Divergent silylium catalysis enables facile poly(vinyl chloride) upcycling to poly(ethylene-co-styrene) derivatives

Abstract

Tandem hydrodechlorination/Friedel–Crafts alkylation of poly(vinyl chloride) (PVC) is achieved using silylium ion catalysts to prepare new styrenic copolymers of polyethylene.

Catalytic tandem dehydrochlorination–hydrogenation of PVC towards valorisation of chlorinated plastic waste

“…Additionally, the PVC does not have to be pretreated by drying before reaction because dehydrochlorination–hydrogenation promoters are not as sensitive to moisture. 10 The double bond content of the product can be tuned by varying the concentration of the Rh hydrogenation catalyst. The active Rh species was found to be of ionic nature, and to occur predominantly as homogeneous Rh chloride complexes, which are formed in the ionic liquid medium during the PVC dehydrochlorination reaction.…”

“…Minimal catalyst use, and avoiding stoichiometric reagents for dehydrochlorination such as silanes or metal hydrides, are important criteria on the road to a sustainable process that allows to tune the polymer product. [10][11][12]…”

“…Of the very few reports on such tandem transformations of PVC, a recent study demonstrated a tandem dechlorination–reduction–Friedel–Crafts alkylation. 10 While this divergent silylium catalysed process effectively converts PVC to polyethylene–polystyrene-like copolymers, it requires stoichiometric amounts of Et 3 SiH, produces Et 3 SiCl as a by-product and consumes part of the aromatic solvent for functionalization of the polymer backbone. So far, no atom efficient methods for PVC valorisation exist, that avoid simultaneous incorporation of carbon groups on the polymer backbone.…”

Precise activation of C–C bonds for recycling and upcycling of plastics

“…The challenges associated with plastic upcycling arise not only from the activation of C aliph –C aliph bonds but also from the poisoning and deactivation of active sites caused by the presence of unmanageable chlorine elements in the feedstock, such as polyvinyl chloride (PVC). 127–130 For instance, Pidko et al illustrated through a DFT study that the presence of Cl atoms in polyolefins significantly inhibits the performance of catalysts. The Cl atoms can form stable molecular complexes with the catalyst, thereby increasing the energy barrier for the activation of C–H bonds as the initial step.…”

“…127 (2) The Cl-transfer strategy involves converting the chlorine element in PVC into Cl-containing organic and inorganic salts. 128,129,132,133 The dechlorinated polyethylene (PE)-like polymer can then be further cleaved into value-added short-chain alkanes. The main distinguishing factor between PVC and PP/PE is the presence of polar chlorine atoms (Fig.…”