THF-Functionalized Polyethers: Biosourced Monomers, Tunable Thermoresponsiveness, and Iron-Selective Adsorption

Biosourced polymers and aqueous thermoresponsive polymers have both received broad attention, but the two attributes are rarely merged. Here, furfural-derived alcohol and carboxylic acid are transformed into tetrahydrofuran(THF)-bearing epoxides, tetrahydrofurfuryl glycidyl ether (F²GE) and glycidyl 2-tetrahydrofuroate, by reacting with epichlorohydrin. Ring-opening polymerization catalyzed by an organic Lewis pair occurs in a highly selective manner, producing THF-functionalized polyethers with controlled molar mass (5.6-22.7 kg mol^-1) and low dispersity (1.09-1.12). Nonbiosourced (tetrahydrofuran-3-yl)methyl glycidyl ether is also synthesized and polymerized for comparison. The polyethers exhibit high thermal stability, minimal cytotoxicity, and structure-dependent cloud point temperature (T_cp) in water with polyF²GE showing the highest T_cp (24.1-37.3 °C) at all concentrations (0.1-1.0 mg mL^-1). Alkali metal halides exhibit variable "salting-in/-out" effects, with T_cp increased by NaI, LiI, or LiBr and decreased by NaCl, NaBr, or KCl. Also interestingly, the THF functionalities allow polyF²GE to selectively adsorb Fe³⁺ (95.3%) from an aqueous solution containing other ions (Ni²⁺, Co²⁺, and Mn²⁺) above T_cp.