Asymmetric‐selective polymerization of DL‐leucine N‐carboxy anhydride with optically active amines

Abstract

AbstractDL‐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 (kLL = kDD; kLL[P*L] > kDL[P*D]; kDD[P*D] > kLD[P*L]) with a constant concentration of active chain ends with D‐ and L‐configurations, ([PL*] = const; [PD*] = const′; [PL*]/[PD*] ≠ 1) resp. The present nomenclature in this field is discussed.