Polymerization of Epoxides via Ring-Opening Coupling on Surfaces

On-surface covalent polymerization is a powerful tool for the atomically precise synthesis of polymeric materials with interesting properties and functions. Although on-surface covalent polymerization has been achieved with several coupling reactions, ring-opening coupling on surfaces is still rarely used. Herein, we report an unprecedented ring-opening coupling reaction of epoxides on Ag(110) and Ag(111) surfaces and investigate the coupling process using scanning tunneling microscopy, noncontact atomic force microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. The Ag(110) surface promoted the ring-opening coupling reaction of 1,4-di(oxiran-2-yl)benzene by acting as a template to direct the formation of a zigzag 1,2-ethylene-bridged parylene polyradical oriented in the [1 (1) over bar0] crystallographic direction. In contrast, the ring-opening coupling reaction of the same precursor on the Ag(111) surface formed irregular polymers. Moreover, the ring-opening coupling reaction of 2-([1,1'-biphenyl]-4-yl)oxirane on the Ag(110) surface was proved to involve ring-opening of the ethylene oxide group, C-C coupling, and deoxygenation, whereas C-C coupling was favored along the [1 (1) over bar0] orientation.