Chirality induction in cyclocopolymerization. 15. Enhancement of chiralityinduction 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 degreesC in the presenc e of triethylaluminum (Et3Al), diethylaluminum chloride (Et2AlCl), and ethy laluminum dichloride (EtAlCl2), which played the role of Lewis acid capable of coordinating on carboxyl groups. After removal of the (2S,3S)-2,3-butan ediyl units, the template-free polymer 3 exhibited an optical activity due to its main chain chirality. The specific rotations ([alpha](435), c 1.0, C HCl3) of polymers 3 prepared with alkylaluminum compound varied from -11.2 to -21.7 degrees, which was higher than those prepared without: alkylalumin um compound (-9.0 degrees). The specific rotation of polymer 3 increased wi th an increase in the acidity of the alkylaluminum compounds (i.e. Et3Al < Et2AlCl < EtAlCl2) and/or with an increase in the molar ratio of alkylalumi num compound to monomer 1. (C) 2001 Elsevier Science Ltd. All rights reserv ed.