Mechanically Tunable, Readily Processable Polyurethane Material by Dual-Stage Polymerization of Glycidyl Azide Polymer

Here, we report a dual-stage polymerization system based on thermally cured polyurethane formation and subsequent UV-activated cross-link reactions, applicable to the fabrication of programmable 3D structures and high-resolution features. Glycidyl azide polymer (GAP) can react with isocyanate cross-linkers to obtain relatively soft intermediate polymer, and upon UV exposure, nitrene species are subsequently generated to induce the formation of a highly cross-linked network. The azide photoreaction at the second stage increases the cross-link density of the network, which leads to a rise of the glass transition temperature from −50 to +60 °C, and Young’s modulus of the second-stage material achieved a 1 order of magnitude increase. In addition, the mechanical performance of the dual-stage resin can be precisely controlled by the application of UV exposure. The dual-stage resin was made into programmable 3D structures and solvent-responsive shape memory materials, which demonstrated its practical use in imprint lithography and biomedical actuators. Azide photoreaction has seen wide applications in organic synthesis and photoresist; however, its function as photoinduced cross-linker in polymer chemistry has not been extensively explored. This approach offers a unique photopolymerization route via azide photochemistry and opens up a variety of possibilities for synthesizing functional material with programmed structures and tunable mechanical properties.