Vogler Charlotte, Naumann Stefan
University of Stuttgart, Institute of Polymer Chemistry 70569 Stuttgart Germany
RSC Adv. 2020 Dec 9;10(71):43389-43393. doi: 10.1039/d0ra08970b. eCollection 2020 Nov 27.
Triethyl borane (EtB), in combination with phosphazene-type superbases, has recently emerged as a powerful co-catalyst for the anionic polymerization of epoxides. Here, it is demonstrated that the monomer-activating property of EtB can also compensate for the application of much gentler organobases. This not only results in simpler setups, but also significantly reduces nucleophilicity/basicity-derived side reactions. Notably, this principle applies to such a degree that simple 4-dimethylaminopyridine (DMAP) or 1,4-diazabicyclo[2.2.2]octane (DABCO) can serve to polymerize propylene oxide (PO). With suitable initiators, this results for example in very well-defined block copolyethers ( ≤ 1.03) without requiring work-up to remove side products such as PPO homopolymer. Performance correlates nicely with the corresponding organobase proton affinities (PAs), and a limiting PA of 220-230 kcal mol was identified for successful PO polymerization.
三乙基硼（EtB）与磷腈类超强碱相结合，最近已成为环氧化物阴离子聚合的一种强大共催化剂。在此，证明了EtB的单体活化性能还可以弥补使用温和得多的有机碱的情况。这不仅导致装置更简单，而且还显著减少了亲核性/碱性衍生的副反应。值得注意的是，这一原理适用程度如此之高，以至于简单的4-二甲氨基吡啶（DMAP）或1,4-二氮杂双环[2.2.2]辛烷（DABCO）就可以用于使环氧丙烷（PO）聚合。使用合适的引发剂，例如这会得到定义非常明确的嵌段共聚醚（Đ≤1.03），而无需进行后处理以除去副产物，如聚环氧丙烷均聚物。性能与相应有机碱的质子亲和力（PAs）密切相关，并且确定成功进行PO聚合的极限PA为220 - 230 kcal mol⁻¹。
