Stereoregular polymerization of propylene oxide by bis-dimethylaluminium oxide

Stereoregular polymerization of propylene oxide (PO) by bis-dimethylaluminum oxide (BMAO) was studied. It is found that at 80°C a relatively high initial rate of the process rapidly dies away. By measuring and identifying the evolved by-product gases of the polymerization it was concluded that the decay of the rate is due to the transfer of a proton from the methyl (Me) group of PO, to the Me-Al groups of BMAO, by forming an aluminium allylalkoxide bond and a methane molecule. However, this transformation (and also the alcoholysis of Me groups of BMAO with several alcohols) apparently increases the stereoregular yield of the process. The polymerization process as well as the ionization of BMAO and the transport properties of ions were studied in the presence and absence of solvents, additives and monomer. Although BMAO extensively ionizes in the polymerization solution, the stereoregular yield of process increases as the dielectric constant of the media decreases. On the basis of present data the mechanism of polymerization was discussed.