Degenerative Transfer Processes

The controlled free-radical miniemulsion polymerization of styrene was performed by Lansalot et al. and Butte et al. in aqueous dispersions using a degenerative transfer process with iodine exchange [91, 92]. An efficiency of 100% was reached. It has also been demonstrated that the synthesis of block copolymers consisting of polystyrene and poly(butyl acrylate) can be easily performed [93]. This allows the synthesis of well-defined polymers with predictable molar mass, narrow molar mass distribution, and complex architecture. 

More recently, several investigations have shown that ITP can produce telechelic oligomers. The degenerative transfer process then requires the use of diiodide compounds instead of the iodide compounds usually employed in ITP. Noteworthy, the Dupont [231] and Ausimont [232] companies were first attracted by this concept (using IC4F8l as the transfer agent) in the CRP of... 

The chemistry for RAFT is illustrated in Scheme 3. The RAFT process is the newest of the living-radical processes and is reported not to have the limitations of the two previously described systems [45], It is essentially a degenerative transfer process in which a polymer chain (P ), initiated with an azo or peroxy initiator, reacts with a (thiocarbonyl)sulfanyl compound, S=C(Z)-S-R, to release R, an alkyl radical which can go on to initiate another polymer chain. Another propagating chain (Pm ) can subsequently react with P -S-C(Z)=S to release P which can go on to add more monomer. This cycle then repeats itself to produce polymer. 

The next volume contains 10 chapters on mechanisms and kinetics of RAFT, other degenerative transfer processes, NMP and OMRP. They are followed by six chapters devoted to molecular architecture accessible by these techniques. Various materials aspects of the resulting pol5miers are covered in six chapters. The last two chapters present commercial application of pol5miers prepared by NMP and RAFT (or MADIX). 

RAFT and MADEX are the two most successful degenerative transfer processes but significant progress has been also demonstrated in iodine DT and in the use of Sb, Bi and other organometallic mediators. " ... 

Matyjaszewski et al. systematically investigated the effect of electron donors (ED), such as pyridine and triethylamine, on the CRP of VAc with Co(acac)2. They proposed that the polymerization mechanism of VAc with Co(acac)2 in the absence of electron donor was a degenerative transfer process as shown in scheme 3(a). The polymerization in the presence of electron donor was a stable free radical polymerization controlled by the reversible homolytic cleavage of cobalt(III) dormant species as shown in scheme 3 (b). ... 

Sawamoto et al. reported in 2002 the polymerization of VAc mediated by dicaibonylcyclopentadienyliron dimer [Fe(Cp)(CO)2)]2 using iodide compounds as initiators and Al(0-i-Pr)3 or Ti(0-/-Pr)4 as an additive." However, this catalyst system was found complicated in mechanism. The metal alkoxide additives and the iodide compounds played important roles in the polymerization of VAc. Without the additive or iodide compounds, the polymerization became extremely slow or even no polymerization occurred. Additionally, the iodine-degenerative transfer process could not be excluded in this polymerization because alkyl-iodides alone could mediate degenerative transfer polymerization of VAc, as discussed in the above section.Thus, the mechanism of this polymerization system was proposed as shown in Scheme 6, but it was not verified and unclear. 

Atom Transfer Radical Polymerization. ATRP is one of the most successful controlled/living radical polymerization (CRP) systems, in addition to NMP and degenerative transfer processes, such as RAFT (5,233,234). The key feature of all of them is the dynamic equilibration between the active radicals and varions tsqjes of dormant species (see Living Radical Polymerization). 

For example, controlled free radical polymerization of styrene based on a degenerative transfer process with iodine exchange was carried out in oil-in-... 

A degenerative transfer process, as already stated above, cannot take place if the OMRP dormant species, the metal complex R-Mt /Lj, has no suitable vacant site to accept the incoming radical or if its electronic configuration does not allow the new bond to be established. In this case, any amount of excess radicals should in principle produce polymer by free-radical... 

---