Patterning Thin Films of Poly(ethylene imine) on a Reactive SAM Using Microcontact Printing

This paper describes the patterning of poly(ethylene imine) (PEI) on a surface into structures having submicron edge resolution. This procedure consists of three steps: (1) formation of a reactive self-assembled monolayer (SAM) terminating in interchain carboxylic anhydride groups on gold and silver; (2) patterning of this SAM by microcontact printing (μCP) using a poly(dimethylsiloxane) (PDMS) stamp inked with PEI (this polymer contains primary and secondary amines that are reactive toward the anhydride groups); (3) hydrolysis of the unreacted anhydride groups with base and removal of noncovalently bound PEI. The patterned thin films of PEI are attached covalently to the SAM by amide bonds. The pendant, unreacted primary and secondary amines of the attached PEI can be used as reactive nucleophilic groups in further steps of chemical modification. This type of postmodification has been illustrated by allowing the amine groups of the covalently attached PEI to react with perfluorooctanoyl chloride, palmitoyl chloride, palmitic anhydride, and poly(styrene-alt-maleic anhydride). The PEI films and their derivatives were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), polarized infrared external reflectance spectroscopy (PIERS), contact angles of water, and X-ray photoelectron spectroscopy (XPS).