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

Abstract

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 (ΔT ≤ 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.

Core–Shell Copolymers with Brush-on-Hyperbranched Arm Architecture: Synthesis, Dual Thermoresponsive Behaviors, and Nanocarriers

“…As shown in Figure b, the transmittance for the aqueous solutions of PEG 350 - g -POG-8, PEG 750 - g -POG-8, and PEG 1900 - g -POG-8 decreased from 100% to almost 0% when the solution was heated up. The cloud point (CP) was defined as the temperature at which the transmittance changed by 50% of the difference from the initial value to the final value, − as indicated in Figure b. Therefore, when the concentration was fixed to 5.0 mg·mL –1 , the CPs for the aqueous solutions of PEG 350 - g -POG-8, PEG 750 - g -POG-8, and PEG 1900 - g -POG-8 were determined to be 105.0, 110.2, and 121.5 °C, respectively, as shown in Figure b.…”

Thermoresponsive Polypeptoids

“…The side-chain architecture, the degree of polymerization (DP), and the polymer concentration were found to have significant effect on the solution properties of the polypeptoids. In recent work, by introducing alkyl or ethylene glycol (EG) units, a systematic study on thermo-responsive polypeptoid exhibited both LCST and UCST-type behavior was prepared into ionic polypeptoids via combining ROP and thiol-ene/yne click chemistry [79]. The phase transition temperature that is dependent on the chain length of pendant groups, the chemical composition, and the species of ionic moieties can be tuned in the range of 29-55 °C.…”

“…Various applications of thermoresponsive polymers have been studied in many research fields such as controlled drug delivery, nanoreactors, smart coatings, and sensors [6,[80][81][82]. PNIPAM as the most widely studied thermoresponsive polymer has been extensively used in many biomedical In recent work, by introducing alkyl or ethylene glycol (EG) units, a systematic study on thermo-responsive polypeptoid exhibited both LCST and UCST-type behavior was prepared into ionic polypeptoids via combining ROP and thiol-ene/yne click chemistry [79]. The phase transition temperature that is dependent on the chain length of pendant groups, the chemical composition, and the species of ionic moieties can be tuned in the range of 29-55 • C. Intriguingly, they demonstrate that the UCST behavior of polypeptoids can be regulated by the hydrophilic EG group, while the LCST behavior can be tuned by the hydrophobic residues.…”

Small dop of comonomer, giant shift of cloud point: Thermo‐responsive behavior and mechanism of poly(methylacrylamide) copolymers with an upper critical solution temperature

“…[12][13][14] Therefore, the rational design of the molecular structure and the regulation to the responsive temperature of UCST polymers have drawn much attention. [15][16][17][18][19] In a recent review, we have summarized the thermodynamic prerequisites for the inventions of UCST polymers and brought up a "thermodynamic map" to guide the fine-tuning to the responsiveness of these polymers. [2] The responsiveness of UCST polymers is generally driven by the hydrogen-bonding (H-bonding) or ionic interaction within polymer chains.…”