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

该项目旨在开发实用、高效的(共)聚合工艺，将伽马-丁内酯(GBL)用于材料科学。由于不利的热力学，这种五元环酯作为单体的应用在历史上一直被忽视；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、可调节的聚酯的令人信服的特性，因此至关重要的是，原料GBL具有丰富的可获得性、廉价和潜在的生物来源。为了充分释放聚合物化学的这种潜力，必须开发相应的聚合催化剂，使其超越目前关于这种特定单体的基本状态。为此，有人建议使用一类特殊的烯烃-所谓的N-杂环烯烃(NHO)-作为一种新的工具来促进GBL均聚和共聚。NHO在本质上消除了迄今为止定义聚(GBL)制备过程中的一些复杂问题，并另外实现了被认为对进一步改进至关重要的替代聚合途径，即由合作的Lewis对进行的两性离子聚合和阴离子聚合。虽然更好地理解GBL均聚将是有益的，但热力学限制总是会严重限制适用反应条件的范围，对经济实现构成挑战。因此，共聚是实现GBL有效利用的一种非常有希望的替代方案，并且将是本项目的一个重点。采用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，使用3，4-二氢香豆素作为共聚单体。第二种策略集中于与欧米伽-十五内酯或1，2-丁二烯的共聚，得到含有GBL的共聚酯或共聚(酯-醚)。将采用一个新的概念，即通过NHO/金属卤化物Lewis对对内酯进行单体选择性活化，以优先激活GBL而不是其共聚单体，从而直接控制共聚参数。本项目中提出的NHO介导的催化将使人们能够获得目前尚不存在的、但非常需要的聚合物。这包括(可降解的)GBL衍生的聚酯醚S；此外，聚(GBL)的制备本身也将受益，因为目前这种有趣的材料的适用性受到端基、相对分子质量(分布)和拓扑结构缺乏控制的限制。

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.