Ring-opening polymerization (ROP) of N-carboxy-alpha-amino acid anhydride (NCA) of gamma-benzyl I.-glutamate (BLG) was investigated under frozen condition for the first time. This cryo-ROP was performed in DMSO or 1,4-dioxane below the freezing point of polymerization mixture. The kinetics was monitored with proton nuclear magnetic resonance spectroscopy and gel permeation chromatography, disclosing the well control over molecular weight, living polymerization features and considerable polymerization rate. Compared with the polymerization proceeded at 30 degrees C, which showed weak linearity regarding the reaction kinetics and relatively broad distribution of molecular weight, the cryo-ROP exhibited excellent first-order kinetics as well as narrow molecular distribution. (C) 2018 Elsevier Ltd. All rights reserved.