NMR Spectroscopy in the Optimization and Evaluation of RAFT Agents

Abstract

The selection of a suitable mediating agent in Reversible Addition‐Fragmentation Chain Transfer (RAFT) mediated polymerization is crucial to the degree of control that can be achieved. An overview of work from the Stellenbosch group is presented in which the use of NMR spectroscopy as a tool for evaluating RAFT‐agents is highlighted. The occurrence of selective initialization, i.e. the selective conversion of a RAFT‐agent into its single monomer adduct is discussed for various classes of monomers, as well as for copolymerization. One of the general rules for living polymerization is that chains should start growing early in the polymerization reaction. Selective initialization is claimed to be the extreme case where all chains have begun growing after the conversion of only one monomer equivalent per RAFT‐agent.

Macromolecular Design by Interchange of Xanthates: Background, Design, Scope and Applications

“…Until recently, little was published on C/LRP of NVP. MADIX polymerization of that monomer follows the same trends than that of VAc: xanthates are particularly suited for the corresponding propagating radicals that are highly reactive, provided the R leaving group is properly selected [28,51,[65][66][67]. The same trend applies for other N-vinyl monomers such as N-vinyl carbazole (N-VCbz) [68].…”

“…Retention of the dithiocarbonate polymer end groups was demonstrated by chain-extension experiments. In contrast, with R = 2-carboxyethyl (X 18 ) as the leaving group, polymerization of NVP exhibited a 'hybrid behavior', but the same MADIX agent showed fast and selective initialization for VAc, although such a difference was not fully explained [28,66]. As already mentioned, Kamigaito and coworkers reported that xanthates X 2 and X 28 gave well-controlled PNVPs, following inhibition periods of 6 and 1 h, respectively.…”

“…A few examples of multifunctional MADIX agents consisting of various S-substituted R leaving groups and O-ethyl or O-trifluoroethyl activating groups aimed to grow star polymers by the R-group approach have been designed in a two-step sequence; these are shown in Fig. 10.8 (X 45 -X 48 ) [66,[105][106][107][108][109]. This has been achieved in particular for VAc, NVP, NVCbz or AA monomers for which MADIX polymerization is highly efficient.…”

Living Radical Polymerization by the RAFT Process - A Second Update

“…The past 2 years has seen the publication of further general reviews detailing the RAFT process which include works by Moad, Rizzardo, and Thang, [9][10][11][12] a Handbook of RAFT Polymerization, [13] and a highlight article by Barner-Kowollik and Perrier [14] on the future of RAFT. Reviews on specific areas include the kinetics and mechanism of RAFT polymerization, [15][16][17][18] the use of RAFT to probe the kinetics of radical polymerization, [19,20] the use of RAFT in organic synthesis, [21] amphiphilic block copolymer synthesis, [22,23] the synthesis of end functional polymers, [24] the synthesis of star polymers and other complex architectures, [25,26] the use of trithiocarbonate RAFT agents, [27] the use of xanthate RAFT agents (MADIX), [28] polymerization in heterogeneous media, [29][30][31][32] RAFT polymerization initiated with ionizing radiation, [33] polymer synthesis in aqueous solution, [34][35][36][37] surface and particle modification, [38,39] synthesis of self assembling and/or stimuli responsive polymers, [36,40] RAFT-synthesized polymers in drug delivery, [22,41] and other applications of RAFTsynthesized polymers. [30,42,43] 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.…”

Molecular Weight and Tacticity of Oligoacrylates by Capillary Electrophoresis - Mass Spectrometry

“…[52,53] This controlled radical polymerization technique is based on a twostep addition-fragmentation mechanism using thiocarbonylthio compounds as transfer agents, although the precise mechanism is still under debate. [54,55] For instance, Klumperman et al [56][57][58][59] have investigated the early polymerization behaviour of several RAFT-mediated polymerizations. The period during which the initial RAFT agent was consumed was termed initialization, with different reaction behaviour observed before and after this period.…”