Functionalised transfer agent

Type 1 The polymerisation of a monomer (M,.) for which the dominant termination mode is combination using functionalised transfer agent and initiator i.e. both transfer agent and initiator possess the desired carboxyl, hydroxyl etc., group, in addition to the, for example, thiol and azo groups, respectively. 

When Cx > 1.0 the rate of polymerisation can sometimes be reduced if the rate of addition of monomer to the radical produced during the transfa- reaction is less than the normal propagation rate. In some cases transfer agents can act as either retarders (when Cx > 1.0) or as inert diluents (when Cx 4 1.0). To be of use in the production of intermediates from which macromers can be synthesised, functionalised transfer agents should possess chain transfer constants within the range 0.1-10, preferably between 0.5-2.0. 

Data on the Cx values of functionalised transfer agents such as thioglycollic acid are even more restricted. For the more commonly encountered vinylic monomers only six Cx values for functionalised transfer agents are available (18). These are ... 

Not all bimolecular radical-radical termination reactions lead to polymer molecules with unwanted functionality. Thus, the weight fraction of polymer molecules produced by bimolecular termination reactions and which posses unwanted functionality (cOt) is dependent upon the dominant bimolecular termination mode of the monomer and the particular combination of initiator and transfer agent used for the polymerisation. The use of a functionalised initiator in conjunction with a functionalised transfer agent causes a decrease in oo, for type monomers and an increase in co, for type monomers. 

In this section we will discuss the use of elemental fluorine for the promotion of organic transformations that do not result in the introduction of fluorine into the substrate. As we described above (Sect. 3), fluorine may be used to prepare many extremely useful reagents which may be employed as, for example, oxidising and oxygen transfer agents. The use of O-F compounds, such as acetyl hypofluorite and the HOF.MeCN complex, in functionalisation processes has been indicated above (Sect. 3.2), and this area has been discussed in detail in an excellent account by Rozen [19]. 

Although the main emphasis with imino functionalised carbene hgands is on their silver complexes, as carbene transfer agents, and on late transition metal complexes - palladium. 

The obtained amino functionalised imidazolium salts could be used to generate the corresponding palladium(ll) carbene complexes using the silver(l) complexes as carbene transfer agents. Application of these palladium(ll) complexes (predominantly in situ) in asymmetric allylic alkylation reactions between ( )-l,3-diphenylprop-3-enyl acetate and dimethyl malonate (a standard reaction for this catalytic process [145]) gave up to 80% ee,... 

The potassium complex of the hydroxyethyl functionalised carbene, once formed, can then be used as a carbene transfer agent. Patel et al. employed this compound in the synthesis of titanium(lV) complexes used as catalysts in the polymerisation of lactides [38]. Synthesis of the catalyst is facile and involves the reaction of the potassium complex of the hydroxyethyl functionaUsed carbene with [TiCOFV) ] (see Figure 4.7). Although the activity of the titanium(lV) carbene complex is considerably less then that of the potassium complex, the titanium complex acts as a masked NHC and thus a highly moisture and air stable NHC source [38]. 

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