Depolymerization protocol for linear, branched, and crosslinked end‐of‐life silicones with boron trifluoride diethyl etherate as the depolymerization reagent

Abstract

An important issue for current society is the accumulation of large amounts of end-of-life polymers, which are mainly deposited in landfills, converted by thermal recycling or down cycling to low-quality materials. In contrast to that, the feedstock recycling of end-of-life polymers to produce new high-quality polymers is only applied to a small portion of waste. In more detail, lowmolecular weight chemicals are generated by this methodology; they can be polymerized in a second step to produce new highquality polymers. Notably, with these depolymerization-polymerization processes, contributions to a more sustainable, resourceconserving, and environmentally benign society can be made. In this regard, we have set up a capable protocol for the depolymerization of polysiloxanes, which are applied extensively in numerous technological applications. Boron trifluoride diethyl etherate was used as a depolymerization reagent to transform SiAO bonds in linear, branched, and crosslinked silicones to SiAF bonds. As depolymerization products, difluorodimethyl silane for linear polysiloxanes and methyl trifluorosilane for branched polysiloxanes were obtained; these were suitable synthons for new polymers and will allow an overall recycling of polysiloxanes.

Full Circle Recycling of Polysiloxanes via Room-Temperature Fluoride-Catalyzed Depolymerization to Repolymerizable Cyclics

“…24−32 These methods range from thermal 27−33 to chemical breakdown (by catalytic or stoichiometric reagent) processes. 5,[27][28][29]34 The earliest methods used thermal energy, often with steam, to impart breakdown to both identifiable and unidentifiable components. 22,35−39 These methods typically result in a broad distribution of products.…”

Insights on toxicity, safe handling and disposal of silica aerogels and amorphous nanoparticles

“…Several depolymerization pathways and reagents have been tested. [145][146][147] Döhlert et al 148 have shown that boron trifluoride dietherate (BF 3 •OEt 2 ) is able to break the siloxane bond in hexamethyl disiloxane (1) -Scheme 2(a). Based on this, the depolymerization of poly(dimethyl siloxane) (4) has also been successfully tested (Scheme 2(b)).…”

“…Environmental Science: Nano Critical review Following this work, the same group has concluded that the depolymerizing effect of BF 3 •OEt 2 (2) does not depend on the structure of the polysiloxane, thus it can also be used for branched and crosslinked polysiloxanes. 147 In all reported cases, the depolymerization products can be used for the synthesis of new high-quality polymers.…”

“…Benzoylchloride and FeF 3 provided the best conditions in terms of depolymerization yield for the formation of dichlorodimethylsilane. 147 This strategy, based on the cleavage of a Si-O bond to produce a Si-X bond (X:F or Cl) 155,156 allows to aim the reuse of monomers to produce new polymers 155 as well as to obtain conditions for the production of benzoyl chloride or fluoride (see Scheme 2(c)), and thus to achieve a circular approach.…”

Solvothermal Alcoholysis Method for Recycling High-Consistency Silicone Rubber Waste

“…Enthaler and colleagues reported synthetic protocols for the depolymerization of various silicone oils (with M n from 0.5 to 110 kDa). They used benzoyl fluoride, boron trifluoride dietherate, a fatty acid anhydride, or combinations of benzoyl chloride or benzoic anhydride with KF to synthesize fluorosilane and fluorodisiloxane derivatives of Me 2 SiF 2 and (Me 2 SiF) 2 O for linear polymers, and Me 2 SiF 2 and SiF 4 for branched polymers. − The obtained fluorinated compounds are attractive starting materials and can be easily polymerized in the presence of H 2 O and NaOH to produce new silicones and NaF . Depolymerization methods were also developed in which catalytic amounts of FeCl 3 or ZnX 2 (X = acac, OAc, or OTf) were used. , The same group also reported the use of poly­(methylhydrosiloxane) in H 2 evolution by methanolysis, deoxygenation of sulfoxides to sulfides, and hydrodeoxygenation of fatty esters to hydrocarbons, prior to the depolymerization procedure described above .…”