The polymerization of acrylic acid with NO2in benzene was carried out. The initial rate of polymerization shows first-order dependence on the monomer concentration and half-power dependence on the initiator concentration. The molecular weight of polymers also shows dependence on monomer and initiator concentrations. The overall activation energy of polymerization was found to be about 22.7 kcal/mol. The kinetic mechanism of polymerization is discussed.