Macromolecular Helicity Induction for Novel Optically Inactive Poly(phenyl isocyanate) Bearing Crown Ether Based on the Host−Guest Complexation

The macromolecular helicity induction of a novel optically inactive poly(phenyl isocyanate) bearing crown ether as a host group (2) based on host−guest complexation was discussed. 4‘-Isocyanatobenzo-18-crown-6 (1) was polymerized with MeLi in THF at −78 °C to afford 2 with 71% yield. The circular dichroism (CD) spectrum of 2 in the presence of the perchloric acid salt of l-phenylalanine (l-Phe·HClO4) showed a negative Cotton effect with the high intensity of −3.7 × 104 deg cm2 dmol-1 in the range from 240 to 340 nm, corresponding to the absorption of the polymer backbone, while a positive Cotton effect was observed for d-Phe·HClO4 and the CD spectrum pattern was the mirror image of that of 2 with l-Phe·HClO4. On the other hand, a clear Cotton effect was not observed at all in the range from 230 to 290 nm for the unimer of 2, 4‘-(N,N-diacetylamino)benzo-18-crown-6 (3), with l-Phe·HClO4, though the cation-binding property of 3 was almost the same as that of 2, indicating that the induced CDs were based on not the inclusion of the chiral guest in the host group but the structure change in the main chain, i.e., the macromolecular helicity induction for 2 through the host−guest interaction. The helical structure of 2 was significantly affected by the molar ratio of the guest and host, the temperature change, and the type of guests.