Hydrogen‐bond‐assisted stereocontrol in the radical polymerization of <i>N</i>‐isopropylacrylamide with primary alkyl phosphate: The effect of the chain length of the straight ester group

Abstract

Abstract The radical polymerizations of N ‐isopropylacrylamide (NIPAAm) were carried out in toluene at low temperatures in the presence of phosphoric acid esters such as trimethyl phosphate, triethyl phosphate (TEP), tri‐ n ‐propyl phosphate, and tri‐ n ‐butyl phosphate (TBP). Syndiotactically rich poly(NIPAAm)s were obtained from −60 to 0 °C, and TEP provided the highest syndiotacticity (racemo dyad = 65%) at −40 °C. On the other hand, lowering the temperature reversed the stereoselectivity of the propagation reaction so that isotactically rich poly(NIPAAm)s were obtained at −80 °C. In particular, TBP exhibited the most isotactic specificity (meso dyad = 57%). Job's plots for NIPAAm–TBP mixtures revealed that NIPAAm and TBP formed a 1:1 complex at 0 °C and a predominantly 1:2 complex at −80 °C through a hydrogen‐bonding interaction. Therefore, the stereospecificity of NIPAAm polymerization should depend on the stoichiometry of the hydrogen‐bond‐assisted complex. Thus, the mechanism for this polymerization system was discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 50–62, 2005