Through treatment of HCPs with sulfonating agents, heterogeneous acid catalysts combining the desirable properties of HCPs with high acid-site densities, so called sulfonated HCPs (SHCPs), are produced. Dong et al. synthesised sulfonated hypercrosslinked benzene networks containing up to 2 mmol•g -1 of SO3H for the selective dehydration of D-(-)-fructose to 5-hydromethylfurfual, reaching conversions of >90%. An analogous set of materials catalysed the selective conversion of carbohydrate substrates to ethyl levulinate in yields of up to 67%. Therein, it was speculated that multiple variables, including surface area, catalyst dose, and acid density played a critical role in the efficiency of the catalytic transformation. Sulfonated carbazole-based HCPs with impressive SO3H densities of 3.7 mmol•g -1 were developed for the esterification of a number of fatty acids to produce biofuels, reaching conversions of up to 99%. Elsewhere, a SHCP containing a phosphonium salt in its structure was used for the two-phase hydrolysis of cyclohexyl acetate to cyclohexanol, achieving conversions and selectivity of up to 93 and 95%, respectively. SHCPs have also shown promise as selective adsorbents, including for propene/propane separation, heavy metal adsorption, and water pollutants. In conventional approaches, sulfonic acid groups are introduced via the post-synthetic treatment of HCPs using sulfonating agents, commonly chlorosulfonic acid. This route involves the swelling of the HCP network in inert solvent, followed by treatment with large excesses of the sulfonating agent. Although effective, control over the degree of sulfonation and the resulting porous properties of the catalyst is lacking. Furthermore, the approach is cumbersome, requiring the complete synthesis and work up of the HCP prior to sulfonation, resulting in a synthesis time of up to 6 days.