Healable, Glassy Azobenzene Polymers at Room Temperature Based on Photoinduced Reversible Solid-to-Liquid Transitions

Designing healable, glassy polymers at room temperature remains a significant challenge due to the higher glass transition temperature (Tg) of glassy polymers than room temperature restricting the molecular or segmental mobility at room temperature. Glassy polymers present low healing efficiency although enabling self-healing through secondary transition of small-sized structural units in molecular chains. Herein, the healable, glassy azobenzene polymers (PnC-AZO) with the tunable methylene-based spacer lengths (n = 0, 3, 6, 9, 12) and the designed number-average molecular weight (Mn < 10 kDa) were synthesized and developed by free radical polymerization of azobenzene monomers. The PnC-AZO (n = 6, 9, 12) with trans-azobenzene structures shows the characteristic transition temperature (Ttrans) in rheology and crystallization melting temperature (Tm) at ∼50 °C much higher than room temperature and yet presents efficient healing ability at room temperature by alternating ultraviolet light and green light irradiation, resulting from the photoinduced reversible solid-to-liquid transitions along with reversible isomerization between thermodynamically stable trans-configuration and metastable cis-configuration of azobenzene units in PnC-AZO. This will provide an alternative toward healable, glassy polymers at room temperature for future sustainable material design.