Substitution reactions for upcycling non-biodegradable commodity polymers

The post-modification of polymers via substitution reactions gained attention as a sustainable alternative to conventional waste management strategies. This review explores advancements in substitution reaction on non-biodegradable commodity polymers, including polystyrene (PS), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). The post-modification strategies for each of these materials were discussed according to their peculiar chemical properties. PS, with its electron-rich aromatic rings, was studied as a substrate for electrophilic substitution reactions. PP and PE, due to their inert nature, required a pre-functionalization step to introduce suitable leaving groups for nucleophilic substitution reactions. The presence of labile chlorine atoms in PVC made this polymer a natural candidate for nucleophilic substitution reactions. Finally, the depolymerization of PET via nucleophilic acyl substitution reactions was discussed. Different types of advanced materials were prepared via substitution reactions of these polymers, focusing on the modification of waste products. Some examples include the preparation of ion exchangers, aerogels, catalyst immobilizers and metal-organic frameworks. Despite significant progress in the field, several challenges remain, including harsh reaction conditions, polymer chain degradation, and the need for more sustainable reagents. To address these problems, recent studies focused on greener methodologies with milder reaction conditions and the use of bio-based electrophilic and nucleophilic compounds. This review provides an overview of substitution reactions as a versatile tool for the post-modification of polymer waste into highly valuable products, paving the way for more sustainable plastic upcycling strategies.