Synthesis and thermoresponsive properties of OEGylated polypeptide with a LCST at body temperature in water and with a UCST in alcohol or ethanol/water solvent mixture

ABSTRACT Thermoresponsive polypeptides bearing oligo(ethylene glycol) (OEG) pendants (i.e., P1‐OEGx and P2‐OEGx, x = 3, 7) were synthesized by copper‐mediated 1,3‐dipolar cycloaddition with high grafting efficiency (≥97%) between side‐chain “clickable” polypeptides, namely poly(γ‐4‐(propargoxycarbonyl)benzyl‐l‐glutamate) (P1) or poly(γ‐4‐(4‐propargoxyphenoxycarbonyl)benzyl‐l‐glutamate) (P2) and azido functionalized OEG (N3‐OEGx). P1 and P2 with similar degree of polymerization (DP = 35 or 37) were prepared from triethylamine initiated ring‐opening polymerization of respective N‐carboxyanhydrides. P1‐OEGx (x = 3, 7) and P2‐OEG7 showed reversible UCST‐type phase transitions in various alcoholic solvents (e.g., ethanol, propanol, n‐butanol, and n‐pentanol). P2‐OEG3 also showed reversible UCST‐type phase transitions in ethanol/water solvent mixtures at the weight percentage of ethanol no less than 50 wt %. P1‐OEG7 and P2‐OEG7 showed reversible LCST‐type phase transitions in aqueous solutions. Variable‐temperature UV–vis spectroscopy revealed that the LCST‐type phase transition temperature (Tpt) of P2‐OEG7 with benzoic acid phenyl ester linkages was at around body temperature and it was barely changed with the variation of polymer concentration, yet it showed noticeable dependence on the nature of salt (i.e., NaCl, NaBr, NaI, or KCl) and salt concentration in the range of 0–300 mM. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 163–173