Preparation Of CO₂-Switchable Graphene Dispersions And Their Polystyrene Nanocomposite Latexes

Graphene has gained increasing attention due to its excellent properties. Liquid phase exfoliation of graphite is considered as one of most promising methods for graphene preparation. However, the as-produced graphene sheets tend to aggregate together due to π-conjugated interactions between themselves. Herein, CO2-switchable surfactants that could stabilize graphene through CH-π interaction were designed and used for liquid phase exfoliation of graphite, which would make breakthroughs in preparing graphene dispersions of high concentration.In this study, exfoliation efficiency of graphite and CO2-switchability of the resultant graphene dispersions were investigated, through the design and synthesis of well-defined CO2-switchable polymeric surfactants. CO2-switchable graphene/polystyrene nanocomposite latexes were also prepared by using the resultant graphene dispersions. The following contents were covered in this thesis:(1) Hyperbranched polyethylene (HBPE) with Br groups was synthesized through copolymerization of ethylene and 2-(2-bromoisobutyryloxy)ethyl acrylate (BIEA) by using palladium diimine complex as the catalyst. It was then used as macroinitiators for atom-transfer radical copolymerization (ATRcoP) of 2-(dimethylamino)ethyl methacrylate (DMA) and 2-(diethylamino)ethyl methacrylate (DEA), resulting in a series of star copolymers HBPE-P(DMA-co-DEA). Linear polymer C28-P(DMA-co-DEA) with octacosyl gourp as hydrophobic block was also prepared.(2) Stable graphene aqueous dispersions with solid contents of 0.15-0.33 mg/mL were achieved by exfoliation of graphite by using the synthesized CO2-switchable surfactants. The conversions of graphite to graphene were approximately 4.5-8.25%. TEM, AFM and XRD measurements have shown that more than 90% of the resultant graphene had lateral dimension of 0.5-2 μm and thickness of 2.2-5.2 nm. The graphene dispersions could be reversibly aggregated by N2 bubbling and redispersed through CO2 treatment for multiple cycles, which would be beneficial for easy control of the graphene dispersion concentration.(3) Stable graphene/polystyrene nanocomposite latexes were prepared through one-pot emulsion polymerization by using CO2-switchable graphene dispersions. The latexes could be destabilized by N2 bubbling, which would provide an environmental-benign approach to prepare graphene/polystyrene nanocomposites. These graphene/polymer nanocomposites possessed a low percolation threshold and good thermal stability.