Stereoelective polymerization of propylene oxide with a chiral aluminium alkoxide initiator

Abstract

AbstractThe polymerization of propylene oxide (PO) was studied with an initiator prepared by the reaction of (R)‐(−)‐3,3‐dimethyl‐1,2‐butanediol (1) with aluminium hydride. When mixed with zinc chloride in a 1:1 mole ratio, the initiator was found to be highly reactive and also stereoelective in the polymerization of PO, preferentially incorporating (R)‐(+)‐PO into the polymer chain. Analysis of the polymer structure by 13C NMR spectroscopy showed that chlorine, hydroxyl and alkoxy end groups, derived from the initiator, were present. Fractionation of poly(propylene oxide) (PPO) in acetone at −30°Cgave about 10% insoluble PPO, shown to be isotactic by 13C NMR. The soluble, largely atactic fraction contained irregular head‐to‐head (h,h) and tail‐to‐tail (t,t) structures. In the absence of coinitiator zinc chloride the PPO product was completely soluble in acetone at −30°Cand contained a greater proportion of irregular h,h and t,t structure.