Department of Chemistry Stanford University , Stanford, California 94305, United States.
J Am Chem Soc. 2013 Dec 18;135(50):18738-41. doi: 10.1021/ja409843v. Epub 2013 Dec 5.
The zwitterionic ring-opening of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (TMOSC) with N-heterocyclic carbenes generates high molecular weight cyclic p(TMOSC). The NHC-mediated polymerization of TMOSC with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes, 1) generates the poly(carbosiloxane) p(TMOSC) with molecular weights from 27,000 < Mn < 80,000 Da (1.4 < Mw/Mn < 2.2) within 30 min at room temp. With the more nucleophilic carbene 1,3,4,5-tetramethyl-imidazol-2-ylidene (4), the ring-opening polymerization occurs within minutes at room temperature to generate cyclic p(TMOSC) with molecular weights up to Mn = 940,000 Da (Mw/Mn = 3.2). The resulting p(TMOSC)s are predominantly cyclic as evidenced by dilute solution viscosity studies and MALDI-TOF MS. DFT calculations provide support for both zwitterionic and neutral, cyclic intermediates.
2,2,5,5-四甲基-2,5-二硅杂-1-氧杂环戊烷（TMOSC）与 N-杂环卡宾（NHC）的两性离子开环反应生成高分子量的环状 p(TMOSC)。NHC 介导的 TMOSC 与 1,3-双(2,4,6-三甲基苯基)咪唑-2-亚基（IMes，1）的聚合反应在室温下 30 分钟内生成分子量为 27,000 < Mn < 80,000 Da（1.4 < Mw/Mn < 2.2）的聚（碳硅氧烷）p(TMOSC)。使用更亲核的卡宾 1,3,4,5-四甲基咪唑-2-亚基（4），开环聚合在室温下几分钟内发生，生成分子量高达 Mn = 940,000 Da（Mw/Mn = 3.2）的环状 p(TMOSC)。稀溶液粘度研究和 MALDI-TOF MS 证明所得的 p(TMOSC)主要是环状的。DFT 计算为两性离子和中性、环状中间体提供了支持。
