Selectively Cleavable Silicone Elastomers Based on Acetal Cross‐Linkers: Synthesis, Properties, and Study of Chemical Degradation

ABSTRACT Silicone elastomers are widely used polymers with unique properties, but no recycling process is established so far due to their cross‐linked network and chemical stability. Cleavable functional groups can be introduced into silicone elastomers to facilitate their degradability. In this study, we report on the synthesis of selectively cleavable silicone elastomers based on acetal cross‐linkers incorporated by hydrosilylation. Acetal cross‐linkers 1,1‐bis(2‐propen‐1‐yloxy)hexane (HexAc), [bis(2‐propen‐1‐yloxy)methyl]benzene (BenzAc), and 1,3‐bis‐{4‐[(allyloxy)methyl]‐1,3‐dioxolan‐2‐yl}‐propane (GluAc) were synthesized and introduced into a silicone formulation of vinyl‐terminated polydimethylsiloxane (Vi‐PDMS) and tetrakis(dimethylsiloxy)silane (TDMSS) using Karstedt 's catalyst for catalyzing the cross‐linking reaction. The acetal‐containing silicones show similar mechanical and thermal properties compared to a reference silicone without acetals. Silicone elastomers with 10 wt.‐% of acetal cross‐linkers degrade quickly and selectively at 50°C in the presence of THF and 0.1 M HCl 9:1 (w:w) while Si–O bonds remain intact at these conditions. These results show the promising potential of using cleavable acetal cross‐linkers as additives in industrially established silicone formulations without the need for novel manufacturing processes. To the best of our knowledge this is the first reported case where cleavable acetal groups were introduced into silicone elastomers by hydrosilylation.