RAFT-Polymerized N-Cyanomethylacrylamide-Based (Co)polymers Exhibiting Tunable UCST Behavior in Water

Temperature-Responsive Zwitterionic Polymers That Undergo UCST-Type Liquid-Liquid Phase Separation under Physiological Ionic Strength

Associative phase separation (complex coacervation) in liquid-liquid phase separation (LLPS) involves the separation of multiple substances into concentrated and dilute phases by electrostatic interactions. Simple phase separation (simple coacervation) occurs when the hydrophilicity and hydrophobicity of a single molecule change dramatically in response to a specific stimulus. Simple coacervation arises from the lower critical solution temperature (LCST)- and upper critical solution temperature (UCST)-type phase separations in aqueous media containing temperature-responsive polymers. LCST- and UCST-type LLPSs induce droplet formation at temperatures above the LCST and below the UCST, respectively. Although there have been several studies on the UCST-type LLPS of temperature-responsive polymers in water, only a few temperature-responsive polymers that exhibit UCST-type LLPS in aqueous media with physiological ionic strength have been reported. In this study, we synthesized temperature-responsive zwitterionic polymers, exhibiting UCST-type LLPS in physiological ionic strength, by copolymerizing two types of zwitterionic monomers─sulfabetaine (SaB) having ammonium and sulfate groups and sulfobetaine (SB) having ammonium and sulfonate groups─in aqueous media with various ionic strengths. The resulting zwitterionic copolymers, P(SaB-co-SB)s, exhibited a cloud point (CP) characterized by a transition from turbidity to transparency as the temperature increased in a buffer with physiological ionic strength. The CP of P(SaB-co-SB) shifted from lower to higher temperatures as the SaB content increased. Microscopic observation showed that P(SaB-co-SB) underwent UCST-type LLPS to form coacervate droplets even in a buffer solution with physiological ionic strength at temperatures lower than the CP; however, the coacervates dissolved above the CP, unlike general UCST-type temperature-responsive polymers. The CPs of the P(SaB-co-SB)s under physiological ionic strength varied with the SaB content and ionic strength of the copolymerization medium. UCST-type LLPSs were induced by strong dipole-dipole interactions between SaB units at physiological ionic strength.

Synthesis of New Glycine-Based Polymers and their Thermoresponsive Behavior in Water

In this work, new glycine-derived polymers are developed that exhibit thermoresponsive properties in water. Therefore, a series of monomers containing one, two, or three amide functional groups and one terminal cyanomethyl group is synthesized. The resulting homopolymers, obtained by free radical polymerization (FRP) and reversible addition fragmentation chain transfer (RAFT) polymerization, display a sharp and reversible upper critical solution temperature (UCST)-type phase transition in water. Additionally, it is shown that the cloud point (TCP) can be adjusted over more than 60 °C by the number of glycyl groups present in the monomer structure and by the polymer's molar mass. These novel thermoresponsive polymers based on cyanomethylglycinamide enrich the range of nonionic UCST polymers and are promising to find applications in various fields.

Synergistic Approaches in the Design and Applications of UCST Polymers

This review summarizes recent progress in the synergistic design strategy for thermoresponsive polymers possessing an upper critical solution temperature (UCST) in aqueous systems. To achieve precise control of the responsive behavior of the UCST polymers, their molecular design can benefit from a synergistic effect of hydrogen bonding with other interactions or modification of the chemical structures. The combination of UCST behavior with other stimuli-responsive properties of the polymers may yield new functional materials with potential applications such as sensors, actuators, and controlled release devices. The advances in this area provide insight or inspiration into the understanding and design of functional UCST polymers for a wide range of applications.

Environmentally Stable, Robust, Adhesive, and Conductive Supramolecular Deep Eutectic Gels as Ultrasensitive Flexible Temperature Sensor

It is essential and of great significance to impart high mechanical performance, environmental stability, and high sensitivity to emerging flexible temperature sensors. In this work, polymerizable deep eutectic solvents are designed and prepared by simply mixing N-cyanomethyl acrylamide (NCMA) containing an amide group and a cyano group in the same side chain with lithium bis(trifluoromethane) sulfonimide (LiTFSI), and obtain supramolecular deep eutectic polyNCMA/LiTFSI gels after polymerization. These supramolecular gels exhibit excellent mechanical performance (tensile strength of 12.9 MPa and fracture energy of 45.3 kJ m^-2 ), strong adhesion force, high-temperature responsiveness, self-healing ability, and shape memory behavior due to the reversible reconstruction ability of amide hydrogen bonds and cyano-cyano dipole-dipole interactions in the gel network. In addition, the gels also demonstrate good environmental stability and 3D printability. To verify its application potential as a flexible temperature sensor, the polyNCMA/LiTFSI gel-based wireless temperature monitor is developed and displays outstanding thermal sensitivity (8.4%/K) over a wide detection range. The preliminary result also suggests the promising potential of PNCMA gel as a pressure sensor.

Mechanism insights in controlling host–guest (de)complexation by thermoresponsive polymer phase transitions

The hydrophobic interactions involved in phase separation of LCST polymers are the critical factor inducing the BBox release from the BBox/naphthalene while the host-guest complexes remain stable during phase separation of UCST polymers upon cooling.

Poly(N-cyanoethylacrylamide), a new thermoresponsive homopolymer presenting both LCST and UCST behavior in water

We have recently demonstrated that poly(N-cyanomethylacrylamide) (PCMAm) synthesized by reversible addition-fragmentation chain transfer (RAFT) radical polymerization exhibits a typical upper critical solution temperature (UCST)-type transition in water with a very...

Synthesis and Characterization of Temperature-Responsive N-Cyanomethylacrylamide-Containing Diblock Copolymer Assemblies in Water

We have previously demonstrated that poly(N-cyanomethylacrylamide) (PCMAm) exhibits a typical upper-critical solution temperature (UCST)-type transition, as long as the molar mass of the polymer is limited, which was made possible through the use of reversible addition-fragmentation chain transfer (RAFT) radical polymerization. In this research article, we use for the first time N-cyanomethylacrylamide (CMAm) in a typical aqueous dispersion polymerization conducted in the presence of poly(N,N-dimethylacrylamide) (PDMAm) macroRAFT agents. After assessing that well-defined PDMAm-b-PCMAm diblock copolymers were formed through this aqueous synthesis pathway, we characterized in depth the colloidal stability, morphology and temperature-responsiveness of the dispersions, notably using cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and turbidimetry. The combined analyses revealed that stable nanometric spheres, worms and vesicles could be prepared when the PDMAm block was sufficiently long. Concerning the thermoresponsiveness, only diblocks with a PCMAm block of a low degree of polymerization (DPn,PCMAm < 100) exhibited a UCST-type dissolution upon heating at low concentration. In contrast, for higher DPn,PCMAm, the diblock copolymer nano-objects did not disassemble. At sufficiently high temperatures, they rather exhibited a temperature-induced secondary aggregation of primary particles. In summary, we demonstrated that various morphologies of nano-objects could be obtained via a typical polymerization-induced self-assembly (PISA) process using PCMAm as the hydrophobic block. We believe that the development of this aqueous synthesis pathway of novel PCMAm-based thermoresponsive polymers will pave the way towards various applications, notably as thermoresponsive coatings and in the biomedical field.