Naumann Stefan, Klein Johannes, Wang Dongren, Buchmeiser Michael R
Institute for Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstraße 34-36, Berlin, Germany.
Beilstein J Org Chem. 2015 Nov 20;11:2261-6. doi: 10.3762/bjoc.11.246. eCollection 2015.
The polymerization of octamethylcyclotetrasiloxane (D4) is investigated using several five-, six- and seven-membered N-heterocyclic carbenes (NHCs). The catalysts are delivered in situ from thermally susceptible CO2 adducts. It is demonstrated that the polymerization can be triggered from a latent state by mild heating, using the highly nucleophilic 1,3,4,5-tetramethylimidazol-2-ylidene as organocatalyst. This way, high molecular weight PDMS is prepared (up to >400 000 g/mol, 1.6 < Ð M < 2.5) in yields >95%, using low catalyst loadings (0.2-0.1 mol %). Furthermore, the results suggest that a nucleophilic, zwitterionic mechanism is in operation, in preference to purely anionic polymerization.
使用几种五元、六元和七元氮杂环卡宾（NHC）研究了八甲基环四硅氧烷（D4）的聚合反应。催化剂由热敏感的二氧化碳加合物原位提供。结果表明，使用高亲核性的1,3,4,5-四甲基咪唑-2-亚基作为有机催化剂，通过温和加热可从潜伏状态引发聚合反应。通过这种方式，使用低催化剂负载量（0.2 - 0.1 mol%），以>95%的产率制备了高分子量聚二甲基硅氧烷（高达>400 000 g/mol，1.6 < Ð M < 2.5）。此外，结果表明，优先发生的是亲核两性离子机理，而非纯粹的阴离子聚合。
