Delocalized bonding at the metal-polymer interface

This paper summarizes our current understanding of the nature of the chemical bond formed at the interface between a deposited metal atom and an underlying polyimide surface. The approach in these studies is based on the use of quantum chemical calculations to interpret photoemission spectroscopy results. By focusing on the initial reaction between a chromium atom and the PMDA-ODA polyimide repeat unit, the bonding is demonstrated to be delocalized, arising from the formation of a charge-transfer complex between the metal atom and the PMDA unit of the polyimide. Stabilization of the complex involves the transfer of electronic charge from the metal d states of chromium to the lowest unoccupied molecular orbital of the π system of the PMDA unit of the polyimide. The complex proposed is energetically favored over that involving a direct local interaction between the chromium atom and one of the carbonyl functional groups. The distribution of single-particle electron energy levels deduced from molecular-orbital calculations can account for the spectroscopy results. The formation of such delocalized metal-polymer complexes is also inferred from a related study of the chromium/PMDA-PDA interface.