Environmental Engineering Reference
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images showed polymer-coated tubes while the blend of the modified material
and the polymer matrix exhibited enhanced properties in tensile testing experi-
ments. They reported the grafting of functionalized polystyrene to CNT via a cy-
clo addition reaction. An azido polystyrene with a defined molecular weight was
synthesized by atom transfer radical polymerization and then added to nanotubes.
In a different approach, chemically modified CNT with appended double bonds
were functionalized with living polystyryllithium anions via anionicpolymeriza-
tion. The resulting composites were soluble in common organic solvents. Using an
alternative method, polymers prepared by nitroxide-mediated free radical polym-
erization were used to functionalize SWNT through a radical coupling reaction of
polymer-centered radicals. The in situ generation of polymer radical species takes
place via thermal loss of the nitroxide-capping agent. The polymer-grafted tubes
were fully characterized by UV-vis, NMR, and Raman spectroscopies.
1.1.5.4.2
“GRAFTING FROM” METHOD
CNT-polymer composites were first fabricated by an in situ radical polymerization
process. Following this procedure, the double bonds of the nanotube surface were
opened by initiator molecules and the CNT surface played the role of grafting
agent. Similar results were obtained by several research groups. Depending on the
type of monomer, it was possible not only to solubilize CNT but also to purify the
raw material from catalyst or amorphous carbon. Through the negative charges of
the polymer chain, the composite could be dispersed in aqueous media, whereas
the impurities were eliminated by centrifugation. In a subsequent work, the same
authors fabricated films consisting of alternating layers of anionic PSS-grafted
nanotubes and cationic diazopolymer. The ionic bonds in the film were converted
to covalent bonds upon UV irradiation, which improved greatly the stability of
the composite material. They prepared polyvinylpyridine (PVP)-grafted SWNT
by in situ polymerization. Solutions of such composites remained stable for at
least 8 months. Layer by layer deposition of alternating thin films of SWNT-PVP
and poly(acrylic acid) resulted in freestanding membranes, held together strongly
by hydrogen bonding. Assemblies of PSS-grafted CNT with positively charged
porphyrins were prepared via electrostatic interactions. The nano assembly gave
rise to photo induced intra complex charge separation that lives for tens of micro-
seconds. The authors have demonstrated that the incorporation of CNT-porphyrin
hybrids onto indium tin oxide (ITO) electrodes leads to solar energy conversion
devices. The raw material was treated with sec-butyllithium, which introduces a
carbanionic species on the graphitic surface and causes exfoliation of the bundles.
When a monomer was added, the nanotube carbon ionsinitiate polymerization, re-
sulting in covalent grafting of the polystyrene chains. They studied the fabrication
of composites by insitu ultrasonic induced emulsion polymerization of acrylates.
It was not necessary to use any initiating species, and the polymer chains were
covalently attached to the nanotube surface. MWNT grafted with poly(methyl
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