Iniferters types

There are two types of A-B and B-B type iniferters. A-B type iniferters thermally or photochemically dissociate into different radicals (Eq. 8) ... 

On the other hand, the B-B type iniferters dissociate into two identical radicals as follows (Eq. 12) ... 

Monofunctional Iniferter R-X > R-tMJj-X End-functional polymer, AB-type block copolymer... 

Difunctional Iniferter X-X > X-QA X Telechelic polymer, AB- or ABA-type block copolymer... 

The A-B type iniferters are more useful than the B-B type for the more efficient synthesis of polymers with controlled structure The functionality of the iniferters can be controlled by changing the number of the A-B bond introduced into an iniferter molecule, for example, B-A-B as the bifunctional iniferter. Detailed classification and application of the iniferters having DC groups are summarized in Table 1. In Eqs. (9)—(11), 6 and 7 serve as the monofunctional iniferters, 9 and 10 as the monofunctional polymeric iniferters, and 8 and 11 as the bifunctional iniferters. Tetrafunctional and polyfunctional iniferters and gel-iniferters are used for the synthesis of star polymers, graft copolymers, and multiblock copolymers, respectively (see Sect. 5). When a polymer implying DC moieties in the main chain is used, a multifunctional polymeric iniferter can be prepared (Eqs. 15 and 16), which is further applied to the synthesis of multiblock copolymers. 

The results of the radical polymerization of MM A in bulk at 60-100 °C with 6 as the A-B type thermal iniferter are shown in Fig. 1 [16,81]. In this polymerization, the molecular weight of the polymers produced increased with the reaction time. 

Controlled/ living radical polymerization (CLRP) processes are well-established synthetic routes for the production of well-defined, low-molecular weight-dispersity polymers [99]. The types of CLRP processes (initiator-transfer agent-terminator (INIFERTER), atom transfer radical polymerization (ATRP), nitroxide-mediated radical (NMRP) polymerization, reversible addition-fragmentation transfer (RAFT)) and their characteristics are described in Section 3.8 of Chapter 3 and in Section 14.8 of Chapter 14. 

Apart from thiuramdisulfides, some other compounds were shown to be useful thermal iniferters, Otsu and Tazaki [89] showed that compounds of the phenylazotriphenylmethane type can act as a thermal iniferter, where the phenyl radical initiates the polymerization, and the triphenylmethyl (tri-tyl) radical is a stable radical which couples with the growing chain, exhibiting a kind of living radical nature ... 

Scheme 3.2 C/LRP of vinyl monomers using unsymmetrical A-B and symmetrical B-B type iniferters.

Iniferters can be classified into two main types according to the structures of radicals formed (unsymmetrical A B and symmetrical B B type iniferters). Unsymmetrical A-B type iniferters decompose into two dilferent radicals where A is the reactive radical, which participates only in initiation, and B is the less or non-reactive radical which cannot enter initiation and acts as a primary radical terminator. On the other hand, the symmetrical B B type iniferters dissociate into two identical radicals where B is the less reactive radical which can enter into both initiation and primary radical termination (Scheme 3.2). 

There are a number of factors that affect the progress of the iniferter polymerization, the extent of its livingness, and thereby the control over the end product. These factors are related to iniferter structures,types of monomer and solvent,and temperature. Since the iniferter itself is incorporated into the growing/propagating polymer chain during polymerization, a desirable end group functionality can be designed by careful choice of iniferter. ... 

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