Dual Effects of Heterocycles and Flexible Long Chains in Pressure-Sensitive Adhesives for Broad-Temperature-Range Flexible Applications

As an emerging interdisciplinary research frontier, flexible electronics are driving transformative innovations in next-generation electronic devices. The adhesive component, serving as a critical constituent in flexible electronic systems, is required to fulfill not only fundamental mechanical bonding requirements but also essential stress dissipation functions. Particularly during bending and folding operations of flexible screens, these adhesives prevent delamination or the warping of functional layers through instantaneous deformation recovery mechanisms. However, in extreme environments (such as high and low temperatures), these properties will be weakened. Therefore, this study synthesized pressure-sensitive adhesives (PSAs) with high-/low-temperature resistance through the copolymerization of heterocyclic monomers (IBOA/DCPA) with acrylic esters, followed by reactions with flexible curing agents (PEGDA 400/PEGDA 1000/PEA 1000). It was observed that the temperature resistance of the samples deteriorated with increasing cross-linking density. D-5@G₁₀₀₀-0.25 demonstrated excellent high- and low-temperature bonding performance, exhibiting a holding time exceeding 188 h at 85 °C and tack at -20 °C comparable to that at room temperature, which indicated that the addition of a heterocyclic monomer and flexible curing agent was beneficial to improve the high-/low-temperature resistance of PSA. At room temperature, all samples showed strain recovery times below 10 s after 100 cyclic stretching tests. This recovery time decreased with higher cross-linking density, reaching 0.5 s for D-20@G₁₀₀₀-0.25 (versus 4.0 s for D-5@G₁₀₀₀-0.25). In addition, excessive amounts of the flexible curing agent at -20 °C failed to reduce the PSA's strain recovery time. Instead, too much led to molecular chain entanglement or stacking, which prolonged the recovery time. The flexible curing agents with large molecular weight had more advantages in low-temperature strain recovery of adhesive because of their softer chain length. This study significantly enhances the adaptability of flexible and foldable displays under an extreme temperature environment.