# Polymer@gold Nanoparticles Prepared via RAFT Polymerization for Opto-Biodetection
## 3 RAFT Polymerization
### General Concepts
Recent examples of such studies include, for example the estimation of rate coefficients of backbiting reactions in acrylates polymerization [74] Another example consists in a comparative study of methods reported in the literature to experimentally determine RAFT transfer coefficients as well as a set of general guidelines for appropriate choice of the method to use [75]. More recently, the group reported the kinetic Monte Carlo model of PLS-SEC study on _n_-butyl acrylate which provided detailed information on chain propagation, chain initiation as well as termination reactivity [76]. These contributions consist in a major asset to develop models which can be used for in silico studies to screen reactants and polymerization conditions efficiently as opposed to conventional \"try & error\" approaches. Nevertheless, experimental validation is still required. Also worthy of notice is [PERSON]'s tutorial review which consists in a clear and didactic guide for the preparation of block copolymers via RAFT [77]. From what was outlined before, besides the relevance of the choice of the RAFT agent, experimental aspects should be also considered thus, examples of the effect of some polymerization conditions are briefly presented. For instance, RAFT polymerization started to be performed in organic medium being compatible with a wide range of organic solvents, but the solubility of the RAFT agent in the solvent should be a concern as well as the hydrolytic sensitivity of some RAFT agents to some solvents. Generally, RAFT polymerization in organic medium can be carried out over a temperature range from room temperature to 140 \({}^{\circ}\)C. Yet, whilst higher temperatures yield better results they can also promote conventional radical polymerization. Additionally, RAFT polymerizations can also be efficiently performed in aqueous medium thus enabling the polymerization of anionic, cationic, zwitterionic and neutral monomers leading to hydrophilic and functional polymers. In homogenous aqueous polymerization, the RAFT agents that have shown higher versatility are the dithiesters and trithiocarbonates. The use of RAFT polymerization in dispersed media has also been widely explored as it allows the preparation of nanostructures with a variety of morphologies, the combination of hydrophobic and hydrophilic monomers, as well as the preparation of stable colloids which can actually encapsulate inorganic nanoparticles as will be discussed later. [PERSON] has reported a rather comprehensive set of guidelines for the synthesis of block copolymer particles of distinct morphologies via RAFT polymerization conducted in dispersed media combined with stabilization through chain crosslinking using bifunctional monomers, which allows novel applications [78]. As regards the type of initiator used, any source of free radicals can be used such as azo and persulfate initiators, UV irradiation, \(\gamma\)-source, plasma field and thermal initiation in the case of styrene. Yet, studies have revealed that the choice of the initiator can also play a major role. For example [PERSON] et al. in their studies to optimize the preparation of multiblock copolymers via one-pot multistep sequential polymerization, used 2,2\({}^{\prime}\)-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044) as initiator which has a rather short half-life at 44 \({}^{\circ}\)C (10 h) [79]. Furthermore, there are additional aspects related to the initiator that need to be taken into consideration: one is the concentration of initiator  
Figure 7: Proposed mechanism of RAFT polymerization; (I and II) homopolymerization and (III) chain extension of a macroCTA. Adapted from [67], Copyright 2008, with permission from Elsevier; and [73], Copyright 2009, with permission from John Wiley & Sons Inc. (Note that for the sake of clarity various dead polymer chains resulting from the different possible paths were omitted. Yet, they are discussed in the text above).