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 (T_g) 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 T_g. Furthermore, standard shape memory cycles demonstrated excellent shape fixity (R_f > 98%) and recovery (R_r > 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.