Polymerization of Epoxides via Ring-Opening Coupling on Surfaces

Abstract

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-2yl)benzene by acting as a template to direct the formation of a zigzag 1,2-ethylene-bridged parylene polyradical oriented in the [11̅ 0] 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 [11̅ 0] orientation.