On the Origins of Nitroxide Mediated Polymerization (NMP) and Reversible Addition–Fragmentation Chain Transfer (RAFT)

Abstract

The early experiments on radical polymerization, which were to lead to a study of nitroxide trapping of the initiation step and the interest in defect groups, particularly the macromonomers formed by termination by disproportionation, are discussed. Results from the nitroxide trapping clearly show that the initiation step ranges from simple clean addition to the head of the monomer, to complex addition/abstraction reactions. Careful selection of the monomer/initiation system is emphasized with particular reference to two common monomers, styrene and methyl methacrylate, and two initiating radicals, t-butoxy and benzoyloxy. The discovery of nitroxide mediated polymerization (NMP) from observations made during the nitroxide trapping work is reported and the ability to have a living radical system demonstrated with numerous examples. Similarly, the study of the copolymerization of macromonomers, formed by disproportionation of the propagating chains, is discussed with the discovery of b-scission and an early form of addition-fragmentation reported. The evolution of reversible addition-fragmentation chain transfer (RAFT) to a highly versatile and commercially attractive radical system is reported and the detailed chemistry behind the discovery of this living radical system discussed. Both NMP and RAFT enable the synthesis of structures not previously possible by radical polymerization and in some cases not possible by any other process.

Hyperbranched polydendrons: a new controlled macromolecular architecture with self-assembly in water and organic solvents

“…The global interest in macromolecular architecture has been driven over the last two and a half decades by advances in controlled polymer synthesis techniques, such as nitroxidemediated polymerisation, 1 atom transfer radical polymerisation (ATRP) 2 and reversible addition-fragmentation chain-transfer polymerisation (RAFT), 1 allowing the accurate tailoring of chain chemistry, composition and degree of polymerisation. Additionally, the appreciation of branched structures such as hyperbranched polymers 3 ( Fig.…”

RAFT Polymerization – Then and Now

“…The invention of RAFT at CSIRO should be seen against a background of research into defining and understanding polymer structures and on controlling the outcome of radical polymerization that had commenced more than two decades earlier. By the mid-nineties this work had already led to significant developments in control of polymer structure using chain transfer processes, to the invention of nitroxide mediated polymerization (NMP), and to the establishment of a Strategic Alliance with DuPont to further these goals (3,6). The discovery of RAFT was aided by a research environment that allowed the rapid shifting of priorities necessary to follow up sometimes serendipitous observations without rigorous justification.…”

“…The historical development of RAFT (reversible addition-fragmentation chain transfer) polymerization at CSIRO (1)(2)(3) and the parallel development of MADIX (macromolecular design via interchange of xanthates) at Rhodia (4,5) has been described in a number of recent reviews. The invention of RAFT at CSIRO should be seen against a background of research into defining and understanding polymer structures and on controlling the outcome of radical polymerization that had commenced more than two decades earlier.…”

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

“…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.…”