Homolytic Bond Strengths and Formation Rates in Half-Sandwich Chromium Alkyl Complexes: Relevance for Controlled Radical Polymerization
Résumé
In the past decade, controlled/living radical polymerization (CRP) processes have seen a considerable surge of interest owing, in part, to their relevance to the accessibility of a variety of well‐defined polymer structures (e.g. predetermined molecular mass, narrow molecular weight distribution).1 We have been interested in the one‐electron reactivity of transition‐metal complexes and its relevance in CRP.2 One way in which transition‐metal complexes can be used to control radical polymerization is through a reversible deactivation. The growing radical chain is trapped by formation of a metal–carbon bond to yield a metal‐capped polymer chain, which is a dormant organometallic species (Figure 1). We refer to this particular control mechanism as “organometallic radical polymerization” (OMRP).2 One of the outstanding challenges in this area is the possibility to control the polymerization of less reactive monomers (e.g. vinyl chloride, vinylidene dichloride, vinyl acetate), for which activation is made difficult by the relatively strong bonds established with common radical traps.
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