Novel synthesis of high molecular weight polymers with extremely low polydispersity by the unique initiation properties of organo-lanthanide complexes

Organolanthanide(III) complexes such as |(C₅Me5₅)₂SmH|₂ and (C₅Me₅)₂SmMe(THF) were found to initiate the living polymerizations of methyl methacrylate (MMA) to give high molecular weight polymers (M _n > 500 × 10³) with extremely low polydispersity (M _w/M_n = 1.04). The syndiotacticity increased up to 95.2% by lowering the temperature to −95°C. The molecular structure of the 1:2 adduct of (C₅Me₅)₂SmH with MMA determined by X-ray method indicates that this intermediate assumes the 8 membered ring conformation where the Sm atom is bound to MMA in an enolate form and the ester of penultimate MMA is coordinated to the metal. Based upon these results, an anionic coordination mechanism has been proposed for the present reaction. Organolanthanide(II) complexes also exhibit high activity and proceed the living polymerizations. Organolanthanide(III) complexes also initiate the living polymerizations of lactones such as ϵ-caprolactone and δ-valerolactone. The stoichiometric reactions indicate that real active species assumes the alkoxylanthanide(III) form.