Grafting from polymer surfaces

Several techniques have been applied in attaching the appropriate functionality to the polymer surface. For example, copolymeri/ation of a monomer containing functionality (alkoxyamine e.g. 358 or 359,744 ATRP initiator, e.g. 352,734 RAFT 

The monomer 359 has been formed in situ by decomposing the initiator (A1BN) in the presence of the corresponding nilroxide in a solution of S or 2-ethoxyethyl acrylate.744 The kinetics dictate that alkoxyamine formation, by coupling of the nitroxide with cyanoisopropyl radicals, will take place before eopolymerization. 

The very small number of growing polymer chains, when compared to the monomer concentration results in a very low overall concentration of free control agent and leads to inefficient capping of chain ends. One solution to this problem is the addition of a free or unbound control agent to the polymerization medium. This can take the form of a low molecular weight alkoxyamine, ATRP initiator, RAFT agent or, alternatively, free deactivator such as nitroxide or Cu(II). This species is often called a sacrificial agent. This solution also leads to the formation of free polymer that must ultimately be removed from the brush. 

I hese conditions correspond to the use of low reaction temperatures in the case of alkoxyamines 358 or 359, the absence of catalyst in the case of ATRP initiator 352, or a copolymerization with MMA where ti ansfer is negligible in the case of RAFT agent 360. 

Grafting from silica particles, silicon wafers, and related surfaces usually involves attaching a chlorosilanc or alkoxysilane derivative. Thus alkoxyamincs (e.g, 362 ) and a wide variety of ATRP initiators e.g. 363 ) have 

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Hyperbranched Polymers Grafted from Planar Surfaces. 28... 

A dense polymer brush is obtained using the grafting from techniques. Surface-initiated polymerization in conjunction with a living polymerization technique is one of the most useful synthetic routes for the precise design and functionalization of the surfaces of various solid materials with well-defined polymers and copolymers. Above all, surface-initiated living radical polymerization (LRP) is particularly promising due to its simplicity and versatility and it has been applied for the synthesis of Au NPs. 

Polymers on surface can change the surface properties drastically. Even physisorbed polymers are usually bound irreversibly due to the large number of binding sites. To produce dense and thick layers, polymers have to be grafted from the surface. 

Polymer brushes are polymers tethered to a surface via one end. The connection to the surface can be covalent or non-covalent, and the brushes can be made via grafting to or grafting from the surface. In the past few years, there has been considerable interest in the growth of polymer brushes via surface-initiated polymerisations from (patterned) initiator-functionalised SAMs.62,63 For example, we have recently shown that surface confined Atom Transfer Radical Polymerisations (ATRP) in aqueous solvents leads to rapid and controlled... 

When polymers are to be tethered to surfaces by covalent bonds, there are two fundamental approaches for achieving this grafting from and grafting onto. Grafting from means surface-initiated polymerization, whereby the polymer chains are created in situ. Grafting onto involves formation of covalent bonds between previously formed polymer chains and reactive groups at a surface (Fig. 9). Both methods have specific pros and cons. 

More recently, Chen et al. described a surface modification whereby the polymer poly(Ar,Ar-dimethyl-Af-(ethoxycarbonylmethyl)-Ar-[2/-(methacryloyloxy)ethyl]-ammonium bromide) was grafted from a surface via ATRP [136], The cationic polymer effectively kills E. coli and is subsequently converted into a zwitterionic polymer by hydrolysis of the head group (Fig. 9). It then repels all attached cells dead or alive. This is the first example of a surface that can kill microbes on contact and repels them after that. The only downside of this elegant system is that it will eventually exhaust and turn into a more or less effective repelling surface. 

In summary, EUV activation although currently strongly dependent on access to a dedicated synchrotron beamline allows well-controlled grafting of polymer brushes from polymer surfaces with high spatial resolution capabilities. The availability of a large variety of monomers suitable for this grafting process, combined with postpolymerization modification processes, opens a wide field to introduce surface functionalities. Select examples are discussed in Chapter 4. 

Another biodegradable polymer, poly(L-lactide) (PLLA), was also grafted from MWCNT surfaces successfully using Sn(Oct)2 as the catalyst. Upon... 

H. Bottcher, M.L. Hallensleben, S. Nup, H. Wurm, ATRP grafting from silica surface to create first and second generation of grafts, Polym. Bull. 2000, 44, 223-229. 

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. 

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