Here we demonstrate a general method for the fabrication of molecularly thin polymer films with well-defined (in-plane) dimensions. The strategy for the synthesis of these materials starts with a sequence of reactions on a patterned selfassembled monolayer (SAM). This pattern, defined by microcontact printing, determines the size and shape of the polymer films on the micrometer scale. The out-of-plane thickness and composition is defined on a nanometer scale by the sequence of chemical reactions.
These molecularly thin polymer films with in-plane crosslinking are a subset of the class of ªtwo-dimensional polymersº. [1] Synthetic routes to two-dimensional polymers include polymerization of reactive monomers in SAMs [2] and lipid bilayers, [3] at oil ± water [4] and air ± water interfaces, [5] and polymerization of monomers that form self-assembled layered structures. [6] Although certain of these approaches have generated two-dimensional polymeric structures, they have not controlled their lateral (in-plane) dimensions. Our strategy for the fabrication of two-dimensional polymers relies on the work of Grainger et al., [7] Crooks et al., [8] and others, [9] who examined covalently bound polymer mono-and multilayers on surfaces. Rubner et al. [10] and Decher [11] also examined structures made up of electrostatically associated layers of polymers. Möhwald et al. described covalently linked hollow shell multilayers [12] and Hammond et al. studied electrostatically deposited multilayers on patterned SAMs. [13] We do not know of any attempts to release these polymeric multilayers into suspension following assembly on a surface.
We began the fabrication of the two-dimensional polymers by using microcontact printing (mCP) [14] to pattern a SAM; this patterned SAM served as a template for the growth of the polymer films (Scheme 1). The synthesis involves four steps: 1) patterning a gold surface by mCP with COOH-and CH 3terminated SAMs; [15] 2) deposition of an amine-containing polymer (polyethyleneimine, PEI) by ionic adsorption onto the CO 2 À -terminated areas; [16] 3) cross-linking the adsorbed PEI covalently by allowing it to react with a polymeric anhydride (poly(octadecene-alt-maleic anhydride), POMA, or poly(ethylene-alt-maleic anhydride), PEMA); [17] and 4) releasing the film from the surface by dissolving the gold substrate completely in 5 mm sodium dodecylsulfate (SDS)/ 30 % aqua regia/0.5 % HF in water. [18] We examined polymeric films patterned into hexagons with 10-mm sides and 10-[