Depolymerization of polydimethylsiloxanes in ammonia – a new approach to silicone recycling†

This work presents a new approach to recycling silicone waste: depolymerization in ammonia. The optimal depolymerization conditions (150 °C, 0.25 mL H₂O, 24 h) to achieve complete polymer conversion were developed using a model siloxane fluid PMS-200. The method performance was demonstrated on model unfilled silicone rubbers obtained by classical methods of curing silicone elastomers such as hydrosilylation, condensation of functional groups and radical polymerization in the presence of benzoyl peroxide. The versatility of this approach for recycling both linear silicones (fluids and gums) and filled rubbers (fillers of different nature) was demonstrated. The completeness of the depolymerization and the analysis of the low molecular weight products were tested by SEC, GC and ²⁹Si NMR spectroscopy. The scalability of the process has been demonstrated.