However, P-DCE, P-FDA and P-DCM show no significant nitrogen uptake in the dried state (Fig. ). For the formation of a porous structure, an adequate stability of the swollen HCP skeleton is crucial to prevent its collapse during the post-synthetic removal of the solvent. Beside an insufficient degree of crosslinking, the non-porosity of the polyphosphines is probably related to the absent rigidity of the building blocks. The phosphine moieties and the ethylene units might not possess the necessary degree of rigidity to withstand the emerging tensions in the drying process.