text: Iodine-transfer polymerization (ITP, also called ITRP), developed by Tatemoto and coworkers in the 1970s gives relatively low polydispersities for fluoroolefin polymers.  While it has received relatively little academic attention, this chemistry has served as the basis for several industrial patents and products and may be the most commercially successful form of living free radical polymerization.  It has primarily been used to incorporate iodine cure sites into fluoroelastomers.
  The mechanism of ITP involves thermal decomposition of the radical initiator (typically persulfate), generating the initiating radical In•. This radical adds to the monomer M to form the species P•, which can propagate to P•. By exchange of iodine from the transfer agent R-I to the propagating radical P• a new radical R• is formed and P• becomes dormant. This species can propagate with monomer M to P•. During the polymerization exchange between the different polymer chains and the transfer agent occurs, which is typical for a degenerative transfer process.
  Typically, iodine transfer polymerization uses a mono- or diiodo-perfluoroalkane as the initial chain transfer agent.  This fluoroalkane may be partially substituted with hydrogen or chlorine.  The energy of the iodine-perfluoroalkane bond is low and, in contrast to iodo-hydrocarbon bonds, its polarization small.  Therefore, the iodine is easily abstracted in the presence of free radicals.  Upon encountering an iodoperfluoroalkane, a growing poly(fluoroolefin) chain will abstract the iodine and terminate, leaving the now-created perfluoroalkyl radical to add further monomer.  But the iodine-terminated poly(fluoroolefin) itself acts as a chain transfer agent.  As in RAFT processes, as long as the rate of initiation is kept low, the net result is the formation of a monodisperse molecular weight distribution.
  Use of conventional hydrocarbon monomers with iodoperfluoroalkane chain transfer agents has been described.  The resulting molecular weight distributions have not been narrow since the energetics of an iodine-hydrocarbon bond are considerably different from that of an iodine-fluorocarbon bond and abstraction of the iodine from the terminated polymer difficult.  The use of hydrocarbon iodides has also been described, but again the resulting molecular weight distributions were not narrow.
  Preparation of block copolymers by iodine-transfer polymerization was also described by Tatemoto and coworkers in the 1970s.
  Although use of living free radical processes in emulsion polymerization has been characterized as difficult, all examples of iodine-transfer polymerization have involved emulsion polymerization.  Extremely high molecular weights have been claimed.
  Listed below are some other less described but to some extent increasingly important living radical polymerization techniques.