Polymerization of NCAs unsubstituted at the 3-position initiated by primary and secondary amines

Polymerization of NCAs unsubstituted at the 3-position initiated by primary and secondary amines. 

To achieve a full appreciation of the reactions of NCAs with primary and secondary amines we must realize that there is no a priori reason for excluding the reaction paths discussed for tertiary-base initiation, provided that the 3-position of the NCA ring is unsubstituted. Thus both 

is a consequence of steric restraint by the bulky isopropyl groups such steric factors are much less important when proton abstraction from the 3-position is involved. There is some indication that reaction at the 5-CO position may involve an intermediate of the types (XVII) and (XVIII), 

The duality in the mechanisms of initiation and propagation described above is reflected in the molecular weights and molecular distributions of the polymeric products. Thus, Stewart and Stahmann [43] found by column chromatography double-peaked distributions in poly-L-lysine samples prepared from e-benzyloxycarbonyl-L-lysine NCA by initiation with ammonia, the samples having both low and high molecular weight 

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