The C--H bond of pendant aromatic groups such as commercial polystyrenes with three types of tacticities (syndiotactic, isotactic, atactic) undergo catalyzed functionalization with boron reagents. A boronic ester group formed on the polymer in the polystyrene was further converted to hydroxy and arene via oxidation and coupling reactions, respectively. These functionalizations proceeded without significantly affecting the molecular weight of starting polymer and the functional concentrations could be easily controlled by changing the ratio of boron reagent to monomer unit.