CPOS Seminar: "Molecular insights to engineer sustainability: Understanding transport and reactivity in catalytic upcycling of polymers"

Speaker: R Bharath Venkatesh, PhD, Department of Chemical Engineering, Rachel Segalman Group, UC Santa Barbara

Unregulated disposal of plastic wastes not only creates environmental pollution issues but also fails to harness the potential of plastics as valuable feedstock to make organics used in applications such as adhesives, surfactants, composites, etc. The emerging paradigm of upcycling employs melt-phase catalytic reactions to cleave polymer chains in waste plastics to convert them into valuable organics. To increase the surface area of active sites, the catalysts are designed to be nanoporous which imposes severe transport limitations as long chain polymers are unable to access nanopores due to entropic limitations to pore entry. Rational design of pores will not only alleviate these transport limitations but also help unlock control over selectivity of the reaction. This opens up opportunities for controlling the activity and selectivity of polymer upcycling reactions by understanding the interaction of polymers with nanoporous materials. In his talk, I will highlight key findings from my doctoral and postdoctoral studies focused on understanding the pore-scale aspects governing (a) rate of entry of polymers into nanopores and (b) chemical transformations of polymer chains inside nanopores.

To understand the factors limiting the entry of polymers into nanopores, I studied the rate of capillary rise of polymers into the interstices of colloidal close-packed assemblies. Depending on the level of entanglement and the extent of confinement, we observed that polymer motion into nanopores can be unexpectedly faster than the bulk or show a size-independent constant rate. Control over selectivity can be achieved by understanding how pore design controls the deconstruction pathways for a polymer chain inside nanopores. To monitor reactivity inside nanopores, segmental dynamics of a reacting polymer melt inside nanopores were tracked using dielectric spectroscopy. This is a first-of-its-kind effort that can extract kinetic information about the rate of intra-pore chain scission decoupled from transport limitations.