Chemically recyclable crosslinked thiol‐ene photopolymers via thiol‐disulfide exchange reactions

Abstract

Conventional crosslinked photopolymers possess permanent network structures, which cannot be remolded/recycled and generally discarded as waste after use. Research has begun to incorporate dynamic bonds into crosslinked photopolymers to make them reprocessable/recyclable, however, previous studies typically require tedious pre‐syntheses to obtain photoreactive building blocks that contain desired dynamic linkages/functionalities. In this study, we report a simple, one‐step, and scalable synthesis of chemically recyclable crosslinked thiol‐ene photopolymers that contain dynamic disulfide bonds from commercially available building blocks. Specifically, liquid polysulfides containing both reactive thiol end groups and internal disulfide bonds, together with multifunctional alkenes, are selected as the building blocks to simultaneously incorporate disulfide bonds during network formation via thiol‐ene photopolymerization. The incorporated dynamic disulfide bonds allow these thiol‐ene networks to be chemically recycled into photoreactive thiol oligomers through base‐catalyzed thiol‐disulfide exchange reactions. The resulting thiol oligomers can be effectively reused, together with the original multifunctional alkenes, for the next‐generation syntheses of crosslinked thiol‐ene photopolymers with chemical compositions and material properties that are nearly identical to those of the originally crosslinked sample. This chemical recycling process can be repeated many (infinite in theory) times to produce recycled thiol‐ene photopolymer networks with full property retention. Overall, the unique chemistry demonstrated in this study could potentially provide a route towards a circular economy of crosslinked photopolymers.

Thiol–Ene Networks with Tunable Dynamicity for Covalent Adaptation

“…Wang et al demonstrated this approach on an epoxy polymer cured with mixtures of disulfide-containing and disulfide-free carboxylic acids at varying proportions. Most recently, Alfarhan et al studied disulfide-containing thiol–ene networks and their depolymerization via base-catalyzed thiol–disulfide exchange that yields repolymerizable thiol oligomers …”

Directing network degradability using wavelength-selective thiol-acrylate photopolymerization

“…The resulting mixture was stirred overnight at room temperature to undergo network deconstruction via base-catalyzed thiol-disulfide exchange reactions. 48 After ∼6 h, a homogeneous solution was obtained, which was then concentrated by rotary evaporation and vacuum dried at room temperature for 24 h to fully remove the volatile triethylamine and acetone.…”

“…S4 †) of the resulting decrosslinked materials confirmed the complete X Green network degradation via base-catalyzed thiol-disulfide exchange reactions (see ESI † for details), in a manner similar to that reported in our previous study. 48 Notably, these decrosslinked materials contain the same amount of [SH] groups as those in the original decrosslinking solution (since [SH] content remains constant after thiol-disulfide exchange), which can be recrosslinked with a stoichiometric amount of triacrylate monomers, if needed. 48 3.2.…”

Loop 3D printing: recyclable photoresins for light-mediated additive manufacturing

“…In a more recent example, Jin and coworkers reported a strategy based on commercially available monomers using the thiol-disulfide exchange to chemically recycle crosslinked thiol-ene photopolymers. 28 An obvious advantage of designing these photocrosslinked polymers is to circumvent the burden of developing resins with limited recyclability.…”