(505h) Polymer Scission in Catalytic Nanopores: Role of Polymer Dynamics in Upcycling

Addressing the issue of plastic waste pollution requires innovations in end-of-life handling of polymer-based products. Upcycling processes that take advantage of catalytic processes to convert waste polymers into commodity products are often limited by low conversion rates and poor selectivity. One way to improve the scalability of such processes is to employ nanoporous solid catalysts that cleave the polymer backbone selectively at high rates. However, the entropic penalty for polymers to enter catalytic nanopores imposes severe transport limitations on large polymers to access these active sites. Yet, several studies report that the physical attributes of nanopores such as pore size and lateral dimensions can control the selectivity of the final products. Batch-scale investigations of catalytic polymer scission are limited in their elucidation of physical principles governing polymer deconstruction, especially pore-level macromolecular reaction mechanisms. To develop an understanding of polymer reactivity decoupled from transport processes, we utilize dielectric spectroscopy to monitor the scission of polymers confined inside Anodized Aluminum Oxide (AAO) nanopores. AAO nanopores are used as model catalytic pores with uniform geometry and 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. A model polyolefin, poly (ethylene-alt-propylene), is then used along with nanopores of varying morphology and active site density to elucidate the factors influencing polymer reactivity inside catalytic nanopores.