(180bn) 2D and 3D Photolithography Using Diels-Alder and Thiol-Ene Click Reactions

The Diels-Alder family of reactions is broadly useful for its thermal reversibility. The forward reaction produces an oxy-norbornene adduct structure at low temperatures, which can undergo a photoinitiated thiol-ene click reaction to create an irreversible structure. When thiol-containing monomers are trapped within a Diels-Alder polymer network, temperature- and light-based control results in a novel type of photolithography, in which the photoresist is crosslinked and highly glassy before exposure. Development takes place at high temperature, where the unexposed regions will depolymerize without the use of solvent. This technique has potential for improvements in layer-by-layer 2D patterning, in which overhanging features are easily achieved without the use of scaffolds, even at very small length scales (~1 µm). Furthermore, the reaction system has been demonstrated to work using 2-photon lithography to pattern specific areas within a 3D Diels-Alder network. The system is highly flexible with regard to monomer, thiol, and photoinitiator selection for fine-tuning material properties.