Master of Engineering Science
Chemical and Biochemical Engineering
Graphene has emerged as a subject of tremendous scientific interest due to its exceptional electrical, mechanical and thermal properties. When incorporated into a polymer matrix, graphene sheets can significantly improve the properties of the host polymer. However, the dispersion of pure graphene throughout a polymer matrix is not homogeneous, due to the strong van der Waals interactions between graphene sheets and the difference in surface compatabilities. To prevent agglomeration of these graphene sheets, surface functionalization is required. The goal of this thesis was to develop a facile approach for growing polymer chains from the surface of graphene sheets via reversible addition-fragmentation chain-transfer (RAFT) polymerization.
Graphene oxide was synthesized by reacting graphite with potassium permanganate and concentrated sulfuric acid. The oxidation and exfoliation of graphite was investigated using FTIR, TEM, and AFM studies. For the methodology of growing polymers from graphene surfaces, polydopamine was coated on graphene oxide as a platform for subsequent “grafting from” RAFT polymerization. This was possible as polydopamine has available hydroxyl groups that can react with carboxylic groups of the RAFT agent via ester linkages. During the formation of polydopamine coating on graphene oxide, graphene oxide can be simultaneously reduced by the released electrons generated by self-polymerization of dopamine. The reduction of graphene oxide was determined by FTIR, UV/Vis, and XPS analysis.
For growing the polymer chains from the graphene surface, the living radical polymerization methodology, RAFT polymerization, was investigated. The RAFT agent, S-dodecyl-S’-(α,α’-dimethyl-α’’-acetic acid)trithiocarbonate, having an available carboxyl group, was chosen to anchor onto the polydopamine coating and then grow chains of PS, PMMA, PNIPAM, and PtBA from this modified surface. The livingness of the polymerization was verified by GPC characterization. The additional free RAFT agents in the reaction system could enhance the control of the polymerization on PDA/RGO surface and in solution as measured by GPC. The polymer grafted polydopamine/reduced graphene oxide (PDA/RGO) nanocomposites showed excellent dispersibility in several organic solvents. The final polymer matrix dispersed of functionalized reduced graphene oxide showed higher maximum decomposition temperature measured by TGA, indicating better thermal stability.
Gu, Renpeng, "Synthesis and Characterization of Graphene-Polymer Nanocomposites via Reversible Addition-Fragmentation Chain-Transfer Polymerization" (2012). Electronic Thesis and Dissertation Repository. 651.