Multi-tunable thermoresponsive behaviors of poly(amido thioether)s

Abstract

Rational macromolecular design can endow polymers with on-demand thermoresponsive behaviors. To achieve multi-tunable LCST/UCST behaviors, stepwise polymerization of N-acryloylhomocysteine thiolactone with primary amines involving glycinamide, N-(3-aminopropyl)imidazole, N,N-diethylethylenediamine, ethanolamine, and 3-amino-1-propanol is adopted to synthesize poly(amido thioether)s (PATEs) with distinct side groups. Under suitable conditions, PATE solutions can exhibit single or dual phase transitions relying on the chemical composition, polymer concentration, additive, external stimuli and solution blending, as evidenced from turbidimetry and fluorometry analyses. Owing to strengthened hydrogen bonding, primary amide-bearing PATE solutions have some advantages such as concentration-insensitive UCST behavior, good thermal stability against high salt concentration, and formation of dual UCSTs in a water/ethanol mixture. Imidazolyl-bearing PATEs in buffer solutions shift from hydrophilic to LCST and LCST–UCST in a specific pH range, and hydroxyl-bearing PATE solutions can present concentration-dependent thermoresponsive behaviors. Meanwhile, solution blending leads to composition-tunable UCST, UCST–LCST and LCST behaviors. As analogues of polyacrylamides, PATEs comprising a thermo/oxidation-responsive and hydrogen bonding-related backbone can usually exhibit some differences in thermoresponsiveness and hold great promise as important thermoresponsive polymers.