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

Abstract

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

How to manipulate the upper critical solution temperature (UCST)?

“…51 For comparison, neutral derivatives of the polypeptides with alkyl or oligo ethylene side chains show UCST behavior only in alcoholic solvents or water/alcohol mixtures. 52,53 Poly(dimethylaminoethyl methacrylate), PDMAEMA, is a pH and thermoresponsive polymer. It displays LCST behavior in aqueous solutions, where the cloud point is affected by the charge of the polymer, that is the pH of the solution.…”

Thermoresponsive polymers in non-aqueous solutions

“…For example, the polypeptide poly((γ-4-oligo(ethylene glycol) benzyl-L-glutamate)-random-(γ-benzyl-L-glutamate)) containing an oligo(ethylene glycol) (OEG) molar content of 0.75 mol% and a degree of Polymer Chemistry Review polymerization (DP) of 3 prepared via triethylamine-initiated ring-opening polymerization (ROP) exhibited a UCST-type phase transition in methanol. 110 The T CP increased from 4 to 34.2 °C with increased concentration from 0.2 to 1 mg mL −1 , as demonstrated by visual inspection and UV-vis analyses.…”

Amphiphilic PEG-Functionalized Gradient Copolymers via Tandem Catalysis of Living Radical Polymerization and Transesterification

“…PEG-based polymers often show lower critical solution temperature (LCST)-type phase separation in water ,,− and upper critical solution temperature (UCST)-type phase separation in 2-propanol. , To investigate the effects of monomer sequence on phase separation in water, we conducted the temperature-dependent turbidity measurements of the aqueous solutions of MMA/PEGMA random, random-gradient, gradient, and bidirectional gradient copolymers at the temperature range between 40 and 80 °C ([polymer] = 10 mg/mL, heating/cooling speed = 1 °C/min, λ = 670 nm). The cloud point (Cp) was defined as the temperature at which the transmittance of the solution becomes 90%.…”