Noncovalent and Dynamic Covalent Chemistry Strategies for Driving Thermoresponsive Phase Transition with Multistimuli and Controlled Encapsulation/Release

Abstract

We report the development of multiresponsive thermally sensitive polymers through both supramolecular and reversible covalent strategies as well as their use in controlled encapsulation and release. Novel acylhydrazone-based dynamic covalent polymers displaying lower critical solution temperature (LCST) or upper critical solution temperature (UCST) were synthesized. A remarkable control over thermal phase transition can be tuned through multimodes, such as anions, cations, solvent, pH, and competing components. In particular, anion recognition allowed disassembly and thus led to a significant decrease of UCST in dimethyl sulfoxide, and the combination of anion and solvent effects offered additional handle for control. Moreover, the use of anions, cations, as well as pH change was employed for the modulation of LCST-type polymer in water. Furthermore, switching on/off thermoresponsiveness was readily achieved by dynamic covalent exchange. Mechanistic studies also shed light on stimuliinduced changes in aggregation behaviors. Finally, thermally controlled encapsulation and release of hydrophobic and hydrophilic dyes were realized with great repeatability and reversibility, respectively, showing potential in delivery and sensing. The results and strategies described should provide opportunities for many aspects, including dynamic assemblies, complex systems, and adaptive materials.

Thermoresponsive dendritic oligoethylene glycols

“…6,7 Most reported thermoresponsive entities are high molar mass polymers or copolymers, such as poly(N-isopropylacrylamide), 8 poly(Nvinylcaprolactam), 9 and oligoethylene glycol (OEG)-based comb-like polymers 10,11 or dendronized polymers. 12 These polymers can be formed via covalent linkages, 13 supramolecular interactions, 14 or dynamic covalent bonds, 15 and have formed a class of intriguing candidates for promising applications, such as actuators, 16 drug delivery, [17][18][19] energy transfer, 20 and smart windows. 21 Monodispersed small molecules of molar masses less than a few thousands exhibiting thermoresponsiveness are rarely reported, partially due to the kinetically determined broad phase transitions and thermodynamically dominated high phase transition temperatures.…”

“…6,7 Most reported thermoresponsive entities are high molar mass polymers or copolymers, such as poly( N -isopropylacrylamide), 8 poly( N -vinylcaprolactam), 9 and oligoethylene glycol (OEG)-based comb-like polymers 10,11 or dendronized polymers. 12 These polymers can be formed via covalent linkages, 13 supramolecular interactions, 14 or dynamic covalent bonds, 15 and have formed a class of intriguing candidates for promising applications, such as actuators, 16 drug delivery, 17–19 energy transfer, 20 and smart windows. 21…”

Aminolysis induced functionalization of (RAFT) polymer-dithioester with thiols and disulfides

“…Post-polymerization functionalization of polymer materials has been a major area of research in the past years, 1,2 as it allows to tailor the properties of polymers with considerable versatility. For example, the thermoresponsive behavior of polymers can be modulated, 3 the polarity can be changed from hydrophobic to hydrophilic or vice versa 4,5 or the polymer architecture be transformed. 6 A versatile way to modulate polymer functionality and properties is via dynamic covalent chemistry, 7 which features covalent bond formation but allows for triggered bond cleavage.…”

Multi-Stimuli-Triggered Shape Transformation of Polymeric Filaments Derived from Dynamic Covalent Block Copolymers

“…Therefore, the dual nature of DCBs is of great importance to construct functional polymeric materials that can adapt, amplify, exchange, sense, self-heal, and respond to a variety of physical and chemical stimuli. − Among the reported DCBs, acylhydrazone bonds have attracted particular attention because they provide not only the dynamic and stable virtues through their reversibility and strength but also the hydrogen-bonding sites through the amide groups . To date, the acylhydrazone bond by the condensation of hydrazide with the formyl group (CHO) has been utilized as a useful way to construct different polymeric materials with adaptive and reversible properties and already led to a series of smart and functional polymeric materials, such as gels, − micelles, − single chain particles, − polydynamers, − and polymeric frameworks. − For example, Jackson and Fulton constructed a broad spectrum of responsive polymeric particles from block copolymers via utilizing the reversible acylhydrazone linkage . Liu and co-workers prepared a kind of dually responsive (thermal and pH) acylhydrazone-bonded amphiphilic block copolymer with tunable properties .…”