Catalytic Hydrosilylation Deoxygenation: Synthesizing Polysiloxanes While Upcycling Polymers to Alkanes

Developing new approaches to fabricate polysiloxane with versatile structures is a challenging project. Meanwhile, sustainable plastic upcycling is an essential issue that needs to be solved urgently. We reported herein a new strategy for synthesizing polysiloxanes by B(C₆F₅)₃-catalyzed hydrosilylation deoxygenation polymerization, which simultaneously degraded the oxygenated polymers like polyethers and polyesters to alkanes. Steric hindrance around the C-O/C = O bonds of these polymers and their solubility, as well as the reaction conditions affected the efficiency of Si-O bond construction and the degree of C-O/C = O bond cleavage. This synthon exhibited generality, enabling the synthesis of various polysiloxanes with adjustable M_n (up to 79.6 kDa) and broad T_g values (-19.9 to -133.9°C), which are difficult to access with the current methods. Moreover, it is tolerant to functional groups that vinyl-modified polysiloxanes have been obtained via the tandem hydrosilylation/deoxygenation and Piers-Rubinsztajn reaction. These vinyl-modified polymers can further transform into re-processable materials with excellent mechanical properties through constructing a dynamically crosslinking bond of borate ester. Density functional theory (DFT) studies revealed that the deoxygenation polymerization proceeds via alkoxysilane intermediates to generate siloxanes, which was confirmed by NMR spectrum monitoring of the model reactions. This work establishes an unprecedented polymer-to-polymer upcycling and provides a platform for fabricating polysiloxanes, bypassing tedious monomer synthesis and purification.