ChemSusChem: Chemistry & Sustainability, Energy & Materials vol:7 issue:2 pages:610-617
There is an urgent need for green technologies to remove halogens from halogenated polymers at the end of their lifetime. Ionic liquids (ILs) were used to dehydrochlorinate and/or dissolve the chlorinated polymers poly(vinyl chloride) (PVC) and chlorinated polyethylene (CPE). The dehydrochlorination activity of an IL depends mainly on its anion and is related to the high hydrogen-bond-accepting ability (beta value) of the anion. Different phosphonium ILs successfully dissolve and dehydrochlorinate
PVC and CPE at temperatures from 808C. PVC is dehydrochlorinated up to 98% after 60 min in tetrabutylphosphonium chloride ([P4444][Cl]) at 180 8C. PVC pieces stabilized by calcium stearate (4 mm3) are dehydrochlorinated more slowly; conversions of 85 and 96% are reached after 1 and 8 h, respectively. Smaller pieces are dehydrochlorinated faster. High loadings, for example, 0.3 g stabilized PVC in 0.5 g IL, can be applied with only a minor loss of conversion. [P4444][Cl] proved to be stable during several consecutive reactions; after each run more than 99% of the IL can be recovered. The structure of the dehydrochlorinated PVC was studied by 13C cross-polarization magic-angle spinning NMR and FTIR spectroscopy; the removal of Cl and the formation of double bonds were confirmed.
Carefully dehydrochlorinated CPE was processed further by acyclic diene metathesis depolymerization with ethylene and the Hoveyda–Grubbs second-generation catalyst to yield alpha,gamma-dienes such as 1,5-hexadiene and 1,6-heptadiene.