Depolymerization/functionalization of silicones in mild conditions: A “Back-to-polymers” strategy to turn wastes into up-cycled polymers

Résumé fourni par la source

Silicones based on polydimethylsiloxanes are widely-spread materials owing to their exceptional mechanical, thermal and chemical properties and biocompatibility, among other characteristics. As for any other man-made plastics, recycling silicone-based materials appears essential to transition to a more sustainable production model, lowering the amount of waste that is then turned into valuable building blocks. While conventional processes of chemical recycling of silicones generally describe the recovery of cyclic organosiloxane monomers, herein we introduce an efficient and robust method that produces polymers instead with limited amount of produced cycles (<2 wt%). It relies on reactions carried out at room temperature that use 4-dodecylbenzene sulfonic acid combined with dialkysiloxanes as chain transfer agents. When starting from a polydimethylsiloxane oil, linear polymer chains are obtained with molecular weight lower than the one of the initial substrates, that can be tuned by both the acid and dialkysiloxane contents. A variety of end-cappers (molecular, oligomeric or polymeric; non-functionalized or functionalized with Si-vinyl or Si-H groups) were successfully used, and a mechanism in agreement with the experimental results is suggested. Our method not only applied on silicone oils but also on filler-free crosslinked polymers and some manufactured silicone elastomers . It is shown that when functionalized with either Si-vinyl or Si-H groups, the so-called “ recycled ” polymers can act as reactive precursors for the preparation of novel silicone elastomer by hydrosilylation reaction. An example of an elastomer made from 100 % recycled silicones is presented. Therefore, our approach represents a robust way to obtain reactive silicone precursors by “upgrading” initially inert oils or by “upcycling” products originally intended to scrap, and in this sense can contribute to enriching circular models for silicone materials.

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