Beside the solvent knitting agent DCE, the aromatic crosslinkers α,α′-dibromo-p-xylene (DBpX) and 4,4′-bis(chloromethyl)biphenyl (BCMBP) were applied in the AlCl3-catalyzed synthesis of the PPh3-based polyphosphines. The crosslinking of the insoluble polymers P-DCE, P-B2 and P-BP is shown by FTIR (Fig. ), revealing deformation vibrations of CH2 groups (1373 cm -1 ) and the characteristic vibration pattern of the aliphatic C-H bonds (2800 cm -1 -2980 cm -1 ). The spectra match in the C-P-vibrations (1435 cm -1 ) and the vibration modes of the benzene ring (650 cm -1 -760 cm -1 ), while especially P-B2 and P-BP exhibit a vibration mode at 875 cm -1 , originating from 1,4-disubstituted benzene moieties of the aromatic crosslinker units. In reference to the relative intensities of the C-P vibration and the P=O vibration bands (1176 cm -1 ), a larger amount of phosphorus centers is oxidized in P-DCE. Generally, the three polyphosphines possess strong structural similarities in the FTIR spectrum, referring to their comparable building units. To obtain detailed insights into the crosslinking mode and the structural properties, the amorphous P-BP (Fig. ) was selected and investigated by solid-state NMR (Fig. ). In the 1 H→ The presence of phosphorus in the frameworks P-BP, P-B2 and P-DCE was detected by XRF, additionally the polyphosphines contain some residues of aluminum and chloride inside their framework (Table ). In comparison to an ideal HCP with entirely crosslinked monomers, only one sixth (P-BP) and one eighth (P-B2) of the monomeric phosphine is present in the insoluble solid. This partial incorporation in the network can be attributed to the self-crosslinking capability of the aromatic crosslinkers, which do not react in a 1:1 ratio with the monomeric PPh3, leading to a lower proportion of interconnected phosphines. Yang et al. reported similar observations, when they used 1,4-dichloromethylnaphthalene for the crosslinking of PPh3. A consequence of this self-condensation of the aromatic crosslinker units is displayed in their influence on the formed porous structure (Fig. ). Starting from the non-porous, solvent knitted polyphosphines like P-DCE, the use of a benzylic crosslinker increases the porosity, whereas the longer biphenylic unit extends the porosity even more. The interconnection of the aromatic crosslinkers presumably enhances the rigidity of the framework and embeds the flexible phosphine units in a stable framework. The nitrogen isotherms of the internally crosslinked pB (620 m 2 g -1 (BET)) and pBP (662 m 2 g -1 (BET)), which result from the exclusive crosslinking of DBpX and BCMBP monomers, reference this stabilization effect (Fig. ). Several other works coincide with the herein described trend and emphasize the promoting impact of longer crosslinker units on the formation of extended porous structures, since the polymers cannot pack space efficiently in the solid state. In alignment with the varying porosity, the morphological appearance of the polyphosphines altered. Scanning electron microscopy (SEM) revealed the change from particle agglomerations with a relatively even surface structure in P-DCE towards interconnected spherical particles in P-B2 and P-BP, which are fused together in cauliflower-like morphologies (Fig. ). Filled symbols denote the adsorption, empty symbols denote the desorption. The quantification of the specific surface area (BET) and the total pore volume can be gathered from Table .