Radical polymerization of N-isopropylacrylamide (NIPAAm) in toluene was investigated in the presence of bidentate Lewis base such as diphosphonates. Isotacticity of the obtained poly(NIPAAm)s slightly increased at -80 degrees C, whereas syndiotactic-rich poly(NIPAAm)s were obtained at -40-0 degrees C. This result corresponded to the results observed in the presence of primary alkyl phosphates. NMR analysis revealed that NIPAArn monomer and tetraisopropyl methylenebisphosphonate formed mono-binding hydrogen-bond-assisted complex at 0 degrees C, but a chelate complex at -80 degrees C. Thus, it was concluded that the stereospecificity in NIPAArn polymerization strongly depended on the complexation mode of the added bidentate Lewis base. (c) 2005 Elsevier Ltd. All rights reserved.