Degradation of silicone-based materials as a driving force for recyclability

Siloxane polymers are an important industrial commodity based on the structure -(R-2-Si-O)-. Scission of the siloxane bond is essential, as it is the first step leading to polymerization or the depolymerization of polymers into smaller units for potential recycling. These highly condition-specific reactions selectively trigger whether polymerization or breakdowns occur and have been extensively studied over the past 80 years. However, studies to recycle siloxanes are still in their infancy. Traditional methods to synthesize silicones involve high capital-intensive and environmental costs using carbothermal reduction. These reactions cause the excessive release of global warming gases such as CO2 and other pollutants into the environment. Therefore, being able to reuse and recycle them in a meaningful manner is highly sought. As a result, ways to controllably rupture the siloxane bond into known products have been a goal of siloxane researchers since the 1950s. Hydrolysis, catalytic depolymerization, thermal depolymerization and radical extractions are the main approaches to imbue the scission of the siloxane bond, resulting in a slew of products, including new polymers, cyclics or monomeric silanes. The present review summarizes the available published data on the degradation and depolymerization of polysiloxanes published up to July 2021. (c) 2021 Society of Industrial Chemistry.