Preparation and Thermoresponsive Properties of UCST‐Type Polypeptide Bearing p‐Tolyl Pendants and 3‐Methyl‐1,2,3‐triazolium Linkages in Methanol or Ethanol/Water Solvent Mixtures

Abstract

A series of ionic polypeptides bearing p‐tolyl pendants and 3‐methyl‐1,2,3‐triazolium linkages is synthesized by N‐alkylation and subsequent ion‐exchange reaction. 1H NMR and Fourier transform infrared (FTIR) analysis verify their molecular structures and reveal quantitative conversions. The nonionic polypeptides bearing p‐tolyl pendants and 1,2,3‐triazole linkages show no thermoresponsiveness in various solvents. The resulting ionic polypeptides (i.e., P2) are able to show reversible upper critical solution temperature (UCST)‐type phase behaviors both in methanol and ethanol/water binary solvent mixtures by incorporation with proper counteranions (i.e., iodide). FTIR analysis reveals that P2 may have interacted with solvent molecules via the van der Waals interaction, H‐bonding, and dipolar–dipolar interactions. Variable‐temperature UV–vis spectroscopy reveals that the UCST‐type phase transition temperatures (Tpts) of P2 are in the range of about 26–37 °C in MeOH and in the range of about 11–46 °C in EtOH/H2O solvent mixtures depending on the main‐chain length, polymer concentration, and the weight percentage of ethanol (fw). image