Hydrogen-bond-assisted stereocontrol in the radical polymerization of N-isopropylacrylamide with bidentate Lewis base

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°C, whereas syndiotactic-rich poly(NIPAAm)s were obtained at –40 to 0°C. This result corresponded to the results observed in the presence of primary alkyl phosphates. NMR analysis revealed that NIPAAm monomer and tetraisopropyl methylenebisphosphonate formed mono-binding hydrogen-bond-assisted complex at 0°C, but a chelate complex at –80°C. Thus, it was concluded that the stereospecificity in NIPAAm polymerization strongly depended on the complexation mode of the added bidentate Lewis base.

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