Expanding the Scope of RAFT Polymerization: Recent Advances and New Horizons

Abstract

Reversible deactivation radical polymerization (RDRP) has revolutionized modern polymer chemistry over the past two decades, thus laying the groundwork for the synthesis of complex macromolecules and enabling the preparation of previously inaccessible materials. Reversible addition-fragmentation chain transfer (RAFT) polymerization has emerged as one of the most promising techniques because of its functional group tolerance, applicability to a wide range of vinyl monomers, and its nondemanding experimental conditions. However, despite the promise and clearly demonstrated utility of RAFT, limitations of the method sometimes still exist, including the occasional need for extended polymerization times, limited access to high molecular weight polymers, low "livingness" due to unavoidable radical termination events, etc. This Perspective focuses on recent advances that have been specifically designed to address many of these perceived limitations to reinforce the promise of RAFT for the synthesis of complex and well-defined polymers under facile conditions.

Electrochemically Mediated Reversible Addition–Fragmentation Chain-Transfer Polymerization

“…25 RAFT polymerization is compatible with many vinyl monomers and solvents, including both homogeneous and heterogeneous conditions. 28 …”

A detailed mechanistic study of bulk MADIX of styrene and its chain extension

“…This mechanism can be used taking into account the fact that the RAFT fragmentation can be expected to be fast and the RAFT addition slow. 7,19,21,32,77 As shown by De Rybel et al, 11 for low RAFT addition rate coefficients (<10 2.5 L mol…”

“…The presence of a delocalizable oxygen electron pair decreases the SvC double-bond character and, consequently, RAFT addition becomes less favourable. 21 The corresponding RAFT polymerization is often referred to as macromolecular design by interchange of xanthates (MADIX), due to historical reasons of its discovery. 22,23 As a result of the low SvC double-bond character of xanthates, microstructural control (Đ < 1.5) can typically only be achieved by employing so-called less activated monomers (LAMs) such as ethylene and vinyl acetate.…”

“…These monomers typically contain a saturated carbon or an oxygen/nitrogen electron pair adjacent to the vinyl group, resulting in more reactive radicals with respect to RAFT addition (C tr(,0) > 10). 17,19,21,[24][25][26][27][28][29] Other more active RAFT agents such as dithioesters and trithiocarbonates (Fig. 1c) lead to the formation of INT radicals considerably more stable than the radicals formed by RAFT fragmentation, resulting in an undesired lowering of the polymerization rate.…”

Cleavage of macromolecular RAFT chain transfer agents by sodium azide during characterization by aqueous GPC

“…2,3 Due to its compatibility with a wide range of monomers and experimental conditions (including aqueous solvents), RAFT has proven to be a particularly versatile and popular technique. 4 RAFT polymerisations have been widely conducted in aqueous solvents in cases where compatibility with organic solvents is poor. For example, bioconjugation of RAFT polymers to proteins is conducted in aqueous solution both for solubility reasons and to prevent protein denaturation.…”