Stereoelective cationic polymerization of propenyl ether by asymmetric catalysts

In order to elucidate the possibility of stereoelective cationic polymerization (asymmetric selective polymerization) of olefinic monomers, racemic cis- and trans-1-methylpropyl propenyl ether and racemic 1-methylpropyl vinyl ether were polymerized by asymmetric alkoxyaluminum dichlorides. In the polymerization of racemic cis-1-methylpropyl propenyl ether with (?)-menthoxyaluminum dichloride in toluene at ?78°C, the polymer obtained showed a positive optical activity, and the residual monomers were converted by BF₃OEt₂ into a polymer having a negative optical activity. Thus, the stereoelective polymerization of racemic cis-1-methylpropyl propenyl ether was beyond any doubt attained in homogeneous cationic polymerization. In the polymerization of the trans isomer by the same catalyst, an optically active polymer was hardly formed. In the polymerization of racemic 1-methylpropyl vinyl ether which has no β-methyl group, stereoelectivity was not observed at all. The cis-1-methylpropyl propenyl ether did not produce an optical active polymer in the polymerization catalyzed by (S)-1-methylpropoxyaluminum dichloride or (S)-2-methylbutoxyaluminum dichloride under the same polymerization conditions.