Main-Chain Azobenzene\nPoly(ether ester) Multiblock\nCopolymers for Strong and Tough Light-Driven Actuators

The stimulus-responsive polymeric materials have attracted\ngreat\nresearch interest, especially those remotely manipulated materials\nwith potential applications in actuators and soft robotics. Here we\nreport a photoresponsive main-chain actuator based on azobenzene poly(ether\nester) multiblock copolymer (mBCP) thermoplastic elastomers, (PTAD-<i>b</i>-PTMO-<i>b</i>-PTAD)<sub><i>n</i></sub>, which were synthesized by a cascade polycondensation-coupling ring-opening\npolymerization method using poly(tetramethylene oxide) (PTMO) and\nazobenzene-containing cyclic oligoesters (COTADs) as monomers. The\nthermal, mechanical, and microphase separation behaviors of mBCPs\ncould be flexibly tuned by altering the ratios of soft-to-hard segments\nand block number (<i>n</i>). The oriented azobenzene mBCP\nfibers were prepared by melt spinning, showing reversible photoresponsive\nproperties with remarkably high strength (∼1000 MPa) and high\nelongation at break comparable to spider silks. Fast photoinduced\nbending and contraction were successfully achieved in these fibers\nwith high work and power densities and energy conversion efficiency,\nenabling it to lift up about 250 times of its own weight. Moreover,\nit can take out materials inside the tube by UV-light control. These\nfibers could be applied in light-driven actuators or telecontrolled\nrobot arms.