Shi L, Boulègue-Mondière A, Blanc D, Baceiredo A, Branchadell V, Kato T. Ring-opening polymerization of cyclic oligosiloxanes without producing cyclic oligomers.
Science 2023;
381:1011-1014. [PMID:
37651508 DOI:
10.1126/science.adi1342]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 07/31/2023] [Indexed: 09/02/2023]
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 D4 without producing undesirable cyclic oligosiloxanes.
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