Non-covalent functionalization

The huge advantage related to physical functionalization is that it does not destroy the conjugated systems of the CNTs sidewalls, and therefore it does not affect the final structural properties of the material. Non-covalent functionalization is an alternative method for tuning the interfacial properties of the CNTs. 

Method Principle Possible damage to CNTs Easy to use Interaction with polymer matrix Re-agglomeration of CNTs in matrix 

Chemical method Side wall Hybridization of C atoms from sp to sp V X S V 

Physical method Polymer wrapping Van der Waals force, 7t-7t stacking X V V X 

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A non-covalently functionalized dendrimer was also applied in a continuous allylic amination reaction.[33] PPI dendrimers functionalized with urea adamantyl groups can act as host molecules for phosphorus ligands equipped with acetyl urea groups (Figure 4.18). The so formed supramolecular complex was reacted with a palladium precursor... 

Figure 4.19. Continuous catalysis with non-covalently functionalized dendrimers a) acid-, b) ester-functionalized guest. (Reprinted with permission from ref. 33. Copyright 2001 American Chemical Society)...

A. Ghosh, K.V. Rao, R. Voggu, S. J. George, Non-covalent functionalization, solubilization of graphene and single-walled carbon nanotubes with aromatic donor and acceptor molecules, Chemical Physics Letters, vol. 488, pp. 198-201, 2010. 

The supramolecular guest—Pd—dendrimer complex was found to have a retention of 99.4% in a CFMR and was investigated as a catalyst for the allylic ami-nation reaction. A solution of crotyl acetate and piperidine in dichloromethane was pumped through the reactor. The conversion reached its maximum ca. 80%) after approximately 1.5 h (which is equivalent to 2—3 reactor volumes of substrate solution pumped through the reactor). The conversion remained fairly constant during the course of the experiment (Fig. 8). A small decrease in conversion was observed, which was attributed to the slow deactivation of the catalyst. This experiment, however, clearly demonstrated that the non-covalently functionalized dendrimers are suitable as soluble and recyclable supports for catalysts. 

Fio. 8. Application of a non-covalently functionalized dendrimer (see fig. 7) in a CFMR in the allylic amination of crotyl acetate and piperidine in dichloromethane (Koch MPF-60 NF membrane, molecular weight cut-off = 400 Da) (21). 

In the majority of the methods discussed above, CNTs are directly mixed with PMMA using ultrasonication or shear forces. Another approach which has been studied to improve quality of dispersion of CNTs in PMMA is third component assisted dispersion of CNTs (65-67). In this method, a third component such as a surfactant or a compatibilizer is added to assist the dispersion of CNTs in a solvent before mixing with the polymer solution (40). This is an effective non-covalent functionalization technique. 

M. Husanu, M. Baibarac, and 1. Baltog, Non-covalent functionalization of carbon nanotuhes Experimental evidence for isolated and bundled tubes, Physica E, 41, 66 9 (2008). 

Metallic and semiconducting SWNTs are apparently wrapped differently by DNA or more generally in the same concept by surfactant molecules, as discussed above for various approaches to exploit such differences for postproduction separation purposes. The nanotubes also have different interactions with selected functionalization or solubilization agents. Such selective interactions, sometimes considered as non-covalent functionalizations, have been found to allow relatively facile post-production separation at significant quantities. ... 

Sun and co-workers exploited the selectivity in the non-covalent functionalization of SWNTs with planar aromatic molecules, such as derivatized porphyrin or pyrene (Figure 6.3), for the post-production separation. The separation method simply splits the starting nanotube mixture by selectively solubilizing semiconducting SWNTs and leaving their metallic counterparts behind, and consequently is capable of handling significant sample quantities. Experimentally, as-produced samples of... 

More recently a molecule with a pair of planar aromatic moieties (Figure 6.4) was synthesized and used to exaggerate the difference between metallic and semiconducting SWNTs in the non-covalent functionalization and solubilization. The molecule representing essentially the molecular tweezers approach (Figure 6.4) exhibited significant selectivity toward... 

Lu et also applied the same non-covalent functionalization approach to the purification of SWNTs. A water-soluble pyrene derivative 1-pyreneacetic acid was used to solubilize the purified (typical nitric acid treatment) SWNTs in aqueous solution, allowing a nearly complete removal of residual metal catalysts and carbonaceous impurities. According to thermogravimetric analysis (TGA) results, the purified sample of SWNTs contained little other carbonaceous impurities and no more than 3% of residual catalysts by weight... 

The selectivity in the non-covalent functionalization of metallic v. semiconducting SWNTs is apparently dependent on the specific planar aromatic molecule, positive for one pyrene derivative (1-docosyloxymethyl-pyrene or... 

Modifying the surface of SWNTs with functional materials is one way to engineer the photoelectrical properties of SWNTs. Hence, chemical functionalization of SWNTs has been a subject attracting much attention. Compared with the covalent functionalization of SWNTs, the non-covalent functionalization method is particularly attractive as this method presents the possibility of attaching chemical handles to SWNTs without severely disrupting the bonding network in SWNTs. The functionalization of SWNTs with chromophores has been reported, while other research groups have used photosensitive polymers to achieve the modulation of the conductance in SWNTs. 

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