Introducing N-Heterocyclic Olefins as a Novel Class of Organocatalysts for Polymerization

引入 N-杂环烯烃作为一类新型聚合有机催化剂

• 批准号: 260748259
• 负责人: Professor Dr. Stefan Naumann
• 金额: --
• 依托单位: Institut für Makromolekulare Chemie
• 依托单位国家: 德国
• 项目类别: Research Fellowships
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2014-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/260748259?language=en
• 关键词: Introducing; Heterocyclic; Olefins; Novel; Class

The ultimate goal of this research is to establish N-heterocyclic olefins (NHOs) as a novel class of organocatalysts/organoinitiators for polymerization reactions, most notably for those monomers (acrylates and epoxides) that remain extremely challenging to polymerise by metal-free methods. Surprisingly, though NHOs have been shown to be excellent nucleophiles and electron density donors, they have not been applied for polymerization catalysis so far. NHOs retain the structural diversity of the related N-heterocyclic carbenes (NHCs) while offering a completely different activity, which is to act as latent, tuneable and completely organo-derived carbanions. The study described herein is therefore aimed at exploring the catalytic potential of NHOs and map out their reactivity profile regarding very different monomers. A range of differently constituted NHOs will be prepared and characterized. The structural motifs that are to be investigated shall include five- and six-membered NHOs fitted with N-alkyl and N-aryl substituents of varying steric demands and electronic properties. These NHOs shall be investigated as catalysts for polymerization of monomers that are susceptible to nucleophilic attack, e.g., epoxides, acrylic monomers and cyclic ester monomers. Special focus shall be put on situations where the range of suitable organocatalysts is still very limited, most notably for acrylates including methyl methacrylate (MMA), the commercially most important acrylate, or epoxide monomers like propylene oxide (PO). Screening suitable polymerization conditions (bulk, solvents, temperature, initiator loading) employing the different NHOs will enable correlation of NHO properties and NHO activity, allowing for the rational design of optimized catalysts. The polymerization mechanism, which is thought to be zwitterionic in nature, shall be elucidated by kinetic experiments and polymer characterization. The zwitterionic growth is expected to retain all the positive features that are found in (an)ionic polymerization (control over molecular weight, facile introduction of end groups), but at the same time offers the possibility to synthesise cyclic polymer architectures in a facile manner, a feature that is otherwise difficult to achieve in a metal-free way.

本研究的最终目标是将N-杂环烯烃(NHO)建立为一类新型的有机催化剂/有机引发剂，用于聚合反应，尤其是那些仍极具挑战性的无金属方法聚合的单体(丙烯酸酯和环氧化物)。令人惊讶的是，尽管NHO已被证明是优秀的亲核剂和电子密度供体，但到目前为止，它们还没有被应用于聚合催化。NHO保留了相关N-杂环卡宾(NHCs)的结构多样性，同时提供了完全不同的活性，即作为潜在的、可调节的、完全有机衍生的碳负离子。因此，这里描述的研究旨在探索NHO的催化潜力，并绘制出它们对非常不同的单体的反应性分布。将准备一系列不同构成的NHO并对其进行表征。要研究的结构模体应包括具有不同空间需求和电子性质的N-烷基和N-芳基取代基的五元和六元NHO。应研究这些NHO作为聚合易受亲核攻击的单体的催化剂，例如环氧化物、丙烯酸酯单体和环酯单体。应特别关注合适的有机催化剂范围仍然非常有限的情况，最明显的是用于丙烯酸酯，包括商业上最重要的丙烯酸酯-甲基丙烯酸甲酯(MMA)，或环氧化物单体，如环氧丙烷(PO)。利用不同的NHO筛选合适的聚合条件(体积、溶剂、温度、引发剂用量)，可以关联NHO的性质和NHO的活性，从而合理地设计优化的催化剂。聚合机理被认为是两性离子的，应通过动力学实验和聚合物表征来阐明。两性离子生长有望保留离子聚合中发现的所有积极特征(控制分子量，易于引入端基)，但同时提供了以容易的方式合成环状聚合物结构的可能性，否则很难以无金属的方式实现这一特征。