Highly Polarized Olefins: Enabling Polymerization Catalysts for Homo- and Copolymers Based on “Non-Polymerizable” gamma-Butyrolactone

本项目旨在开发实用、高效的（co）聚合工艺，以利用γ -丁内酯（GBL）用于材料科学。由于不利的热力学条件，这种五元环酯在作为单体应用时一直被忽略；直到最近，只有低聚物才会在最恶劣的条件下产生。然而，新的研究揭示了聚（GBL）作为一种完全可回收，可调节的聚酯的引人注目的特性，其中关键的原料，GBL，是丰富的，廉价的和潜在的生物来源。为了充分释放聚合物化学的潜力，必须开发相应的聚合催化，使其超越目前这种特定单体的基本状态。为此，建议采用一类特殊的烯烃- n -杂环烯烃（NHOs）作为一种新的工具来推进GBL的同构和共聚。NHOs固有地消除了迄今为止制备确定聚（GBL）的一些复杂问题，并且另外实现了对进一步改进至关重要的可选聚合途径，即两性离子聚合和阴离子对合作路易斯聚合。虽然更好地了解GBL均聚反应将是有益的，但热力学约束总是严重限制了适用反应条件的范围，给经济实现带来了挑战。共聚技术可以规避这些限制，因此是一种非常有前途的替代方案，可以实现GBL的有效利用，这将是本项目的重点。将遵循两种互补策略来制备高gbl含量的共聚物。首先，这将是交替共聚，以3,4-二氢香豆素为共聚单体。第二种策略侧重于与omega- pentadecal内酯或1,2-butylene oxide共聚，产生含gbl的共聚聚酯或共聚（酯醚）。一个新的概念，NHO/金属卤化物刘易斯对对内酯的单体选择性活化，将被采用并系统地研究，以优先激活GBL而不是其共聚单体，从而直接操纵共聚参数。本项目中提出的nho介导的催化将使人们能够获得目前无法获得但又非常需要的聚合物。这包括（可降解的）gbl衍生的聚（酯醚）s；此外，聚（GBL）本身的制备也将受益，因为目前这种有趣的材料由于缺乏对端基、分子量（分布）和拓扑结构的控制，其适用性受到限制。

This project aims for the development of practicable, efficient (co)polymerization processes to utilize gamma-butyrolactone (GBL) for materials science. This five-membered cyclic ester has historically been largely ignored for application as monomer on account of adverse thermodynamics; until recently, only oligomers would result from the harshest of conditions. However, new research has revealed the compelling properties of poly(GBL) as a fully recyclable, tunable polyester, whereby crucially the feedstock, GBL, is abundantly available, cheap and potentially bio-sourced. To fully unlock this potential for polymer chemistry, the corresponding polymerization catalysis must be developed beyond its current rudimentary state regarding this specific monomer. To this end, it is proposed to employ a special class of olefins – so-called N-heterocyclic olefins (NHOs) – as a novel tool to advance GBL homo- and copolymerization. NHOs inherently eliminate some of the issues complicating the preparation of defined poly(GBL) to date, and additionally enable alternative polymerization pathways which are considered crucial for further improvement, namely zwitterionic polymerization and anionic polymerization by cooperative Lewis pairs.While a better understanding of GBL homopolymerization will be rewarding, thermodynamic constraints will always severely limit the range of applicable reaction conditions, imposing a challenge for economic realization. Copolymerization, where some of these limitations can be circumvented, is therefore a highly promising alternative to achieve efficient utilization of GBL and will be a focus of this project. Two complementing strategies will be followed to prepare high GBL-content copolymers. For one, this will be alternating copolymerization, using 3,4-dihydrocoumarin as comonomer. The second strategy concentrates on copolymerization with omega-pentadecalactone or with 1,2-butylene oxide, resulting in a GBL-containing copolyester or copoly(ester-ether). A novel concept, monomer-selective activation of lactones by NHO/metal halide Lewis pairs, will be employed and systematically investigated to preferentially activate GBL over its comonomers resulting in a direct manipulation of the copolymerization parameters.The NHO-mediated catalysis as proposed in this project shall enable access to polymers which are currently not available, yet highly desired. This includes (degradable) GBL-derived poly(ester-ether)s; also, the preparation of poly(GBL) itself will profit, since presently this interesting material is limited in its applicability by a lack of control over end groups, molecular weight (distribution) and topology.