Syntheses of poly[β‐(l)‐menthyl D‐ and L‐aspartates] and their secondary structures

Abstract β‐( l )‐Menthyl D ‐ and L ‐aspartates were prepared by a fusion reaction of N ‐phthalyl D ‐ and L ‐aspartic anhydrides with l ‐menthol, followed by hydrazinolysis. The monomers were then polymerized to poly[β‐( l )‐menthyl D ‐ and L ‐aspartates] by the N ‐carboxyanhydride method. These polymers were soluble in many organic solvents, such as diethyl ether, tetrahydrofuran, chloroform, n ‐bexane, and dioxane. From the results obtained by a study of the optical rotatory dispersions and circular dichroisms, poly [β‐( l )‐menthyl D ‐aspartate] was found to be a β form structure in solution. On the other hand, poly[β‐( l )‐menthyl L ‐aspartate] was a random‐coil structure. These results suggest that the asymmetry of the l ‐menthyl chromophore in the side chain interacts with the polypeptide main chain and causes an extraordinary optical rotation.