Synergistic effects of azobenzene and thiourea backbones in multiresponsive copolymers for sensing and adhesive technologies.

Abstract

Stimuli-responsive polymers have garnered significant attention for their ability to adapt to environmental changes, offering applications in sensing, smart coatings, and adaptive devices. However, challenges remain in developing multifunctional polymers that combine dynamic responsiveness with robust mechanical properties. In this study, we design and synthesize multifunctional azobenzene-based copolymers, poly(thiourea triethylene glycol)-<i>co</i>-azobenzene (PTUEG₃-<i>co</i>-Azo) copolymers, through a controlled polycondensation process to address these limitations. The flexible PTUEG₃ backbone, with its strong hydrogen-bonding networks, is combined with azobenzene moieties to impart thermal isomerization, acid-base responsiveness, and enhanced adhesion performance. The azobenzene groups exhibited thermally induced <i>cis</i>-to-<i>trans</i> isomerization, leading to structural reorganization, increased molecular packing, and elevated glass transition temperatures (<i>T</i>_g). Additionally, the azobenzene moieties demonstrated reversible acid-base responsiveness, undergoing distinct and repeatable color changes upon protonation and deprotonation. By balancing the flexibility of the PTUEG₃ backbone with the rigidity of azobenzene groups, PTUEG₃-<i>co</i>-Azo copolymers achieved strong adhesion performance and tunable dynamic properties. The 4 : 1 PTUEG₃-<i>co</i>-Azo composition demonstrated superior adhesive strength, attributed to the synergistic effects of hydrogen bonding and azobenzene-induced reorganization under thermal activation. These results present PTUEG₃-<i>co</i>-Azo as a versatile material, bridging the gap between dynamic responsiveness and mechanical robustness, with potential applications in smart sensing, adhesives, and functional coatings.