Surface and Site-Specific Ring-Opening Metathesis Polymerization Initiated by Dip-Pen NanolithographyWe acknowledge the AFOSR, DARPA through ARO (no. DAAD19-03-1-0065), and NSF for support of this research. We thank P. A. Bertin and J. M. Gibbs for providing the norbornenyl monomers.

Patterned polymeric structures have attracted significant interest for possible applications in the development of sensors, catalysis, and optical devices. Thus far, several strategies, based upon photolithography, electron beam lithography, and microcontact printing have been developed for generating polymer arrays. While useful for many applications, these methods do not allow one to control nanostructure composition in a site-specific manner and, therefore, do not allow one to fabricate complex multicomponent polymer arrays over the nanoto micrometer length scales. Having the capability to generate multicomponent arrays with nanoscopic features could afford one the opportunity to construct and study high-density combinatorial libraries of novel macromolecular systems. Herein, we report a novel approach, based upon dip-pen nanolithography (DPN) and ring-opening metathesis polymerization (ROMP), to the fabrication of polymer brush arrays on the nanometer length scale. The combined approach utilizes the attributes of DPN and ROMP for synthesizing high-density polymer brush arrays with control over feature size (on the nanometer length scale), shape, and interfeature distance. Furthermore, the capability of directly delivering monomers through a standard AFM microcantilever will allow one to generate small, but diverse, libraries of nanoscale polymer brushes that comprise large numbers of structurally distinct compounds by assembling many possible combinations of small building monomers containing desired active functionalities. To explore the potential of the combined approach and provide the basis for the studies leading to the design of combinatorial polymer libraries, two complementary routes have been developed for synthesizing arrays of the nanoscale polymer brushes based on DPN and ROMP. Route 1 is an approach based on growing polymers from a DPN-patterned template (Scheme 1). To test the viability of this route, 10(exo-5-norbornen-2-oxy)decane-1-thiol molecules were patterned on a gold substrate by bringing a tip coated with norbornenylthiol in contact with the substrate. The exo isomer rather than the corresponding endo isomer was used to optimize ROMP reactivity. Subsequently, the substrate