2023-09-12 09:30:01
The synthesis of silicones is accompanied by the formation of cyclic oligosiloxanes, small molecules potentially toxic to the environment and health. A team of researchers is proposing a new catalytic system that helps prevent their formation.
Silicones are used in many fields, from cosmetics to aerospace. However, during their industrial synthesis from octamethylcyclotetrasiloxane (D4), 10 to 15% of cyclic oligosiloxanes are formed. These small molecules are potentially toxic to the environment and suspected of being endocrine disruptors. The REACH directive requires manufacturers to eliminate them to limit contamination of finished products to 0.1%.
To prevent the formation of these cyclic oligosiloxanes, a team of scientists from the fundamental and applied heterochemistry laboratory (CNRS/University of Toulouse Paul Sabatier) as well as the company Elkem Silicones have just developed a new process. They publish their results in Science this September 1st.
Avoid the formation of cyclic oligosiloxanes
When manufacturing polysiloxane chains, two reactions compete: propagation of the polymer chain by ring-opening polymerization of cyclic monomers and backpolymerization at the ends of the polymer chain. “During polymerization, the end of the chain is active: the polymer grows by grafting the monomers, but it can also come back on itself and break the chain, which results in the production of small cyclic oligosiloxanes”explains Antoine Baceiredo, research director at CNRS and co-author of the study.
As part of this study, the researchers developed a new basic catalytic system (phosphonium alkoxide) for the synthesis of silicones by ring opening. By adding an alcohol to the medium, they avoid retropolymerization, leading to controlled polymerization of D4 without producing undesirable cyclic oligosiloxanes. “We exceed 99.9% yield, there is no formation of cyclic oligosiloxanes, there simply remains a little unreacted monomerassures Antoine Baceiredo. Alcohol serves as an initiator and is consumed as polymerization progresses. The chain can only grow, and when there is no more alcohol, the catalyst self-destructs. »
The project has shown the effectiveness of the synthesis in the laboratory, other tests are underway. Although the industrial benefits might be significant, there is still a long way to go before we see the process applied in factories. “For an industrial reaction, it is necessary to make the catalyst more robust, to be strong enough, to be handled by the worker and profitable for the industrialist”warns Antoine Baceiredo.
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