In Situ X-Ray Scattering Methods for the Characterization of Polymers During Recycling

A fundmanetal understanding of the macromolecular interactions with the catalyst, and how they evolve over the course of the deconstruction is important for designing efficient deconstruction chemistries. We investigated Volatile Catalyst (VolCat), a process for deconstructing polyethylene terephthalate (PET), a semi-crystalline polymer with crystalline regions embedded in an amorphous matrix. Under reaction conditions, PET is in the solid state and there is an interplay between the morphology and the deconstruction kinetics. We monitored the VolCat reaction kinetics by characterizing the structural evolution (crystallinity, polymer conformation) of reactants and products over the course of the reaction without altering the sample or taking aliquots.

Using in situ/operando small- and wide-angle X-ray scattering (SAXS/WAXS) techniques at the Stanford Synchrotron Radiation Lightsource (SSRL), we probed polymer deconstruction from the nano (~1-100 nm) to atomic (<1 nm) length scales. Coupled to microkinetic modelling, we differentiated the reaction rate constants for the amorphous and crystalline fractions and explained the average observed reaction rates in terms of interchange between amorphous and crystalline fractions throughout the deconstruction process. The understanding gained from these studies will enable expansion to other polymer systems and deconstruction reactions.