Tunable LCST/UCST-Type Polypeptoids and Their Structure-Property Relationship.

Bioinspired thermoresponsive polymeric materials with tunable phase-transition behaviors are highly desirable for biomedical applications. Here, we reported a facile approach for the synthesis of both lower critical solution temperature (LCST) and upper critical solution temperature (UCST) types of thermoresponsive polypeptoids with tunable phase-transition temperature in the range of 29--55 °C. The introduction of alkyl groups and ethylene glycol (EG) units results in a controlled phase-transition behavior under fairly mild conditions. A very sharp transition (Δ ≤ 1.5 °C) is observed by simply adjusting pH and the alkyl chain length. In particular, the carboxyl-containing polypeptoids display designable UCST behavior, which can be finely tuned in both water and methanol. All these features make the obtained polymers beneficial for practical applications. More interestingly, we demonstrate that the hydrophilic EG group behaves as an excellent regulator to tune the UCST behavior, while the hydrophobic alkyl residues show remarkable capability to regulate the LCST behavior of the system. We hope that such systematic structure-property studies will enable the design of smart polymer materials to meet the specific needs of future applications.