(604i) Design of Depolymerizable Polyolefins By Amide-Functionalization

Depolymerization and degradation of polyolefins prepared by ring-opening metathesis polymerization of high strain monomers remain tremendous challenges due to their high ceiling temperatures. In this project, we aimed to develop a series of depolymerizable polyolefins by amide-functionalization with a programmable enzyme response. By polymerizing oxanorbornene monomers with amide groups using ring-opening metathesis polymerization (ROMP), we synthesized poly (N-hydroxyethyl 5-Norbornene 2,3-dicarboxymide (PNHND). PNHND films are dark brown films with hydrophilic surfaces and thermal and mechanical properties comparable to commercially available polyethylene terephthalate (PET). We found that chitinase was effective in depolymerizing PNHND under mild conditions (37°C, atmospheric pressure, and neutral pH) with shaking at 200 rpm. We hypothesized that chitinase facilitated the depolymerization on these polyolefins by scavenging nitrogen, initiating the pathways for hydrolases to expedite the degradation process. This hypothesis was corroborated by four pieces of evidence. Firstly, using RNA-sequencing, we confirmed that chitinase was the key enzyme that microorganism Pseudomonas aeruginosa PAO1 used to depolymerize PNHND because the gene (chiC) encodes chitinase was upregulated by 4.3 and 5.0 log2-fold compared to the control. Secondly, we found that dark brown PNHND films became colorless after depolymerization. Since the brown color of PNHND films codes for the nitrogen atom, the disappearance of brown color suggested the absence of nitrogen atom in the transparent product. Thirdly, the ¹H-NMR results confirmed the disappearance of PNHND after depolymerization, suggesting that chitinase depolymerized PNHND by scavenging out the nitrogen atoms. Lastly, using three-dimensional (3D) fluorescent imaging of depolymerized products with Acridine Orange (AO) labeling and Echo Revolve fluorescent microscope, we found that chitinase altered the 3D structures of an intact PNHND film and transformed the intact PNHND films into porous and water-soluble hydrogels after the 7-day incubation. This hydrogel was fully dissolved in 3% (wt/vol) SDS solutions, while the PNHND films that was not incubated with chitinase did not show changes. All these results suggested that we can develop a series of depolymerizable polyolefins by amide-functionalization.