Degenerative transfer polymerization

Like RAFT, ITP is a degenerative transfer polymerization using alkyl halides [10,11]. ITP was developed in the late 1970s by Tatemoto et al. [226-229]. In ITP, a transfer agent RI reacts with a propagating radical to form the dormant polymer chain P -1. The new radical R can then reinitiate the polymerization. In ITP, the concentration of the polymer chains is indeed equal to the sum of the concentrations of the transfer agent and of the initiator consumed. The newly formed polymer chain P- can then propagate or react with the dormant polymer chain P -1 or R -1 [230]. The mechanism of ITP with alkyl iodide is shown in Scheme 41. 

Controlled/ Living radical polymerization (CRP) of vinyl acetate (VAc) via nitroxide-mediated polymerization (NMP), organocobalt-mediated polymerization, iodine degenerative transfer polymerization (DT), reversible radical addition-fragmentation chain transfer polymerization (RAFT), and atom transfer radical polymerization (ATRP) is summarized and compared with the ATRP of VAc catalyzed by copper halide/2,2 6 ,2 -terpyridine. The new copper catalyst provides the first example of ATRP of VAc with clear mechanism and the facile synthesis of poly(vinyl acetate) and its block copolymers. 

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. 

VAc has been successfully polymerized via controlled/ living radical polymerization techniques including nitroxide-mediated polymerization, organometallic-mediated polymerization, iodine-degenerative transfer polymerization, reversible radical addition-fragmentation chain transfer polymerization, and atom transfer radical polymerization. These methods can be used to prepare well-defined various polymer architectures based on PVAc and poly(vinyl alcohol). The copper halide/t is an active ATRP catalyst for VAc, providing a facile synthesis of PVAc and its block copolymers. Further developments of this catalyst will be the improvements of catalytic efficiency and polymerization control. 

Alkyl Iodide Transfer Agents Used in Degenerative Transfer Polymerization with Alkyl Iodides 160... 

Mechanism and Kinetics of Degenerative Transfer Polymerization with Alkyl Iodide 161... 

Terminally brominated PE as PE macroinitiator can be produced by other methods. It has been reported that vinyl terminated PE produced by a bis(phenoxy-imine)metal complex and MAO catalyst system (Mn = 1800, Mw/Mn = 1.70) was converted to terminally 2-bromoisobutyrate PE through the addition reaction of 2-bromoisobutyric acid to the vinyl chain end. Polyethylene-Wodc-poly( -bulyl acrylate) (PE-fo-PnBA) from terminally brominated PE by ATRP procedure has also been produced [68]. It was reported that degenerative transfer coordination polymerization with an iron complex can be used to prepare terminally brominated PE as a macroinitiator [69]. A Zn-terminated PE prepared using an iron complex and diethylzinc,... 

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. 

The cleavage of C l bond can be achieved by various methods [149-151]. However, from well-chosen monomers, two main ways have been developed in order to control telomerization from alkyl iodides Iodine Transfer Polymerization (FTP) and degenerative transfer. 

If an overall conclusion could be made, it might be considered that the counterradicals vary considerably (Scheme 3). They can either be stable (e.g., nitroxyls, arylazooxyls), semi persistent (e.g., from thiourams) and also metallic (e.g., acetoacetato metals). In addition, if these radicals either terminate or transfer, non-living (or inactive) species will be produced. But, in order to preserve the living character, the radicals must propagate and in specific cases (e.g., iodine transfer polymerization or degenerative transfer) active species will be obtained. The more that one of these latter steps is favored, the more living is the tendency of the radical polymerization, with a very high kinetic control of this reaction. 

In fact, the RAFT process resembles the degenerative transfer (DT) process [274]. In a polymerization in which an alkyl iodide is used as the degenerative transfer agent, the iodine atom is exchanged between a polymeric radical and a dormant chain, similar to the dithiocarbonate exchange in RAFT. However, in the case of degenerative transfer there is a direct equilibrium between the dormant and growing chains, without formation of an intermediate radical. 

