Phenyl isocyanate-functionalized and hydrazine-reduced reduced graphene oxide (rG-O) is treated to produce chlorinated rG-O (Cl-rG-O) platelets. The dielectric constant of the composite film containing Cl-rG-O shows a 5.5-fold increase over that of composites of untreated rG-O and this cyanoethyl-based polymer, a consequence of the combination of polar and polarizable C-Cl bonds and the increased interfacial polarization.