Reversible addition-fragmentation nanoparticles

Spherical gold nanoparticles coated with poly(N-isopropylacrylamide) (PNIPAM) grafts have been synthesized by controlled radical polymerization. The polymerization of N-isopropylacrylamide was initiated from the surface of the nanoparticles modified with 4-cyanopentanoic acid dithiobenzoate for reversible addition-fragmentation chain-transfer polymerization. The mean diameter of the Au core was 3.2 nm, as observed by means of high-resolution transmission electron microscopy [90]. 

CRP provides a versatile route for the preparation of (co) polymers with controlled molecular weight, narrow molecular weight distribution (i.e., Mw/Mn, or PDI < 1.5), designed architectures, and useful end-functionalities. Various methods for CRP have been developed however, the most successful techniques include ATRP, stable free radical polymerization, " and reversible addition fragmentation chain transfer (RAFT) polymerization. " " CRP techniques have been explored for the synthesis of gels " " and cross-linked nanoparticles of well-controlled polymers in the presence of cross-linkers. 

Taking into account all of the above mentioned applications, the synthesis of magnetic latex will be discussed in two parts first, the preparation of iron oxide nanoparticles and, second, the preparation of magnetic latex. Depending on the aim of researchers, many polymerization techniques are applied such as suspension, dispersion, emulsion, microemulsion and miniemulsion polymerization in combination with controlled radical polymerization techniques like atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) and nitroxide-mediated radical polymerization (NMP). The preparation of hybrid magnetic latex by emulsion polymerization will be the focus of this review. 

A. B. Lowe, B. S. Sumerlin, M. S. Donovan, and C. L. McCormick, Facile preparation of transition metal nanoparticles stabilized by well-defined (co)poiymers synthesized via aqueous reversible addition-fragmentation chain transfer polymerization, J. Am. Chem. Soc., 124, 11562-11563 (2002). 

Li CZ, Benicewicz BC (2005) Synthesis of well-defined polymer brushes grafted onto silica nanoparticles via surface reversible addition-fragmentation chain transfer polymerization. Macromolecules 38 5929-5936... 

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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