Combination of phosphazene base and triisobutylaluminum for the rapid synthesis of polyhydroxy telechelic poly(propylene oxide)

Abstract

Anionic ring-opening polymerization of propylene oxide, initiated with protonated phosphazene alkoxides and based on monomer activation with a Lewis acid, is investigated. Alcohols bearing one or several protected hydroxyl groups, namely 1,2-isopropylideneglycerol, 1,2:3,4-di-O-isopropylidene-D-galactopyranose and poly(propylene glycol), are firstly deprotonated with a phosphazene base. Their combination with triisobutylaluminum enables quantitative and controlled synthesis of poly(propylene oxide) in a very short time (hours), at room temperature and in hydrocarbons. The chain-ends determination showed a main population initiated by the protonated phosphazene alkoxide. A population coming from the residual transfer to monomer is also observed but in very low intensity. Molar masses of 80 000 g mol⁻¹ with relatively narrow dispersity could be prepared. After deprotection of protected hydroxyl functions, tri- and penta-hydroxy telechelic poly(propylene oxide) were obtained. Dihydroxy telechelic polymers of high molar masses are also rapidly and directly synthesized from poly(propylene glycol).