Photo‐cross‐linkable poly(p‐phenylene)s. Synthesis, Langmuir‐Blodgett multilayer film properties and pattern formation

We describe the synthesis of a soluble poly( p ‐phenylene) (PPP) derivative with hydroxy‐functionalities in the side chain by copolycondensation. This allows the introduction of further functionalities by polymer analogous reactions. Esterification with cinnamoyl chloride leads to a photo‐reactive material that can be processed by the Langmuir‐Blodgett (LB)‐technique to form ultrathin, highly anisotropic films. Photo‐irradiation of these films leads to the formation of cross‐links which lock in the long range ordered structure of the layered films which then becomes stable to temperatures of more than 160°C. Cross‐linking is achieved by direct irradiation into the absorption band of the photo‐reactive units or by use of sensitizers, which gives rise to more efficient reaction conditions with fewer side‐reactions. Since the cross‐linked film is insoluble in all solvents, the photo‐reactive material serves as photo‐resist. Irradiation through a mask followed by dissolution of the non‐cross‐linked film can be used for microlithography at micron scale resolution.