Stereosequencing in poly(leucine) obtained from stereoselective polymerization of racemic leucine <i>N</i>‐carboxy anhydride

Abstract

Abstract Polymerization of mixtures of D ‐ and L ‐isomers of α‐amino acid N ‐carboxy anhydrides follow normal copolymerization behavior, and sometimes even ideal copolymerization, which is conventionally interpreted as leading to a random distribution of monomer units along the polymer chains. Equations are dereived which relate the fraction of isotactic L ‐diads to experimental data from the previously reported methods involving sequential and stereospecific cleavage with enzymes. The application of these equations to poly( D , L ‐leucines), which were prepared by polymerization of racemic leucine N ‐carboxy anhydride with chiral and achiral primary amines as initiators, indicated that the polymers contain between 94 and 98% isotactic diads. The poly(leucines) thus consist of long stereoblocks despite the observed ideal copolymerization behavior.