Syntheses and polymerizations of novel chiral poly(acrylamide) macromonomers and their chiral recognition abilities

Abstract

Chiral poly(acrylamide) macromonomers (PMB-1, PMB-2, PPAE-1, and PPAE-2) were synthesized from 2-methacryloyloxyethyl isocyanate and prepolymers, that is, poly[(S)-methylbenzyl acrylamide] or poly(L-phenylalanine ethylester acrylamide with a terminal carboxylic acid or hydroxy group. Radical homopolymerizations of poly(acrylamide) macromonomers were carried out under several conditions to obtain the corresponding optically active polymers. A strong temperature dependence on the specific optical rotation was observed for poly(PPAE-2) in comparison with that for the corresponding prepolymer. This might have resulted from a change in the conformation caused by hydrogen bonds between polymer-graft branches in the polymacromonomer. Radical copolymerizations of poly(acrylamide) macromonomers with styrene and methyl methacrylate were performed with azobisisobutyronitrile in tetrahydrofuran at 60 °C. Chiroptical properties of the copolymers were slightly influenced by comonomer units. Chiral stationary phases were prepared by the radical polymerization of poly(acrylamide) macromonomers in the presence of silica gel containing vinyl groups on the surface. Some racemic compounds such as menthol and mandelic acid were resolved on the chiral stationary phases for high-performance liquid chromatography. The conformation based on hydrogen bonds between polymer-graft branches in the polymacromonomers may play an important role in chiral discrimination.