Plurifunctional electrophiles

A second method, using also anionic polymerization techniques was developed to achieve a better knowledge of the functionality of the branch points. In this method the bifunctional living polymer species is prepared under the same conditions as above. It is then reacted with a stoichiometric amount of a plurifunctional electrophilic reagent14,1S. The chief difficulty is to find a reagent the electrophilic functions of which are isoreactive, to ensure that the reaction will go to completion. 

Two general strategies are possible for the synthesis of star-shaped copolymers The arm-first method is based on the reaction of living chains with plurifunctional electrophiles carrying at least three reacting groups alternatively, polymerization can be initiated by a multifunctional initiator according to the core-first method. 

The convergent method is particularly appropriate for anionic polymerization as plurifunctional electrophilic deactivators are available in large number. 

In general, star polymers can be synthesized by two different approaches, known as arm-first and core-first methods [23]. The arm-first method consists of either terminating the living chain end by plurifunctional electrophiles or reinitiation using bis unsaturated monomers. In the core-first method, a plurifunctional initiator core is first synthesized by reaction of an initiator with a bis-unsaturated monomer (e.g., reaction of -BuLi with divinyl-benzne). The plurifunctional initiator core is used to initiate fiirther polymerization. The synthetic advantages and drawbacks of the two methods are summarized in Table 4. 

Elastic chains 163 Elastomers 27, 32, 33, 63, 65 Electron affinity, monomers 150 Electrophiles 155-157, 162 —, plurifunctional 162 Electrophilicity 149... 

Adequate mixing has also to be provided for. Upon reaction, the polymer solution gels, and it can be expected that the precursor chains are converted into elastic chains, whereas the crosslinks should exhibit the functionality of the electrophilic reagent15,16. Suitable electrophilic reagents are tris(allyloxy)s-triazine(trifunctional) and a similar tetrafunctional compound. Plurifunctional isocyanates have also been used successfully for such syntheses17. ... 

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