In Situ Near Edge X-Ray Absorption Fine Structures Spectroscopy for The Characterization of Deploymerization Rate during Polymer Recycling

The circular polydiketoenamine (PDK) elastomers cover a broad range of thermo-mechanical properties to meet various application demands, and they can be fully deconstructed back to monomers through acid mediated hydrolysis. It is found that the deconstruction rates can be controlled by tuning the anions in the acidic media, i.e., the deconstruction rate is accelerated when switching from a hydrogen sulfate anion to a bromide anion. To quantitatively quantify the deconstruction rate, we developed an in-situ NEXAFS method combining with time dependent density function theory (TD-DFT) predictions to investigate the deconstruction of the PDK elastomers, which produced chemo-specific spectrums that are subsequently interpreted with specific assignment to functional groups. Briefly, we sealed a PDK403 thin film with a layer of acid in a sandwiched SiNx membrane windows as the in-situ liquid cell for the collection of NEXAFS spectrum. With careful manupulation of X-ray flux to avoid radiation damage, we consistenly observed an increasing peak at 289.4 eV and a decreasing peak at 286.6 eV over time, indicating the progression of chemical transformation. With accurate peak assignemnt from DFT calculations, the increases at 289.4 eV is ascribed to the release of solvated T-403. The progressively increase in the peak intenisty works for the quantification of depolymerization rate of PDK403. This is the first time to in situ characterize the deconstruction of crosslinked polymers as a solid that do not dissovle in a solvent enviorment. This methodology opens up the possibility to characterize the chemical transformations in various crosslinked vitrimers and elastomers.