Polymerization Mechanism of <i>N</i> -Phenyloxycarbonyl Amino Acids: Polycondensation or Cyclization to NCA?

N NMR data and validated by Monte Carlo simulation. Two possible polymerization pathways are evidenced by a density functional theory (DFT) calculation. The ICA-meditated NCA ring-closing pathway is preferred over the direct NCA ring-closing pathway for lower Gibbs energy barriers. A direct ring-closing path is feasible only for Sar-NPC, which explains its low polymerization reactivity.