Multitunable Thermoresponsive and Aggregation Behaviors of Linear and Cyclic Polyacrylamide Copolymers Comprising Heterofunctional Y Junctions

Abstract

The incorporation of asymmetric Y junctions into thermoresponsive polymers allows access to hierarchical selfassembly, and self-assembly of cyclic polymers can further amplify the topology effect. At present, systematic insights into the influence of Y junctions on physicochemical properties remain at the early stage. A diversity of linear and cyclic polyacrylamide copolymers with substituent-variable Y junctions are designed to reveal the effects of topology, chain length, composition, concentration, and temperature. With the increasing size of substituents, copolymer aqueous solutions gradually shift from dual upper and lower critical solution temperatures (UCST/ LCST) to a single LCST until the lack of phase transition. The LCST can be elevated by introduction of a cyclic architecture, longer polymer chain, and smaller substituent. Owing to the changes in degree of hydration of subunits, heat can induce sphere− vesicle−nanosheet−nanoribbon−sphere (linear copolymer) and sphere−nanosheet−nanoribbon (cyclic copolymer) transitions. In addition, the cyclization effect is also reflected in cooperative hydration of distinct subunits upon heating, higher ceiling temperatures to form stable lamellae, and more pronounced hysteresis of the turbidity curve upon cooling. This research using Y junction bearing thermoresponsive copolymers may provide a promising platform to achieve on-demand phase transitions and nanostructures.

Recent advances in the self-assembly of sparsely grafted amphiphilic copolymers in aqueous solution

“…Furthermore, a significant variation in the phase transition temperature between cyclic and linear graft copolymers, which is also an interesting phenomenon, was observed. Differences in thermo-responsivity between cyclic and linear graft copolymers have been reported by Zhao et al, 139,140 suggesting that differences in polymer topology affect not only self-assembly behaviour but also the thermal properties of graft copolymers. This seminal research clearly shows that self-assembled structures and phase transition temperatures can be controlled by changing the topology of the main chain.…”

Dual Thermo-Responsive and Strain-Responsive Ionogels for Smart Windows and Temperature/Motion Monitoring

“…To overcome the disadvantage of hydrogels, ionogel materials based on ionic liquid (IL) have been developed recently, owing to the unique properties of IL, such as nonvolatility, a wide liquid temperature range, strong dissolving capacity, and excellent thermal stability. − Importantly, the ionogels have the advantages of a good ionic conductivity and wide electrochemical window from IL that other gels do not have, which can be used in some important fields, including energy storage and strain sensors. − However, some methods for preparing ionogel are not in situ, and the preparation process is too complicated (two steps or three steps), and lots of the stretchable ionogels need variety of monomers and cross-linkers, which greatly limits the development and application of the ionogels as strain sensors . On the other hand, the good designability of the anion–cation couple structure of the ILs makes the ionogel show tunable hydrophobicity and hydrophilicity with different polymers. − The obtained high performance stimuli-responsive ionogels with outstanding designability and tunable thermo-responsive behaviors can be applied in a wider field. − However, the reported thermo-responsive ionogels need complex monomers or a complex preparation process, especially when the strain is less than 300%. Therefore, it is urgent to develop simple an in situ preparation technology using a monomer with a simple structure to construct stable and highly stretchable thermo-responsive ionogel materials.…”

Rational design of a multi-in-one heterofunctional agent for versatile topological transformation of multisite multisegmented polystyrenes

“…[6][7][8] With the incorporation of reversible or irreversible covalent linkers, polymer segments can be subjected to stimuli-triggered cleavage and rearrangement, leading to the formation of other polymers with distinct topology, composition or molar mass (M n ). Representative reversible covalent linkers comprise thermoresponsive Diels-Alder (DA) adduct [9][10][11][12] and alkoxyamine, a photo/thermoresponsive anthracene dimer (AntD) [13][14][15][16] and a redox-sensitive disulfide group, and typical irreversible covalent linkers mainly include a UV-cleavable o-nitrobenzyl group, 17 a thermo-labile azo group, and pH-labile ester, 18 acetal 19 and thioketal [20][21][22][23] groups. Rational incorporation of smart linkers leads to versa-tile topological transformations among linear, cyclic and branched polymers.…”