Hydrogen-Bond-Assisted Stereocontrol in the Radical Polymerization of N-Isopropylacrylamide with Secondary Alkyl Phosphate : The Effect of the Bulkiness of the Ester Group

Radical polymerization of N-isopropylacrylamide (NIPAAm) in toluene at low temperatures was investigated in the presence of triisopropyl phosphate (TiPP). The addition of TiPP induced a syndiotactic-specificity that was enhanced by lowering polymerization temperature, whereas atactic polymers were obtained in the absence of TiPP regardless of temperature. Syndiotactic-rich poly(NIPAAm) with racemo diad = 65% was obtained at –60°C with a fourfold amount of TiPP, but almost atactic poly(NIPAAm)s were obtained by lowering temperature to –80°C. This result contrasted with the result in the presence of primary alkyl phosphates, such as tri-n-propyl phosphate, that stereospecificity varied from syndiotactic to isotactic by lowering polymerization temperature. NMR analysis at –80°C revealed that TiPP predominantly formed 1:1 complex with NIPAAm, although primary alkyl phosphates preferentially formed 1:2 complex with NIPAAm. Thus, it was concluded that a slight increase in bulkiness of the added phosphates influenced the stoichiometry of the NIPAAm-phosphate complex at lower temperatures and consequently a drastic change in the effect on stereospecificity of NIPAAm polymerization was observed.

This is the peer reviewed version of the following article: Hirano, T., Kitajima, H., Ishii, S., Seno, M. and Sato, T. (2005), Hydrogen‐bond‐assisted stereocontrol in the radical polymerization of N‐isopropylacrylamide with secondary alkyl phosphate: The effect of the bulkiness of the ester group. J. Polym. Sci. A Polym. Chem., 43: 3899-3908., which has been published in final form at https://doi.org/10.1002/pola.20883. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.