Xianjing Zhou

Thermoresponsive 1,2,4-triazolium-functionalized PNIPAm microgels were prepared as recyclable aqueous nanoreactors for benzoin condensation. The as-made microgels are spherical in shape with a hydrodynamic size of 232–282 nm at 25 °C and a volume phase transition near 28 °C. Under mild alkaline conditions in water, the optimized PNT-10 microgel promoted benzaldehyde condensation to benzoin in near-quantitative yield and could be recycled over five cycles. Control experiments with noncharged triazole polymers and imidazolium microgels confirmed the importance of the 1,2,4-triazolium functionality. NMR studies using model compounds are consistent with the transient carbene-derived adduct formation. The interfacial tension and DLS tests suggest favorable benzaldehyde–microgel network interaction. These results establish triazolium-functionalized PNIPAm microgels as responsive polymer nanoreactors in which catalytic triazolium sites, substrate–microgel interaction, and thermoresponsive microgel architectures can jointly regulate aqueous C–C bond formation.

Dynamic regulation of polymer solution phase behavior with real-time reversibility remains challenging. Here, we report a light-responsive poly(ethylene glycol) (PEG) system that enables reversible switching between linear and cyclic topologies, allowing continuous modulation of thermally induced phase transitions. Linear PEG functionalized with styrylpyrene end groups undergoes efficient intramolecular [2 + 2] photocycloaddition under visible light to form cyclic polymers, while UV irradiation restores the linear precursor. This reversible topology interconversion allows continuous tuning of the cyclic/linear ratio. As a result, the cloud point temperature of aqueous solutions can be modulated over a wide range from 37 to 65 °C. Aggregation appears to be enhanced in linear polymers through end-group-mediated π-π stacking and intermicellar bridging, whereas it is suppressed in cyclic polymers due to topological constraints and reduced stacking interactions. This work establishes topology switching as a noninvasive strategy for dynamically regulating polymer solution thermodynamics and highlights topology as a tunable parameter for controlling thermoresponsive behavior.

Homogeneous catalysts of high activity and selectivity often face challenges in the separation from feedstocks and products after reactions. In contrast, heterogeneous catalysts are easier to separate, usually at the cost of compromised catalytic performance. By designing catalysts capable of switching between homogeneous and heterogeneous states for catalysis and separation, the merits of both could be synergistically combined. In this study, a thermoresponsive 1,2,4-triazolium-based poly(ionic liquid) (PIL) was applied as a temperature-switchable organocatalyst for the controlled synthesis of porous organic cages in methanol. Variation of the reaction temperature induced a phase transition of the PIL, causing the polymer chains to dissolve or collapse in methanol, thereby exposing or shielding the catalytically active sites to proceed or retard the reaction, respectively. To note, at a sufficiently low temperature, the PIL as a catalyst precipitated out of its methanol solution and could be separated by centrifugation or filtration for reuse, similar to common heterogeneous catalysts. Such switchable and recyclable properties of polymeric catalysts will inspire the design of efficient and adaptable organic or hybrid nanoreactors in liquid media.

The density evolution of polystyrene (PS) adsorbed layers on phenyl-modified SiO₂-Si substrates was investigated. The thickness and density of flattened layer on substrates with above 75% phenyl content increased over annealing time and could approach 4.7 nm and 1.37 g/cm³ at equilibrium, respectively, which were much higher than those on SiO₂-Si. The annealing time for flattened chains to reach equilibrium increased with an increasing phenyl content on the substrate. The interface sensitive sum frequency generation vibrational spectroscopy (SFG) technique revealed that both the amount and the strength of the interfacial π-π interaction between the phenyl groups of substrates and in PS chains increased with annealing time. This resulted in more stretched chains perpendicularly, leading to a denser and thicker adsorbed layer with a closest-packing structure, driven by favorable enthalpy processes. Our work provides important insight into the densification mechanism of adsorbed flattened layers.

Triazoliums are a family of five-membered heterocyclic cations that contain three nitrogen and two carbon atoms. In contrast to the widely studied imidazolium cations, triazoliums are less explored. In terms of the chemical structure, triazolium replaces a carbon atom in the imidazolium cation ring with an electron-withdrawing nitrogen atom, which makes the triazolium more polarized. Among the many physical properties, the thermal responsiveness of triazoliums is of particular interest to us but has been rarely investigated. In this contribution, we prepared a series of 1,2,4-triazolium-based poly(ionic liquid)s (PILs) with varying alkyl substituents and counteranions and studied their thermal-responsive behavior. We found that 1,2,4-triazolim-based PILs with a polymeric backbone structure similar to that of polyimidazoliums exhibited opposite thermal phase transition processes in solvents. For example, methyl-substituted 1,2,4-triazolium-based PILs exhibited an upper-critical-solution-temperature (UCST)-type phase transition in methanol when the counterion was I^- and a lower-critical-solution-temperature (LCST)-type phase transition in acetone when the counterion was PF₆ ^-. The thermal responsiveness was reversible and concentration-dependent. Interestingly, the thermal response of 1,2,4-triazolim-based PILs could be retained in the organogel form, which was applied in the pretreatment of anion-containing organic waste liquids and temperature-controlled "smart" switches.

The adsorption of loose chains occurs on free sites remaining after the adsorption of flattened chains, indicating that flattened chains dominate the adsorption dynamics of loosely adsorbed chains.