Peptide block copolymers by N‐carboxyanhydride ring‐opening polymerization and atom transfer radical polymerization: The effect of amide macroinitiators

The synthesis of polypeptide‐containing block copolymers combining N ‐carboxyanhydride (NCA) ring‐opening polymerization and atom transfer radical polymerization (ATRP) was investigated. An amide initiator comprising an amine function for the NCA polymerization and an activated bromide for ATRP was used. Well‐defined polypeptide macroinitiators were obtained from γ‐benzyl‐ L ‐glutamate NCA, O ‐benzyl‐serine NCA, and N ‐benzyloxy‐ L ‐lysine. Subsequent ATRP macroinitiation from the polypeptides resulted in higher than expected molecular weights. Analysis of the reaction products and model reactions confirmed that this is due to the high frequency of termination reactions by disproportionation in the initial phase of the ATRP, which is inherent in the amide initiator structure. In some cases selective precipitation could be applied to remove unreacted macroinitiator to yield well‐defined block copolymers.