Chain transfer agent functional polymer method

Before the development of living cationic polymerization in the 1980s, Kennedy and his co-workers devised another way to synthesize end-functionalized polymers, which uses special reagents called inifer, or initiator-chain transfer agents [129]. The method is primarily for the synthesis of polyisobutene with a tertiary chlorine terminal, which is, however, a synthon for a variety of other functional groups. These developments have been reviewed extensively [1,3,130] and fall outside the scope of this chapter. 

A special case of controlled initiation is the inifer method. The word inifer (front initiator transfer agentsl describes compounds that function simultaneously as initiators and as chain transfer agents. The inifer technique provided the first carbocationic route toward the synthesis of telechelic ta. to functional) polymers. 

RAFT is a highly versatile method of polymerization that utilizes a chain-transfer agent (CTA) to produce the dormant form of the growing polymer chains. The CTA is commonly a di- or tri-thiocarbonylthio compound that forms a stabilized radical intermediate. Chain equilibration between actively growing and dormant chains leads to uniform rate of chain growth for all polymers, and is linearly related to conversion. Since transition metal catalysts are not required, RAFT has increased compatibility with a wider anay of monomer functionalities than other polymerization methods, hut the... 

Preparations of macro-initiators or telechelic polymers by cationic methods have been executed primarily by polymerizing isobutylene in the presence of a co-initiator that also functions as a chain transfer agent. A typical reaction sequence is shown in Scheme 1, outlining the synthesis of difunctional polyisobutylene (PIB), which is then used to initiate the polymerization of a-methyl styrene (ffi-MS) to produce an A-B-A type block copolymer. By similar methods, polyisobutylenes with phenol, phenyl, cyclopentadiene, and olefin termini have been synthesized. 

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