Selective Photo-induced Cross-linking of Polynorbornens: Towards the Fabrication of Polymer 2D- and 3D- Microstructures

Full text: Ring opening metathesis polymerization (ROMP) has become an important tool for the synthesis of highly defined polymers and various polymer architectures. In the present work, the residual double bonds in ROMP derived polymeric materials were exploited for a photoinduced thiol-ene reaction in order to achieve a selective cross-linking of the macromolecules. To demonstrate the versatility of this reaction for the realization of polymeric microstructures, thin films of poly(norbornene dicarboxylic acid, dimethylester) were structured by means of photolithography. Besides the photoinduced thiol-ene reaction, which was investigated by means of FTIR measurements, also the cross-linking of the macromolecules and thus the change in the solubility were assessed by means of sol-gel analysis. Thin films of this polymer were laterally patterned using conventional single photon lithography leading to resolutions in the μm range. Going a step further, this approach can also be used for realizing 3D polynorborne microstructures employing the two photo absorption writing technique. The obtained 3D features have been visualized by scanning electron microscopy and atomic force microscopy, respectively. The accessibility and reactivity of the polynorbornene main chain C = C double bonds in the thiol-ene reaction paves the way towards novel strategies for the realization of polymer 2D and 3D microstructures. (author)