Active species-heterocyclic monomer addition

Kinetics of addition of various heterocyclic monomers to the same active species was studied recently in our laboratory. The 1-methyltetrahydrofuranium cation was used as a model of ionic species while ethyltriflate was employed as a model of the covalent ones. 

Rate constants for the addition of heterocyclic monomers to the model active species CC6H5NO2, 35°) ( ), shown in scheme 8. 

The synthesis of block copolymers by sequential polymerization requires a living polymer prepared from the less nucleophilic monomer (first block) and the addition of a more nucleophilic monomer to the active species located on this first block. The general order of nucleophilicities of heterocyclic monomers is as follows Siloxanes orthoesters < acetals < ethers < sulfides < oxazolines < amines. Depending on substitution and ring strain some changes may occur in these positions. 

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