Chirality induction in cyclocopolymerization. 15. Enhancement of chirality induction during cyclocopolymerization of (2S,3S)-2,3-butanediyl bis(4-vinylbenzoate) with styrene using alkylaluminum compounds

The cyclocopolymerization of (2S,3S)-2,3-butanediyl bis(4-vinylbenzoate) (1) with styrene was carried out in dry toluene at 40°C in the presence of triethylaluminum (Et3Al), diethylaluminum chloride (Et2AlCl), and ethylaluminum dichloride (EtAlCl2), which played the role of Lewis acid capable of coordinating on carboxyl groups. After removal of the (2S,3S)-2,3-butanediyl units, the template-free polymer 3 exhibited an optical activity due to its main chain chirality. The specific rotations ([α]435, c 1.0, CHCl3) of polymers 3 prepared with alkylaluminum compound varied from −11.2 to −21.7°, which was higher than those prepared without alkylaluminum compound (−9.0°). The specific rotation of polymer 3 increased with an increase in the acidity of the alkylaluminum compounds (i.e. Et3Al<Et2AlCl<EtAlCl2) and/or with an increase in the molar ratio of alkylaluminum compound to monomer 1.