Telechelic telomerization

Depending on the choice of transfer agent, mono- or di-cnd-functional polymers may be produced. Addition-fragmentation transfer agents such as functional allyl sulfides (Scheme 7.16), benzyl ethers and macromonomers have application in this context (Section 6.2.3).212 216 The synthesis of PEG-block copolymers by making use of PEO functional allyl peroxides (and other transfer agents has been described by Businelli et al. Boutevin et al. have described the telomerization of unsaturated alcohols with mercaptoethanol or dithiols to produce telechelic diols in high yield. 

This review summarizes different synthetic methods of obtaining either molecular or maeromolecular fluorinated telechelic compounds. These compounds may be obtained either by direct synthesis or by syntheses which need many steps. Thus, reactions of polycondensation, polymerization, telomerization, fluorination of oligomers or the use of functional initiators are described in detail. On the other hand, the emphasis is also focussed on the interest of each method of preparation. Specific properties (solubility, thermal stability, surface properties. ..) of the obtained fluorinated telechelic products are discussed with regard to modern industrial requirements. We can observe that the compounds obtained by recently developed methods may be listed in two classes those which exhibit better surface properties and those which have better thermal stability. 

Finally, an original method to obtain telechelic polydienes is also possible — it can be associated to the telomerization of allylic alcohol with butadiene. 

As has been mentioned, radical initiation has greatly contributed to iJie search for new telechelic polymers either by the u of functional initiators or by telomerization. In both cases, besides the methods known from 1955, recent surveys have been investigated and, several applications have been found. However, such reactions require, from the synthetic point of view, the obtaining of new initiators and telogens and from the kinetical point of view, vay selective reactives which have a very high reactivity (great transfer constant rralue). 

In the review paper of Boutevin [2], the different conventional radical polymerizations, such as telomerization or DEP, were mentioned to lead to a telechelic structure. Since 1990 these radical techniques have shown some progress in the synthesis of telechelic oligomers. We can remark that recent investigations into the understanding of the kinetics of the DEP of... 

The telomerization process is based on the use of a transfer agent to control both the molecular weight and the chain-end functionality. The mechanism was developed in previous work [12,13]. For a long time, telomerization remained almost the only technique allowing for the synthesis of telechelic oligomers. 

Since the introduction of LRP, only a few studies have been realized on the synthesis of telechelic oligomers by means of telomerization reaction. It is, however, interesting to give a summary of the studies realized in this area since 1990 because very attractive chain-end functionalities can be easily obtained. 

The oligomers were analyzed by MALDI-TOF and different populations were characterized telechelic oligomers were produced from direct initiation with ACVA and telechelic oligomers were produced from telomerization with thioglycolic acid. 

DEP afforded the synthesis of telechelic oligomers [29]. With the telomerization process, DEP appeared to be the first free-radical polymerization leading to telechelic oligomers. Tobolsky [30] first stated the conditions of DEP, i.e., the half life of the growing species has to be equivalent to that of the initiator. These specific conditions result in an unusual high rate of termination, which allows for the synthesis of oligomers. The telechelic structure will be obtained by combining a termination mode exclusively by recombination with the use of a difunctional initiator. 

These iodine-TFE compounds are known as telechelics (or a, co-difiinctional derivatives) and find use as chain-transfer agents for the telomerization of TFE, HFP, or VDF, well reported in a book [66] and a review article [67]. No reports of HFP analogs to the iodine-TFE compounds could be found. 

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