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Peer-reviewedCC BY-NC-ND 4.0ACS Omega

Fluoride-Free Siloxane Circularity at Room Temperature: Tetrabutylammonium Hydroxide as a Dual-Functional De- and Repolymerization Initiator for Silicone Oils, Elastomers, and Hybrid Coatings

  • Christopher Fischer1,2
  • Dominik Zupaniec1,2
  • Diana Lau1
  • Claudia Stauch1
  • Katja Scherbaum1
  • Jochen Moesslein3
  • Dirk Wacker3
  • Gerhard Sextl1,2
  1. 1Fraunhofer Institute for Silicate Research , Neunerplatz 2 , ,
  2. 2Julius Maximilians University Würzburg , , Röntgenring 11 , ,
  3. 3Polysecure GmbH , Sankt-Georgener Straße 19 , ,
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Abstract

With increasing EU restrictions on fluoride chemistries and their toxicity related to the potential generation of hydrofluoric acid (HF) as well as their corrosivity, there is an urgent need to develop fluoride-free depolymerization methods to enable safe and sustainable siloxane recycling. In this regard, we here present a fluoride-free, at room-temperature (RT) operating depolymerization method, where tetrabutylammonium hydroxide (TBAOH), identified as a highly effective dual-functional de- and repolymerization initiator, transforms silicone-based elastomers into reusable cyclic siloxanes. Thereby, the solvent/polymer ratio (v/w) is the key for controlling the product distribution: at 10/1 (v/w), the depolymerization mixture shifts from D4-rich to high proportions of byproducts greater than 40 mol % and ultimately stops the process, leaving solid educt silicone at even lower dilutions. Under optimized reaction conditions above a threshold of 0.29/1 (w/w) for the TBAOH/polymer ratio, a relative proportion of up to 88 mol % cyclic siloxanes (D3 to D5), with D4 as the main product, is obtained. This corresponds to 77 mol % absolute NMR conversion into cyclic siloxanes. Additionally, it is worth noting that the fluoride-free, RT operating reaction conditions are effective for a very broad educt scope ranging from linear polydimethylsiloxane (PDMS) oils, (filled) Pt-cross-linked silicone elastomers, to inorganic–organic hybrid polymers and coatings. Compared to sodium hydroxide (NaOH) as an alkaline reference, TBAOH affords fewer noncyclic byproducts (12–26 mol % vs 25–30 mol %) and a higher D3 (4–14 mol % vs 1–3 mol %) relative proportion, highlighting its distinct reactivity. Fluoride-free siloxane circularity is demonstrated at RT by two complementary repolymerization routes. Within the first method, TBAOH uniquely acts as the initiator for both the depolymerization and the subsequent anionic ring-opening polymerization (AROP) without prior workup, while the second involves the isolation of cyclic siloxanes followed by base-catalyzed AROP. Thus, this TBAOH-enabled, fluoride-free depolymerization method, which operates at RT, provides tunable product distributions and a broad substrate applicability for practical silicone circularity.

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Cite

BibTeXRIS
BibTeX
@article{fischer2026fluoridefree,
  title = {{Fluoride-Free Siloxane Circularity at Room Temperature: Tetrabutylammonium Hydroxide as a Dual-Functional De- and Repolymerization Initiator for Silicone Oils, Elastomers, and Hybrid Coatings}},
  author = {Christopher Fischer and Dominik Zupaniec and Diana Lau and Claudia Stauch and Katja Scherbaum and Jochen Moesslein and Dirk Wacker and Gerhard Sextl},
  journal = {ACS Omega},
  year = {2026},
  month = nov,
  doi = {10.1021/acsomega.6c07298},
  url = {https://pubs.acs.org/acsodf/article/doi/10.1021/acsomega.6c07298/5463372/Fluoride-Free-Siloxane-Circularity-at-Room},
  note = {CC BY-NC-ND 4.0},
}
RIS
TY  - JOUR
TI  - Fluoride-Free Siloxane Circularity at Room Temperature: Tetrabutylammonium Hydroxide as a Dual-Functional De- and Repolymerization Initiator for Silicone Oils, Elastomers, and Hybrid Coatings
AU  - Christopher Fischer
AU  - Dominik Zupaniec
AU  - Diana Lau
AU  - Claudia Stauch
AU  - Katja Scherbaum
AU  - Jochen Moesslein
AU  - Dirk Wacker
AU  - Gerhard Sextl
PY  - 2026
DA  - 2026/11/04
JO  - ACS Omega
DO  - 10.1021/acsomega.6c07298
UR  - https://pubs.acs.org/acsodf/article/doi/10.1021/acsomega.6c07298/5463372/Fluoride-Free-Siloxane-Circularity-at-Room
AB  - With increasing EU restrictions on fluoride chemistries and their toxicity related to the potential generation of hydrofluoric acid (HF) as well as their corrosivity, there is an urgent need to develop fluoride-free depolymerization methods to enable safe and sustainable siloxane recycling. In this regard, we here present a fluoride-free, at room-temperature (RT) operating depolymerization method, where tetrabutylammonium hydroxide (TBAOH), identified as a highly effective dual-functional de- and repolymerization initiator, transforms silicone-based elastomers into reusable cyclic siloxanes. Thereby, the solvent/polymer ratio (v/w) is the key for controlling the product distribution: at 10/1 (v/w), the depolymerization mixture shifts from D4-rich to high proportions of byproducts greater than 40 mol % and ultimately stops the process, leaving solid educt silicone at even lower dilutions. Under optimized reaction conditions above a threshold of 0.29/1 (w/w) for the TBAOH/polymer ratio, a relative proportion of up to 88 mol % cyclic siloxanes (D3 to D5), with D4 as the main product, is obtained. This corresponds to 77 mol % absolute NMR conversion into cyclic siloxanes. Additionally, it is worth noting that the fluoride-free, RT operating reaction conditions are effective for a very broad educt scope ranging from linear polydimethylsiloxane (PDMS) oils, (filled) Pt-cross-linked silicone elastomers, to inorganic–organic hybrid polymers and coatings. Compared to sodium hydroxide (NaOH) as an alkaline reference, TBAOH affords fewer noncyclic byproducts (12–26 mol % vs 25–30 mol %) and a higher D3 (4–14 mol % vs 1–3 mol %) relative proportion, highlighting its distinct reactivity. Fluoride-free siloxane circularity is demonstrated at RT by two complementary repolymerization routes. Within the first method, TBAOH uniquely acts as the initiator for both the depolymerization and the subsequent anionic ring-opening polymerization (AROP) without prior workup, while the second involves the isolation of cyclic siloxanes followed by base-catalyzed AROP. Thus, this TBAOH-enabled, fluoride-free depolymerization method, which operates at RT, provides tunable product distributions and a broad substrate applicability for practical silicone circularity.
SN  - 2470-1343
ER  -