Chiral Diboranes as Metal-free, Cooperative Catalyst Setups for the Stereoselective Polymerization of Propylene Oxide and other Substituted Epoxides

脂肪族聚醚通常衍生自环氧化物的开环聚合（ROP），是化学工业中最重要的产品之一，并且事实上在我们的日常生活中无处不在。然而，尽管取得了这一成功，但毫无例外，相关规模的聚合并没有将立体化学（立构规整度）的控制作为进一步优化聚醚基产品的明显调节位点（即，聚（环氧丙烷），PPO）。这在很大程度上归因于可用的有机金属催化剂的不相容性。该项目旨在开发一种无金属（有机催化）聚合装置，用于制备全同立构和全同立构富集（it）聚醚，关键是将定制的聚醚部分掺入更复杂的聚合物结构（嵌段共聚物）中。总体动机是识别和理解具有明显官能团耐受性的高度选择性、可扩展和用户友好的催化剂系统，以规避迄今为止阻止聚醚充分利用的关键问题。这些目标是通过建立在硼烷支持的ROP的取代的环氧化物观察到的合作聚合机制：通过连接两个硼烷官能团通过手性骨架，立体选择性，动力学有利的环境将被生成。具体的工作包将包括对催化剂调节位点（手性骨架、硼烷和骨架之间的连接体长度、硼中心的电子缺陷）的详细研究。结合关于PO聚合的系统筛选，应得到充分理解的结构-性能相关性，重点是立体选择性（如通过全同立构三单元组位置测量的，% mm）、TON、TOF和窄摩尔质量分布，旨在获得高选择性以产生半结晶聚醚（> 90% mm）。在该项目的后续阶段，这一原则将扩展到其他取代环氧化物（如1-环氧丁烷、烯丙基缩水甘油醚、氧化苯乙烯）和不同类型的大分子引发剂。重要的是，对于后者，敏感聚合物（即，聚酯、聚碳酸酯），以产生聚酯-嵌段-（IT）-聚醚（多）嵌段共聚物，从而解决了不能用已建立的催化装置制备的结构，并因此填补了迄今为止众所周知的阻碍聚醚基添加剂制造的空白。

Aliphatic polyethers, typically derived from the ring-opening polymerization (ROP) of epoxides, are among the most important products of chemical industry and de facto ubiquitous in our daily lives. Yet in spite of this success, without exception, polymerizations on relevant scale do not address control of stereochemistry (tacticity) as an obvious tuning site for a further optimization of polyether-based products (i.e., poly(propylene oxide), PPO). This is largely down to insufficiencies of the available organometallic catalysts. This project aims for the development of a metal-free (organocatalytic) polymerization setup for the preparation of isotactic and isotactic-enriched (it) polyethers, crucially targeting the incorporation of the thus tailored polyether moieties into more complex polymer architectures (block copolymers). The overall motivation is to identify and understand a highly selective, scalable and user-friendly catalyst system with pronounced functional group tolerance to circumvent the key issues which to date prevent utilization of polyethers to their full extent. These aims are to be achieved by building on the cooperative polymerization mechanism observed for borane-supported ROP of substituted epoxides: by connecting two borane functionalities via a chiral backbone, a stereoselective, kinetically favored environment will be generated. The specific work packages will include a detailed investigation of the catalyst tuning sites (chiral backbones, linker length between borane and backbone, electron deficiency at the boron centers). In conjunction with systematic screening regarding the polymerization of PO, a well understood structure-performance correlation should result, focusing on stereoselectivity (as measured by isotactic triad placement, % mm), TON, TOF and a narrow molar mass distribution, aiming for high selectivity to result in semi-crystalline polyether (> 90% mm). In a subsequent phase of the project, this principle is to be extended to other substituted epoxides (such as 1-butylene oxide, allyl glycidyl ether, styrene oxide) and different types of macroinitiators. Importantly, for the latter, sensitive polymers (i.e., polyesters, polycarbonates) will be selected to create polyester-block-(it)-polyether (multi)block copolymers, thereby addressing structures which cannot be prepared with established catalytic setups and thus filling a gap which to date notoriously aggravates the manufacture of polyether-based additives.