Shi Limiao, Boulègue-Mondière Aurélie, Blanc Delphine, Baceiredo Antoine, Branchadell Vicenç, Kato Tsuyoshi
Laboratoire Hétérochimie Fondamentale et Appliquée (UMR 5069), Université de Toulouse, CNRS, F-31062 Toulouse, France.
Elkem Silicones, ATRiON, 69190 Saint-Fons, France.
Science. 2023 Sep;381(6661):1011-1014. doi: 10.1126/science.adi1342. Epub 2023 Aug 31.
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 without producing undesirable cyclic oligosiloxanes.
与硅氧烷合成相关的一个长期存在的问题是聚合物产品被10%至15%的环状低聚硅氧烷污染，这是由聚合物链端的回咬反应导致的。这个过程与环状单体通过开环聚合（ROP）进行的链增长相互竞争，被认为是不可避免的，并且通常会导致形成热力学控制的反应混合物（聚合物/环状低聚硅氧烷 = 85/15）。在此，我们报道简单的醇与阴离子链端配位可防止回咬过程，并且精心设计的鏻阳离子在配位醇失去时作为自猝灭系统，在回咬过程开始前停止反应。这两种效应的结合使得八元硅氧烷环D能够进行热力学控制的ROP，而不会产生不需要的环状低聚硅氧烷。
