Asymmetric‐selective polymerization of <scp>DL</scp>‐leucine <i>N</i>‐carboxy anhydride with optically active amines

Abstract

Abstract DL ‐Leucine N ‐carboxy anhydride was polymerized in dioxane, benzene, tetrahydrofuran, butanone, and N,N ‐dimethyl formamide at temperatures between 10 and 55°C using 15 optically active primary and secondary amines as initiators. The optical yield of polymer can be described satisfactorily by an ideal copolymerization equation for monomer conversions between 3 and 94% ( R = const). The highest R was found for the initiation with (—)‐L‐proline methyl ester in dioxane at 25°C ( R = 1,30). Ten different models are shown to fit the ideal copolymerization equation depending on whether homopropagation, heteropropagation, homoadsorption, and/or heteroadsorption is taken into account. Most reasonable on the basis of other published evidence seems to be a pure or by far dominating homopropagation ( k LL = k DD ; k LL [P * L ] &gt; k DL [P * D ]; k DD [P * D ] &gt; k LD [P * L ]) with a constant concentration of active chain ends with D ‐ and L ‐configurations, ([P L * ] = const; [P D * ] = const′; [P L * ]/[P D * ] ≠ 1) resp. The present nomenclature in this field is discussed.