Reprocessable Polymer Network Formation and Deconstruction using Light-Responsive Star Polymers
ORAL · Invited
Abstract
Many polymeric materials are permanently crosslinked networks, which are challenging to deconstruct into reusable, reprocessable components. For example, transparent hydrogels for contact lenses, flexible rubbers for medical tubing, strong epoxies for versatile adhesives, and expandable foams for home insulation all have constituent network structures that provide mechanical resilience for prolonged use. A promising approach to engineer reprocessability and circularity into polymer networks is to leverage polymers that undergo reversible photochemical reactions. We investigate the photochemical reprocessing of polymer networks, which is enabled by end-functionalization of poly(ethylene glycol) star polymers with anthracene (PEG-anthracene). Anthracene is photoreversible: ultraviolet A (UVA) light promotes anthracene dimerization and polymer network formation, and ultraviolet C (UVC) light drives anthracene dimer dissociation and network deconstruction. We demonstrate multiple cycles of polymer network formation, deconstruction, and reformation by repeated cycles of UVA and UVC irradiation of PEG-anthracene. Network formation and deconstruction dynamics are monitored using in situ photorheology and ultraviolet–visible (UV–vis) absorbance to connect bulk mechanical properties to molecular-scale anthracene conversion. Network formation is faster for star polymers with more arms due to a greater number of reactive end groups per macromolecule. Subsequent reprocessing of solid networks into liquid resins is fastest for polymer samples with fewer arms and lower concentrations, highlighting an interplay between polymer architecture and anthracene dimerization dynamics. Reprocessability is further enhanced by tuning light exposure profiles and reducing the total dose of UVA and UVC irradiation. The photochemical processing insights provided by this work advance the rational molecular design and formulation of light-responsive polymers as reprocessable polymer networks.
*National Science Foundation CBET-2400010 and DGE-2146755, ACS Petroleum Research Fund Doctoral New Investigator Grant 66560-DNI7, Precourt Institute at Stanford University, Arnold and Mabel Beckman Foundation
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Publication:M. C. Burroughs, E. L. Quirk, B. M. Wirtz, T. H. Schloemer, D. N. Congreve, D. J. Mai. Light-Responsive Star Polymers for Reprocessable Network Formation and Deconstruction. Macromolecules, 58(12), 6066–6076 (2025). E. L. Quirk, M. C. Burroughs, D. J. Mai. In situ Photo-rheology Monitors Viscoelastic Changes in Photo-responsive Polymer Networks. Journal of Visualized Experiments, 220, e68394 (2025). M. C. Burroughs, T. H. Schloemer, D. N. Congreve, D. J. Mai. Gelation dynamics during photocrosslinking of polymer nanocomposite hydrogels. ACS Polymers Au, 3(2), 217–227, (2023).
