RAFT Agent Design and Synthesis

Abstract

This Perspective reviews the design and synthesis of RAFT agents. First, we briefly detail the basic design features that should be considered when selecting a RAFT agent or macro-RAFT agent for a given polymerization and set of reaction conditions. The RAFT agent should be chosen to have an optimal C tr (in most circumstances higher is better) while at the same time it should exhibit minimal likelihood for retarding polymerization or undergoing side reactions. The RAFT agent should also have appropriate solubility in the reaction medium and possess the requisite end-group functionality for the intended application. In this light we critically evaluate the various methods that have been used for RAFT agent synthesis. These methods include reaction of a carbodithioate salt with an alkylating agent, various thioacylation procedures, thiation of a carboxylic acid or ester, the ketoform reaction, thiol exchange, radical substitution of a bis­(thioacyl) disulfide, and radical-induced R-group exchange. We also consider methods for synthesis of functional RAFT agents and the preparation of macro-RAFT agents by modification of, or conjugation to, existing RAFT agents. The most used methods involve esterification of a carboxy functional RAFT agent, azide–alkyne 1,3-dipolar cycloaddition, the active ester–amine reaction, and RAFT single unit monomer insertion. While some of these processes are described as “click reactions”, most stray from that ideal. The synthetic method of choice is strongly dependent on the structure of the desired RAFT agent. Finally, we outline some of the current challenges in RAFT agent design and synthesis.

Living Radical Polymerization by the RAFT Process – A Third Update

“…The factors which influence choice of RAFT agent for a particular polymerization has been presented in various reviews. [17][18][19]28,137] The effectiveness of the RAFT agent depends on the monomer being polymerized and is determined by the properties of the free radical leaving group R and the group Z which can be chosen to activate or deactivate the thiocarbonyl double bond of the RAFT agent (1) and modify the stability of the intermediate radicals (2) and (4). For effective RAFT polymerization (Scheme 1, Fig.…”

“…include those on the kinetics and mechanism of RAFT polymerization, [26,27] RAFT agent design and synthesis, [28] the use of RAFT to probe the kinetics of radical polymerization, [29] microwaveassisted RAFT polymerization, [30,31] RAFT polymerization in microemulsion, [32] end-group removal/transformation, [33][34][35][36] the use of RAFT in organic synthesis, [37] the combined use of RAFT polymerization and click chemistry, [38] the synthesis of star polymers and other complex architectures, [39][40][41][42] the synergistic use of RAFT polymerization and ATRP, [43,44] the synthesis of self assembling and/or stimuli-responsive polymers, [45][46][47] and the use of RAFT-synthesized polymers in green chemistry, [48] polymer nanocomposites, [49][50][51] drug delivery and bioapplications, [41,46,47,[52][53][54][55][56][57][58][59][60] and applications in cosmetics [61] and optoelectronics. [62] The process is also given substantial coverage in most recent reviews that, in part, relate to polymer synthesis, living or controlled polymerization or novel architectures.…”

Graft copolymers of hydroxyethyl cellulose by a ‘grafting to’ method:15N labelling as a powerful characterisation tool in ‘click’ polymer chemistry

“…The CTA 5 was then used to polymerise N-vinylpyrrolidone (NVP) in a controlled manner to give PVP chains with alkyne end groups (Supplementary Information, Scheme S3). In the literature [38][39][40][41][42] , both xanthate and dithiocarbamate chain transfer agents were shown to be good candidates for polymerising NVP, a monomer that is a member of the "less activated monomers" (LAM) class described by Keddie et al 43 Furthermore, Patel et al 44 and Akeroyd et al 31 reported the preparation of alkyne-terminated RAFT agents which were used for preparing "macro-RAFT agents" or clickable polymers respectively. The ratio RAFT agent : initiator (AIBN) was optimised to obtain relatively high conversion and good control of the polymerisation, and we found that 1:0.7 was a good compromise, giving a monomer conversion and a Ɖ M of 80% and 1.4 respectively.…”

Macromolecular Architectures Designed by Living Radical Polymerization with Organic Catalysts

“…A sufficiently large number of activation-deactivation cycles are required for low polydispersity [4][5][6][7]. Examples of the capping agent (X) include nitroxides, dithioesters, tellurides, and halogens [8][9][10][11][12][13][14][15]. Halogens are combined with transition metal catalysts [13][14][15].…”