Tracking the segmental dynamics of polymers undergoing scission inside catalytic nanopores: dielectric spectroscopy as a tool to advance waste plastics upcycling

The emerging paradigm of upcycling promises to address the issue of plastic waste pollution by extracting value out of polymer-based products. Upcycling processes employing nanoporous catalysts are often limited by low conversion rates and poor selectivity as the entropic penalty for polymers to enter catalytic nanopores imposes severe transport limitations on large polymers to access these active sites. However, several studies report that the physical attributes of nanopores such as pore architecture can control the selectivity of the final products. Batch-scale investigations of catalytic polymer scission lack information on the pore-level macromolecular deconstruction pathways and often conflate unselective, extra-pore scission with the catalytic action. To understand the physical factors influencing polymer scission inside nanopores decoupled from transport processes, we utilize dielectric spectroscopy to monitor the scission of polymers confined inside Anodized Aluminum Oxide (AAO) nanopores. Acid sites, capable of chain scission, can be localized along the pore walls. Change in the segmental dynamics of reacting polymer chains, obtained from dielectric spectra, serve as an indicator of the progress of the reaction and help map out the effective reaction rates inside nanopores. We demonstrate the validity of this technique by tracking the degradation of poly (propylene carbonate) inside AAO nanopores in catalytic and non-catalytic scenarios.