Telomerization telogens

Telomerization. Polymerization of DAP is accelerated by telogens such as CBr, which are more effective chain-transfer agents than the monomer itself (65) gelation is delayed. The telomers are more readily cured in uv than DAP prepolymers. In telomerizations with CCl with peroxide initiator, at a DAP/CCl ratio of 20, the polymer recovered at low conversion has a DP of 12 (66). 

The essential difference in chemical behavior of chlorides and bromides used as telogens (addends) can be distinctly seen when the reactions of chloro- and bromoacetates are compared. In addition and telomerization reactions monochloroacetates react with 1-alkenes exclusively at C-H bond [under initiation... 

Dibromodichoromethane was studied as telogen in the reaction with vinyl chloride (ref. 7). The authors showed that the reaction occurred as telomerization (under usual conditions) the changes in monomer / telogen ratio (from 1.5 to 15) allowed to vary the adduct content from 80 to 30 %. 

CO2 [67]. Early work examining the free-radical telomerization of TFE in supercritical C02 took advantage of the high solubility of the low molecular weight perfluoroalkyl iodides products to prepare these materials homogeneously [77]. In these reactions, we utilized perfluorobutyl iodide as the telogen... 

Table 2. Experimental results from the telomerizations of TFE in supercritical C02. Perfluorobutyl iodide was employed as the telogen [77]...

Interestingly, the (co)telomers used behave as further potential telogens for subsequent telomerizations, and all of them can be end-capped with ethylene (E). 

We have constructed thermoresponsive systems utillizing semitelechelic PIPAAm chains with freely mobile ends, synthesized by telomerization using telogens as a following reaction [6] nM -i- HS-X H-(M)n-S-X. 

The telomerization of butadiene (1) with protected pentoses has been particularly studied using 2,3,4-tri-(9-acetyl-D-xylopyranose (5) [21] and 2,3,4-tri-O-benzyl-p-D-arabinofuranose (8) [22] as the telogens, in a 50-mL stainless steel autoclave... 

The telomerization has also been carried out using o-glucose (17) as the telogen. As expected, the increase of the amount of 1 and reaction time under conditions depicted in Fig. 11 increased the relative quantity of di-and tri-octadienylglycosides... 

It has been reported that the use of aqueous-organic biphasic systems may enhance the selectivity (Sect. 1.2) [12, 16, 47, 48]. In fact, sugar diethers are quasi insoluble in water and can be extracted in the organic phase. When the telomerization is carried out in the presence of Me2NCi2H25 and a large excess of 1 (15 equiv., Table 9), the conditions are already biphasic the diethers of 15 have thus been obtained in a 57% yield at 99% conversion of the telogen. 

Telomerization is the reaction of olefins having conjugated double bonds (conjugated dienes) in the presence of a nucleophile (telogen). The main... 

Later, Apsey et al. [96] and Balague et al. [97] used i-C3F7I and linear CnF2n+1I (n=4,6,8) telogens, leading to telomeric distributions, with a better reactivity of the branched transfer agent. Recently, we have shown that, while the monoad-... 

Works from photoinduced telomerisation have led to most impressive investigations, with interesting kinetics performed by Tedder and Walton [93, 151 -153]. VDF is used for the obtaining of lower telomeric distributions mainly for monoadducts, but yielded several by-products from brominated telogens. 

Telomerization with Biomass-Derived Multifunctional Telogens. 65... 

In addition to the industrial developments listed above, much academic efforts have also been devoted over the years to (1) the expansion of the scope of the telomerization reaction, (2) the elucidation of the details of the reaction mechanism and (3) process modifications that allow more efficient production and separation of the desired products. The scope of substrates that can be used in this reaction has indeed been shown to be very broad. 1,3-Butadiene is most often used as the conjugated diene, since it is cheap, readily available and provides a linear octadienyl chain. The use of other dienes, such as isoprene [13-16], piperylene [17] and myrcene [18,19], has also been described, but they have been far less commonly studied. Such substituted telogens come with an additional selectivity challenge as many more isomers can potentially be obtained, which is illustrated for isoprene in Fig. 1. 

The focus of this review will be on those recent and older contributions to the telomerization field that primarily deal with the palladium-catalyzed telomerization with multifunctional oxygenates. First, a short glossary of commonly used ligands and catalysts is given, followed by a description of the mechanistic intricacies of the process and, finally, the different classes of multifunctional, renewable telogens that are treated in detail. This review complements two other excellent overviews of the telomerization reaction, each with its own primary focus. Behr and co-workers published an extensive review article summarizing the research on telomerization done in the period 1984—2008 with a particular focus on process developments [25]. 

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