Surface Polymerization of Poly(<i>p</i>-phenylene-terephthalamide) on Ag(111) Investigated by X-ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy

Abstract

The formation of poly(p-phenylene-terephthalamide) (PPTA) by surface-assisted polymerization of terephthaloyl chloride (TPC) and p-phenylenediamine (PPD) on Ag(111) has been studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Analysis of the XPS data reveals that the polymer is formed in the (sub-) monolayer regime already at room temperature. Upon vacuum deposition of TPC onto the single-crystal surface, the carbon–chlorine bond is cleaved, and the polymerization proceeds via a p-phenylene dicarbonyl species, which is presumably surface stabilized. This contrasts the reaction mechanism in solution, where the chlorine atom is expelled after a nucleophilic attack by the amine group. Annealing of the sample leads to desorption of residual PPD monomers, lateral ordering of the polymer chains, and further progress of the polymerization that can be followed by XPS. The chain length distribution of the polyamide, as extracted from the XP spectra, is consistent with the typical chain lengths found in STM images.