The use of mechanical force to facilitate post‐polymerization, solvent‐free thiol substitution reactions is described. These reactions are amenable to halogen‐containing materials prepared using ring opening metathesis polymerization and free radical polymerization reactions. Reactions of these polymers with various thiols can be carried out in a ball mill and are complete in a matter of minutes. Further, 1H NMR and GPC analysis show no significant decomposition of the polymer chain.