Strategies to Improve the Sustainability of Silicone Polymers.

Silicones underpin an enormous range of simple and advanced technologies. Often, only small quantities of silicone are used to enable a technology such that, on a "per use" basis, one might suppose the environmental impact is low. However, silicone preparation processes have a very high carbon footprint, and billions of kg are produced each year. To provide context to the consideration of new strategies to improve silicone sustainability, we first outline traditional silicone chemistry and then describe strategies to improve the degree to which silicones are green, sustainable and circular. One strategy involves dilution of the silicone oil or elastomer by tethering organic entities, particularly natural products, that may provide new properties including facilitated degradation in nature at end-of-life. A greater focus is given to strategies that permit extensive reuse and repurposing of oils and elastomers (e.g., with thermoplastic elastomers), before the silicone undergoes recycling. Each reuse, repurposing or recycling step reduces the net carbon footprint. These mostly involve straightforward, high-yielding organic chemical processes that work efficiently in a silicone milieu. Silicones will eventually end up in the environment, where linear oils are known to rapidly degrade, particularly when compared to organic polymers. Alternative strategies that permit triggered or biological degradation of oils and, more importantly elastomers, are described, including enzymatic degradation and composting.