Ring-opening polymerization of cyclic oligosiloxanes without producing cyclic oligomers.
basic_science · Level V
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- Record sourced from PubMed, PMID 37651508.
- Also identified by DOI 10.1126/science.adi1342.
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Abstract
A long-standing problem associated with silicone synthesis is contamination of the polymer products with 10 to 15% cyclic oligosiloxanes that results from backbiting reactions at the polymer chain ends. This process, in competition with chain propagation through ring-opening polymerization (ROP) of cyclic monomers, was thought to be unavoidable and routinely leads to a thermodynamically controlled reaction mixture (polymer/cyclic oligosiloxanes = 85/15). Here, we report that simple alcohol coordination to the anionic chain ends prevents the backbiting process and that a well-designed phosphonium cation acts as a self-quenching system in response to loss of coordinating alcohols to stop the reaction before the backbiting process begins. The combination of both effects allows a thermodynamically controlled ROP of the eight-membered siloxane ring D<sub>4</sub> without producing undesirable cyclic oligosiloxanes.