Circular Design and Functionalized Upcycling of Waste Commodity Polystyrene via C-H Activation Using Microwave-Assisted Multicomponent Synthesis

Abstract

The inefficient reuse and recycling of plastics—and the current surge of medical and take-out food packaging use during the pandemic—have exacerbated the environmental burden. This impels the development of alternative recycling/upcycling methods to pivot toward circularity. We report the use of the Mannich three-component coupling reaction for the modification of polystyrene (PS) recovered with a 99.1% yield from waste food containers to form functionalized nitrogen and oxygen-rich PS derivatives. A series of functionalized PS with increasing moles of formaldehyde (F) and morpholine (M) (0.5 × 10−2, 1.0 × 10−2, and 2.0 × 10−2 mol) was achieved using a sol–gel-derived Fe-TiO2 catalyst in a solvent-free, microwave-assisted synthesis. Modified polymers were characterized with viscometry, 1H NMR, 13CNMR (DEPT) FTIR, XPS, UV, and TGA. Functionalization scaled with an increasing ratio, validating the 3CR approach. Further functionalization was constrained by a competing oxidative degradation; however, the varying hydrogen bond density due to nitrogen and oxygen-rich species at higher ratios was shown to compensate for molecular weight loss. The integration of the N-cyclic quaternary ammonium cations exhibited the potential of functionalized polymers for ion-exchange membrane applications.

Keywords

• polymer functionalization
• circular design
• waste commodity polystyrene
• multicomponent reactions
• C-H activation
• sol–gel catalyst