Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

Sub-Department

Chemistry

First Advisor

Brian C Benicewicz

Abstract

This research focuses on exploring new synthetic approaches to prepare polymer-based advanced nanomaterials using highly efficient chemical tools, such as reversible addition-fragmentation chain transfer (RAFT) polymerization and click reactions.

In the first project, novel synthetic routes to produce fullerene-based polymers were designed. First, mono-alkynyl functionalized fullerene was prepared starting with pristine fullerene (C60). Methyl methacrylate and 6-azido hexyl methacrylate were then randomly copolymerized via RAFT polymerization with well-controlled molecular weights and copolymer compositions. Finally, the two moieties were covalently assembled into a series of well-defined side-chain fullerene polymers (SFP's) via the copper-catalyzed click reaction. The TGA and UV-vis analyses demonstrated consistent and high conversions for most of the samples. Furthermore, the SEM images of these polymers showed the formation of various supramolecular nanoparticle assemblies and crystalline-like clusters depending on the fullerene contents and polymer chain lengths. Additionally, "tadpole-like" fullerene polymers (TFP) were generated from bi-alkynyl functionalized fullerene, followed by a click reaction to anchor azido-capped polymers as "tails". The resultant polymers behaved as surfactants to significantly improve the solubility of graphene. The UV-vis and FT-IR spectra indicated the strong π-π stacking interactions between the TFP's and graphene. TEM images also displayed different dispersions of the complexes of TFP's and graphene in various solvents.

Another aspect of this Ph.D. research was the fabrication of Janus nanoparticles (NP's). A critical challenge in NP functionalization has been the preparation of polymer-grafted asymmetric (Janus) NP's (dia. <100 >nm). After multiple trials using different protection-deprotection methods and face-blocking moieties, such as wax beads and planar silica wafers, we designed a robust and cyclic method to synthesize such NP's involving a reversible click reaction and a "grafting to" strategy. A novel mechanochemical approach was introduced into the particle interactions to selectively achieve the protection-deprotection of NP's, which was combined with polymer modification of the unprotected surfaces of the NP's via a "grafting to" approach. The azide-functionalized larger particles could be recycled as face-blocking moieties. Using this pathway, we prepared 15 nm silica NP's that were partially functionalized with poly(methyl methacrylate). Additionally, the unique self-assembly behaviors of the resultant Janus NP's and their interactions with isotropic NP's were investigated in different solvents and concentrations by TEM and AFM analyses.

The dispersion of NP's in polymer matrices is a critical factor in determining the properties of the resulting nanocomposites. In the last part, we studied on NP's modification via surface-initiated RAFT polymerization using various functional monomers, and the dispersion of the NP's in different polymer matrices. Kinetic studies were investigated for each polymerization to demonstrate the controlled nature of the polymerization on the surface of the NP's. In addition to the homopolymers, multi-layers of block copolymer brushes were grafted on silica NP's by sequential RAFT polymerizations. Moreover, "pseudo" gradient copolymer brushes were also prepared by inserting a third random copolymer block into the middle of the two homopolymer blocks, which was established as an easy and straightforward method to synthesize gradient brushes on NP's.

Rights

© 2013, Junting Li

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