Hydrogen-Bond-Assisted Stereocontrol in the Radical Polymerization of N-Isopropylacrylamide with Primary Alkyl Phosphate : The Effect of the Chain Length of the Straight Ester Group

Radical polymerizations of N-isopropylacrylamide (NIPAAm) were carried out in toluene at low temperatures in the presence of phosphoric acid esters such as trimethyl, triethyl (TEP), tri-n-propyl, and tri-n-butyl phosphates (TBP). Syndiotactic-rich poly(NIPAAm)s were obtained at the temperature range from –60°C to 0°C, and particularly TEP provided the highest syndiotacticity (racemo diad = 65%) at –40°C. On the other hand, lowering temperature reversed the stereoselectivity of the propagation reaction so that isotactic-rich poly(NIPAAm)s were obtained at –80°C. In particular, TBP exhibited the most isotactic-specificity (meso diad = 57%). Job's plots for NIPAAm-TBP mixtures revealed that NIPAAm and TBP formed 1:1 complex at 0°C and predominantly 1:2 complex at –80°C through a hydrogen-bonding interaction. Therefore, it is considered that the stereospecificity of NIPAAm polymerization should depend on the stoichiometry of the hydrogen-bond-assisted complex. Thus, the mechanism for the present polymerization system was discussed.

This is the peer reviewed version of the following article: Hirano, T., Ishii, S., Kitajima, H., Seno, M. and Sato, T. (2005), Hydrogen‐bond‐assisted stereocontrol in the radical polymerization of N‐isopropylacrylamide with primary alkyl phosphate: The effect of the chain length of the straight ester group. J. Polym. Sci. A Polym. Chem., 43: 50-62., which has been published in final form at https://doi.org/10.1002/pola.20475. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.