Grafting, from silicon surfaces

Paripovic D, Klok H-A (2011) Improving the stability in aqueous media of polymer brushes grafted from silicon oxide substrates by surface-initiated atom transfer radical polymerization. Macromol Chem Phys 212 950... 

Finally, polymers can be grafted from a surface and a bare silicon AFM tip can be used to measure their length. With this configuration, good length distributions of grafted polymers have been obtained. ... 

Grafting from silica particles, silicon wafers, and related surfaces usually involves attaching a chlorosilanc or alkoxysilane derivative. Thus alkoxyamincs (e.g, 361,744,749 3627 0) and a wide variety of ATRP initiators (e.g. 363751) have been attached directly to surfaces and used to initiate grafting from" processes. 

Chen et al. utUized a direct chemical reaction with a given solution (wet treatment) to modify the surface of the silicone rubber. The presence of a layer of PEO on a biomaterial surface is accompanied by reductions in protein adsorption, and cell and bacterial adhesion. In order to obtain a PEO layer on top of the silicone rabber surface, the surface was firstly modihed by incorporating an Si-H bond using (MeHSiO) , and followed by PEO grafting to the surface using a platinum-catalyzed hydrosilylation reaction. These PEO-modified surfaces were demonstrated by fibrinogen adsorption both from buffer and plasma, as well as albumin adsorption from buffer. Reductions in protein adsorption of as much as 90% were noted on these surfaces. 

Fig. 15. Schematic representation of the synthesis of hyperbranched, branched, and linear polymers grafted from functionalized silicon wafers SFM images and XPS spectra of the surface-grafted polymers. (Reproduced with permission from [48],Copyright 2001 American Chemical Society.)...

During the last 5 years, there have been several reports of multiblock copolymer brushes by the grafting-from method. The most common substrates are gold and silicon oxide layers but there have been reports of diblock brush formation on clay surfaces [37] and silicon-hydride surfaces [38]. Most of the newer reports have utilized ATRP [34,38-43] but there have been a couple of reports that utilized anionic polymerization [44, 45]. Zhao and co-workers [21,22] have used a combination of ATRP and nitroxide-mediated polymerization to prepare mixed poly(methyl methacrylate) (PMMA)Zpolystyrene (PS) brushes from a difunctional initiator. These Y-shaped brushes could be considered block copolymers that are surface immobilized at the block junction. 

Investigations of 5 with different R groups showed that fast grafting can be obtained for the most inert radicals, R = Aik (from Me to C18H37) and ethynyl, whereas for more reactive 12, e.g. Ar, side reactions were observed, in particular electropolymerization on the silicon surface. For example, such behavior was found for 5r and the first steps of the formation of a polymeric layer can be described by equations 23. 

An amino-functional spacer arm is introduced at the 5 position of the ODN in the last step of its automated synthesis. ODN can be grafted via various functions available on flat carriers (such as flat silicon surfaces or wafers covered in silane) or on latex particles. Table 2 shows a list of various activation agents used and the reactive group resulting from the activation depending on the compound involved when available, the maximum grafting amount is also reported. 

A recent approach to ocular inserts was presented by Chetoni et in a study of cylindrical devices for oxytetracycline, made from mixtures of silicone elastomer and grafted on the surface of the inserts with an interpenetrating mueoadhesive polymeric network of polyacrylic acid or polymethacrylic acid. The inserts were tested for drug release and retention at rabbit eyes. It was shown that some of the inserts are able to maintain prolonged oxytetracycline concentrations in the lacrimal fluid for 36 h. 

Zhao and Brittain also used the grafting from technique to grow polymers off silicon surfaces [329]. In their example, however, they first prepared tethered pSt cationically, which was terminated with a chlorine chain end, then used it as the initiator for the ATRP of MMA using the CuBr/PMDETA catalyst system. Use of a chlorine-terminated pSt chain in conjunction with a CuBr catalyst, however, produces a mismatch between the rates of cross-propagation and the rate of po-... 

---