Polymer radicals living” macroradicals

New approaches based on the introduction of reactive species into reaction mixtures that tend to cap the growing chains reversibly allow, in many cases, production of well-defined polymers and copolymers with narrow polydispersi-ties. Up to few years ago, such a possibility was unobtainable by a classical free radical process. The proposed principle of control of macroradical reactivity is very interesting conceptually, and represents a very powerful tool to prepare block copolymers with well-controlled structures. However, it is clear that the true living character as demonstrated by some anionic polymerizations is still not obtained and much more work needs to be done to understand and control this new process better. 

Fig. 1 Main activation-deactivation equilibria in controUed/Living radical polymerization. The first two are reversible termination reactions and the last two are reversible chain transfer reactions. Pj stands for a macroradical with i monomer subunits. In the initial control agent, the polymer chain is replaced by a low molar mass leaving/initiating group, often referred to as...

NMP is historically the first widespread CRP method. In NMP processes, nitroxide derivatives control the polymerization. "" Such persistent aminoxyl radicals couple reversibly at high temperature with macroradicals (i.e., growing polymer chains), which lead to the formation of an equilibrium between a small fraction of active chains and a large fraction of inactive chains (also known as dormant chains) capped by an alkoxyamine moiety. As a consequence, NMPs exhibit a controlled/living behavior and therefore allow wide possibilities of macromolecular engineering. "... 

The concentration of surviving macroradicals decreases with time after irradiation [13]. Their living time is on the order of 24 hours in the amorphous phase, but macro alkyl radicals can be found in the polymer bulk even after years, probably trapped in the crystalline phase [14]. The mechanism of decay of macro alkyl radicals is still unknown. 

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