Photo-induced crosslinking and thermal de-crosslinking in polynorbornenes bearing pendant anthracene groups

Functional polynorbornenes bearing anthracene molecules in their side chain were synthesized by ring opening methathesis polymerization (ROMP). The pendant anthracene molecules undergo a [4π + 4π] cycloaddition upon irradiation with UV-light, which was studied by means of UV–Vis spectroscopy in thin films of these polymers. This photodimerization reaction also leads to a crosslinking of the macromolecules due to the photodimer formation, resulting in a decrease in solubility of the UV illuminated areas. A thermally induced de-crosslinking could be obtained, revealing the reversibility of this photoreaction. The influence of the flexibility of the macromolecules, i.e. the mobility of the anthracene groups in the polymeric material, on the conversion rate, reversibility and the crosslinking behavior was studied by means of spectroscopy and sol–gel analysis. Furthermore, photo-patterned films were obtained by structured illumination and subsequent development with dichloromethane revealing a negative resist behavior.