Are N‐substituted glycine N‐thiocarboxyanhydride monomers really hard to polymerize?

ABSTRACT N ‐Substituted glycine N ‐thiocarboxyanhydrides (NNTAs) are promising cyclic monomers to synthesize polypeptoids with the advantages of easier preparation and higher stability during purification and storage than N ‐substituted glycine N ‐carboxyanhydrides (NNCAs). NNTAs were commonly considered too stable to polymerize for their low reactivity. In this contribution, we report controlled polymerizations of N ‐ethylglycine NTA (NEG‐NTA) and sarcosine NTA (Sar‐NTA) using primary amines as initiator under proper polymerization conditions. The controllability has been fully supported by 1 H NMR end group analyses, MALDI‐ToF mass spectra, kinetic data, block copolymerizations by sequential monomer addition, and low polydispersities (1.14–1.17) of polypeptoids. Variation of the [NNTA]/[initiator] ratio allows well control of the molar mass, and degrees of polymerization (DPs) up to 287 can be reached for poly( N ‐ethylglycine) or DPs up to 262 for polysarcosine. NNTAs exhibit excellent activity and they are potential to synthesize polypeptoids with controllable polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 404–410