Raft polymerisation

Uzulina, I., Kanagasapatty, S. and Claverie, J. (2000) Reversible addition fragmentation transfer (RAFT) polymerisation in emulsion. Macromol. Symp., 150, 33-8. 

RAFT is the newest methodology and is performed by adding a thioester compound to a conventional free-radical polymerisation, as shown in Figure 4(b). The mechanism of RAFT polymerisation is envisaged to involve a series of addition-fragmentation sequences. Polymers with narrow molecular weight distribution can be made, and block or star polymers are also possible. 

RAFT polymerisation is a useful technique to synthesis HBP with pendent norbornene functionalities (Figure 2.7) [49]. HBP are well-known for their multiple and simultaneous bacterial activities. They can capture multiple bacteria via the coreshell covering. As mentioned in the synthesis section, HBP are able to form micelles via self-assembly in solution and, as a result, they act as HDP. They are positively charged polymers and non-toxic to mammalian cells as are cationic polyamino acids and cationic polyelectrolj es. It has been reported that to retard the harmful microbial growth of infected tissue, HDP make a neutral core-shell on it [50, 51]. 

Figure 2.7 Synthesis of HBP with pendent norbornene functionalities via RAFT polymerisation of a novel asymmetrical divinyl monomer. Adapted with permission from Z-M. Dong, X-H. Liu, X-L. Tang and Y-S. Li, Macromolecules, 2009, 42, 13, 4596. 2009, American Chemical Society [49]...

Stenzel MH, Bamer-Kowollik C, Davis TP, Dalton HM. Amphiphilic block copolymers based on poly (2-acryloyloxyethyl phosphorylehobne) prepared via RAFT polymerisation as biocompatible nanoeontainers. Macromol Biosci 2004 4 445-453. 

Baussard J-F, Habib-Jiwanb J-L, Laschewskya A, Mertogluc M, Storsberg, J. New chain transfer agents for Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerisation in aqueous solution. Polymer 2004 45 3615-3626. 

RAFT polymerisation is controlled radical polymerisation technique that is highly versatile and can be used with a wide range of monomers [38]. In RAFT polymerisation, a chain-transfer agent, typically a thiocarbonyl compound such as a xanthate, dithioester or thiocarbamate, is used in conjunction with a free-radical initiator to control the polymerisation (Figure 2.10). RAFT polymerisation has been... 

Figure 2.10 The RAFT polymerisation mechanism [39]. Reproduced with permission from R.T.A. Mayadunne, E. Rizzardo, J. Chiefari, Y.K. Chong, G. Moad, and S.H. Thang, Macromolecules, 1999, 32, 21, 6977. 1999, ACS...

This section will describe RAFT polymerisations carried out under miniemulsion conditions. The first detailed study of the use of SDS or for that matter any ionic stabiliser with a hydrophobe led to destabilisation of the miniemulsion for polymerisations of styrene or ethyl hexyl methacrylate (EHMA) (Tsavalas et al, 2001). However, a linear increase in Mn was found with conversion with polydispersities as high as 2. Conductivity measurements were also carried out to study the extent of surfactant migration into the aqueous phase. The results showed that SDS did migrate, but only after polymerisation was initiated. The destabilisation mechanism is still unknown. Lansalot et al. (2002) showed that they could find conditions where colloidal stability was observed when using SDS. However, the polydispersity found in their experiments ranged between 1.7 and 2, suggesting that these systems gave non-ideal RAFT polymerisation. 

Recently, Narain and co-workers synthesised cationic glycopolymer-based DTC conjugates using RAFT polymerisation and subsequent modification of pendant amine groups with carbon disulfide under basic conditions (Scheme 1.5). The resulting novel glycopolymer-DTC derivatives and their gold complexes were evaluated for their cytotoxicity profiles in a number of cell lines [109]. 

The RAFT polymerisation method offers a versatile platform for the controlled synthesis and molecular engineering of glycopolymers. This field is rapidly expanding, with more exciting and new opportunities yet to explore. However, it is crucial to note that selection of the appropriate RAFT agent and reaction conditions remains key to successful RAFT polymerisation. 

RAFT polymerisation has also been used in conjunction with CuAAC for the preparation of highly branched, hyperbranched and neo-glycopolymers [134, 135]. For instance, Stenzel and co-workers reported the synthesis of a new class of glycomonomer (4-vinyl-l, 2,3-triazole), followed by its RAFT polymerisation in water/methanol at 60 C (Scheme 1.9) [135]. 

Figure 3.4 Outline of the synthesis of glycopolymer-peptide bioconjugate PGlcEMA-GSH via RAFT polymerisation and thiol-disulfide exchange. Reagents and conditions a) DTP, ethanolamine, acetonitrile, RT, 24 h and b) sodium methoxide, CHsCl/MeOH (1 1), RT, 1 h. Reproduced with permission from H. Shi, L. Liu, X. Wang and J. Li, Polymer Chemistry, 2012, 3, 1182. 2012, Royal Society of Chemistry [45]...

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