Reversible addition-fragmentation chain amphiphilic block copolymers

Mertoglu M, Gamier S, Laschewsky A, Skrabania K, Storsberg J. Stimuli responsive amphiphilic block copolymers for aqueous media synthesised via reversible addition fragmentation chain transfer polymerisation (RAFT). Polymer 2005 46(18) 7726-40. 

Figure 6.2. Examples of amphiphilic block copolymers synthesized by atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization (end groups and block-linking groups are omitted).

A block copolymer of poly(A-isopropylacrylamide) (PNI-PAAm) and PLA may combine the thermosensitive property of PNIPAAm and the biodegradable property of PLA. Polymeric micelles from such polymers can improve protein release properties. Temperature change can alter the hydro-philicity and conformation of PNIPAAm, which may affect the physicochemical properties of microspheres of the polymer. Amphiphilic block copolymers of P(NIPAAm-Z -LA) have been prepared by ROP of LA in toluene using Sn(Oct)2 as a catalyst and hydroxyl-terminated PNIPAAm, as depicted in Figure 4.6 [62]. Such copolymers have recently been synthesized by ROP of lactide using the two hydroxyl groups of 5, 5 -bis(2-hydroxyethyl-2 -butyrate)trithiocarbonate (BHBT). PLA-Z -PNIPAAm-Z -PLA was prepared by reversible addition-fragmentation chain transfer (RAFT) polymer-... 

Well-defined amphiphilic block copolymers can be prepared by various controlled polymerization reactions, such as atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), and nitroxide mediated polymerization (NMP). The amphiphilic copolymers most frequently used in bio-inspired strategies consist of hydrophilic blocks, such as poly(aciylic acid) (PAA), poly(ethylene oxide) (PEO), or poly(2-methyl oxazoline) (PMOXA), and a hydrophobic block, such as... 

Since the self-assembly phenomena requires well-defined block copolymers with narrow molecular weight distribution, only living/controlled polymerization techniques have been exploited for the preparation of polymeric nanoparticles via PISA. In particular, in aqueous media, the controlled radical polymerizations have been the methods of choice, taking the advantage of the compatibility of the reactions with water and the ability to create a wide variety of amphiphilic polymers. Atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), and reversible addition-fragmentation chain transfer (RAFT) polymerization have been the most studied techniques. The three methods possess certain advantages however, RAFT remains particularly the most attractive due to the wide variety of polymers that can be produced in a controlled manner at low polymerization temperatures. 

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