Synthesis of polymethylacrylamide carrying R-phenylglycine pendant groups and effect of hydrogen bonds on main chain helicity

Abstract

A series of chiral methacrylamide derivatives, RR-PEBM, RS-PEBM, and R-PMBM, were separately synthesized and radically polymerized to obtain the corresponding polymers (poly(RR-PEBM)s, poly(RS-PEBM)s, and poly(R-PMBM)s) in the present study. An interesting effect of the chiral carbon atom, which was away from the backbone, on the formations of the hydrogen bonds between the amide groups and chiroptical properties of polymers was observed. The chiroptical properties of the resulting polymers were investigated in detail by polarimetry, circular dichroism (CD), and UV–Vis spectroscopies. The specific optical rotation of poly(RS-PEBM) and poly(R-PMBM) showed a slight dependence on the solvent polarity, but in contrast, the polarity of the polymerization solvents clearly affected the values of the specific rotation of the poly(RR-PEBM)s. The polymers prepared in toluene displayed a larger optical rotation and stronger cotton effects than the one prepared in methanol. These results indicated that the hydrogen bonds formed between the amide groups in the polymers played an important role in both the polymerization process and the formation of the partial helical structure of the polymer. The secondary structure of poly(RR-PEBM) was relatively stable upon heating but unstable in THF by adding MeOH.