Surface-initiated RAFT

FIGURE 6.8 (a) Schematic illustration of the procedure for the synthesis of polymeric capsules based on surface-initiated RAFT polymerization using silica nanoparticles as templates, (b) TEM image of polymer grafted silica nanoparticles, (c) SEM and (d) TEM images of the synthesized polymeric capsules. Source Huang et al. [15]. Reproduced with permission of American Chemical Society. 

Tria, M.C.R., Grande, C.D.T., Ponnapati, R.R., and Advincula, R.C. 2010. Electrochemical deposition and surface-initiated RAFT polymerization protein and cell-resistant PPEGMEMA polymer brushes, H ... 

Li, Y., Benicewicz, B. C., Functionalization of Silica Nanoparticles via the Combination of Surface-Initiated RAFT Polymerization and Click Reactions, Macromolecules 2008, 41, 7986-7992. 

Tria MCR, Advincula RC. Electropatteming of binary polymer brushes by surface-initiated RAFT and ATRP. Macromol Rapid Commun 2011 32 966-971. 

Li Y, Benicewicz BC (2008) Functionalization of silica nanoparticles via the combination of surface-initiated RAFT polymerization and click reactions. Macromolecules 41 7986—7992... 

Huang X, AppeUians D, Formanek P, Simon F, Voit B (2011) Synthesis of well-defined photo-cross-hnked polymeric nanocapsules by surface-initiated RAFT polymerization. Macromolecules 44 8351-8360... 

Table 1 Surface-initiated ATRP and RAFT polymerization of MMA... 

The need to better control surface-initiated polymerization recently led to the development of controlled radical polymerization techniques. The trick is to keep the concentration of free radicals low in order to decrease the number of side reactions. This is achieved by introducing a dormant species in equilibrium with the active free radical. Important reactions are the living radical polymerization with 2,2,4,4-methylpiperidine N-oxide (TEMPO) [439], reversible addition fragment chain transfer (RAFT) which utilizes so-called iniferters (a word formed from initiator, chain transfer and terminator) [440], and atom transfer radical polymerization (ATRP) [441-443]. The latter forms radicals by added metal complexes as copper halogenides which exhibit reversible reduction-oxidation processes. 

SCHEME 83 Schematic illustration of the synthesis of PVDF- -PAAc copolymer hy RAFT-mediated graft polymerization, the preparation of the PVDF-g-PAAc membrane with hving surfaces, and the preparation of the pH- and temperature-sensitive PVDF-g-PAAc-h-PNIPAM microporous membrane via surface-initiated block copolymerization. PVDF, polyfvinyhdene fluoride) AAc, acrylic acid NIPAM, V-isopropylacrylamide. Reprinted with permission from Reference 92. Copyright 2004 American Chemical Society. 

Among the different CRP techniques that are available, surface-initiated ATRP and RAFT have been most extensively used to grow polymer brushes from the membrane and pore surfaces [129,139-143]. Both methods can tailor and manipulate the structure and length of the grafted chains on the membrane and pore surfaces, which in return, are able to tune the pore size and pore size distribution to avoid pore blocking. Furthermore, ATRP and RAFT can produce more uniform and smoother surfaces, which have a more prominent effect on protein adsorption and fouling during the microfiltration or ultrafiltration process, than conventional radical polymerization. 

To overcome these problems, a surface-initialed living radical polymerization technique is used for preparing polymer brush surfaces, where precisely controlled polymer chains are densely tethered. The technique also can be used to construct block copolymer on the surfaces by sequentially grafting another polymer via the active polymer-end groups of a first-grafted polymer brush. As a typical surface-initiated Uving radical polymerization, atom transfer radical polymerization (ATRP) and reversible addition-fragmentafion chain transfer radical (RAFT) polymerization are... 

All LRPs such as NMP, ATRP, RAFT, TERP, or RTCP have already been applied to surface-initiated polymerization by fixing dormant species or conventional radical initiators. For details, readers are referred to other relevant chapters. 

Rowe-Konopacki, M. D., Boyes, S. G., Synthesis of Surface Initiated Diblock Copol5mier Brushes from Flat Silicon Substrates Utilizing the RAFT Polymerization Technique, Macromolecules 2007,40,879-888. 

Zhai, G. Q., Yu, W. H., Kang, E. T., Neoh, K. G., Huang, C. C., Liaw, D. J., Functionalization of Hydrogen-Terminated Silicon with Polybetaine Brushes via Surface-Initiated Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization, 2004, 43,1673-1680. 

---