Living/controlled anionic polymerization and copolymerization of epichlorohydrin with tetraoctylammonium bromide-Triisobutylaluminum initiating systems
Résumé
A weakly nucleophilic initiating system obtained by the combination of triisobutylaluminum and tetraoctylammonium bromide has been successfully used to achieve the controlled polymerization of epichlorohydrin (ECH) in hydrocarbon at temperatures ranging from -30 degrees C to room temperature. Besides the formation of a 1:1 aluminate complex of low nucleophilicity between the aluminum derivative and the tetraalkylammonium salt, the strategy consists of the formation of a strongly activating complex between the Lewis acid and the epoxide monomer. To that aim trialkylaluminum is added in slight excess with respect to the tetraalkylammonium salt ([i-BU3Al]/[NOct(4)Br] > 1). In these conditions the reactivity of ECH toward nucleophiles is strongly enhanced and the ring opening polymerization proceeds in the presence of weak nucleophiles leading to nonreacted chloromethyl function of the epichlorohydrin. This contrasts with conventional anionic polymerization, which requires much stronger nucleophiles for the ring opening. Fast and controlled polymerization of ECH up to high molar masses and the synthesis of random and block copolymers with propylene oxide were readily achieved.