Dual-stage thermosetting photopolymers for advanced manufacturing

We report a dual-stage photocrosslinked polymer network based on sequential ultraviolet (UV)-triggered radical polymerization and thermally activated etherification, applicable to the fabrication of tailorable and programmable high-resolution structures. The first stage involves photoinitiated polymerization of monomer and crosslinker to obtain an intermediate polymer network. As such, sophisticated two-dimensional (2D) and micro-scale three-dimensional (3D) structures can be made by using UV-based advanced manufacturing technologies. These complex structures can then be readily programmed into other desired, permanent shapes, in the second stage, via thermally triggered etherification which results in a highly crosslinked, robust polymer network. The intermediate network (Stage I) is characterized to have a Young's modulus ranging from 342 to 1146 MPa and a glass transition temperature from 52 °C to 83 °C, depending on the concentration of crosslinker. The same material attains a glass transition temperature ranging from 67 °C to ~105 °C and a Young's modulus of up to 1607 MPa after the subsequent heating process (Stage II). Originally 3D printed 2D structures can be further programmed into rigid, permanent 2.5/3D ones. Micropatterns fabricated from intrinsically hydrophilic dual-stage crosslinked photopolymers through soft lithography show superhydrophobicity, and can subsequently be molded with different curvatures for practical applications.