Helicity Induction of Polyisocyanate with a Crown Cavity on the Main Chain Synthesized by Cyclopolymerization of α,ω-Diisocyanate

Abstract

Polymerization of a novel α,ω-diisocyanate monomer, 1,14-bis(4-isocyanatophenoxy)-3,6,9,12-tetraoxatetradecane (1), was carried out in DMF using MeLi to afford a gel-free linear polymer according to a cyclopolymerization mechanism. The resulting polymer was assignable to poly(phenyl isocyanate) with a C2 symmetrical crown cavity on the main chain (2). The circular dichroism (CD) spectrum of 2 in the presence of the perchloric acid salt of l-phenylglycine (l-Pgly·HClO4) showed a negative Cotton effect with a high intensity of −3.2 × 104 deg cm2 dmol-1 in the range from 245 to 330 nm, corresponding to the absorption of the polymer backbone, while a positive Cotton effect was observed for d-Pgly·HClO4, and the CD spectrum pattern was a mirror image of that of 2 with l-Pgly·HClO4. Thus, this suggested that the novel type of poly(phenyl isocyanate) with the crown cavity on the main chain (2) formed a one-handed helical structure driven by the host−guest complexation with the chiral guest molecules. Although the solvent significantly influenced the CD intensities of 2, the CD intensities hardly changed at any temperature.