Preparation of Well‐Defined Diblock Copolymers with Short Polypeptide Segments by Polymerization of N‐Carboxy Anhydrides

Summary: The ring‐opening polymerization of N ‐carboxy anhydrides (NCA) of γ ‐benzyl‐ L ‐glutamate and β ‐benzyl‐ L ‐aspartate was studied in the presence of an ammonium chloride‐functionalized poly(ethylene oxide) macroinitiator, which possibly prevents side reactions such as NCA deprotonation. Although polymerization initiated by such macroinitiators was found to be quite slow, well‐defined conjugates of poly(ethylene oxide)‐ block ‐poly( γ ‐benzyl‐ L ‐glutamate) and poly(ethylene oxide)‐ block ‐poly( β ‐benzyl‐ L ‐aspartate) with polydispersity indexes as low as 1.05 were prepared. Moreover, the presence of ammonium chloride chain ends significantly prevented end‐group cyclization of poly( γ ‐benzyl‐ L ‐glutamate) after polymerization. Gel permeation chromatograms recorded for the diblock copolymers of poly(ethylene oxide)‐ block ‐poly( γ ‐benzyl‐ L ‐glutamate) prepared by N ‐carboxy anhydride polymerization initiated either by PEO‐NH 2 macroinitiator or PEO‐NH Cl − macroinitiator. image Gel permeation chromatograms recorded for the diblock copolymers of poly(ethylene oxide)‐ block ‐poly( γ ‐benzyl‐ L ‐glutamate) prepared by N ‐carboxy anhydride polymerization initiated either by PEO‐NH 2 macroinitiator or PEO‐NH Cl − macroinitiator.