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

• Applicant: Professor Dr. Stefan Naumann
• Subject Area: Preparatory and Physical Chemistry of Polymers
• Term: from 2014 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 260748259

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.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Professor Dr. Andrew Dove