Asymmetric anionic polymerizations of N-substituted itaconimides having chiral amino-acid esters

Abstract

Chiral itaconimides bearing the amino-acid methyl ester (MRII), such as phenylglycine-, phenylalanine- and leucine-methyl ester, at the side chain (S)- or (R)-MPGII, (S)-MPAII and (S)-MLII, respectively, were successfully synthesized and then polymerized with organometal–chiral ligand complexes such as n-butyllithium/(−)-sparteine [n-BuLi/(−)-Sp], n-BuLi/(S,S)-(1-ethylpropylidene)bis(4-benzyl-2-oxazoline) [n-BuLi/(S,S)-Bnbox], Et2Zn-(−)-Sp and Et2Zn-(S,S)-Bnbox in toluene or tetrahydrofuran (THF) to obtain optically active polymers. The effects of polymerization conditions on optical activity and the structure of poly(MRII)s were investigated by gel permeation chromatography (GPC), circular dichroism, specific rotation and 13C nuclear magnetic resonance measurements. The yields of methanol-insoluble part of the polymer and the Mns, as well as the chiroptical properties of poly(MRII)s, were strongly affected by organometals, ligands, solvents and temperature. The behaviors of poly(MRII)s were different according to N-substituents. In addition, the polymers obtained with n-BuLi as the anionic initiator had higher stereoregularity than those obtained with a radical initiator.