Elementary Reactions in the Cationic Ring-Opening Polymerization

ELEMENTARY REACTIONS IN THE CATIONIC RING-OPENING POLYMERIZATION 

Initiation is the reaction in which active species are generated through interaction of initiator and monomer molecules. In cationic ring-opening 

Protonation of vinyl monomers directly produces species with a structure similar to the structure of propagating species  

The reactivity of both species may be quite different. Because the protonation, at least when it involves proton exchange, is fast, the ratedetermining step in initiation may be the reaction of protonated monomer with the next monomer molecule to form tertiary oxonium ion. 

Formally similar scheme may also operate for other initiating systems. Thus, for polymerization of cyclic acetals initiated with triphenyl-methylium (trityl) salts, the cationation of the monomer is a fast, reversible reaction [7], The next reaction, however, due to the steric hindrance, is very slow and consequently active species are formed by a parallel path involving hydride transfer (cf., Section II.A.2) [8,9], 

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II. ELEMENTARY REACTIONS IN THE CATIONIC RING-OPENING POLYMERIZATION... 

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