Grafting from approach

The grafting from approach is based on the initial immobilization of initiators on to the nanotube surface followed by in situ polymerisation with the formation of the polymer molecules bound to the nanotube. The benefit of this technique is that polymer-functionalised nanotubes with high grafting density can be produced. However, this method requires a strict control of the amounts of initiator and substrate. 

An example of the grafting from strategy is a treatment of SWNTs with sec-butyllithium that generates carbanions on the nanotube surface. These carbanions can serve as initiators of anionic polymerisation of styrene for in situ preparation of polystyrene-grafted tubes. This procedure allows the debundling of SWNTs and the production of a homogeneous dispersion of nanotubes in polystyrene solution. 

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The preparation of polymer brushes by controlled radical polymerization from appropriately functionalized polymer chains, surfaces or particles by a grafting from approach has recently attracted a lot of attention.742 743 The advantages of growing a polymer brush directly on a surface include well-defined grafts, when the polymerization kinetics exhibit living character, and stability due to covalent attachment of the polymer chains to the surface. Most work has used ATRP or NMP, though papers on the use of RAFT polymerization in this context also have begun to appear. 

Hijazi, I., et al., Formation of Linear and Hyperbranched Porphyrin Polymers onto Carbon Nanotubes via CuAAC Grafting from" Approach. Journal of Materials Chemistry, 2012. 22(39) p. 20936. 

Norborn-2-en-5-ylmethylenoxy)terpyridine can be polymerized by ROMP. The polymerization fulfilled the requirement of a class V living system [10]. The corresponding surface-grafted support was prepared applying a grafting-from approach as described above (Scheme 8.3) [20]. 

Fig. 37 Synthesis of graft copolyesters by the grafting from approach...

A similar approach to modifying Au-surfaces was reported by Grubbs et al, who used the more rigid tether molecule 4-(4-(norborn-5-ene-2-ylmethylenoxy)phenylethynyl)tolane-4 -thiol, shown in Fig. 2. N-Methyl-7-oxanorborn-5-ene-5,6-dicarbimide and 2,3-bis(tert-butoxydimethylsilyloxy-methylene)-norborn-5-ene were used in a grafting-from approach [31]. 

Fig. 2 4-(4-(Norborn-5-ene-2-ylmethylenoxy)phenylethynyl)tolane-4 -thiol used as anchor group in a grafting-from approach to the surface modification of Au surfaces...

Similarly, gold particles were surface-modified with norborn-5-ene-2-ylmethanthiol and the surface-immobilized norborn-2-ene groups were subsequently used for norborn-2-ene polymerization in a grafting-from approach. The resulting material was used to construct a field effect transistor [32]. 

Many applications of surface modified maferials (such as in molecular electronics, separation science or continuous flow catalysis) require the use of mechanically and pressure-stable carriers. Grubbs et al. and later Nuzzo et al. reported on the surface modification of Si(lll). Conversion of surface Si - H into Si-allyl groups allowed them to pursue the grafting-from approach shown in Schemes [36,37]. The thickness of the polymer layer could be... 

Scheme 6 Surface functionalization of silica via ROMP. Grafting-from approach (top), grafting-to approach (bottom)...

In a comparative study, poly(7-oxanorborn-5-ene-2,3-dicarboxylic acid)-grafted silica supports, again prepared via a grafting-from approach, possessed better separation behavior than the analogous coated separation media [45]. 

Following this grafting-from approach, monoliths containing 7p,mol (0.07%) Pd were prepared. In a model reaction between styrene and iodoben-zene, TOFs of 1.2-1.6 s were found. These figures clearly exceed those... 

The grafting from approach (polymers are grown from initiators bound to surfaces) is a superior alternative because the functionality, density, and thickness of the polymer brushes can be controlled with almost molecular precision. 

So far, there have been only few reports about the synthesis of amphipolar polymer brushes, i.e. with amphiphilic block copolymer side chains. Gna-nou et al. [115] first reported the ROMP of norbornenoyl-endfunctionalized polystyrene-f -poly(ethylene oxide) macromonomers. Due to the low degree of polymerization, the polymacromonomer adopted a star-like rather than a cylindrical shape. Schmidt et al. [123] synthesized amphipolar cylindrical brushes with poly(2-vinylpyridine)-block-polystyrene side chains via radical polymerization of the corresponding block macromonomer. A similar polymer brush with poly(a-methylstyrene)-Wocfc-poly(2-vinylpyridine) side chains was also synthesized by Ishizu et al. via radical polymerization [124]. Using the grafting from approach, Muller et al. [121, 125] synthesized... 

Fig. 32 Schematic presentation of grafting to and grafting from approaches for synthesis of binary polymer brushes...

In the grafting from approach, a surface, that was previously activated e.g. by plasma treatment, is exposed to a monomer solution (Huang et al. 2003). A more simple, one-step procedure is to inadiate a polymeric surface like TCP, which is covered with the monomer solution, by an electron beam (Yamada et al. 1990). Alternatively, ultraviolet light and a photosensitiser can be utilised to initiate polymerisation and cross-linking (Curti et al. 2005). A completely different route to prepare thin SRP coatings with good adhesion to solid substrates is plasma polymerisation (Biederman and Osada 1992). In this case, NIPAAm is used as a precursor in a plasmachemical thin film deposition process (Cheng et al. 2005 Pan et al. 2001). 

S. K. Pillalamarri, F.D. Blum, and M.F. Bertino, Synthesis of polyaniline-gold nanocomposites using grafting from approach, Chem. Commun., 4584-4585 (2005). 

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