Poly brushes grafting-from method

In this review, synthesis of block copolymer brushes will be Hmited to the grafting-from method. Hussemann and coworkers [35] were one of the first groups to report copolymer brushes. They prepared the brushes on siUcate substrates using surface-initiated TEMPO-mediated radical polymerization. However, the copolymer brushes were not diblock copolymer brushes in a strict definition. The first block was PS, while the second block was a 1 1 random copolymer of styrene/MMA. Another early report was that of Maty-jaszewski and coworkers [36] who reported the synthesis of poly(styrene-h-ferf-butyl acrylate) brushes by atom transfer radical polymerization (ATRP). 

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. 

Cylindrical polymer brushes composed of a poly(DPA) main chain and poly(oxyethylene) side chains have been prepared by the so-called graft-from method. For example, l-(p-trimethylsilylphenyl)-2-(m-methylphenyl)acetylene is at first polymerized into a high-MW polymer (M = 2x 10 ), then the m-methyl group is converted into the chloromethyl... 

Farhan et al. [25] reported surface-initiated polymerizations from polymeric surfaces of commercially important polyester films, poly(ethylene terephthalate) (PET), and poly(ethylene naphthalate) (PEN). Patterned self-assembled monolayers (SAMs) of the trichlorosilane initiator were first immobilized on the surface through a soft lithographic method of microcontact printing (ICP). Grafting from the surface was initiated via controlled ATRP, under aqueous conditions, to create patterned brushes of the ther-moresponsive polymer poly(N-isopropylacrylamide) (PNIPAm), as shown in Figure 1.8. 

An alternative photo-SIP approach was described by Kang and coworkers, where they used an argon plasma to oxidize alkylthiolate SAMs on planar gold [55]. The plasma treatment oxidized carboxy-terminated SAMs to peroxide moieties. UV irradiation in the presence of acryhc acid and allylpentafluorobenzene yielded ultra-thin graft layers of 6-7nm. The poly(acrylic acid) layers were found to adsorb Fe " ions from solution. This particular photoinitiation method yields low-density polymer brush films. 

A variant on the grafting method is to use a diblock copolymer made out of two distinct blocks, as shown in Fig. 3c. The first block is insoluble and is attracted to the substrate, and thus acts as an anchor fixing the chain to the surface it is drawn as a thick line in Fig. 3c. It should be long enough to cause irreversible fixation on the surface. The other block is a soluble one (the buoy ), forming the bmsh layer. For example, fixation on hydrophobic surfaces from a water solution can be made using a polystyrene-poly(ethylene oxide) (PS-PEO) diblock copolymer. The PS block is insoluble in water and is attracted towards the substrate, whereas the PEO forms the brush layer. The process of diblock copolymer fixation... 

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