End-Capping of Living Polymeric Cations

The use of an unsaturated nucleophile to introduce into the chain end of the macromolecule a double bond has also proved successful for the synthesis of poly-THF macromonomers. The oxolane polymerization is started with any efficient initiator. When the growing chains have reached the desired length, the unsaturated deactivator is added. The reaction between the oxonium sites and the nucleophile should be fast and free of side reactions. Various unsaturated nucleophiles have been employed, e.g. p-vinylphenoxide used by Asami50). The THF polymerization was initiated with triethyloxonium tetrafluoroborate and carried out atO °C. Addition of the nucleophile (obtained by reaction of the phenol with NaH) yields the corresponding macromonomer the structure of which was characterized by various techniques  

This method was directly derived from Saegusa s deactivation method 47). 

The macromonomers obtained cover a molecular weight range from 2000 to 10000 g/mol and their structure has been determined by means of NMR, UV, GPC, 

It has been detected that each molecule contains a terminal p-vinylbenzyl or p-iso-propenylbenzyl group. 

However, in this example the terminal double bond is ), 2-disubstituted and its reactivity in free-radical copolymerization can be expected to be rather low. In fact, Richards and Schue53) studied this process with the purpose of performing a transformation reaction 54) from cationic to anionic, the anionic site being generated by the addition of butyllithium to the terminal cinnamyl double bond. However, this addition also occurs in rather low yields. 

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