Summary: Reversible addition‐fragmentation chain transfer (RAFT) polymerization is a recent and very versatile controlled radical polymerization technique that has enabled the synthesis of a wide range of macromolecules with well‐defined structures, compositions, and functionalities. The RAFT process is based on a reversible addition‐fragmentation reaction mediated by thiocarbonylthio compounds used as chain transfer agents (CTAs). A great variety of CTAs have been designed and synthesized so far with different kinds of substituents. In this review, all of the CTAs encountered in the literature from 1998 to date are reported and classified according to several criteria : i) the structure of their substituents, ii) the various monomers that they have been polymerized with, and iii) the type of polymerization that has been performed (solution, dispersed media, surface initiated, and copolymerization). Moreover, the influence of various parameters is discussed, especially the CTA structure relative to the monomer and the experimental conditions (temperature, pressure, initiation, CTA/initiator ratio, concentration), in order to optimise the kinetics and the efficiency of the molecular‐weight‐distribution control.

Biomolecule-polymer conjugates are widely used in bio-related fields, but their synthesis is often tricky, especially the introduction of a single biomolecule at one chain end. This paper describes a new straightforward approach to prepare such conjugates via RAFT polymerization. By designing appropriate bio-related RAFT agents, polymer chains of controlled chain length (Mn = 10 000-40 000 and PDI < 1.1) carrying a single biomolecule as an alpha-end group (a sugar or a biotin) linked by a stable amide bond are obtained. Considering the versatility of the RAFT process, this strategy appears to be very attractive for the design of a variety of conjugates.

Homopolymers of N-acryloylmorpholine (NAM), a water-soluble bisubstituted acrylamide derivative, have been synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). Several dithioesters were used as chain transfer agents:  carboxymethyl dithiobenzoate (CMDB), tert-butyl dithiobenzoate (tBDB), menthonyl dithiobenzoate (MDB), and a bifunctional dithiobenzoate, 1,3-bis(2-(thiobenzoylthio)prop-2-yl)benzene (TPB). Whereas CMDB is a commercial reagent, tBDB and MDB were synthesized by a novel biphasic process based on a thioacylation reaction and leading to very high yields. The performances of the four dithiobenzoates were compared in term of kinetics and molecular weight distribution control. Very good control of NAM polymerization was obtained with tBDB and MDB, with a linear increase of M n vs conversion over the whole conversion range and with polydispersity indices (PDI) below 1.1, as determined by aqueous size exclusion chromatography with on-line light scattering detection. In addition, a degradation phenomenon of the dithioester functions was evidenced during the course of the polymerization, correlated with a M n vs conversion curve leveling off and even sometimes decreasing above 80% conversion. Such observations were assumed to be the consequence of the formation of side products in the polymerization media, subsequently acting as nondegradative irreversible transfer agents.

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A matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI−TOF MS) study of N-acryloylmorpholine (NAM) homopolymers, as obtained by reversible addition−fragmentation chain transfer (RAFT) polymerization technique, is reported. Polymerization of NAM was performed in dioxane using azobis(isobutyronitrile) (AIBN) as initiator and tert-butyl dithiobenzoate as RAFT chain transfer agent. Polymer samples of low molecular weights (<10 000 g mol-1) and low polydispersity indices (PDI < 1.1) were obtained, which are essential requirements for such MALDI−TOF MS analysis. First, analysis of poly(NAM) samples in linear mode led to values very close to both size exclusion chromatography/light scattering (SEC/LS) and 1H NMR values as well as to the theoretical ones. Then, an accurate examination of chain end groups was performed using the reflectron mode. Two main chain populations were identified:  (i) dormant chains (i.e., initiated by a tert-butyl and terminated by a dithiobenzoate group) together with sulfine and thioester-ended chains probably resulting from oxidation of dithiobenzoate chain ends during storage; (ii) proton-terminated chains mainly produced by fragmentation of the former chains in the spectrometer. In addition, some chains which could correspond to termination reactions onto the intermediate radicals involved in the RAFT equilibrium were suspected. Finally, comparison of polymer samples before and after aminolysis indicated that dithioester-ended chains constituted the majority of chains initially present in these samples. This study confirms that it is indeed possible to use MALDI−TOF MS to investigate the structure of polymer chains synthesized by the RAFT technique.

Controlled radical polymerization of the bisubstituted acrylamide derivative N-acryloylmorpholine (NAM) has the potential to yield telechelic polymers, one end of which can subsequently be grafted to latex particles. Once grafted, the other chain end of the polymer can be used as an immobilization site for species with applications in molecular biology and biomedicine. The controlled polymerization of NAM using reversible addition−fragmentation chain transfer (RAFT) is performed using two new chain transfer agents SC(Z)−SR bearing the same functional propanoic acid group (R) and two different Z groups, benzyl (CTA 1) and phenyl (CTA 2). RAFT polymerization of NAM mediated by CTA 1 is very fast (>80% conversion in less than half an hour at 65 °C). The linear evolution of M̄ n and the low polydispersity indices (M̄ w/M̄ n < 1.2) are in accord with the expected characteristics of a living polymerization. CTA 2 leads to broader M̄ w/M̄ n's (<1.4). The resulting CTA-capped polymers were further used to yield an amphiphilic polyNAM-block-polystyrene. These α,ω-functionalized polyNAM chains were characterized by 1H NMR and MALDI-ToF mass spectrometry.

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