Off-stoichiometry improves the photostructuring of thiol–enes through diffusion-induced monomer depletion

Abstract

Thiol–enes are a group of alternating copolymers with highly ordered networks and are used in a wide range of applications. Here, “click” chemistry photostructuring in off-stoichiometric thiol–enes is shown to induce microscale polymeric compositional gradients due to species diffusion between non-illuminated and illuminated regions, creating two narrow zones with distinct compositions on either side of the photomask feature boundary: a densely cross-linked zone in the illuminated region and a zone with an unpolymerized highly off-stoichiometric monomer composition in the non-illuminated region. Using confocal Raman microscopy, it is here explained how species diffusion causes such intricate compositional gradients in the polymer and how off-stoichiometry results in improved image transfer accuracy in thiol–ene photostructuring. Furthermore, increasing the functional group off-stoichiometry and decreasing the photomask feature size is shown to amplify the induced gradients, which potentially leads to a new methodology for microstructuring.

Simultaneous Replication of Hydrophilic and Superhydrophobic Micropatterns through Area‐Selective Monomers Self‐Assembly

“…As polymer matrix, thiol‐ene monomers were used, since they form a densely cross‐linked network and because they exhibit interesting features for lab‐on‐chip applications, such as tunable mechanical properties, easy covalent surface bonding and surface grafting, and excellent photolithographic capabilities …”

E-Beam Nanostructuring and Direct Click Biofunctionalization of Thiol–Ene Resist

“…113 Photostructuring of off-stoichiometric thiol−ene prepolymer 114 mixture depletes the deficient monomer in the nonexposed 115 region immediately adjacent to the exposed prepolymer, which 116 suppresses gelation caused by radical diffusion in that region. 18 We hypothesize that a similar effect occurs during e-beam 118 exposure. The addition of inhibitor compound further prohibits the broadening of features by scavenging radicals in 120 nonexposed areas.…”

Photopatternable Electrolytes for Conducting Polymer Actuators

“…Thiol-ene coupling reaction has a significant potential for the development of complex micro/nano polymer-based patterns and structures, which have been explored by various patterning techniques including classic photolithography, electron beam lithography, reaction injection molding and soft lithography [135][136][137][138].…”

“…Figure 3.2 compares the patterning results using these two types of photoresists in a photolithographic process. The step-growth mechanism in the thiol-ene coupling chemistry and the associated delayed gelation, rapid reaction kinetics, uniform polymer network, negligible oxygen inhibition, and low shrinkage stress, make this thiol-ene reaction suitable to develop negative-toned photoresist materials in the photolithographic patterning process [138][139][140]. The delayed gelation and low shrinkage stress lead to sharp photolithographic profiles, which possess a well-defined and distinct boundary between exposed and unexposed photoresist regions.…”