## 2 HCL Polystyrenes
### Synthetic Routes  
[PERSON] synthesised the first HCP starting from polystyrene that was dissolved in an organic medium (up to 10-11% \(w/v\)) in the presence of a crosslinker and a Friedel-Crafts catalyst. The crosslinking agents were bifunctional aromatic acyl or alkyl halides, and the media were several organic solvents that were able to dissolve PS without deactivating the Friedel-Crafts catalyst. During hyper-crosslinking, the solution was rapidly transformed into a gel block, which eventually shrinked and crushed over the completion of the reaction. Thus, the resulting HCL polymer resulted in the form of rigid particles of an irregular shape. Then, DVB was included as a comonomer of ST, in the range 0.3-2 mol %, and this permitted also to obtain precursor copolymers in the form of spherical gel-type beads. In this case, the reaction medium was any solvent that was able to swell the precursor copolymer [30,44]. The beads preparation was further developed by many research groups. Beads were obtained by suspension polymerization, usually leading to polydisperse particles in the range 10-500 um, which showed morphological changes during the Friedel-Crafts reaction. Emulsion polymerization, on the other hand, allowed for obtaining smaller and more homogeneous particles, as [PERSON] et al. [45] demonstrated by preparing near monodisperse beads with 420 nm medium diameter, able to preserve their shape even after hyper-crosslinking. Non-aqueous dispersion polymerization (NAD) and precipitation polymerization (PP) were also employed to obtain uniform particle size, giving, respectively, beads with 4-10 um diameter, and monodisperse 4 um beads. Apart from size and shape, the precursor polymerization synthesis was also found to influence the HCP final SSA and porosity. In particular, for NAD and PP, an amount of VBC higher than 50 mol % was required to obtain HCP with SSA higher than 1000 m\({}^{2}\)/g [46]. In contrast, for suspension polymerization, 20 mol % of VBC monomer was sufficient to obtain HCP with SSA over 1000 m\({}^{2}\)/g. The highest surface area HCP, as obtained by suspension polymerization, showed SSA up to 2090 m\({}^{2}\)/g and it was prepared using DVB, ST and VBC in the molar ratio DVB:ST:VBC = 2:0:98 [37]. Another synthetic approach was proposed by [PERSON] and [PERSON] [10], who prepared DVB/ST/VBC based HCP in the form of monolith performing in situ hyper-crosslinking in capillary columns in the presence of organic porogens (toluene and 1-dodecanol), obtaining a material with SSA of 663 m\({}^{2}\)/g. In another work, [PERSON] et al. [47] compared monolithic and bead-shaped DVB/VBC hyper-crosslinked polymers for methane storage, evidencing the advantage of avoiding packing problems, which are typical of particulate materials. In their case, the hyper-crosslinked monolith and beads exhibited roughly similar porous and adsorption properties, but the monolith display a 116% higher methane storage capacity for equal volume. A further synthetic route that pursued to obtain high surface area hyper-crosslinked polymers is the self-condensation of benzyl chloride containing monomers. [PERSON] and [PERSON] [48], in 2002, first reported the polycondensation of \(p\)-dichloroxylene (\(p\)-DCX) in presence of SnCl\({}_{4}\). [PERSON] et al. [49] prepared HCP that was characterized by SSA of \(\sim\)2500 m\({}^{2}\)/g, using benzyl chloride terminated double-four-ring cubic siloxane cages as precursors. This particular procedure was based on the contemporary polymerization of the benzyl chloride terminations and the destruction of the siloxane cages, and led to obtaining a highly porous material that was characterized by hierarchical micro/meso porosity. [PERSON] et al. [50] prepared high surface area polymers from self-condensation of carbam that were previously functionalized by the simple grafting of two benzyl chloride groups.