The mechanism of Co(acac)2-mediated polymerization of Vac is still an open question. On the basis of an early work by Wayland and coworkers on the controlled radical polymerization of acrylates by complexes of cobalt and porphyrins, Debuigne and coworkers proposed a mechanism based on the reversible addition of the growing radicals P to the cobalt complex, [Co(II)], and the establishment of an equilibrium between dormant species and the free radicals (equation 8). Maria and coworkers, however, proposed that the polymerization mechanism depends on the coordination number of cobalt . Whenever the dormant species contains a six-coordinated Co in the presence of strongly binding electron donors, such as pyridine, the association process shown in equation 8 would be effective. In contrast, a degenerative transfer mechanism would be favored in case of five-coordinated Co complexes (equation 9). 

This technique for controlling radical polymerizations is based on one of the oldest technique, that of chain transfer, and has often been used in telomeriza-tion [83]. Similar to the concept of degenerative transfer with alkyl iodides [50, 51, 84], reversible addition fragmentation chain transfer with dithio esters (RAFT) [52-55, 85] is successful because the rate constant of chain transfer is faster than the rate constant of propagation. Analogous to both nitroxide-medi-... 

First block copolymers by degenerative transfer technique were prepared by using alkyl iodides/AIBN in polymerization of BA and St. For example, at 70 °C pSt with Mn=2500 and Mw/Mn=1.45 was extended to pSt-b-pBA with Mn=8630 and Mw/Mn=2.20. Although polydispersities were relatively high, a clean shift of the entire MW distribution was observed. In a similar way pBA with Mn=2820 and Mw/Mn=1.60 was extended to pBA-b-pSt with Mn=6290 and Mw/Mn=1.75. Conversion of the first block was above 95% and the second 80% in both cases [51]. 

Figure 6.26 Reaction scheme of controlled free-radical polymerization, based on degenerative chain transfer, of butyl acrylate (R = C4H9COO-) in the presence of secondary alkyl iodide (R = CH3CH(Ph)-, X = I) as the degenerative transfer agent. The latter alone does not initiate polymerization. (After Matyjaszewski et al., 1995.)...

Living polymerization is another rapidly developing area where the degenerative transfer of xanthates and related derivatives (e.g. dithioesters, dithiocarbamates, trithiocarbonates) is having a significant impact [38] (see also Volume 1, Chapter... 

The fifty chapters submitted for publication in the ACS Symposium series could not fit into one volume and therefore we decided to split them into two volumes. In order to balance the size of each volume we did not divide the chapters into volumes related to mechanisms and materials but rather to those related to atom transfer radical polymerization (ATRP) and to other controlled/living radical polymerization methods reversible-addition fragmentation transfer (RAFT) and other degenerative transfer techniques, as well as stable free radical pol5mierizations (SFRP) including nitroxide mediated polymerization (NMP) and organometallic mediated radical polymerization (OMRP). 

CRP LRP in Figure 1), ATRP or atom transfer (radical) polymn ( ATRP only , this search does not include terms such as metal mediated or metal catalyzed (living) radical polymerization), NMP or SFRP or nitroxide mediated polymn ot stable free polymn ( SFRP NMP ) and RAFT ox reversible addition transfer or degenerative transfer or catalytic chain transfer ( RAFT DT CT ). The latter two terms were refined with a term radical polymn since they coincide with other common chemical names such as N-methylpyrrolidone or raft-associated proteins. In summary, since 1995 over... 

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). ... 

There are several techniques for performing CRP, but the most popular and successful ones so far are as follows stable free radical (SFR) or nitroxide-mediated radical polymerization (NMRP) [44, 45, 49], atom transfer radical polymerization (ATRP) [50, 51], and degenerative transfer techniques, including particularly reversible addition-fragmentation transfer (RAFT) polymerization [3]. These are examined in some detail in the following sections. 

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