Covalent Functionalization Of Carbon Nanotubes With Crystallization Behavior Of Their Blends

Carbon nanotubes (CNTs) have been covalently functionalized with polymers using"grafting-onto"approach. The polymer functionalized CNTs have showed good solubility in a wide range of solvents. For the polystyrene (PS) functionalized single walled carbon nanotubes (SWNT-PS), solution-based method was used to produce syndiotactic polystyrene (sPS) and SWNT-PS blends (sPS/SWNT-PS). Subsequently, non-isothermal crystallization kinetics of sPS and sPS/SWNT-PS blends has been carried out of with DSC techniques. The main contents were as follows:(1) Preparation of SWNT-PS and non-isothermal crystallization kinetics of pure sPS and sPS/SWNT-PS blends. Polystyrene functionalized full-length single walled carbon nanotubes (SWNT-PS) was prepared by copper (I) catalyzed"Click"coupling of alkyne-decorated SWNTs with well-defined, azide-terminated polystyrene. Subsequently, sPS/SWNT-PS blends were prepared by a solution blending. Non-isothermal crystallization kinetics of pure sPS and the sPS/SWNT-PS blends has been carried out of with DSC techniques. It was found that the non-isothermal crystallization behavior of sPS/SWNT-PS blends depended significantly on the SWNT-PS content and cooling rate. The crystallization temperature for the sPS/SWNT-PS blends decreased with increasing cooling rate for a given SWNT-PS content and increased with increasing SWNT-PS content for a given cooling rate. The incorporation of SWNT-PS caused a change in the mechanism of nucleation and the crystal growth of sPS crystallites, this effect being more significant at lower SWNT-PS content. Combined Avrami and Ozawa analysis was found to be effective in describing the non-isothermal crystallization of the sPS/SWNT-PS blends. The activation energy of sPS determined from non-isothermal data decreased with the presence of small quantity of sPS/SWNT-PS in the blends and then increased with increasing SWNT-PS content. The result indicated that lower nanotubes content probably induced the heterogeneous nucleation (a lowerΔE), while higher nanotubes content probably reduced the transportation ability of sPS polymer chains during crystallization processes (a higherΔE_a), despite the presence of more heterogeneous nucleation.(2) Covalent functionalization of multiwall carbon nanotubes (MWNTs) with poly(ethyl glycol) (PEG) and hydroxyl-terminated polybutadiene (HTPB). Polymer functionalized WMNTs are synthesized through two-stages process. Firstly, the hydroxyl functionalized MWNTs (MWNT-OH) directly reacted with excess toluene 2,4-diisocyanate (TDI) to produce isocyanate functionalized MWNTs (MWNT-NCO). This chemistry allows for preferential reaction between the para-isocyanate group and OH groups on the MWNT surface, leaving the ortho-isocyanate group intact due to steric hindrance within the TDI molecule. Then the ortho-isocyanate group can react with OH groups on the chain-end of PEG and HTPB at a higher temperature to produce PEG functionalized MWNTs (MWNT-PEG) and HTPB functionalized MWNTs (MWNT-HTPB). FTIR and TGA analysis indicated that both nanotubes and polymers were present within the material isolated from the polymerization reaction. Unlike simple blends of polymers and nanotubes, the two components of our composites could not be separated from one another by extensive filtration and washing, indicating that they are covalently bound. Analysis of these structures by TEM provided further evidence for the formation of polymerized nanotubes. Additionally, the polymer-functionalized tubes exhibited high solubility in organic solvents.