Journal of Polymer Science Part A: Polymer Chemistry, Vol.54, No.21, 3444-3453, 2016
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 gamma-benzyl-L-glutamic acid based N-carboxyanhydride (OEG(m)BLG-NCA, m=2, 3) and gamma-benzyl-L-glutamic acid based N-carboxyanhydride (BLG-NCA). H-1 NMR analysis verified copolypeptides structures and determined the OEG molar content (x). FTIR analysis further confirmed the molecular structures, indicated alpha-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 (T(pt)s) of the copolypeptides in alcohols decreased as x or m value increased or as polymer concentration decreased. T(pt)s 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). (C) 2016 Wiley Periodicals, Inc.