Cross-linked polyvinyl polymersversus polyureas as designed supports for catalytically active M0 nanoclusters Part III. Nanometer scale structure of the cross-linked polyurea support EnCat 30 and of the PdII/EnCat 30 and Pd0/EnCat 30NP catalysts

Abstract

The cross-linked polyurea support EnCat 30, its related macromolecular complex Pd^II/EnCat 30 and its related Pd⁰/EnCat 30NP nanocomposite are thoroughly investigated with SEM, TEM, ISEC and ESR in the solid state (SEM and TEM) and swollen state in THF (ISEC and ESR). Pd^II/EnCat 30 and its related Pd⁰/EnCat 30NP are obtained by microencapsulation of palladium acetate in a polyurea framework, which is formed upon hydrolysis/condensation of mixtures of multi-functional oligo-arylisocyanates in dichloroethane. Most remarkably, both Pd^II/EnCat and Pd⁰/EnCat 30NP turn out to be far more (nano)porous and swellable materials than the blank polyurea matrix (EnCat 30). It is proposed that there is a strong nanostructural effect exerted by Pd^II species due to its interaction with functional groups (amines stemming from the hydrolysis of the isocyanato groups or ureido groups belonging to the polymer chains) during the growth of the cross-linked polymer framework. As a consequence, the catalytic species in both Pd^II/EnCat 30 and Pd⁰/EnCat 30NP are much more accessible to molecules diffusing from liquid phases in contact with the materials and, hence, are better catalysts than expected from the morphology of blank polyurea EnCat 30.