Cyclic poly(alpha-peptoid)s and their block copolymers from N-heterocyclic carbene-mediated ring-opening polymerizations of N-substituted N-carboxylanhydrides.

N-Heterocyclic carbene (NHC)-mediated ring-opening polymerization (ROP) of N-substituted N-carboxylanhydride ((N)R-NCA) yields cyclic poly(alpha-peptoid)s with controlled molecular weights (M(n) = 3-30 kg mol(-1)) and narrow molecular weight distributions (PDI = 1.04-1.12). The reactions exhibit characteristics of a living polymerization with minimal chain transfer. This enables the facile synthesis of cyclic diblock copoly(alpha-peptoid)s through sequential monomer addition. The cyclic polymer architectures were verified by MALDI-TOF mass spectrometry and intrinsic viscosity measurements. Mark-Houwink-Sakurada plot analyses revealed that cyclic poly(alpha-peptoid)s prepared from NHC-mediated polymerizations exhibit lower intrinsic viscosities than their linear analogues prepared from primary amine-initiated polymerizations. The ratio of their intrinsic viscosities is consistent with the former being mostly cyclic.