Synthesis And Hands-ray Properties Of Methacrylamide Optically Active Polymers

In recent years, optically active polymers have attracted much attention because of their unique functions such as molecular recognition, optical resolution for racemates and catalytic activity in asymmetric transformations as well.In general, bulky side-chain and hydrogen bonding are in favor of the formation of stable helical conformation for polymers, which endows them with high optical property and some special performance. In the present work, we have developed an effective synthesis for a novel type of optically active N-substituted methacrylamides (OPMAM), including N-[o-(4-phenyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl] methacryl-amide((R)-PhOPMAM), N-[o-(4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl]-methacrylamide((S)-Pr~iOPMAM), and N-[o-(4-methyl-4,5-dihydro-1,3-oxazol-2-yl)-phenyl]methacrylamide ((S)-M0PMAM). The present procedure gave the monomers in moderate yields under milder reaction conditions. The structure of monomers was examined through FT-IR, 1H NMR, and elemental analysis.The radical polymerization of these chiral N-substituted methacrylamides produced corresponding polymers with high specific rotation in moderate to good yields. 1H NMR spectra proved that the addition polymerization took place in the C=C double bond in the methacrylamide unit and the oxazoline groups were not destroyed during the polymerization Resulting poly(OPMAM)s had relatively low molecular weights (Mn = 4000-14000) and showed good solubility in common organic solvents such as THF, chloroform, and dichloromethane. Increase in absolute value of specific rotation was observed for the polymer of (S)-MOPMAM. Interestingly, the formed polymer was dextrorotatory, which is opposite to that of monomer. It was found that the polymerization is significantly influenced with the substitutents in oxazoline ring. The CD and UV-Vis spetra showed that the optical activity of poly(OPMAM)s were attributed not only to the chirality of oxazolinyl groups in monomelic units but also to the partial helical structure for poly(MOPMAM).The effects of Lewis acid, that is, rare earth metal trifluoromethanesulfonates(Ln(OSO2CF3)3), on the free-radical polymerization of these monomers were examined under different solvents. A catalytic amount of Ln(OSO2CF3)3 affected the stereochemistry of (S)-MOPMAM during radical polymerization: the polydispersities (Mw/Mn) of the polymers prepared in the presence of the Lewis acid were broader than those without the Lewis acid and the absolute value of specific rotation decreased in a majority of solvents. The phenomena were similar to the previously reported results in literature. Based on 13C NMR analysis, these optical active polymers possessed isotactic-rich structure.