Chemical Reactivity in Organized Medium: Building up a Two-Dimensional Polymer
Résumé
The building up of a true two-dimensional polymer is reported. The polymer is built up via a solid-state oxidative coupling which occurs between tetrafunctionalized semiamphiphilic porphyrins preorganized as a regular paving of the plane by the Langmuir-Blodgett (LB) technique. The precursor LB film, together with the polymerized one, is extensively studied. Hence, the orientation of the macrocyclic rings before and after the oxidative coupling is derived from linear dichroism, electron spin resonance, and X-ray measurements. The oxidative coupling itself is followed by infrared and Raman spectroscopy. Evidence is given for the formation of covalent links between adjacent porphyrins within each monolayer. Transmission X-ray experiments indicate the emergence of a new crystalline phase in the plane of the monolayer after the two-dimensional oxidative coupling. The solubility behavior of the precursor and polymerized LB films is consistent with the polymerization process. This two-dimensional polymer exhibits outstanding mechanical properties since holes up to 0.01 mm2 in area can be bridged by only one monolayer. This strengthening of the lateral cohesion of the film, when compared with classical LB films, is consistent with the two-dimensional character of the polymerization process. The semiamphiphilic character of the polymerized film allows finally the complete removal of the aliphatic chaine from the polymerized LB film leading to a strong ultrathin and chain-free polymerized film