Synthesis and UCST-type phase behaviors of OEGylated random copolypeptides in alcoholic solvents

A series of OEGylated random copolypeptides with similar main-chain lengths and different oligo(ethylene glycol) (OEG) molar content and chain lengths were prepared from triethylamine initiated ring-opening polymerization (ROP) of OEGylated γ-benzyl-L-glutamic acid based N-carboxyanhydride (OEGmBLG–NCA, m = 2, 3) and γ-benzyl-L-glutamic acid based N-carboxyanhydride (BLG–NCA). 1H NMR analysis verified copolypeptides structures and determined the OEG molar content (x). FTIR analysis further confirmed the molecular structures, indicated α-helical conformations of copolypeptides in the solid-state, and revealed H-bonding interactions between OEG pendants and alcoholic solvents. The copolypeptides exhibited a reversible upper critical solution temperature (UCST)-type phase behavior in various alcoholic solvents (i.e., methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol) depending on the x values and OEG side-chain lengths (m). Variable-temperature UV–vis analysis revealed that the UCST-type transition temperatures (Tpts) of the copolypeptides in alcohols decreased as x or m value increased or as polymer concentration decreased. Tpts of copolypeptides with high x values (x ≥ 0.50) increased as the number of methylene of the alcoholic solvent increased from 3 (i.e., 1-propanol) to 5 (i.e., 1-pentanol). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3444–3453