Surface-Initiated RAFT Polymerization

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. 

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... 

To make further use of the azo-initiator, tethered diblock copolymers were prepared using reversible addition fragmentation transfer (RAFT) polymerization. Baum and co-workers [51] were able to make PS diblock copolymer brushes with either PMMA or poly(dimethylacrylamide) (PDMA) from a surface immobihzed azo-initiator in the presence of 2-phenylprop-2-yl dithiobenzoate as a chain transfer agent (Scheme 3). The properties of the diblock copolymer brushes produced can be seen in Table 1. The addition of a free initiator, 2,2 -azobisisobutyronitrile (AIBN), was required in order to obtain a controlled polymerization and resulted in the formation of free polymer chains in solution. 

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

Baum et al. apphed RAFT polymerization to synthesize brushes of PS, PMMA, poly(Nd -dimethylacrylamide) (PDMA), and their copolymers on azo-initiator-bound sihcate surfaces [127]. 2-Phenylprop-2-yl dithiobenzoate was added as a free (unboimd) RAFT agent to control the graft polymerization. Because of a very low concentration of surface-bound initiator, a free... 

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. 

---