Designing recyclable inorganic-organic hybrid polymer coatings through integrating silicone-based molecular scission points

Abstract

Inorganic-organic hybrid polymer coatings (IOHPCs) enhance the sustainability and the quality of life during their use e.g., as PFAS-free hydrophobic coatings on glass surfaces. Yet, their modular and complex structure poses significant challenges for end-of-life recycling. This work introduces, for the first time, the concept of using silicone chains as molecular scission points in IOHPCs, making the entirel material accessible to existing recycling techniques. Therefore, we integrated polydimethylsiloxane (PDMS) chains with different concentrations (4 -20 mol%) and mass average molar masses (Mw 550 and 3400 g/mol) into the IOHPC matrix. The resulting coatings consistently exhibited a hydrophobic character (89 -110 ° contact angle against water) with tunable pencil hardness covering the full range from very soft 6B to very hard 6H. We applied a room-temperature (RT) silicone recycling technique using catalytic amounts of tetrabutylammonium fluoride (TBAF) in ethyl acetate (EtOAc) or tetrahydrofuran (THF), thereby, selectively cleaving and separating the silicone bonds from the complex material by fluoride-induced backbiting in a single step. The silicone depolymerization yielded soluble cyclic siloxanes with D4 as the main product across all investigated formulations. Upcycling of cyclic siloxanes via ring opening reactions yielded linear PDMS. The hybrid matrix components precipitated as a solid during the depolymerization process and were isolated by centrifugation showing only few remaining PDMS moieties. Accordingly, the substrate was completely delaminated, remained intact, and was still reusable after four delamination cycle. This study demonstrates that recyclability can be successfully integrated into the design phase of IOHPC, making them compatible with existing recycling techniques, without compromising on performance while additionally enabling substrate recovery.