Residual vinyl groups in macroporous monosized polymer particles of poly(meta-DVB) and poly(para-DVB) prepared with toluene and 2-EHA as porogens have been reacted with aluminum chloride as Friedel-Crafts catalyst with and without the presence of lauroyl chloride. In the reaction between aluminum chloride and pendant vinyl groups a post-crosslinking by cationic polymerization takes place. A reaction occurring simultaneously is the addition of HCl to the double bonds. The progress of these reactions was studied by characterization of vinyl group conversion, pore size distribution, specific surface area, morphology, and swelling behavior. In the reaction with aluminum chloride the poly(para-DVB) particles showed a substantially higher conversion of pendant vinyl groups than the particles made of poly(meta-DVB) independent of porogen type. The reaction with aluminum chloride led to a reduced swelling in organic solvents and an increased rigidity of the particles prepared with toluene as porogen. This is confirmed by an increase in the total pore volume in the dry state and a change in the pore size distribution of these particles. Also in the reaction with lauroyl chloride poly(para-DVB! particles have shown a higher conversion of pendant vinyl groups than poly(meta-DVB) particles and the acylation was almost complete at the early stage of the reaction. The swelling in organic solvents is reduced as a result of the incorporation of acyl groups into the particles prepared with toluene as porogen.