Photo–Thermally Sequentially Responsive Shape Memory Polymers Based on Side–Chain Azobenzene–Functionalized Epoxy

To address the critical limitations of traditional photothermal–responsive epoxy–based shape memory polymers (ESMPs), such as poor compatibility and cyclical instability, a series of side–chain azobenzene (Azo)–functionalized linear ESMPs (EPDm) were successfully synthesized via chemical bonding. Highly rigid 4–aminoazobenzene (Azodm) units were covalently integrated into the Bisphenol A–type epoxy backbone as functional photo–responsive side chains. Systematic characterizations confirmed that the glass transition temperature (Tg) of the EPDm polymers could be precisely tuned from 41.53 °C to 53.26 °C by adjusting the Azodm content. Benefiting from the proposed homogeneous covalent architecture, the EPDm films exhibited superior photothermal sequential behavior and remarkable shape memory stability despite a slight reduction in tensile strength (≈10–12 MPa). Under 365 nm UV irradiation, the pre–stretched EPDm10 specimen achieved a rapid macroscopic bending angle of over 150° within 15 s, driven exclusively by the trans–to–cis molecular photoisomerization of the Azo side chains well below the matrix Tg. Furthermore, standard shape memory cycles demonstrated excellent shape fixity (Rf > 98%) and recovery (Rr > 95%) ratios, alongside exceptional anti–fatigue performance with minimal strain variance (≈5%) over consecutive cycles. This work establishes a robust and high–efficiency molecular design strategy for photo–thermally sequentially responsive shape memory polymers, offering immense potential for smart actuators and flexible electronics.