"Pore level deconstruction rates monitored inside nanopores by dielectric spectroscopy"

R Bharath Venkatesh^a, Jon Bingaman^a, Susannah Scott^a, Rachel Segalman^a

^aDepartment of Chemical Engineering, University of California, Santa Barbara, 93106Catalytic upcycling of polymers is an emerging paradigm that promises to convert waste plastic to valuable chemicals. Many promising catalytic reaction schemes that cleave polyolefins to form smaller paraffins and olefins are hampered by limited selectivity and slow kinetics.

Furthermore, it is tough to differentiate chain cleavage occurring outside the pores from chain scission within the pores due to limited accessibility of porous active sites by long chains. Effective reaction engineering of upcycling processes demands an understanding of the intrinsic activity of catalyst pores for macromolecular deconstruction. We propose a method to use changing segmental dynamics as marker to track the progress of chain scission inside porous catalysts by using the evolving dielectric signature of reacting polymer. Nanoporous membranes of anodic aluminum oxide are filled with poly(propylene-carbonate) as a model for polymer-filled catalytic pores. Change in the measured dielectric properties upon thermal depolymerization is correlated to the rate of scission of polymeric species. To highlight the applicability of this technique to catalytic upcycling of commercial polyolefins, scission of poly(ethylene-alt-propylene) is tracked inside functionalized nanopores with acidic sites that can cleave the backbone polyolefin bonds.

We acknowledge the support of the Department of Energy Office of Basic Energy Sciences Chemical Upcycling award (DE-SC0022294). This research used the facilities at the MRSEC center in Materials Research Laboratory at UCSB (DMR 2308708).