Thermoresponsive Poly(N-C3 glycine)s

Ring-opening polymerization of N -substituted glycine N -carboxyanhydrides (NCAs) was applied to prepare a series of well-defined poly( N -C3 glycine)s (C3 = n- propyl, allyl, propargyl, and isopropyl), polypeptoids, with molecular weights in the range of 1.8–6.6 kg mol –1 . Poly( N -isopropyl glycine), a previously unreported polypeptoid, could be obtained by bulk polymerization of the corresponding NCA in the melt. The samples were characterized by spectroscopy (NMR and FT-IR), size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI–ToF MS). The polymers could be dispersed in water up to 20–40 g L –1; the poly( N -propargyl glycine) was not soluble in water. Turbidity measurements of the three water-soluble polypeptoids illustrated cloud point temperatures dependent on structural and electronic properties of the side chain. The cloud point temperatures were found to increase in the order C3 = n -propyl (15–25 °C) < allyl (27–54 °C) < isopropyl (47–58 °C). Long-term annealing of the aqueous solution of poly( N -{ n- propyl} glycine) and poly( N -allyl glycine) above the cloud point temperature resulted in the formation of crystalline microparticles with melting points of 188–198 and 157–165 °C (differential scanning calorimetry, DSC), respectively, and rose bud type morphology (scanning electron microscopy, SEM).