Asymmetric‐selection polymerization of d,l‐propylene oxide by (FeCl₃‐propylene oxide) complex — H₂O catalyst containing d‐bornyl ethyl ether

Racemic propylene oxide ( d,l ‐PO) was polymerized by the catalyst which was the reaction mixture from the partial hydrolysis of the FeCl 3 –PO complex carried out in the presence of d‐bornyl ethyl ether (d‐BEE). The unreacted monomer recovered from the polymerization system was shown to be optically active, the concentration of l‐monomer preponderated over that of d‐monomer. The polymer product, however, was of no optical activity although it contained a considerable amount of isotactic crystalline part. In another separate experiment, d,l ‐PO was added to the asymm. catalyst system at a lower temperature where no polymerization occurred and the monomer was recovered by distillation under reduced pressure at —20°C. Triethylamine was added to the residue and volatile material was distilled again. By optical activity measurement, the PO fraction of the first distillate (before amine addition) was shown to be rich in l‐monomer and that of the second distillate (after amine addition) was rich in d‐monomer. Thus it has been shown that d‐monomer is predominant over l‐monomer both in adsorption and in polymerization. A kinetic consideration showed that the d/l ratio in the adsorbed monomer agreed with that of the consumption rate in polymerization. These findings lead us to the conclusion that the propagation reaction of polymerization consists of two steps, adsorption (coordination) and ring opening steps, and that the unequality in polymerization rate between d‐ and l‐monomers is controlled chiefly by the adsorption step. The formation of crystalline polymer of no optical activity from the asymm . consumption of monomer is discussed.