Understanding the competition between hydrodechlorination and Friedel–Crafts alkylation in PVC dechlorination with silylium ions

Abstract

The combination of hydrodechlorination and Friedel–Crafts alkylation using silylium ions is a rapid route to fully dechlorinate poly(vinyl chloride) (PVC), while producing organic and chlorine-based products that have value for a second life. This silylium reaction has been optimized for full dechlorination under ambient conditions for a range of temperatures. Additionally, tetramethyldisiloxane is introduced as a cheaper and more moisture-stable silane, which shows similar activity as triethylsilane. While high selectivity for Friedel–Crafts alkylation has been achieved for molecular silylium chemistry, analogous attempts with PVC as a substrate have revealed a maximum arene incorporation below 30%. However, reaction conditions and choice of aromatic solvent show dramatic changes in thermal properties of the polyethylene-co-poly(vinyl arene) polymer product. These differences in thermal properties align with a variable side reaction of secondary Friedel–Crafts alkylation, either intramolecularly to form polyindene repeating units or intermolecularly to form crosslinks.