Anionic Ring-Opening Polymerization of cis-2,4,6-Trimethyl-2',4',6'-triphenyl Cyclotrisiloxane (cis-P_3) in Cyclohexane

摘要

The anionic ring-opening polymerization of cis-2,4,6-trimethyl-2',4',6'-triphenyl cyclotrisiloxane (cis-P_3) in cyclohexane has been investigated. By employing a non-polar solvent with a small amount of tetrahydrofuran (THF) as a promoter, both an intermolecular reaction (propagation) and an intramolecular reaction (back-biting) occur. It is proposed that the reduced reactivity of the nucleophile at the chain end and the solvation of any phenyl-phenyl interactions may facilitate the intramolecular reaction. A mechanism for the intramolecular back-biting reaction in this system is described that is consistent with the stereochemistry of the linear PMPS structure formed.