Optically active polyacrylamides bearing an oxazoline pendant: Influence of stereoregularity on both chiroptical properties and chiral recognition

Abstract

Enantiopure acrylamide derivatives, N-[o-(4-methyl-4,5-dihydro-1,3-oxazol-2-yl) phenyl]acrylamide (MeOPAM), N-[o-(4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl]acrylamide (PrⁱOPAM), and N-[o-(4-phenyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl]acrylamide (PhOPAM), were synthesized and radically polymerized in the presence of rare earth metal trifluoromethanesulfonates (Ln(OTf)₃, Ln = La, Nd, Sm, and Y) to yield corresponding optically active polymers. Among these Lewis acids, Y(OTf)₃ was found to be most effective for increasing the isotactic specificity during the radical polymerizations when using n-butanol as solvent. Also, the effect of the Lewis acids was significantly influenced by the ratio of Ln(OTf)₃ to monomer. The relationship of both chiroptical property and the chiral recognition with the stereoregularity was then examined for the resulting polymers having various tacticity by spectroscopic techniques such as NMR, fluorescence, and circular dichroism. The results indicated that the polymers rich in isotacticity exhibited a favorable enantioselective discrimination ability toward 1,1′-bi-2-naphthol as evidenced by ¹H NMR study, where the characteristic hydroxyl proton signal was split into two peaks that ascribed respectively to the levo- and dextro-isomer; furthermore, the splitting magnitude was linearly correlated with the diad isotacticity of the polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010