Mechanism of the formation of macrocycles during the cationic polymerization of cyclotrisiloxanes. End to end ring closure versus ring expansion

Abstract

Abstract Studies of the distribution of cyclic oligomers formed in the first step of the cationic polymerization of hexamethylcyclotrisiloxane disclosed a correlation between the kinetically controlled concentrations of cyclic species and the statistical conformations adopted by the corresponding acyclic chains. The correlation found experimentally is in good agreement with the theoretical one predicted by the macrocyclization theory for non‐equilibrium chemical system and can be taken as evidence for the formation of macrocycles (even those containing about 100 atoms in the skeleton) by the intramolecular reaction between chain ends, a process which competes with the linear growth of the macromolecule. This approach may be useful in solving mechanistic problems involving polyreactions.