(styrene-co-vinyl phenol) (PSVPh-SH) copolymers was attempted starting with bromine-terminated poly(styrene-co-4-tert-butoxystyrene) copolymers, followed by thiolation and hydrolysis. Our NMR results indicate that the conversion of the bromine-end groups of the copolymers to thiol-end groups by thiolation was complete. However, the conversion of the tert-butoxy groups of the thiolated copolymers to hydroxyl groups by hydrolysis using HCI was not successful. Furthermore, NMR data suggests that this hydrolysis may impact the thiol-end groups of the thiol-terminated copolymers. Our NMR results may provide guidelines such that carefully controlled reaction time and/or HCl amount would improve the success of the PSVPh-Sh synthesis.

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