Directing network degradability using wavelength-selective thiol-acrylate photopolymerization

Wavelength-selective photopolymerization employs light at controlled wavelengths to trigger orthogonal photochemical reactions to fabricate multimaterials with unique combinations of building blocks and material properties. Prior wavelength-selective photopolymerization studies mainly focused on modulating the thermomechanical properties of the resulting multimaterials, which are often permanently crosslinked, non-degradable polymer networks. Here, we combine wavelength-selective photopolymerization with dynamic covalent chemistry to fabricate multimaterials with programmable, stimuli-responsive degradability in selected regions. Specifically, this study employs a thiol-acrylate photoresin comprising both wavelength-selective photoinitiators/photosensitizers and dynamic disulfide bonds. Green light irradiation triggers photobase generators to catalyze the thiol-acrylate Michael addition reactions, forming a step-growth polymer network with dynamic disulfide bond-based crosslinks. This green light-cured network can subsequently undergo degradation/decrosslinking by reacting with excess reactive thiols through thiol-disulfide exchange reactions. Meanwhile, UV light irradiation cleaves radical photoinitiators and thus promotes both radical-mediated acrylate homopolymerization and thiol-acrylate addition reactions, forming a permanently crosslinked chain-growth network that cannot be degraded. Promisingly, this thiol-acrylate photoresin can undergo orthogonal wavelength-selective photopolymerization under patterned green- and UV-light irradiation to form crosslinked multimaterials with pre-designed degradable regions, which can be selectively removed to reveal the underlying photomasks' patterns. Overall, the chemistry demonstrated herein can be used to fabricate complex patterns and hierarchical structures, holding promise for applications ranging from photolithography to 3D printing. Thiol-acrylate photoresin containing dynamic disulfide bonds undergoes wavelength-selective photopolymerization under green vs. UV light to produce a degradable step-growth network vs. permanent chain-growth network.