Grafting-to technique

As mentioned above, the grafting to technique enables in a one-pot reaction the synthesis of Au NPs stabilized by sulfur-containing polymers, which bear functional groups such as dithioester, trithioester, thiol, thioether and disulfide at the end of a polymer chain or in the middle. This method leads to nanoparticles similar to those obtained by the Brust-Schiffrin method in which alkanethiol-protected Au NPs of small size are obtained. This grafting to technique leads to very stable nanomaterials that also present a high surface graft density of polymer brush on the Au NP surface. 

Au NPs protected with a thermo-responsive polymer such as PNIPAM by the covalent grafting to technique with different end-functional PNIPAMs and various ratios between PNIPAM and HAuC14 has been studied. PNIPAM samples were synthesized through either conventional radical polymerization or living/controlled radical polymerization. With this approach, very small and quite monodisperse Au NPs are obtained with diameters ranging from 1.5 to 2.3 nm [94]. 

Methylstyrenic polymer containing thioether side groups, PMS-(CH2SCH3)n, has also been used to stabilize Au NPs using the grafting to technique, leading to small size Au NPs of approximately 3.5 nm diameter [98]. 

Chen et al. used a "grafting to" technique to synthesize PLLA-MWCNT nanocomposites (64). In this study, MWCNTs were first treated with acid to yield the carboxylic-acid-functionalized MWCNTs (MWCNT-COOH), which subsequently reacted with... 

In the grafting-to technique, the functional groups of the polymer to be grafted react with the functional groups generated by the plasma at the membrane surface (Figure 7.1). 

A marked advantage of the covalent grafting to technique is the possibility of achieving a high surface graft density of polymer brush on the GNP surface. 

Chen et al. [63] synthesized PLA/CNT nanocomposites using a grafting to technique. To understand the effect of molecular weight on the properties of the final nanocomposites, they used PLA of three different molecular weights. They first oxidized MWCNTs by acid treatment. In a typical procedure, a 500 mL flask charged with 2.5 g of the crude MWCNTs and 200 mL of 60% HNO3 aqueous solution was sonicated in a bath (28 kHz) for 30 min. The mixture was then stirred for 12 h under reflux. After the solution was cooled to room temperature, it was diluted with 400 mL of deionized water and vacuum filtered through a 0.22 pm polycarbonate membrane. The solid was washed with deionized water until the pH of the filtrate reached approximately 7. The solid was then dried under vacuum for 12 h at 60°C to yield 1.5 g of the carboxylic acid-functionalized MWCNT (MWCNT-COOH). 

Items Grafting from technique Grafting to technique References... 

Azido photochemistry was frequently used to introduce functional groups onto polymeric substrates. It is also the main so-called grafting-to technique usually used to efficiently modify or functionalize surfaces [HAR 91, THO 98, ZIA 99]. This method was employed to covalently graft carbohydrates [KNA 01] or polysaccharides [BAR 01, BHA 08] containing azide groups to polymer substrates and was successfully used to modify a wide range of other substrates such as glass, tin oxide, silicon and aluminum. 

Figure 10.7. Photografting mechanisms of AQ-Dext on the surface of PHBHV microfibrous scaffolds according to the "grafting-to" technique. (1) Hydrogen abstraction from PHBHV surface and generation of free radicals on the surface of PHBHV microfibrous scaffolds. (2) Covalent grafting of AQ-Dext on PHBHV fibers. Reproduced with permission from. The Royal Society of Chemistry [VER 13a]...

Polymer brushes are ultrathin polymer coatings that consist of polymer chains with one end covalently tethered to a substrate, i.e., a surface either needing modification or serving as a support [20]. There are two methods to synthesize polymer brushes grafting to and grafting from. Grafting to techniques employ prefabricated, end-functionalized polymer chains that are... 

In the grafting-to technique, end-functionalized polymer reacts from solution onto a suitable substrate surface to form polymer brushes. This method is particularly suitable for homogeneous brushes using linear polymers with a narrow molecular weight distribution. However, the amount of polymer that can be attached to the substrates is low, giving very thin layers of limited density. 

The grafting-to approach is based on the attachment of already preformed end-functionalized polymer molecules to fimctional groups on the nanotube surface via appropriate chemical reactions. An advantage of this method is that commercially available polymers containing reactive fimctional groups can be utilized. However, the main limitation of grafting-to technique is that initial binding of polymer chains sterically prevents diffusion of additional macro-... 

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