Functional dyes offer fascinating properties in response to external stimuli and enable unique stimuli-responsive functions in materials by chemical incorporation into polymers. In this review, we highlight our recent studies conducted in the last half decade on stimuli-responsive smart polymers and polymeric materials offering, for example, switchable adhesion, mechanical actuation, and chemical sensing based on functional dyes that are chemically incorporated into the structures, with a particular focus on the stimuli of light, force, electric fields, and chemicals including water.

The degree of gel-gel phase separation (GGPS) was compared using multi-arm poly(ethylene glycol) (PEG) hydrogels. GGPS can occur at c < c*, with 8-arm PEG exhibiting a stronger turbidity (D) indicating stronger GGPS compared to 4-arm PEG. This indicates that phase-separated PEG can be obtained at low concentrations simply by increasing the number of branches. Furthermore, phase-separated 8-arm PEG showed higher osteogenic differentiation in vitro.

Sodium alginate and carboxymethyl chitosan were used as raw materials, and the dynamic imine bonding network formed by the two was combined with the coordination bonding network formed by acrylic acid and aluminum ions. The dual-network structure of the hydrogel not only gives the hydrogel excellent self-healing properties, but also gives the hydrogel excellent mechanical properties, with a strain at break as high as 3787%. In addition, the hydrogel has the antibacterial property of inhibiting the growth of E. coli and S. aureus and good electrical conductivity.

Heat insulators are key materials for efficient energy use and reduction of CO₂ emissions. Recently, we examined cross-linked polymethylsilsesquioxane (MSQ) for use as the basic structure of heat-resistant insulation materials. In this study, we prepared MSQs with different cross-linking units and examined the effects of their structures on the heat resistance and heat insulation properties. Among those, MSQ linked by diethynylbenzene had sufficiently low thermal diffusivity and moderately high heat resistance.

In this study, branched polymers with different copolymerization composition ratios of α-chloro-ε-caprolactone (α-ClCL) and ε-caprolactone (ε-CL) were prepared using α-ClCL and trimethylolpropane as the initiator. Furthermore, acryloyl groups were introduced at each chain ends of branched polymer to form macromonomers capable of cross-linking reactions. Films obtained by photo-crosslinking macromonomers with chloro groups showed shape-memory properties. In addition, the chloro group introduced by α-ClCL was converted into an azide group. This film is expected to be applied to various functional surfaces through the click reaction in the future.

Physical modification of carbon materials using polymers is a useful technique for altering surface properties. The adsorption phenomenon of polybenzimidazole (PBI) in organic solvents onto different carbon materials with different surface morphologies and chemical compositions was examined to assess the key parameter controlling the adsorption phenomena. Adsorption isotherm measurements revealed that the adsorption of PBI was irreversible and thermodynamically favourable when interaction between solvent-carbon or PBI-solvent is low. PBI did not diffuse into micropore and the coverage ratio of the PBI onto mesopore and macropore surface was around 60%.

A novel electrochemically stable composite polymer electrolyte (CPE) containing a lignin derivative and dilignol was exploited for battery application for the first time. The lignin derivatives improved both the ionic conductivity and mechanical performance of the polymer-based electrolytes. Notably, the LiFePO₄/Li cell had improved stability and recovery capacity, and the Coulombic efficiency was approximately 100%, with a capacity of more than 150 mAh g⁻¹. The resulting alterations in the coordination number led to enhanced Li⁺ mobility and consequently, increased conductivity and cell capacity.

This work shows that the length of flexible spacers in azobenzene (Azo)-based polymers is crucial for achieving room-temperature photoliquefaction (i.e., UV light-induced solid‒liquid phase transition). By adjusting the length of dithiol-functionalized flexible spacers, the melting temperature (T_m) of Azo polymers can be effectively modulated. Incorporating longer spacers decreases the T_m to a temperature achievable by the photothermal effect of Azo molecules, thus enabling photoliquefaction of Azo polymers at room temperature.

High performance polymer alloy films with high T_g, heat resistance, and sufficient toughness were prepared by blending a polyfunctional benzoxazine monomer (OP-p) and 4,4′-bismaleimidodiphenylmethane (BMI; 10–90 wt.%), followed by thermal curing up to 240 °C. The T_g increased to 228 °C and 329 °C for the polymer alloy films with BMI contents of 60 wt.% and 75 wt.%, respectively, which were higher than those of the POP-p or PBMI homopolymer. Despite the improvement in the T_g, the alloy films exhibited sufficient toughness as evidenced via the tensile test.